Note: Descriptions are shown in the official language in which they were submitted.
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MULTIPLE PISTON PUMP
BACKGROUND OF THE INVENTION
r 1. Field of the Invention
This invention concerns a reciprocating piston pump that provides
substantially
pulseless delivery of a liquid. This pump is particularly suited for supplying
liquids used in
chromatographic analysis devices, where pulseless flow at low flow rates (0.2 -
1 ml/min) is
required to achieve high instrument sensitivity.
2. General Description of the Background
Constant volume, pulseless reciprocating pumps have been disclosed in U.S.
Patent
Nos. 3,816,029;U.S. 4,028,O18;U.S. 4,687,426and U.S. 4,556,371. A piston pump
using a spool
valve to control liquid outlet from the pistons is similarly shown in European
Patent
No. A20 172 780.
Pulseless delivery of a liquid is described in detail in U.S. Patent No.
4,359,312 which
IS discloses a reciprocating piston pump with two pistons connected in
parallel on the discharge
side. One of the pistons draws in fluid while the other is delivering fluid.
The pistons are
controlled by a cam, which is in turn operated by a computer program to
compensate for the
compressibility of liquid in the pump. The rotational speed of the cam is
varied to compensate
for the compressibility of liquid in the pump and achieve a constant pump
output.
U.S. Patent No. 2,010,377describes a dual piston pump that achieves non-
pulsating
fluid output by overlapping the power strokes of each piston in the pump, and
controlling the
volumetric displacement of the pump per cycle. The combined delivery of the
two pistons, per
unit time, is substantially constant or non-fluctuating.
Each of the pumps shown in the patents described above is relatively large and
not
well adapted for pumping and delivering very small amounts of liquid at a
constant flow rate,
as required in chromatographic analyzers. The prior pumps are particularly
unsuitable for
placement in a compact pumping assembly. Some of these previous pumps also
suffer from
the disadvantage of requiring complicated computer programs and automated
control
mechanisms to achieve constant pump output.
It is accordingly an object of the present invention to provide a multiple
piston pump
that is compact and suitable for delivery of very small amounts of liquid.
It is yet another object of this invention to provide such a pump that is
compact.
Finally, it is an object of the invention to provide a piston pump that is
simpler in
operation than some previous pumps, and particularly is free of the necessity
for complez
i
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mechanical or computer-assisted operation can be used with the present
invention).
SUMMARY OF TI~)~ INVENTION
The foregoing objects are achieved in one embodiment of the present invention
by
providing a pump having at least a first and second piston, wherein the first
piston communicates
with a first pumping chamber and the second piston communicates with a second
pumping
chamber. An inlet flow path communicates with the first pumping chamber when
the first piston
is reciprocating in a direction that draws fluid into the first pumping
chamber, and with the second
pumping chamber when the second piston is reciprocating in a direction that
draws fluid into the
second pumping chamber. An outlet flow path communicates with the first
pumping chamber
when the first piston is reciprocating in a direction that expels fluid out of
the first pumping
chamber, and with the second pumping chamber when the second piston is
reciprocating in a
direction that expels fluid out of the second pumping chamber.
A control valve alternately moves between a first position and a second
position, such that
when the control valve is in the first position the inlet flow path to the
first pumping chamber is
continuous and the outlet flow path from the first pumping chamber is
interrupted, and the inlet
flow path to the second pumping chamber is interrupted and the outlet flow
path form the second
pumping chamber is continuous. When the control valve is in the second
position, the inlet flow
path to the second pumping chamber is continuous and the outlet flow path from
the second
pumping chamber is interrupted, and the inlet flow path to the first pumping
chamber is
interrupted and the outlet flow path from the first pumping chamber is
continuous. The control
valve preferably includes grooves inscribed in the control surface that
establish and break fluid
connections as the cam rotates.
Each reciprocating piston is reciprocated by a cam having a bearing surface
that rotates
around an axis that is substantially parallel to the pistons. The bearing
surface has a variable
shape that reciprocates the pistons, which are spring biased against the
bearing surface. The
variable shape of the bearing surface may be provided by a raceway in the cam,
or a slanted
surface with a constant slope. In particularly preferred embodiments, the
bearing surface
surrounds the control surface, and both are rotated at the same rotational
velocity by the cam.
In another particular embodiment, the pump includes a plurality of
reciprocating pistons,
wherein each piston communicates with a pumping chamber to draw fluid into the
pumping
chamber as the piston moves in a first direction, and to force fluid out of
the pumping chamber
as the piston moves in a second direction. An inlet flow path delivers fluid
to the pump, and an
outlet flow path delivers fluid from the pump. A rotary cam rotates around an
axis of rotation and
reciprocates the pistons as the cam rotates.
A control surface carried by the cam has flow channels inscribed therein. One
of the flow
control channels is a continuous annular outer channel. Another channel is a
discontinuous
annular inner channel circumscribed by the outer continuous annular channel.
The inner channel
has a first arc shaped portion and a second arc shaped portion that do not
communicate with each
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other. A localized indentation is provided at the center of rotation of the
cam. A first
communicating channel extends between the localized indentation and the first
arc shaped inner
channel portion. A second communicating channel extends between the outer
channel and the
second arc shaped inner channel portion.
A stationary control plate fits against the control surface to form closed
passageways
between the control plate and the channels in the control surface. The control
plate has a first
opening through the control plate positioned in alignment with the continuous
annular outer
channel as that channel rotates on the cam. The first opening establishes
fluid communication
between the annular outer channel and the inlet flow pathway. A second opening
through the
control plate is positioned in alignment over the local surface indentation at
the axis of rotation
of the control surface. The second opening establishes fluid communication
with the outlet flow
pathway. A plurality of pumping chamber openings through the control plate are
positioned on
a common circle to establish fluid communication between the pumping chamber
flow paths and
the discontinuous annular inner channel on the control surface.
In yet another embodiment, a multiple piston pump has a housing containing at
least first
and second spring-biased pump piston assemblies. The first pump piston
assembly includes a first
elongated piston bore with a reciprocating piston disposed therein, and an
enlarged volume area
in the first piston bore that forms a first pumping chamber. The second pump
piston assembly
similarly includes a second elongated piston bore with a second reciprocating
piston disposed in
the second piston bore, and an enlarged volume area in the second piston bore
that forms a
second pumping chamber. The enlarged volume area in each piston bore is
provided, in one
embodiment, by a step or diameter transition, and volumetric displacement is
proportional to the
differential piston area at the step.
An inlet flow path is provided through the housing that communicates with the
first
pumping chamber when the first piston is reciprocating in a direction that
draws fluid into the first
pumping chamber. The inlet flow path alternately communicates with the second
pumping
chamber when the second piston is reciprocating in a direction that draws
fluid into the second
pumping chamber. An outlet flow path is also provided through the housing to
communicate with
the first pumping chamber when the first piston is reciprocating in a
direction that expels fluid out
of the first pumping chamber. The outlet flow path alternately communicates
with the second
pumping chamber when the second piston is reciprocating in a direction that
expels fluid out of
the second pumping chamber.
The bore axes for the two piston bores are substantially parallel, and each
reciprocating
piston is reciprocated by a cam that rotates about an axis parallel to the
bore axes. The cam
moves the first and second pistons in such a manner that the first piston
expels fluid while the
second piston draws fluid in, and the first piston draws in fluid while the
second piston expels fluid.
Hence, the pistons are 180 degrees out of phase. The cam further moves the
control valve
between the first and second positions, with the control valve in the first
position during the period
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in which the first piston draws in fluid and the second piston expels fluid.
The control valve is
moved to assume the second position when the first piston expels fluid and the
second piston
draws in fluid.
It is a particular advantage of some embodiments of the present invention that
the cam
has an impingement surface that impinges the pistons, and reciprocates them in
such a manner
that fluid delivery from the pump is substantially constant. Such constant
fluid delivery is achieved
by providing an impingement surface on the cam that alternately displaces each
piston in a positive
displacement direction away from a neutral position to create a positive
pressure that expels fluid
from the pumping chamber. Such positive displacement of each piston is
followed by a reversal
of piston direction to a negative displacement direction, which creates a
negative pressure that
draws fluid into each pumping chamber. The period of time during which
negative displacement
of each piston occurs is less than the period of time during which positive
displacement of each
piston occurs. Moreover, the positive displacements of the first and second
pistons are in
staggered phases, such that the output flows of the first and second piston
pumps are
superimposed to provide a substantially continuous fluid flow from the pump.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a graph showing piston speed versus time for the first piston
(piston A) and
second piston (piston B) of one embodiment of the dual piston pump, with the
respective inputs
and outputs of the two pistons shown within the curves of the graphs.
Fig. 2 is a graph similar to Fig. 1, but showing the superimposed inputs and
outputs of
pistons A and B in Fig. 1, and the corresponding position of the valve.
Fig. 3 is a cross-sectional view through a first embodiment of the piston pump
of the
present invention.
Fig. 4 is a view of the cam and control valve for the piston pump, taken along
lines 4-4
of Fig. 3, with the position of control valve passageways shown on the cam.
Fig. 5 is a view of the control valve portion of Fig. 4, showing the position
of the control
valve passageways after the control valve has rotated through a 180 degree
rotation from the
position shown in Fig. 4.
Fig. 6A is an enlarged, cross-sectional view through one of the piston bores
illustrating
the differential piston area that is proportional to volumetric displacement.
Fig. 6B is an
alternative pumping chamber embodiment.
Fig. 7 is a schematic view of a continuous cross-section through a cam raceway
of the
operating cam of Figs. 3-5, illustrating a groove configuration that controls
the power stroke of
each piston and permits precise, constant volumetric displacement of a small
volume of liquid.
Fig. 8 is a schematic cross-sectional view of a second embodiment of a pump,
in which
the control valve is a spool valve in a first position.
Fig. 9 is a view of the piston pump of Fig. 8, but in which the control valve
has been
moved to a second position.
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Fig. 10 is a graph showing the piston and valve positions of one embodiment of
the pump,
as the operating cam rotates through a 360 degree cycle.
Fig. 11 is a cross-sectional view of another embodiment of the pump, in which
the bearing
surface of the cam is a slanted, annular wobble plate.
Fig. 12 is a view of the control surface carned by the cam, in which grooves
have bin
inscribed to form fluid passageways in cooperation with an overlying control
plate.
Fig. I3 is a cross-sectional view, taken along view line 13-13 in Fig. 11, but
with the cam
rotated counterclockwise from the position shown in Fig. 12.
Fig. 14 is a view, similar to Fig. 13, of a three piston embodiment of the
pump.
DETAILED DESCRIPTION OF SEVERAL PREFERRED EMBODIMENTS
A dual piston pump 10, shown in Fig. 3, is capable of substantially pulseless
delivery of
a fluid, such as liquid water. The pump includes a housing 12 that contains
first pump piston
assembly 14 and second pump piston assembly 16. First assembly 14 includes a
reciprocating first
piston 18 in a first piston bore 20 that extends from an upper surface of
housing 12. Piston 18 has
a large diameter portion 22 that fits within a correspondingly enlarged
diameter portion of bore
20. The piston has a rounded bearing tip 23 that extends into a cam chamber 24
to engage a cam
bearing surface. Piston 18 also includes a reduced diameter portion 25 with an
upper spring seat
surface 26, that fits within a reduced diameter portion of bore 20. Piston 18
is capable of
reciprocating in bore 20 against the bias of a helical spring 28 with an upper
end that seats against
an internal shoulder 30 of bore 20, and spring 28 extends through bore 20 to
sit on a flat upper
face 26 of portion 25 of piston 18.
A pair of parallel, spaced, annular seals 32, 34 are placed around piston 18
with seal 32
circumscribing portion 22, and seal 34 circumscribing portion 25 slightly
above an annular face 35
betw~n portions 22, 25 of piston 18. A first pumping chamber 36 is formed in
the bore 20 by the
necked down portion of piston 18, and extends from seal 34 to the annular face
35. Chamber 36
is shown in a compressed condition in Fig. 3, but the chamber expands as
piston 18 is forced
downwardly by spring 30, and the expanding chamber creates a suction pressure
that draws liquid
into the chamber in a manner described below.
Second assembly 16 is similar to assembly 14 described above. Second assembly
16
includes a reciprocating piston 48 in second piston bore 50 that extends from
an upper surface of
housing 12 through to cam chamber 24, where it abuts a cam raceway described
below. Piston
48 has a large diameter portion 52 that fits within a correspondingly enlarged
diameter portion of
4
bore 50. The piston has a rounded bearing tip 53 that extends into cam chamber
24. Piston 48
also has a reduced diameter portion 55. Piston 48 is capable of reciprocating
in bore 50 against
the bias of a helical spring 58 that seats on an internal shoulder 60 of bore
50 and extends through
bore 50 to also seat on a flat upper face 59 that forms the top surface of
portion 55 of piston 48.
A pair of parallel, spaced, seals 62, 64 are placed around piston 48 with seal
62
circumscribing portion 52, and seal 64 circumscribing portion 55 slightly
above an annular face 65
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between portions 52, 55 of piston 48. A pumping chamber 66 is formed in the
bore 50 by the
necked down portion of piston 48. Chamber 66 extends from seal 64 to annular
face 65. Chamber
66 is shown in a fully expanded condition in Fig. 3, with piston 48 displaced
completely downward
by the expansion of spring 58 and the changing surface of the cam described
below. The volume
of chamber 66 will diminish as piston 48 is subsequently moved upwardly, which
will create a
positive pressure in chamber 66 as its volume is reduced.
Large diameter portions 22, 52 of pistons 18, 48 extend into cam chamber 24 to
contact
a raceway 84 of cam 80. The cam moves at a constant rotational speed and has a
surface that
impinges against the pistons 18, 48 to reciprocate them against the bias of
their respective springs
28, 58. Cam 80 includes a cylindrical cam collar 81 having a flat upper
bearing surface 82 (Figs.
3 and 4) with a continuous annular cam raceway 84 having a center of curvature
at the axis of
rotation of the cam. The bearing tips 23, 53 of pistons 18, 48 abut against
and ride within the
groove 84, and are maintained in contact therewith by the bias of springs 28,
58. Raceway 84 has
a varying depth, described further below, which moves pistons 18, 48 against
the bias of springs
28, 58 to stagger the pulsatile outflow from each of piston assemblies 14, 16
and achieve
substantially continuous liquid outflow from pump 10.
Cam 80 further includes a downwardly extending annular bearing collar 86
through which
a drive shaft 88 extends. Shaft 88 is fixed to collar 86 to rotate cam 80 as
shaft 88 rotates. Shaft
88 extends along the axis of rotation 90 of collars 81, 86, and the axis 90 is
substantially parallel
to the longitudinal axes of bores 20, 50. An interior spring chamber 92 of cam
80 contains a
helical spring 94 that is seated on annular surface 96 around shaft 88. Spring
94 extends upwardly
around a portion of shaft 88 and toward a flat bearing face 98 of a control
valve 100 (Figs. 3-5),
to support the control valve. Control valve 100 is carried by cam 80 and
rotates with collar 81.
A wear plate 104 is fixed to housing 12, does not rotate with cam 80, and has
an internal bearing
surface 106 (Fig. 3) that bears against opposing bearing surface 82 (Figs. 4-
5).
Bearing surface 108, on the upper surface of control valve 100, acts as a
control surface
that has a series of grooves inscribed thereon that, in cooperation with the
overlying stationary
plate 104, form enclosed passageways that direct the flow of fluid through the
control valve 100.
A first groove complex 118 is generally epsilon-shaped, with an arcuate back
120 and a straight
cross portion 122 that extends toward and terminates at an axis of rotation
124 of the control valve
100 (which is coincident with the axis of rotation 90). The portion of the
passageway at the axis
of rotation 124 is enlarged (compared to the width of the remainder of groove
complex 118) and
F.
cylindrical or hemispherical. Arcuate back 120 falls on a portion of a circle
that has a center of
curvature at axis 124.
A second groove complex I30 is also inscribed into surface 108. Complex 130
includes
an annular groove 132 that circumscribes first groove complex 118, and has the
same center of
curvature as arcuate back 120, but a greater radius of curvature. A side-arm
groove 134 extends
from groove 132, toward axis 124, but stops short of reaching it. Groove 134
terminates in an
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arcuate groove 136 that is on the same circle as arcuate back 120, but does
not overlap groove 120.
Groove 136 has the same center of curvature and radius of curvature as groove
120. Each of
groove completes 118, 130 are covered by internal bearing surface 106 of wear
plate 104, which
forms a fluid tight seal with the grooves, such that the groove complexes 118,
130 and bearing
surface 106 form fluid passageways of the same configuration as the grooves
described above.
An inlet bore 140 extends through plate 104 from the internal surface 106
thereof, and
the distance from axis 124 to groove 132 is the same as the radius of the
circle formed by groove
I32. Hence, bore 140 communicates with the passageway formed by annular groove
I32 at ali
times during the rotation of cam 80. Bore 140 also communicates with an inlet
flow path line 142
that extends through housing 12 to the exterior thereof, for connection
through an orifice 143 to
a source of liquid (not shown) that is to be pumped through pump 10.
A first pumping chamber bore 144 also extends through plate 104, with the
distance from
axis 124 to bore 144 the same as the radius of the circle on which grooves
120, 136 are inscribed.
Hence, bore 144 is positioned to communicate with the arcuate passageway
formed by groove 120
when control valve 100 is in the position shown in Fig. 4, and to communicate
with the passageway
formed with arcuate groove I36 when control valve 100 has rotated to the
position shown in Fig.
5. As demonstrated in the drawing, groove 120 extends through an arc of about
200 degrees, while
groove 136 extends through an arc of only about 90 degrees, hence bore 144
will communicate
with groove 120 through about 200 degrees of rotation of cam 80. Bore 144 will
communicate with
groove 136 through only about 90 degrees of rotation. Bore 144 extends away
from surface 108
to communicate with first chamber fluid line 146 that extends through housing
12 to first pumping
chamber 36. Through line 146, pumping chamber 36 alternately communicates with
first groove
complex 118 (through arcuate groove 120) and second groove complex 130
(through groove 136).
An outlet bore 150 extends through wear plate 104 to connect the end portion
of groove
122 at axis of rotation 124 with an outlet flow line 152 that extends through
housing 12 to
communicate with an outlet line (not shown) that delivers fluid from pump 10
through an orifice
153. Finally, a second pumping chamber bore 154 extends through plate 104 at a
distance from
axis 124 that is equal to the radius of the common circle on which grooves
120, 136 are formed.
Hence, bore 154 is positioned to contact groove 136 when control valve 100 is
in the position of
Fig. 4, and alternately contact groove 120 when valve 100 is in the position
shown in Fig. 5. In
between these two positions, bore 154 will communicate with groove 120 through
about 200
degrees of rotation of cam 80, and with groove 136 through about 90 degrees of
cam rotation.
Bore 154 communicates with a second pumping chamber passageway I56 that in
turn extends
through housing 12 to communicate with second pumping chamber 66.
Bores 140, 144, 150 and 154 are all aligned on a common diameter of the
surface 108 of
cylindrical valve member 102.
Assemblies 14, 16 operate by reciprocation of pistons 18, 48 as cam 80 rotates
through
a complete revolution around axis 90, and cam raceway groove 84 in bearing
surface 82 moves the
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pistons in a specific, coordinated manner to provide a substantially constant
volumetric flow rate
of liquid through outlet Line 152. Cam raceway 84 is shaped as shown in Fig.
7, wherein the cam
raceway cross-section is shown as a longitudinal section to better illustrate
the changing depth of
the raceway throughout its circumference. The cam 80 rotates in a direction
such that free ends
of the pistons abut against and ride over the raceway in the direction of
arrow 158. The pistons
are spaced 180 degrees apart on the circular raceway, and have simultaneous
movements that will
be more fully detailed in Fig. 10.
The raceway has an upwardly inclined segment 160, followed by a horizontal
segment 162
that is parallel to top surface 82 of cam 80, and then a downwardly inclined
segment 164. A
horizontal segment 166 is then followed by the upwardly sloping segment 160,
as the continuous
raceway circuit is completed and begins to repeat. Flat surface 166 is formed
by the flat bottom
surface of raceway 84. Upward incline 160 is longer and less steep than
downwardly inclined
surface 164.
The dimensional relationships of surfaces 160-166 are better illustrated in
Fig. 10. The
lines labeled P1 Position and P2 Position refer to the position of the first
piston P1 (piston I8) and
second piston P2 (piston 48), where the free end of each piston 18, 48 abuts
the surface' of raceway
84. Hence, the P1 and P2 position also traces the configuration of the raceway
surface that moves
the pistons. The segments 160-166 are therefore labeled on the graph of Fig.
10. Piston 18 (P1)
has an initial upward displacement along raceway incline 160, followed by a
period of zero
displacement as the piston rides along flat raceway segment 162. Piston 18
then undergoes a steep
downward displacement along surface 164, and then a period of zero
displacement along flat
bottom raceway segment 166. Piston 48 (P2) similarly has an upper period of
zero displacement
as it rides along top flat segment 162, followed by steep downward
displacement along segment
164, then a period of zero displacement along flat bottom segment 166,
followed by upward
displacement along raceway incline 160. The movements of pistons 18, 48 are
identical, but 180
degrees out of phase. Hence, second piston 48 (P2) reaches the position of
flat segment 162 at
about S degrees of rotation, while first piston 18 (P1) reaches that same
position at 185 degrees.
The bearing surface in raceway 86 is shaped to accelerate the first piston 18
in a positive
displacement direction (as bearing tip 23 rides up segment 160) through about
180 degrees of
rotation to progressively reduce the volume of first pumping chamber 36 and
force fluid out of that
pumping chamber. Tip 23 of piston 18 then reaches the flat segment 162, which
holds the positive
displacement of the first piston I8 at a constant maximum displacement
position through about
72 degrees of cam 80 rotation, during which fluid is neither drawn into nor
expelled from chamber
36. Tip 23 then rides down over segment 164, to displace piston 18 (with the
bias of spring 28)
in a negative displacement direction through about 72 degrees of cam rotation
until a maximum
negative displacement position is reached as piston 18 arrives at segment 166
of groove 84. Piston
18 occupies constant negative displacement position 166 through about 36
degrees of cam rotation,
during which fluid is neither drawn into nor expelled from chamber 36. During
negative
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displacement of first piston I8, fluid is drawn into first pumping chamber 36
as that chamber
volume expands.
The continuous impingement of the rotating annular control groove against both
piston
tips 23, 53 provides simultaneous movement of second piston 48 as first piston
I8 is moving, but
180 degrees out of phase with each other, as shown in Fig. 10.
Displacement of the first piston 18 in the positive displacement direction
along segment
160a begins at about S degrees rotation, as arbitrarily shown at A in Fig. 10.
The beginning of
positive displacement of first piston 18 coincides with second piston 48 first
reaching it maximum
positive displacement at segment 162. Displacement of first piston 18 in the
positive displacement
direction along segment 160 continues during the entire period in which the
second piston 48 is
in maximum positive displacement along segment 162. Positive displacement of
piston 18 also
continues while second piston 48 is displaced in the negative displacement
direction as tip 53
moves along segment 164 (beginning at B), and reaches the maximum negative
displacement
position of the second piston at segment 166 (at C). Maximum constant positive
displacement of
first piston 18 begins as tip 23 initially rides on to segment 162 (at D), at
the same time that
displacement of the second piston 48 in the positive direction begins.
Displacement of first piston 18 in the negative displacement direction begins
at E as tip .
23 begins to ride down segment 164. Point E occurs about midway through
displacement of the
second piston 48 in the positive displacement direction (as tip 53 rides along
segment 160). The
first piston 18 reaches its maximum negative displacement position at F during
the continued
displacement of second piston 48 in the positive displacement direction.
Hence, the period from
E to F to A all occurs during the latter one-half of the positive displacement
stroke of second
piston 48 from D to A. Therefore, the period during which fluid is drawn into
each piston is
shorter than the period during which fluid is pumped out. In the disclosed
embodiment_ the
period of pumping out is approximately three times longer than the period of
pumping in.
Control valve 100 is fined to and rotates with cam 80, about a common axis 90.
As cam
80 rotates to actuate the piston pumps 14, 16, the control valve rotates to
direct the flow of fluid
through inlet and outlet paths. Control valve 100 moves between a first
position shown in Fig. 5,
and a second position shown in Fig. 4. In the first position (Fig. 5), fluid
communication is
established between the inlet line 142 and first pumping chamber 36 through
passageway 146.
Inlet line !42 communicates through bore 140 with groove I32, and passageway
146 communicates
through bore 144 with groove 136 when the control valve is in the position
shown in Fig. 5. Hence
fluid can flow through the communicating passageways formed by grooves 132,
134 and 136 to
establish fluid communication between inlet line 142 and chamber line 146.
This fluid
communication continues as long as bore 144 is above arcuate groove 136, and
the arcuate shape
of groove I36 maintains it below bore 140 through about one-quarter (90
degrees) of the rotation
of control valve 100.
With the control valve in this same position (Fig. 5), outlet line 152
communicates through
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bore 150 with cross portion 122 at axis of rotation 124, and passageway 156
communicates through
bore 154 with areuate groove 120. Hence inlet line 152 communicates with
second pumping
chamber 66 through line 156 when the control valve is oriented as in Fig. 5.
Continuous fluid
communication is established because the passageways formed by grooves 120 and
122 are
continuous, and interconnect Lines 152,156. Bore 150 is always positioned
above center of rotation
124, and the passageway formed by groove 120 will remain positioned below bore
154 through
about one-half rotation of control valve 100 because of the arcuate shape and
length of the groove.
When control valve 100 rotates through 180 degrees around axis 90, it reaches
the position
shown in Fig. 4, at which time inlet Line 142 is connected with second pumping
chamber 66
through line 156, and first pumping chamber 36 is connected with outlet line
152. Inlet line 142
always communicates with groove 132 on control valve 100 through bore 140,
because the
continuous annular groove 132 forms a complete circle that is always
positioned below bore 140
as control valve 100 rotates. In Fig. 4, line 142 is connected to second
chamber 66 because line
156 communicates with groove 136 through bore 154. Grooves 132 and 136 are
connected by
groove 134, hence fluid flows through the passageways formed by grooves 136,
134 and 132 from
inlet line 142 to pumping chamber 66.
With the control valve in the position shown in Fig. 4, outlet line 152
communicates with
first pumping chamber 36. Inlet line 152 always communicates through bore 150
with groove 122
at center of rotation 124, throughout the entire rotation of control valve
100. Passageway 146 to
first pumping chamber 36 communicates with groove 120 through bore 144 during
the period of
90 degree rotation of cam 80, during which the arcuate groove 120 rotates
beneath bore 144.
Hence fluid may flow from pumping chamber 36, through line 146, into the
passageway formed
by groove 120, through cross portion 122, and through outlet line 152.
In operation, with control valve 100 in the position shown in Fig. 5, the cam
raceway 84
on cam 80 is configured to negatively displace first piston 18 to draw fluid
into first chamber 36
during the period in which lines 142 and 146 are connected by control valve
100 as groove 136
rotates beneath bore 144. During this same period, cam 80 moves second piston
48 in a positive
displacement direction to force fluid out of second piston chamber 66 and
through Lines 156,152
while groove 120 rotates beneath bore 154 for about 200 degrees of rotation of
cam 80. Fluid will
therefore be drawn into first pumping chamber 36 at the same time that fluid
is forced out of
second pumping chamber 66. The period during which groove 120 rotates beneath
bore 154 is
about twice as long as the period during which groove 136 rotates beneath bore
144, hence the
r
period of drawing fluid into chamber 36 is about half as long as the period
during which fluid is
pumped out of chamber 66.
When the cam and control valve rotate to the position shown in Fig. 4, fluid
is pumped
through inlet line 142 into second pumping chamber 66, as second piston 48 is
displaced
downwardly by the force of spring 58 against piston 48. At the same time,
fluid moves through
line 146 into outlet line 152 as cam 80 displaces first piston 18 upwardly
against the bias of spring
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28 to reduce the volume of first pumping chamber 36. Fluid is therefore drawn
into second
pumping chamber 66 at the same time that fluid is forced out of first pumping
chamber 36. The
period during which groove 120 rotates beneath bore 144 is about twice as long
as the period
during which groove 136 rotates beneath bore 154. Hence, the period during
which the control
valve establishes fluid communication between lines 146 and I52 for outflow,
is about twice as long
as the period during which the control valve establishes fluid communication
between lines 142 and
156 for inflow into chamber 66.
The effect of these superimposed, staggered inputs and outputs of varying
duration from
the first and second piston pumps 16, 18 is shown schematically in the graphs
of Figs. 1 and 2.
Fig. 1 represents piston speed versus time, and the area enclosed within each
graph is proportional
to the volume of fluid displaced by each piston. Fluid output for first piston
I8 is shown as Piston
A, and fluid output for second piston 48 is shown as Piston B. Enclosed areas
above the x-axis
are volumes pumped out, while areas enclosed below the x axis are volumes
drawn into the piston
chamber. Piston A accelerates rapidly in an output power stroke 172a which
begins to deliver
fluid from pump 10, then at 173a achieves a substantially constant power
stroke speed I74a for
a period of time. At 175a, it slows rapidly along line 176a to a stop point at
178a. It then begins
its return or input stroke at an even greater speed along line 180a, at 181a
achieves a stable return
stroke speed along line 182a, then at 183a slows rapidly along line 184a to a
stop point 186a.
The graph for piston speed versus time of second piston pump 16 (Piston B) is
similar,
but is offset by 180 degrees along the time axis. Piston B accelerates rapidly
in an output power
stroke 172b, then at 173b achieves a substantially constant power stroke speed
174b for a period
of time. At 175b it slows rapidly along line 176b to a stop point at 178b. It
then begins its return
stroke at an even greater speed along line 180b, achieves at 181b a stable
return stroke speed
along line 182b, then at 183b slows rapidly along line I84b to a stop point
186b.
A simplified schematic time relationship between the output power strokes and
input
strokes is shown by dotted lines in Fig. l , which interconnect simultaneous
time events for the two
piston pumps 14, 16. Return strokes 180-184 occur more rapidly than output
power strokes 172-
178, such that output power strokes are able to partially overlap and
superimpose their fluid
outputs. This summation of outputs provides a substantially constant fluid
output from the pump
10, as shown in Fig. 2. The output power stroke of Piston A begins at 186a,
coincident with the
time that the output power stroke of piston B begins to reverse at 175b.
Acceleration to output
power stroke along 172a coincides with the deceleration of the output stroke
in Piston B. The
entire period of the input power stroke 178b-186b then occurs, and takes the
same amount of time
as the constant velocity portion 174a of the output stroke of Piston A.
Acceleration of the output
stroke of Piston B along 172b then occurs in the same time that deceleration
of the output stroke
of Piston A occurs along 176a. The entire input stroke of Piston A
(180a,182a,184a) then occurs
during the same time that constant velocity portion 174b of output stroke for
Piston B occurs. In
this manner, the output strokes of Pistons A and B overlap, as shown in Fig.
2, to provide a
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substantially constant flow rate from pump 10.
A second embodiment of the invention is shown in Figs. 6, 8 and 9, in which
the control
valve is a spool valve. As in the earlier described embodiment, pump 210 is
capable of
substantially pulseless delivery of a fluid, such as liquid water. The pump
includes a housing 212
that contains first piston assembly 214 and second piston assembly 216. First
piston assembly 214
includes a reciprocating first piston 218 in a first piston bore 220. Piston
218 has a first large
diameter portion 222 with a rounded bearing tip 223, and a second large
diameter portion 224,
with a flat top surface 226. Piston 218 is capable of reciprocating in bore
220 against the bias of
a helical spring 228 that seats against and extends between a housing cover
230 and surface 226
of piston 218.
A series of pumping chambers 232, 234 are located along piston 218, and are
formed by
necked down diameter portions of the piston. Fig. 6A illustrates a
representative pumping
chamber 232 in which portions 222, 224 of piston 218 meet at necked down
portion 235. A
clearance seal circumscribes portion 224,and a clearance seal circumscribes
portion 222,delimiting
chamber 232 therebetween to form chamber 232. Hence, chamber 232 varies in
volume as piston
218 reciprocates in the bore. An alternative embodiment of the pumping chamber
is shown in Fig.
6B wherein portion 222 necks down to a portion 224 that then reciprocates in a
narrower diameter
piston bore.
A bearing end of piston 218 extends beyond a bottom surface 238 of housing 212
and
engages raceway 239 in a cam 240, similar to the cam 80 discussed in
connection with an earlier
embodiment. The cam has the same principle of operation as the cam 80, at
least with respect
to reciprocation of pistons 218, 248, and it will not be described again. The
surface of the cam
raceway 239 is the same as the surface configuration of raceway 84.
Second piston assembly 216 is similar to piston assembly 214 described above.
Second
piston assembly 216 includes a reciprocating piston 248 in second piston bore
250. Piston 248 has
a series of necked down portions that form chambers 252 and 254. Piston 248 is
capable of
reciprocating in bore 250 against the bias of a helical spring 258 that seats
against and extends
between housing cover 230 and surface 260 of piston 218. A bearing end 262 of
piston 248 extends
beyond the bottom surface 238 of housing 212 and engages raceway 239.
A spool valve 266 is provided in a bore 268 that extends through housing 212
parallel to
bores 220, 250. Bore 268 is offset from the longitudinal axis of housing 212.
The spool valve
includes a reciprocating piston 270 in bore 268. Piston 270 has two necked
down portions that
form chambers 272, 274 that provide flow paths through spool valve 266. Piston
270 is capable
of reciprocating in bore 268 against the bias of a helical spring 276 that
seats against and extends
between housing cover 230 and surface 278 of piston 270. A bearing end 280 of
piston 270 extends
beyond the bottom surface 238 of housing 212 and engages a cam raceway 241,
which reciprocates
piston 270 in a manner described below.
An inlet line 284 opens at an orifice 285 on the exterior of housing 212, and
line 284
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extends through the housing parallel to spool valve bore 268, and between
spool valve 266 and
second piston 248. Communicating fluid lines 286, 288 extend from inlet line
284 to spool valve
bore 268. Line 286 communicates with chamber 272 when the spool valve is in
the position shown
in Fig. 9, but not when the spool valve is in the position shown in Fig. 8.
Line 288 is positioned
to communicate with chamber 274 when the spool valve is in the position shown
in Fig. 8, but not
when the spool valve is in the position shown in Fig. 9.
An outlet fluid line 296 extends through the housing 212 parallel to spool
valve bore 268,
and opens through the exterior of housing 212 at orifice 298. Lines 300, 302
extend from line 296
to spool valve bore 268. Line 300 communicates with chamber 272 when the spool
valve is in the
position shown in Fig. 8, but not when the spool valve is positioned as in
Fig. 9. Line 302
communicates with chamber 274 when the spool valve is in the position shown in
Fig. 9, but not
when the spool valve is in the position shown in Fig. 8.
Lines 304, 306 communicate between chambers 252, 254 and chambers 272, 274.
Line 304
always communicates with chambers 252 and 272, at all times throughout
reciprocation of spool
valve 270. Line 306 always communicates with chamber 254, but only
communicates with chamber
274 when the spool valve is in the position shown in Fig. 8. Line 306 thereby
serves as a fluid leak
line to redirect fluid, that bleeds past clearance seals, back into the pump.
Another Iine 308
communicates between chamber 274 and chamber 232. Line 308 always communicates
with
chambers 274 and 232 as the spool valve reciprocates.
In operation, cam 240 moves the pistons 214, 248 and spool valve piston 270
between the
positions shown in Figs. 8 and 9. Referring first to Fig. 9, in which the
spool valve is in the
position shown, piston 248 is moving down while piston 218 is moving up. Fluid
flows from a
supply source (not shown) through orifice 285 into lines 284 and 286. Fluid in
line 284 is able to
communicate with line 304 through chamber 272 with which both lines 284, 304
communicate.
With the spool valve in this position, simultaneous downward movement of
piston 248 creates a
negative pressure that draws fluid through line 284, 286, chamber 272, and
into line 304 and
chamber 252.
Simultaneous with the drawing of fluid into chamber 252 in Fig. 9, piston 218
is moving
upwardly and forcing fluid out of its chamber 232. As chamber 232 diminishes
in volume, fluid
is forced out of chamber 232, through line 308, chamber 274, and into lines
302, 296. Hence fluid
within chamber 232 is expelled through outlet 298 while new fluid is drawn in
through inlet 285
into chamber 252.
Cam 240 is continuously rotating through repeated 360 degree rotations during
operation
of the valve 210, and the bearing surface of the cam has a pair of concentric
raceways 239, 241 that
move the pistons of the valve by impinging against their ends 236, 262 and
280. After cam 240
rotates through 180 degrees from the position shown in Fig. 9, the pistons
218, 248 and 270 are
in the position shown in Fig. 8, with spool valve piston 270 having moved
down, piston 218 moving
downwardly in the direction of arrow 310, and piston 248 moving upwardly in
the direction of
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arrow 312.
With the pistons arranged as in Fig. 8, fluid still moves in through line 284,
but it can no
longer communicate with chamber 252 because spool valve 270 has moved
downwardly from the
position it occupied in
Fig. 9. Instead, fluid moves through inlet line 284, into line 288, thence to
spool valve chamber
274 and into chamber 232 through line 308. The piston 218 is moving down,
hence supplying
negative pressure in chamber 232 that draws fluid into chamber 232 from inlet
line 284.
Simultaneous with movement of fluid into chamber 232 (Fig. 8), upward movement
of the
other piston 248 is expelling fluid from chamber 252. As piston 248 moves up,
positive pressure
in that chamber forces fluid out through line 304, which communicates with
chamber 272, that in
turn communicates with lines 300 and 296. Fluid forced out by chamber 252 is
expelled through
outlet orifice 298.
Cam 240 continues to rotate, and after a further 180 degree rotation from that
shown in
Fig. 8, will once again assume the configuration shown in Fig. 9. The
continuous upward and
downward movement of piston 218, 248, with the varying position of spool valve
266, provides for
a continuous flow of fluid out of the valve. The outputs and inputs of pistons
218, 248 will follow
the pattern shown in Fig. 1, and the superimposed flows of the two pistons
will provide a
substantially uniform flow output, as demonstrated in Fig. 2.
Line 306 is a fluid leak return line that helps diminish the amount of liquid
that leaks out
of the pump. Liquid can seep past the clearance seals around chamber 252. The
seeping liquid
will reach chamber 254, and be directed back into the inlet line through line
306. Other leak lines
are shown in Figs. 8 and 9 (for example from chamber 234), and their function
is the same as line
306.
. Another embodiment of the invention is shown in Fig. 11, wherein a pump 400
in housing
401 includes a first piston 402 and a second piston 404 that reciprocate in
their respective piston
bores. A tip 406 of piston 402 has a bearing cap 408 with a circumferential
collar 410 that is
spring biased by spring 412 that seats against and extends between collar 410
and an interior ledge
414 of housing 401. A tip 420 of piston 404 similarly has a bearing cap 422
with a circumferential
collar 424 that is spring biased by spring 426 that seats against and extends
between collar 424 and
an interior /edge 428 of housing 401.
Piston 402 communicates with a pumping chamber 430 in a control plate 432 that
is part
of housing 401, while piston 404 communicates with a pumping chamber 434 that
is also in control
plate 432. The control plate forms the inner end of the bore in which each
piston reciprocates,
and each pumping chamber is formed by a recess in the plate 432 that forms the
inner portion of
the piston bore. An inlet flow path 440 is formed through the control plate
432 and the wall of
housing 401 betw~n an external inlet opening 441 and an orifice 442 opening on
an inner control
surface 444 of the control plate 432. An outlet flow path 446 is formed
through control plate 432
and a wall of housing 401 between an external outlet opening 448 and an
orifice 450 opening on
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inner surface 444 of plate 432. A pumping chamber flow path 452 extends
through control plate
432 of housing 401 from pumping chamber 430 to an orifice 454 opening on inner
surface 444.
Another pumping chamber flow path 458 extends through the control plate 432 to
an orifice 460
opening on inner surface 444. Orifices 454, 460 are on a common circle.
A rotary cam 466 is positioned in housing 401,and includes a central post
portion 468 that
' projects away from a surrounding circumferential bearing collar 470. The
bearing collar 470 is
inclined at a constant angle of about 15 degrees to the axis of rotation of
cam 466. An annular
wobble plate 472 with a smooth top surface is positioned on top of collar 470
to provide a bearing
surface that impinges against bearing caps 408, 422. As cam 466 rotates,
impingement of the
wobble plate against the caps 408, 422 reciprocates the pistons. The bearing
surface of plate 472
rotates around an axis of rotation 492 of the cam 466. The bearing surface of
plate 472 is non
circumferential, that is it is not on the curved circumferential face 473 of
the collar 470. The non
circumferential bearing surface is instead in a plane that intersects axis of
rotation 492. Axis 492
preferably extends substantially parallel to pistons 402, 404, and through a
control member 476
discussed below.
The central post 468 of cam 466 includes a top cylindrical portion that
extends between
an annular shoulder 474 and a disc-shaped control member 476. The post 468 has
an annular
ridge 478 that fits within a complementary annular indentation in a bottom
face of control member
476. A spring 482 extends around post 468 between shoulder 474 and a bottom
surface of control
member 476 to force member 476 tightly against control plate 432. Tight
engagement between
the control plate 432 and disc-shaped control member 476 establishes fluid
tight passageways
between the plate 432 and grooves that form channels inscribed in a control
surface 484 of
member 476.
Fig. 12 shows the control surface of member 476. The control surface has a
continuous
annular outer channel 486 that circumscribes an inner channel 488. Inner
channel 488 is
discontinuous, and includes a first arc shaped inner channel portion 488a and
a second arc shaped
inner channel portion 488b. The portions of the channel 488 both run along a
common circle, but
the portions 488a, 488b are interrupted so that they do not communicate with
each other. In the
embodiment of claim 12, portion 488b extends along approximately 170 degrees
of the circle, while
portion 488a extends along approximately 170 degrees of the common circle. The
channel portions
488a, 488b are symmetric mirror images of each other. Discontinuity between
channel portions
488a, 488b prevent fluid communication between these channels. In other
embodiments, a
completely circular inner channel 488 can be provided, but with occlusions
within the channel that
break the channel into discrete channel segments. In yet other embodiments,
the channels may
' 35 be asymmetric, for example portion 488a extending along approximately 180
degrees of the
common circle, and the portion 488b extending along approximately 120 degrees.
A localized, indentation 490 is located on control surface 484 along the axis
of rotation
492 of cam 466. A first communicating channel 494 extends between and connects
the localized
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indentation 490 and the first arc shaped channel portion 488a. A second
communicating channel
496 extends between second arc shaped channel portion 488b and outer channel
486.
The stationary control plate 432 fits against control surface 484 to convert
the channels
into closed fluid passageways. The orifices in control plate 432 are
positioned to establish and
break fluid connections as cam 466 rotates, as best shown in Fig. 13. When the
cam is in the
position shown in that drawing, orifice 450 is centered around axis of
rotation 492, and aligned
over indentation 490. This alignment is maintained throughout rotation of cam
466 so that fluid
communication between indentation 490 and outlet flow path 446 is always
present. Similarly,
orifice 442 is aligned over channel 486 so that inlet flow path 440 is always
in communication with
the passageway formed by channel 486 throughout rotation of cam 466.
Orifice 454 is aligned over the circle on which inner channel 488 lies. In
Fig. 13, orifice
454 communicates with arc 488b to establish fluid connection between arc 488b
and the flow path
452 leading to pumping chamber 430. Orifice 460 communicates with arc 488a to
establish fluid
connection betw~n arc 488a and the flow path 458 leading to pumping chamber
434.
Communication between orifice454and arc488bcontinues throughout approximately
170 degrees
of rotation of cam 460, while orifice 460 communicates with arc 488a
throughout approximately
170 degr~s of cam rotation. As rotation of cam 466 and control surface 484
continues, orifice
454 will then communicate with arc 488a and not 488b through about 170 degrees
of cam rotation,
while orifice 460 will communicate with arc 488b and not 488a through about
170 degrees of cam
rotation. Orifices 454, 460 are in a common circle overlying the annular path
of channel 488.
As cam 466 rotates, wobble plate 472 also reciprocates spring biased pistons
402, 404.
The constant slope (both in the negative and positive directions) of the
bearing surface of wobble
plate 472 provides a substantially constant velocity of each piston as it
reciprocates in each
direction. The two pistons are 180 degrees apart, hence the pistons 402, 404
reciprocate
approximately 180 degr~s out of phase. For example with the cam in the
position shown in Fig.
13, as piston 404 moves into chamber 434, it pumps fluid out of chamber 434
through pathway 458
and orifice 460, through arc 488a, pathway 494, orifice 450, and outlet flow
pathway 446.
Simultaneously, the other piston 402 is moving out of chamber 430, to draw
fluid into the chamber
from inlet 441, which communicates with flow path 440 through orifice 442,
channels 486, 496,
488b, orifice 454 and flow path 452. Rotation of the cam 466 (for example a
180 ° rotation from
that shown in Fig. 13) reverses these relationships, such that as piston 402
subsequently
r~iprocates into chamber 430, fluid flows out of the chamber through path 452,
orifice 454, arc
488a, segment 494, orifice 450, and outlet flow path and opening 448.
Similarly, reciprocation of
piston 404 away from chamber 434 will draw fluid in through pathway 458,
orifice 460,~arc 488b,
segment 496, outer channel 486, orifice 442, pathway 440 and inlet opening
441.
Another embodiment of the piston pump is shown in Fig. 14, wherein like parts
have been
given like reference numerals to the embodiment shown in Fig. 13, with the
exception of the
pistons and the orifices with which they communicate. This embodiment of the
multiple piston
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pump has three pistons, which are designated 502, 503 and 504, which
respectively communicate
through flow paths 552, 555, 558 with orifices 554, 557 and 560 in control
plate 432. Each of these
orifices is positioned on a circle below which inner channel 488 extends, so
that the orifices will
be in communication with either arcs 488a or 488b at different times
throughout cam 466 rotation.
The addition of additional pistons in this manner can decrease pulsation in
outflow from the pump
by summing the simultaneous outflow of multiple pistons.
A particular advantage of the three piston embodiment is that it reduces
pulsation of flow
from the pump. This is an advantage that persists with other pumps in
accordance with the
present invention that have an odd number of pistons, for example three, five
or seven pistons.
Although the disclosed embodiments show inflow through opening 441 and outflow
through opening 448, the inflow and outflow can be reversed so that opening
441 is an outflow and
opening 448 is an inflow. The flow of fluid through the pump would them be
reversed.
Pulsations of flow from the pump can also be further reduced by controlling
cam rotation
speed over the course of rotation. The rotational speed can be increased at
times of decreased
flow output, and decreased at times of increased flow output.
Having illustrated and described the principles of the invention in several
preferred embodiments, it should be apparent to those skilled in the art that
the invention can be
modified in arrangement and detail without departing from such principles.
Therefore, the
illustrated embodiments should be considered only as preferred examples of the
invention and not
as a limitation on the scope of the claims. We therefore claim as our
invention all modifications
and equivalents to the illustrated embodiments coming within the scope and
spirit of following
claims.
