Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF THE INVENTION:
Control System for reciprocating drive
FIELD OF THE INVENTION
The present invention relates to a control system for a reciprocating drive
for use in
such applications as reciprocating actuators, reciprocating power generators,
and
reciprocating pumps commonly used for chemical injection on gas producing
wells.
BACKGROUND OF THE INVENTION
United States Patent 6,263,777 (Lauder 2001) entitled "Control System for
reciprocating device", describes a problem currently being experienced with
reciprocating
pumps. At low speeds of operation at low pressure, the reciprocating pump can
become
stuck. The control system described in the Lauder reference includes a
reciprocating device
that moves in a first direction due to fluid pressure and in a second
direction due to a spring,
when pressure is reduced. A trigger on the reciprocating device engages a
connector, which
has a spring. The spring is compressed, storing energy as the reciprocating
device moves in
the second direction. This stored energy is used to assist in moving a toggle
switch through a
middle position, where it might otherwise become stuck, during movement in the
first
direction.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided a control system
for a
reciprocating drive. The drive has a reciprocating shaft which reciprocally
moves in a
first direction and a second direction opposed to the first direction. The
reciprocating shaft
2 5 has a first end and a second end. A piston is mounted at the first end of
the shaft. The piston
has a first side and a second side. A fluid retaining piston chamber houses
the piston. The
piston chamber has a first side fluid communication port on the first side of
the piston and a
second side fluid communication port on the second side of the piston. The
second end of the
shaft serves an intended function as it reciprocates. The control system
includes a gas
3 0 manifold having a gas inlet adapted for connection to a gas source
supplying gas to the gas
manifold and a gas exhaust adapted to exhaust gas from the gas manifold. Means
are
provided for configuring the gas manifold in a first mode, with the gas inlet
connected to the
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first side fluid communication port to supply gas to the piston chamber on the
first side of the
piston to cause the piston to move in a first direction. The second side fluid
communication
port concurrently is connected to the gas exhaust to exhaust gas from the
piston chamber on
the second side of the piston as the piston moves in the first direction.
Means are also
provided for configuring the gas manifold in a second mode, with the gas inlet
connected to
the second side fluid communication port to supply gas to the piston chamber
on the second
side of the piston to cause the piston to move in a second direction. The
first side fluid
communication port concurrently is connected to the gas exhaust to exhaust gas
from the
piston chamber on the first side of the piston as the piston moves in the
second direction.
Means are provided for switching between the first mode and the second mode,
such that the
shaft of the drive is reciprocated solely by gas pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the invention will become more apparent from the
following description in which reference is made to the appended drawings, the
drawings are
for the purpose of illustration only and are not intended to in any way limit
the scope of the
invention to the particular embodiment or embodiments shown, wherein:
FIG. 1 is a top plan view, in section, of a control system constructed in
accordance
2 0 with the teachings of the present invention, with the control system in
the first mode.
FIG. 2 is a top plan view, in section, of the control system illustrated in
FIG.1, with
the control system in the second mode.
FIG. 3 is a detailed side elevation view of a trigger mechanism from the
control
system illustrated in FIG.1.
2 5 FIG. 4a through 4g are a series of detailed side elevation views of the
trigger
mechanism illustrated in FIG. 3, showing movement of through an activation
sequence.
FIG. 5 is a detailed side elevation view of a cylindrical seal carrier for the
control
system illustrated in FIG.1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment, a control system for a reciprocating drive will now
be
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described with reference to FIG. 1 through 5. A chemical injection application
has been
chosen for purposes of illustration. It will be appreciated, however, that the
described control
system can be used for an infinite variety of other reciprocating
applications.
Structure and Relationship of Parts:
Referring to FIG. 1 and FIG. 2, there is provided a drive, generally indicated
by
reference numeral 10 and a control system for that drive, generally indicated
by reference
numeral 12. Most reciprocating drives require a minimum gas pressure of
approximately 30
pounds per square inch (psi.) in order to operate. Below that pressure, they
tend to flutter and
stall. As gas wells age, they experience a decrease in pressure. An increasing
number of gas
wells are incapable of providing 30 psi pressure. Efforts were, therefore made
when
developing control system 12 and reciprocating drive 10, to have them capable
of operating
together at pressures of 10 psi or less. There will now be described how this
was
accomplished. Of course, drive 10 and control system 12 are still capable of
operating at
pressures greater than 10 psi.
Referring to FIG. 1 and FIG. 2, drive 10 has a reciprocating shaft 14.
Referring to
FIG.1, shaft 14 reciprocally moves in a first direction, as indicated by arrow
16. Referring to
FIG. 2, shaft reciprocally moves in a second direction, (opposed to the first
direction), as
2 0 indicated by arrow 18. Referring to FIG. 1 and FIG. 2, reciprocating shaft
14 has a first end
and a second end 22. A piston 24 is mounted at first end 20 of shaft 14.
Piston 24 has a
first side 26 and a second side 28. A fluid retaining piston chamber 30 houses
piston 24.
Piston chamber 30 has a first side fluid communication port 32 positioned on
first side 26 of
piston 24 and a second side fluid communication port 34 positioned on second
side 28 of
2 5 piston 24. There may be than one first side fluid communication port and
more than one
second side fluid communication port, if the intake and exhaust functions are
separated. As
will hereinafter be further described, in the preferred embodiment the intake
and exhaust
functions are integrated with the same fluid communication port used for both
functions.
Second end 22 of shaft 14 is connected to a displacement rod 23 which is
adapted to control
3 0 flow from a chemical source (not shown). The type of device which is being
controlled by
movement of second end 22 of shaft 14 is not critical to the present
invention. There is
illustrated one possible configuration of chemical injector showing a fluid
conduit 36.
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Displacement rod 23, which is connected to second end 22 of shaft 14, acts as
a plunger
capable of extending transversely across fluid conduit 36 between two one way
valves 38 and
40, which only permit a flow in a direction indicated by arrow 42. When shaft
14 moves
reciprocally in the second direction indicated by arrow 18, displacement rod
23 is withdrawn
and chemicals can flow freely along fluid conduit 36. When shaft 14 moves in
the first
direction indicated by arrow 16, displacement rod 23 becomes positioned across
fluid conduit
36 and the flow of chemical is blocked. An annular seal, generally indicated
by reference
numeral 44, is positioned around displacement rod 23 to prevent the incursion
of chemicals
from the chemical source into drive 10.
Referring to FIG. 1 and FIG. 2, control system 12 includes a gas manifold 46.
A gas
inlet 48 is provided which is adapted for connection to a gas source (not
shown) supplying
gas to gas manifold 46. A gas exhaust 50 is provided which is adapted to
exhaust gas from
gas manifold 46. Gas manifold has a first mode, which is illustrated in FIG. 1
and a second
mode, which is illustrated in FIG. 2. Referring to FIG. 1, in the first mode,
gas inlet 48 is
connected to first side fluid communication port 32 to supply gas to piston
chamber 30 on
first side 26 of piston 24 to cause piston 24 to move in the first direction,
as indicated by
arrow 16. Second side fluid communication port 34 is concurrently connected to
gas exhaust
50, to exhaust gas from piston chamber 30 on second side 28 of piston 24 as
piston 24 moves
2 0 in the first direction. Referring to FIG. 2, in the second mode, gas inlet
48 is connected to
second side fluid communication port 34 to supply gas to piston chamber 30 on
second side
28 of piston 24 to cause piston 24 to move in a second direction, as indicated
by arrow 18.
The first side fluid communication port 32 is concurrently connected to gas
exhaust 50 to
exhaust gas from piston chamber 30 on first side 26 of piston 24 as piston 24
moves in the
2 5 second direction. A switch, generally indicated by reference numeral 52 is
used as means for
switching between the first mode illustrated in FIG. 1 and the second mode,
illustrated in
FIG. 2. It is to be noted that with control system 12, shaft 14 of drive 10 is
reciprocated
solely by gas pressure. Prior art control systems used a spring to bias shaft
14 is one
direction. This meant that sufficient gas pressure had to be provided to
overcome the biasing
3 0 force of the spring return for shaft 14. By having control system 12
operated solely by gas
pressure, control system 12 is able to operate at lower levels of gas
pressure.
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The operation of gas manifold 46 will now be described in greater detail.
Referring to
FIG. 1 and FIG. 2, gas manifold 46 consists of a barrel 54, which has been
extended through
the use of a first fitting 55 positioned at a first end 56 and a second
fitting 57 positioned at a
second end 58. For the purpose of this description, the extensions provided by
first fitting 55
5 and second fitting 57 will be considered part of barrel 54. Gas inlet 48 is
positioned at first
end 56. A gas control valve 49 is position upstream of gas inlet 48. Barrel 54
has a series of
radial ports, a first radial port 59, a second radial port 60, a third radial
port 62, a fourth radial
port 64, and a fifth radial port 66. These radial ports are sequentially
spaced at spaced
intervals along barrel 54 from first end 56 to second end 58. Second radial
port 60 is
connected to second side fluid communication port 34, so it is always in fluid
communication
with second side 28 of piston 24. Third radial port 62 is connected to gas
exhaust 50. Fourth
radial port 64 is connected to first side fluid communication port 32, so it
is always in fluid
communication with first side 26 of piston 24. First radial port 59 is
connected to fifth radial
port 66, which connection plays a role in switching, as will be hereinafter
further explained.
Switch 52 has a first member 68 and a second member 70, that move axially in
barrel 54 to
effect a change in the relationship between the radial ports.
Referring to FIG. 1, in the first mode, first member 68 of switch 52 is
positioned
between first radial port 59 and second radial port 60. Second member 70 of
switch 52 is
2 0 positioned between third radial port 62 and fourth radial port 64. Gas
supplied through gas
inlet 48 flows into barrel 54 where it encounters first member 68. The only
place the gas can
go is to pass out through first radial port 59, re-entering barrel 54 at fifth
radial port 66. Gas
entering barrel 54 through fifth radial port 66 encounters second member 70.
The only place
that the gas can go is to pass out fourth radial port 64 leading to first side
fluid communication
2 5 port 32 and into piston chamber 30. Once in piston chamber 30, the in
flowing gas creates
pressure on first side 26 of piston 24, causing piston 24 to move in the first
direction, as
indicated by arrow 16. This movement of piston 24 in the first direction,
forces gas out of
piston chamber 30 through second side fluid communication port 34. The exhaust
gas enters
into barrel 54 through second radial port 60. Once within barrel 54, the
exhaust gas is
3 0 confined between first member 68 and second member 70. The only place the
exhaust gas
can go is to pass out third radial port 62 to gas exhaust 50.
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Referring to FIG. 2, in the second mode, first member 68 of switch 52 is
positioned
beriveen second radial port 60 and third radial port 62. Second member 70 of
switch 52 is
positioned between fourth radial port 64 and fifth radial port 66. Gas
supplied through gas
inlet 48 flowing into barrel encounters first member 68 and concurrently
passes out first radial
port 59 and second radial port 60. Gas flowing out of first radial port 59 re-
enters barrel 54
through fifth radial port 66, where it encounters a dead end in barrel 54
created by the
positioning of second member 70. Gas flowing out of second radial port 60
passes through
second side fluid communication port 34 into piston chamber 30 on second side
28 of piston
24. The pressure exerted by the inflowing gas causes piston 24 to move in the
second
direction, as indicated by arrow 18. The movement of piston 30 in the second
direction,
forces exhaust gas out of piston chamber 30 through first side fluid
communication port 32
and into barrel 54 through fourth radial port 64. Exhaust gas in barrel 54 is
confined between
first member 68 and second member 70. The only place the exhaust gas can go is
to exit out
of third radial port 62 to gas exhaust 50.
Switch 52 is what is termed a "four way two position snap switch". Switch 52
has a
switch lever 72. Switch lever 72 is activated when reciprocating shaft 14
moves in the first
direction by a first trigger mechanism 74, which is carried by reciprocating
shaft 14.
Conversely, switch lever 72 is activated when reciprocating shaft 14 moves in
the second
2 0 direction by a second trigger mechanism 76 carried by reciprocating shaft
14. Drive 10 and
control system I2 has been operated at speeds as low as one stroke every three
minutes. This
is an incredibly slow speed, compared to the prior art. In order to facilitate
such a slow speed,
without fluttering or stalling, first trigger mechanism 74 and second trigger
mechanism 76 are
of unique construction. Referring to FIG. 3, each trigger mechanism includes a
spring 78,
2 5 which is coiled around a sleeve 79, which slides over reciprocating shaft
14. Spring 78 has a
fixed end 80 and a free end 82. A stop 84 engages fixed end 80 of spring 78 to
prevent axial
movement of spring 78 along reciprocating shaft 14. In the illustrated
embodiment, stop 84
consists of a collar 86 on sleeve 79. A set screw 88 extends through collar 86
to secure sleeve
79 to reciprocating shaft 14. Set screw 88 facilitates the selective
positioning of the trigger
3 0 mechanism along reciprocating shaft 14, which determines stroke length. A
trigger member
90 is biased by free end 82 of spring 78. In the illustrated embodiment,
trigger member 90 is
an annular pivot ring 92 having a central aperture 94. Sleeve 79 extends
through central
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aperture 94. A second stop 96 is the form of a snap ring retainer. This second
stop 96 is
adapted to limit axial movement of trigger member 90 along sleeve 79 and
prevents trigger
member 90 from separating from sleeve 79. The functioning of the trigger
mechanism can
best be understood by following the sequential order of FIG. 4a through 4g.
Referring to FIG. 5, annular seal 44 includes a housing 98 having an interior
sidewall
100 defining a cylindrical seal chamber 102. In the prior art, seal chamber
was filled with
chevron packing (also known as "V" packing). This chevron packing exerted
considerable
friction upon displacement rod 23, for the length of housing 98. In order to
reduce friction, a
different form of sealing has been used, while leaving the structure of
housing 98 substantially
the same. A cylindrical seal carrier 104 is provided which is adapted to fit
within cylindrical
seal chamber 102. Seal carrier 104 has an exterior surface 106 and an interior
surface 108.
Interior surface 108 serves to define a central bore 110, which is adapted to
receive
displacement rod 23. An exterior circumferential seal groove I 12 is provided
on exterior
surface 106 of seal carrier 104. Two interior circumferential seal grooves
114, one at each
end, are provided on interior surface 108 of seal carrier 104. An exterior
seal ring 116
positioned in exterior circumferential seal groove 112 and is adapted to from
a seal between
exterior surface 106 of seal carrier 104 and interior sidewall 100 of housing
98. An interior
seal ring 118 is positioned in each interior circumferential seal groove 114.
Each interior seal
2 0 ring 118 is adapted to from a seal between interior surface 108 of seal
carrier 104 and
displacement rod 23. Housing 98 has an end cap 120, which closes seal chamber
102. End
cap 120 is removed to provide access to seal chamber 102 to permit the
insertion and removal
of seal carrier 104. When chevron packing is used, a pressure member 122 is
used to exert a
compressive force upon the chevron packing. As the packing wears, end cap 120
is tightened
2 5 to apply more pressure upon the chevron packing, via pressure member 122.
Annular seal 44
is shown as having a pressure member 122. When used with seal carrier 104,
pressure
member 122 merely serves to hold seal carrier 104 securely in place so there
is no axial
movement in housing 98. Where pressures exceed 100 p.s.i., the use of chevron
packing is
still recommended. However, where pressures are under 100 p.s.i., the sealing
system
3 0 illustrated is preferred.
Installation and Operation:
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Installation and operation will now be described with reference to FIG. 1
through
FIG. 5, in order to obtain the benefits of all aspects of the present
invention. Referring to
FIG. 1 and FIG. 2, when assembling drive 10, sleeves 79 of first trigger
mechanism 74 and
second trigger mechanism 76 are placed over reciprocating shaft 14. Referring
to FIG. 3, set
screw 88 is then used to secure sleeves 79 at the desired locations along
reciprocating shaft
14. It must be noted that central aperture 94 of pivot ring 92 must be larger
than the diameter
of sleeve 79 to allow movement of pivot ring 92, while being smaller than the
outside
diameter of spring 78 in order to be biased by spring 78. Referring to FIG. 1
and FIG. 2, gas
manifold 46 is connected to drive 10. Second radial port 60 is connected to
second side fluid
communication port 34, so it is always in fluid communication with second side
28 of piston
24. Third radial port 62 is connected to gas exhaust 50. Fourth radial port 64
is connected to
first side fluid communication port 32, so it is always in fluid communication
with first side
26 of piston 24. Gas inlet 48 is connected to a gas source. Seal carrier 104
is inserted into
annular seal 44 in place of chevron packing, where the operating pressures are
low enough to
warrant such a substitution.
Referring to FIG. 1, operation of drive 10 begins in the first mode, with
first member
68 of switch 52 positioned between first radial port 59 and second radial port
60 and second
member 70 positioned between third radial port 62 and fourth radial port 64.
Gas supplied
2 0 through gas inlet 48 flows into barrel 54 where it encounters first member
68. Gas passes out
through ftrst radial port 59, re-entering barrel 54 at fifth radial port 66.
Gas entering barrel 54
through f fth radial port 66 encounters second member 70. Gas passes out
fourth radial port
64 leading to first side fluid communication port 32 and into piston chamber
30. Once in
piston chamber 30, the in flowing gas creates pressure on first side 26 of
piston 24, causing
2 5 piston 24 to move in the first direction, as indicated by arrow 16. This
movement of piston 24
in the first direction, forces gas out of piston chamber 30 through second
side fluid
communication port 34. The exhaust gas enters into barrel 54 through second
radial port 60.
Once within barrel 54, the exhaust gas is confined between first member 68 and
second
member 70. Gas then passes out third radial port 62 to gas exhaust 50.
Referring to FIG. 4a through 4g, the operation of first trigger mechanism 74
is
sequentially illustrated. Referring to FIG. 4a, movement of reciprocating
shaft 14 carries first
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trigger mechanism 74 toward switch lever 72 of switch 52. Referring to FIG.
4b, as
reciprocating shaft 14, pivot ring 92 comes into contact with switch lever 72.
Refernng to
FIG. 4c, upon continuing movement pivot ring 92 will start to tilt backwards,
with such
movement being resisted by spring 78. As reciprocating shaft 14 continues to
move, spring
78 becoming increasingly compressed, which creates an increasing preload by
first trigger
mechanism 74 upon switch lever 72. Referring to FIG. 4d, eventually there is
enough stored
energy to cause switch lever 72 to start to change direction. Referring to
FIG. 4e, the
movement of switch lever 72 is rapid and deliberate. This rapid and deliberate
movement is
the result of three forces: the forward momentum of reciprocating shaft 14,
the release of
spring tension from spring 78, and the inherent snap acting characteristics of
switch lever 72.
Referring to FIG. 4f, once switch lever 72 has changed position the momentum
of
reciprocating shaft 14 slows in preparation for movement in the second
direction. Referring
to FIG. 4g, first trigger mechanism 74 then moves away from switch lever 72 as
a change in
direction occurs and second trigger mechanism 76 will approach switch lever 72
from the
opposite direction. The operation of second trigger mechanism 76, upon
movement in the
opposite direction is identical and will, therefore, not be further described.
Referring to FIG. 2, when switch lever 72 is switched to the second mode,
first
member 68 of switch 52 is positioned between second radial port 60 and third
radial port 62
2 0 and second member 70 is positioned between fourth radial port 64 and fifth
radial port 66.
Gas continues to be supplied through gas inlet 48 flowing into barrel, however
now as it
encounters first member 68 it concurrently passes out first radial port 59 and
second radial
port 60. Gas flowing out of first radial port 59 re-enters barrel 54 through
fifth radial port 66,
where it encounters a dead end in barrel 54 created by the positioning of
second member 70.
2 5 Gas flowing out of second radial port 60 passes through second side fluid
communication port
34 into piston chamber 30 on second side 28 of piston 24. The pressure exerted
by the in
flowing gas causes piston 24 to move in the second direction, as indicated by
arrow 18. The
movement of piston 30 in the second direction, forces exhaust gas out of
piston chamber 30
through first side fluid communication port 32 and into barrel 54 through
fourth radial port
3 0 64. Exhaust gas in barrel 54 is confined between first member 68 and
second member 70.
The exhaust gas then exits out of third radial port 62 to gas exhaust 50.
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Referring to FIG. 1 and FIG. 2, when drive 10 is operated with control system
12,
considerably less gas is used. The reason for this is that all of the gas
supplied is used to
power piston 24, as opposed to other systems in which gas at higher pressures
was required to
overcome the biasing force of a return spring for the reciprocating shaft.
There are some
5 systems which operate by having a constant bleed of gas through poppet
valves. Control
system has a much lower gas consumption than such systems and is, therefore, a
more
environmentally responsible system. Referring to FIG. 4a through 4g, the use
of trigger
mechanisms 74 and 76, help further facilitated slow, low pressure operation.
What is meant
by slow is speeds as low as one stroke every three minutes. What is meant by
low pressure is
10 pressure in a range of 7 to 10 psi. Referring to FIG. 5, the use of seal
carrier 104 in place of
chevron packing, assists further in reaching this objective of slow, low
pressure operation, by
reducing overall friction and resistance considerably. It also serves a
secondary function of
maintaining displacement rod 23 centred in housing 98. It is preferred that
grease be packed
into central bore 110 between interior seal rings 118 at the time of insertion
of displacement
rod 23. This gives annular seal 44 a self lubrication quality and further
reduces friction as the
grease will move between interior seal rings 118, during reciprocating
movement. Referring
to FIG.1 and FIG. 2, it will be understood that the speed of the unit is
ultimately determined
by gas control valve 49 position upstream of gas inlet 48. The stroke of
reciprocating shaft 14
is set by the positioning of first trigger mechanism 74 and second trigger
mechanism 76.
In this patent document, the word "comprising" is used in its non-limiting
sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
2 5 possibility that more than one of the element is present, unless the
context clearly requires that
there be one and only one of the elements.
It will be apparent to one skilled in the art that modifications may be made
to the
illustrated embodiment without departing from the spirit and scope of the
invention as
3 0 hereinafter defined in the Claims.
