U.S. patent application number 13/495853 was filed with the patent office on 2012-12-13 for air-driven hydraulic pump with pressure control.
Invention is credited to Baohua Qi, Mi Yan.
Application Number | 20120315163 13/495853 |
Document ID | / |
Family ID | 47293351 |
Filed Date | 2012-12-13 |
United States Patent
Application |
20120315163 |
Kind Code |
A1 |
Yan; Mi ; et al. |
December 13, 2012 |
Air-driven hydraulic pump with pressure control
Abstract
A hydraulically driven pump with driving pressure controlled
within a predetermined range. The hydraulically driven pump has a
driving-fluid port fluidly coupled to a compressed air source and
ambient, a driven-fluid inlet port fluidly connected to a tank, and
a driven-fluid outlet port. A pressure sensor is used for providing
sensing values indicative to the driving pressure in the
hydraulically driven pump, and the driving pressure is controlled
in closed loop by releasing and filling air through the
driving-fluid port. The hydraulically driven pump has a suction
stroke, in which driven fluid is refilled into the pump, and a
pressing stroke, in which driven fluid is pressed out. A hydraulic
buffer is used to provide driving pressure during a suction stroke
and two hydraulically driven pumps can work alternately in
providing continuous pressure control.
Inventors: |
Yan; Mi; (Columbus, IN)
; Qi; Baohua; (Columbus, IN) |
Family ID: |
47293351 |
Appl. No.: |
13/495853 |
Filed: |
June 13, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61520630 |
Jun 13, 2011 |
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Current U.S.
Class: |
417/375 |
Current CPC
Class: |
F04B 9/12 20130101; F04B
19/20 20130101 |
Class at
Publication: |
417/375 |
International
Class: |
F04B 19/20 20060101
F04B019/20 |
Claims
1. A hydraulically driven pump system comprising: a pump housing
having a pump chamber therein and at least one driving-fluid port
fluidly connected to said pump chamber; a driving-fluid flow
control means fluidly connected to said driving-fluid port and a
first fluid for controlling supply and release of said first fluid,
wherein said driving-fluid flow control means includes at least one
electrically controlled solenoid valve; a driven-fluid inlet port
fluidly coupled to said pump chamber through a driven-fluid flow
control means, which only allows a second fluid to flow into said
pump chamber; a driven-fluid outlet port though which said second
fluid flows out from said hydraulically driven pump system under a
driving pressure; at least one pressure sensor for providing
pressure sensing values indicative to said driving pressure; and a
closed-loop controller configured to control said driving pressure
within a predetermined range by electrically energizing and
de-energizing said at least one electrically controlled solenoid
valve in said driving-fluid flow control means according to at
least said pressure sensing values obtained from said at least one
pressure sensor.
2. The hydraulically driven pump system of claim 1, further
comprising: a piston reciprocable in said pump chamber separating
said pump chamber into a driving fluid chamber, which is fluidly
connected to said driving-fluid port, and a driven fluid chamber,
which is fluidly connected to said driven-fluid inlet port, and
fluidly coupled to said driven-fluid outlet port.
3. The hydraulically driven pump system of claim 1, wherein at
least one electrically controlled solenoid valve in said
driving-fluid flow control means is a three-way solenoid valve.
4. The hydraulically driven pump system of claim 1, further
comprising: a stroke controller configured to switch in between a
suction stroke, in which said driving-fluid flow control means is
controlled to release said first fluid from said pump chamber for
drawing said second fluid into said pump chamber, and a pressing
stroke, in which said driving-fluid flow control means is
controlled to keep said second fluid from flowing into said pump
chamber.
5. The hydraulically driven pump system of claim 4, wherein said
closed-loop controller is further configured to work only when said
stroke controller is operating in said pressing stroke.
6. The hydraulically driven pump system of claim 4, further
comprising: a level sensor for providing level sensing values
indicative to the volume of said second fluid in said pump chamber,
wherein said stroke controller is further configured to switch in
between said suction stroke and said pressing stroke according to
at least said level sensing values obtained from said level
sensor.
7. The hydraulically driven pump system of claim 4, wherein said
stroke controller is further configured to switch from said
pressing stroke to said suction stroke according to at least said
pressure sensing values obtained from said at least one pressure
sensor.
8. The hydraulically driven pump system of claim 4, wherein said
stroke controller is further configured to switch from said
pressing stroke to said suction stroke according to at least the
release time of said second fluid from said driven pump system in
said pressing stroke.
9. The hydraulically driven pump system of claim 1, further
comprising: a hydraulic buffer including a buffer chamber, a buffer
inlet port, which is fluidly coupled to said pump chamber through a
flow control means, which only allows fluid to flow from said pump
chamber to said buffer chamber, and a buffer outlet port, which is
fluidly connected to said driven-fluid outlet port.
10. The hydraulically driven pump system of claim 9, wherein said
at least one pressure sensor includes a pressure sensor providing
sensing values indicative to the pressure in said buffer
chamber;
11. The hydraulically driven pump system of claim 9, wherein said
hydraulic buffer further includes a piston reciprocable in said
buffer chamber separating said pump chamber into an upper chamber
and a lower chamber fluidly connected to said buffer inlet port and
said buffer outlet port.
12. The hydraulically driven pump system of claim 11, further
comprising: a spring positioned in said upper chamber.
13. The hydraulically driven pump system of claim 11, further
comprising: a stroke controller configured to switch from a suction
stroke, in which said driving-fluid flow control means is
controlled to release said first fluid from said pump chamber for
drawing said second fluid into said pump chamber, to a pressing
stroke, in which said driving-fluid flow control means is
controlled to keep said second fluid from flowing into said pump
chamber, before said pressure sensing values indicate that said
driving pressure is lower than a predetermined threshold.
14. A hydraulically driven pump system comprising: a first pump
housing having a first pump chamber therein, and at least one first
driving-fluid port fluidly connected to said first pump chamber; a
second pump housing having a second pump chamber therein, and at
least one second driving-fluid port fluidly connected to said
second pump chamber; a first driving-fluid flow control means
fluidly connected to said first driving-fluid port and a first
fluid for controlling supply and release of said first fluid,
wherein said first driving-fluid flow control means includes at
least one electrically controlled solenoid valve; a second
driving-fluid flow control means fluidly connected to said second
driving-fluid port and said first fluid for controlling supply and
release of said first fluid, wherein said second driving-fluid flow
control means includes at least one electrically controlled
solenoid valve; a driven-fluid inlet port, which is fluidly coupled
to said first pump chamber through a first driven-fluid flow
control means that only allows a second fluid to flow into said
first pump chamber, and fluidly coupled to said second pump chamber
through a second driven-fluid flow control means that only allows
said second fluid to flow into said second pump chamber; a
driven-fluid outlet port though which said second fluid flows out
from said hydraulically driven pump system under a driving
pressure; at least one pressure sensor for providing pressure
sensing values indicative to said driving pressure; and a
closed-loop controller configured to control said driving pressure
within a predetermined range by electrically energizing and
de-energizing said at least one electrically controlled solenoid
valve in said first and second driving-fluid flow control means
according to at least said pressure sensing values obtained from
said at least one pressure sensor.
15. The hydraulically driven pump system of claim 14, further
comprising: a first driven-fluid flow control means fluidly
connected to said first pump chamber and said driven-fluid outlet
port for only allowing said second fluid to flow from said first
pump chamber to said driven-fluid outlet port; a second
driven-fluid flow control means fluidly connected to said second
pump chamber and said driven-fluid outlet port for only allowing
said second fluid to flow from said second pump chamber to said
driven-fluid outlet port; and a pump controller configured to
switch among at least a first suction mode, in which said first
driving-fluid flow control means is controlled to release said
first fluid from said first pump chamber for drawing said second
fluid into said first pump chamber while said second driving-fluid
flow control means is controlled to keep said second fluid from
flowing into said second pump chamber, and a second suction mode,
in which said second driving-fluid flow control means is controlled
to release said first fluid from said second pump chamber for
drawing said second fluid into said second pump chamber while said
first driving-fluid flow control means is controlled to keep said
second fluid from flowing into first second pump chamber.
16. The hydraulically driven pump system of claim 15, wherein said
pump controller is configured to operate in a third mode, in which
said first driving-fluid flow control means is controlled to keep
said second fluid from flowing into said first pump chamber, and
said second driving-fluid flow control means is controlled to keep
said second fluid from flowing into said second pump chamber.
17. The hydraulically driven pump system of claim 15, wherein said
at least one pressure sensor includes a first pressure sensor
providing a first pressure sensing value indicative to the pressure
inside said first pump chamber and a second pressure sensor
providing a second pressure sensing value indicative to the
pressure inside said second pump chamber, and said closed-loop
controller is further configured to control said driving pressure
by operating said second driving-fluid flow control means according
to said second pressure sensing value, when said pump controller is
in said first suction mode, and control said driving pressure by
operating said first driving-fluid flow control means according to
said first pressure sensing value, when said pump controller is in
said second suction mode.
18. The hydraulically driven pump system of claim 17, wherein said
at least one pressure sensor includes a buffer pressure sensor
providing sensing values indicative to the pressure in said buffer
chamber.
19. The hydraulically driven pump system of claim 14, further
comprising: a hydraulic buffer including a buffer chamber, a buffer
inlet port, which is fluidly connected to said first pump chamber
through a first buffer flow control means that only allows said
second fluid to flow from said first pump chamber to said buffer
chamber, and fluidly connected to said second pump chamber through
a second buffer flow control means that only allows said second
fluid to flow from said second pump chamber to said buffer chamber,
and a buffer outlet port fluidly connected to said driven-fluid
outlet port.
20. The hydraulically driven pump system of claim 19, wherein said
hydraulic buffer further includes a piston reciprocable in said
buffer chamber separating said pump chamber into an upper chamber
and a lower chamber fluidly connected to said buffer inlet port and
said buffer outlet port.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM
LISTING COMPACT DISC APPENDIX
[0003] Not Applicable
FIELD OF THE INVENTION
[0004] This present application claims priority from U.S.
provisional application No. 61/520,630 having the same title as the
present invention and filed on Jun. 13, 2011.
[0005] This invention relates to pumps, and more particularly, to
hydraulic injection pumps used in injecting fluid into a vessel,
the pressure inside which is controlled within a predetermined
range.
BACKGROUND OF THE INVENTION
[0006] Air-driven hydraulic pumps use compressed air to drive
reciprocating actions in delivering pressurized liquid. With a
stepped piston having its large diameter side contacting compressed
air in an air cylinder and small diameter side driving liquid in a
high pressure injection cylinder, an air-driven hydraulic pump is
able to provide high driving pressure, which is multiple times of
compressed air pressure, and the multiplication ratio is determined
by the ratio of the large diameter to the small diameter. To
complete a reciprocation cycle, which includes a suction stroke and
a pressing stroke, it needs to control the air pressure inside the
air cylinder by filling and releasing compressed air. Normally, the
pressure control is realized by using relay valves that use sealed
air and switches to fill and release the sealed air in controlling
the relay valves (U.S. Pat. Nos. 3,963,383, 4,645,431, and
6,386,841). Therefore, the reciprocating rate is determined by air
pressure, air filling and releasing rate, and switch position. As a
result, fluctuations in compressed air supply pressure affect both
reciprocating rate and driving pressure. Also, in the pressing
stroke, compressed air expands and results in pressure drop. The
pressure change in compressed air is then amplified by the pump and
causes larger change in driving pressure.
[0007] To accurately control the driving pressure, a primary object
of the present invention is to provide controls means to adjust the
driving pressure, thereby with a closed-loop control, the driving
pressure can be controlled within a predetermined range.
[0008] A further object is to replace the relay valve using the
controls means set forth in the foregoing object to provide a
simplified pump structure.
[0009] A further object is to provide controls means to avoid the
effects of the suction stroke in controlling driving pressure.
BRIEF SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, a hydraulically
actuated pumping apparatus with driving pressure controlled within
a predetermined range is provided.
[0011] According to one embodiment of the invention, an air-driven
hydraulic injection pump is provided that has a pressure
multiplication ratio of 1.0, however, has no piston device inside.
The stroke control and pressure control are accomplished by
energizing and de-energizing two solenoid valves to control air
pressure inside the pump according to pressure sensing values
obtained from a pressure sensor.
[0012] According to another embodiment of the invention, an
air-driven hydraulic injection pump is provided that has a pressure
multiplication ratio higher than 1.0. This pump has a piston inside
and strokes and pressure are controlled by energizing and
de-energizing two solenoid valves to release and fill compressed
air according to pressure sensing values obtained from a pressure
sensor.
[0013] According to another embodiment of the invention, a
hydraulic buffer is provided with an air-driven hydraulic injection
pump. The hydraulic buffer decreases pressure drops associated with
suction strokes in which compressed air is released from the
pump.
[0014] According to another embodiment of the invention, a
hydraulically driven pump system including two air-driven hydraulic
injection pumps are provided. These two pumps work alternately to
control driving pressure within a predetermined range.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1a depicts an air-driven hydraulic pump system with two
two-way solenoid valves and a pump without piston;
[0016] FIG. 1b depicts an air-driven hydraulic pump system with a
two-way solenoid valve, a three-way solenoid valve, and a pump
without piston;
[0017] FIG. 2 is a flow chart of a control algorithm for
controlling strokes and pressure;
[0018] FIG. 3 depicts a cross sectional elevation view of a
hydraulic pump housing used with the same stroke and pressure
controls in a system as shown in FIG. 1;
[0019] FIG. 4 depicts a cross sectional elevation view of a
hydraulic pump housing and a hydraulic buffer that is to decrease
pressure drops associated with suction strokes;
[0020] FIG. 5 illustrates a timing chart of pressure changes in
systems with and without a hydraulic buffer;
[0021] FIG. 6 depicts a system with two hydraulic pumps working
together to control driving pressure within a predetermined
range;
[0022] FIG. 7 is timing chart of control mode changes in a system
shown in FIG. 6
DETAILED DESCRIPTION OF THE INVENTION
[0023] Referring to FIG. 1a, a pump 100 includes a gas port 101, a
liquid inlet port 105, a liquid outlet port 102, and a pressure
sensor 103. Through a liquid passage 132, the liquid inlet port 105
is fluidly connected to a port 131 of a liquid tank 130, which
contains a fluid 133. Inside the inlet port 105, a check valve 106
only allows liquid to flow from the liquid tank 130 to the pump
100. Fluid in the pump 100 flows out through the liquid outlet port
102, which has a check valve 104 included, while pressure inside
the pump is measured by the pressure sensor 103 and the sensing
value is sent to a controller 110. The gas port 101 of the pump 100
is fluidly coupled to the outlet of a two-way solenoid valve 126
through a Tee connector 127 and an air passage 125, and the inlet
of the solenoid valve 126 is connected to a compressed air supply
(not shown in FIG. 1a). The Tee connector 127 is also fluidly
connected to the inlet of another two way solenoid valve 122
through an air passage 121. To lower down the noise when releasing
air, an optional muffler 124 can be connected to the outlet of the
solenoid valve 122 through an air passage 123. Both of the solenoid
valves 122 and 126 are electrically connected to the controller
110. At normal states, i.e., before the solenoid valves 122 and 126
are energized, the compressed air is disconnected to the gas port
101 and the gas port 101 is fluidly connected to ambient through
the solenoid valve 122.
[0024] Stroke control and pressure control for the pump 100 are
accomplished by using the combination of controls to the solenoid
valves 122 and 126. The controls to the two valves have four modes
shown in the following table:
TABLE-US-00001 TABLE 1 Mode Status of the Status of the number
valve 126 valve 122 Actions 0 Not energized Not energized Releasing
air from pump 1 Not energized Energized Keeping air in pump 2
Energized Not energized Leaking compressed air 3 Energized
Energized Filling air to pump
[0025] In Mode 0, both of the solenoid valves 122 and 126 are not
energized, and the pump is releasing air to ambient. In Mode 1,
since solenoid valve 122 is energized, the pump is disconnected
from ambient. At the same time, the solenoid valve 126 is not
energized. Therefore, in this mode, the air is trapped in the pump.
Mode 2 is a special mode needs to be avoided, since in this mode
the compressed air is directly released into ambient. Mode 3 is an
aspiration mode. In this mode, the solenoid valve 122 disconnects
the pump from ambient, while the solenoid valve 126 fluidly
connects the pump the compressed air supply.
[0026] The pumping control starts with a suction stroke. When fluid
in the pump reaches a certain level, a pressing stroke is triggered
and driving pressure is controlled in a range commanded by the
user. The pump goes back to suction stroke when a refill event is
triggered.
[0027] In a suction stroke, Mode 0 is triggered. As mentioned
above, in Mode 0, the pump releases air to ambient. After the air
pressure inside the pump drops, under gravity or the pressure
inside the fluid tank 130, the fluid 133 flows through the port
131, the passage 132, and the check valve 106 inside the port 105
into the pump. In the suction stroke, no fluid flows out of the
pump.
[0028] After a suction stroke, the controller enters Mode 3, in
which compressed air flows into the pump 100 through the solenoid
valve 126, the passage 125, the Tee connector 127, and the gas port
101. Under the air pressure, fluid in the pump is able to flow out
through the port 102.
[0029] Sensing values obtained from the pressure sensor 103 are
used in controlling strokes and liquid driving pressure. One
embodiment of a control algorithm is realized with a service
routine running periodically in the controller 110 for a timer
based interrupt. As depicted in FIG. 2, in this routine, firstly a
suction-stroke trigger flag is examined, if a suction stroke is
triggered, then the controller goes to Mode 0 to release air from
the pump 100. Then the status of the suction stroke is checked. If
the suction stroke is completed, then the routine ends after a
pressing-stroke trigger flag is set and the suction-stroke trigger
flag is reset, otherwise, the time in the suction mode is checked
in a step 201. If it is too long, then a fault is set in a step
202, and the routine ends. Referring back to the examination of the
suction-stroke trigger, if a suction stroke is not triggered, then
the pressing-stroke trigger flag is examined. If a pressing stroke
is not triggered as well, then the suction-stroke trigger flag is
set and the routine ends, otherwise, the pressure sensing value
obtained from the pressure sensor 103 is checked. When the pressure
value is above a threshold Thd1 but below another threshold Thd2,
the controller switches to Mode 1, in which the compressed air is
hold in the pump. If the pressure is not lower than the threshold
Thd2, then the controller goes into Mode 0 to release air, while if
the pressure is not higher than the threshold Th1, the controller
then switches to the Mode 3 to fill air into the pump to increase
air pressure. The status of the pressing stroke is checked
thereafter. The routine ends if the pressing stroke is not
completed, otherwise, the suction-stroke trigger flag is set and
the pressing-stroke trigger flag is reset. After the changing of
the trigger flag values, the time in Mode 1 is also checked in a
step 203. If it is too short, then a fault is set in a step 204
before the routine ends.
[0030] In the stroke and pressure control, to avoid momentarily
going into Mode 2, in changing modes from Mode 3 to Mode 0, the
controller should de-energize the solenoid valve 126 first, while
in switching modes back to Mode 3 from Mode 0, the controller
should energize the solenoid valve 122 first. To further avoid
troubles caused by Mode 2, as shown in FIG. 1b, a three-way
solenoid valve 142 together with a two-way solenoid valve 141 can
be used to replace the two-way solenoid valves 122 and 126.
Referring to FIG. 1b, the inlet of the two-way solenoid valve 141
is fluidly connected to the port 101 through a passage 121, while
the outlet is fluidly connected to the inlet of three-way solenoid
valve 142 through a passage 143. One outlet of the three-way
solenoid valve is connected to the compressed air supply, and the
other one can be fluidly connected to the muffler 124 through the
passage 123 to decrease air releasing noise. With the three-way
solenoid valve 142 and the two-way solenoid valve 141, the controls
modes are shown in the following table:
TABLE-US-00002 TABLE 2 Mode Status of the Status of the number
valve 142 valve 141 Actions 0 Not energized Not energized Releasing
air from pump 1 Not energized Energized Keeping air in pump 2
Energized Energized Keeping air in pump 3 Energized Not Energized
Filling air to pump
[0031] According to Table 2, in the system depicted in FIG. 1b,
there is no leaking mode in which compressed air supply is directly
connected to ambient. Also, different from that listed in Table 1,
the Mode 2 in Table 2 has all the solenoid valves 141 and 142
energized rather than just one energized, while Mode 3 has just the
solenoid valve 142 energized rather than both of them
energized.
[0032] In the stroke control, two events, a refill event and a pump
full event, can be used to switch strokes. A refill event is
triggered when a low liquid level in the pump is detected or the
calculated liquid volume is low. To detect liquid level in the
pump, a level sensor can be further installed inside the pump (not
shown in FIG. 1), while the liquid volume can be calculated using
the liquid releasing time and the pump driving pressure.
[0033] Two methods can be used in calculating the liquid volume in
the pump in a pressing stroke. One is calculating the amount of
liquid being released from the pump. Under the driving pressure
inside the pump, when liquid starts to flow out of the pump, the
flow rate of liquid through the port 102 is a function of the
driving pressure. If the driving pressure is controlled constant,
the flow rate is a constant value. Therefore, when the driving
pressure is controlled within a narrow range, the lost liquid
volume in a pressing stroke is approximately proportional to the
liquid releasing time, and the liquid volume thus can be calculated
by using the following equation:
V=V.sub.0-K*t (1)
, where V is the current liquid volume inside the pump; V.sub.0 is
the liquid volume when a pressing stroke starts; K is a constant,
and t is the liquid releasing time. To more accurately calculate
the current volume, liquid releasing rate, which is proportional to
the square root of the driving pressure, can be used in the
calculation:
V=V.sub.0.intg..sub.t.sub.0.sup.tC {square root over (P)}dt (2)
where C is a constant; P is the driving pressure at moment t, and
t.sub.0 is the time moment when a pressuring stroke starts. When
the flow through port 102 is further controlled by a solenoid valve
(not shown in FIG. 1), the liquid releasing time is the open time
of the solenoid valve in a pressing stroke. In this situation, in
the equations (1) and (2), V.sub.0 and t.sub.0 are, respectively,
the liquid volume and the time moment when the solenoid valve
starts to open.
[0034] The other method is using the ratio of pressure change in
Mode 1 to the amount of liquid released during the pressure change.
According to the idea gas law, in Mode 1, since the air is trapped
in the pump, if the effect of liquid pressure in the pump is
negligible and temperature is constant, then we have the following
relation:
V P = - ( V t - V ) / P , ( 3 ) ##EQU00001##
where dP is the change in the driving pressure; dV is the volume
change when driving pressure changes dP, and V.sub.t is the tank
volume. The liquid volume then can be calculated using the
following equation:
V = V t + P V P . ( 4 ) ##EQU00002##
According to equation (4), unlike the first method, this method
doesn't require the liquid volume at the beginning of a pressing
stroke, V.sub.0, in calculation.
[0035] The pump full event can be triggered using the pressure
sensing value. In a suction stroke, when pressure inside the pump
is released, the gauge pressure obtained by the sensor 103 is a
proportional to the liquid level in the pump. Accordingly, the
liquid level can be calculated using the pressure sensing value
through the following equation:
L=Kp*P (5)
where Kp is a constant. When the calculated liquid level is above a
threshold, a pump full event is triggered.
[0036] In addition to the pressure sensing value, the refill time
is also an indication to the liquid volume in the pump. The liquid
refill flow-rate to the pump 100 is a function of the difference
between the pressure at the port 131 and that at the port 105.
Therefore, in a system of FIG. 1a and FIG. 1b, the liquid refill
flow-rate, r.sub.f, is a function of the level of the liquid 133 in
the tank 130, L.sub.t:
r.sub.f=f(L.sub.t) (6)
. In a control algorithm, the function in equation (6) can be
realized using a lookup table, the values in which are populated
with testing data. According to equation (6), the liquid volume in
the pump then follows the equation below:
V=.intg..sub.0.sup.t.sup.ff(L.sub.t)dt (7)
, where t.sub.f is the refill time. A pump full event can be
triggered when the calculated liquid volume is higher than a
threshold.
[0037] Since air density is much lower than liquid density, if the
liquid tank 130 is empty, then in a suction stroke, the pressure
sensing value is low. Therefore, pump full event will not be
triggered with the pressure sensing method. By detecting a failed
pump full event, we then can detect an empty liquid tank. Steps 201
and 202 in FIG. 2 show this detection.
[0038] Also, if the liquid tank 130 is empty, then air will be
released from the pump rather than liquid due to the interrupt of
liquid supply. It is hard to establish the driving pressure due to
high volumetric releasing rate caused by low air density.
Accordingly, by detecting the time of Mode 1 in a pressing stroke,
we can detect an empty liquid tank or a leak pump. Steps 203 and
204 in FIG. 2 show this detection.
[0039] The pump depicted in FIG. 1 can only generate a driving
pressure lower than the compressed air pressure. When higher
driving pressure is required, a piston can be used to multiply the
compressed air pressure. Referring to FIG. 3, inside a pump housing
300, a piston 302 has a large diameter surface 303 contacting
compressed air. The other side of the piston 302 has a small
diameter surface 304 contacting liquid. The piston 302 divides the
pump housing 300 into three spaces: compressed air space 340,
middle space 310 and liquid space 330. The compressed air space 340
is sealed from the middle space 310 with an o-ring 301 on the
piston 302, while the liquid space 330 is sealed from the middle
space 310 by a seal 321 in bore 320. A spring 305 is used to
support the piston 302. When a pressure Pc is applied in the
compressed air space 340, with the force delivered by the piston
302, the driving pressure obtained in the liquid space 330 is Pl,
and
Pl=(Pc*A303-ks*x-f0)/A304 (8)
where A303 is the area of large diameter surface 303, ks is the
spring constant of spring 305, x is the distance from natural
position of the piston 302 to the current position, f0 is the
friction force plus the static spring force, and A304 is the area
of small diameter surface 304. According to equation (8), if spring
force and friction force is small compared to that applied by the
compressed air on the surface 303, the ratio between the areas A303
and A304, A303/A304, determines the driving pressure.
[0040] In a pressing stroke, when compressed air establishes
pressure in the space 340, the piston goes downward under the
pressure, pressing the spring 305 and generating driving pressure
in the space 330. In a suction stroke, when the compressed air is
released, the piston goes upward under the force provided by the
spring 305. Thereby liquid is pulled in the space 330. Compared to
the pump 100 shown in FIG. 1a and FIG. 1b, in the pump of FIG. 3,
the suction stroke has a forced suction process. Gravity or a
pressure in the liquid tank is not required in pushing the liquid
into the pump.
[0041] The controls for the pump of FIG. 3 are the same as that for
the pump of FIG. 1. However, the driving pressure control range is
different. For a pump of FIG. 1, the driving pressure control range
is from the block pressure of the check valve 104, Pb104, to the
compressed air pressure Pc, while that of FIG. 3 according to
equation 3 is from Pb104 to Pl(Lm),
Pl(Lm)=(Pc*A301-ks*Lm-f0)/A304 (9)
where Lm is the max. displacement of the spring 305 in the pump
300. Compared to the air-driven pumps in the previous arts (e.g. in
U.S. Pat. Nos. 6,386,841, 4,645,431, and 3,963,383), in the present
invention, in addition to driving pressure being controlled in
closed loop, with the same compressed supply air pressure, the
driving pressure in the pump is also adjustable within a broad
range. Typically, the lower end of the range is limited by the
check valve block pressure, while the upper end is determined by
the compressed supply air pressure and the ratio of the large
diameter and small diameter of the piston. The adjustable driving
pressure separates driving pressure from compressed air supply
pressure and thereby enables more flexible applications of the
air-driven pump.
[0042] Air-driven pumps need to be refilled with a suction stroke,
during which the driving pressure drops and fluid stops flowing out
from the pump. For some applications with high liquid flow rate,
the pump needs to be refilled from time to time. To decrease
pressure drops and provide continuous fluid flow, a hydraulic
buffer can be used with the pump. Referring to FIG. 4, a hydraulic
buffer 400 is fluidly connected to the port 102 of the pump 300
through a port 408 and a passage 407. The hydraulic buffer has a
cylindrical body 401, inside which a piston 403 separates the space
into an upper chamber 410 and a lower chamber 420. To seal the
lower chamber from the upper chamber, a sealing O-ring 411 is
carried in an annular groove of the piston 403. In the upper
chamber 410, a spring 402 is positioned in between the inner top of
the cylindrical body 401 and the top of the piston 403, and the two
ends of the spring are retained in grooves. In the lower chamber
420, a retainer 409 limits the position of the piston 403 when
pressure in the lower chamber is released, and a pressure sensor
406 is used to measure the pressure inside the lower chamber 420.
The pressure sensor 406 is electrically connected to the pump
controller 110 (FIG. 1) for controlling the driving pressure, under
which the liquid flows out of the hydraulic buffer through a port
404 with a check valve 405 included.
[0043] When pressure is established in the space 330 of the pump
300, through the port 102, the check valve 104, the passage 407,
and the port 408, liquid flows into the lower chamber 420 of the
hydraulic buffer 400 and builds up pressure therein. The pressure
inside the lower chamber 420 pushes the piston 403 moving upward
and pressing the spring 402. In a pressing stroke, pressure inside
the lower space 420 is controlled by the controller 110 (FIG. 1)
through adjusting the air pressure in the space 340 using the
pressure values obtained with the pressure sensor 406. The same
controls algorithm with flow chart shown in FIG. 2 can be used for
the pressure control. In a suction stoke, when pressure is released
in the space 330 of the pump 300, the liquid stops flowing out from
the pump 300. Under the force applied by the spring 402, the piston
403 moves downward, continuously providing a pressure for the
liquid in the lower chamber 420. The pressure provided by the
piston 403 and the spring 402 is lower than the controlled driving
pressure and will decrease with time when more liquid flows out of
the hydraulic buffer. Before the pressure inside the lower chamber
420 drops below a threshold, the suction stroke finishes and the
driving pressure is built up again in the next pressing stroke.
[0044] FIG. 5 shows the timing chart of pressure change. In FIG. 5,
a curve 501 shows the change of pressure downstream from an
air-driven pump without hydraulic buffer, e.g. the pressure
downstream from the check valve 104 of the pump 300 depicted in
FIG. 3, while another curve 502 shows the pressure change
downstream from an air-driven pump with a hydraulic buffer, e.g.
the pressure change downstream from the check valve 405 of the
hydraulic buffer 400 shown in FIG. 4. In a pump without hydraulic
buffer, after a pressing stroke starts, compressed air enters the
pump and a pump pressure is established. When the pump pressure is
higher than a check valve threshold 503, as the curve 501 shows,
the pressure downstream from the pump rises up, following the pump
pressure until it reaches a steady controlled value. After a
suction stroke is triggered, the pressure downstream from the pump
drops with the pump pressure and drops sharply to zero when the
pump pressure is lower than the check valve threshold 503. In a
pump with a hydraulic buffer, as shown in the curve 504, the
pressure change downstream from the hydraulic buffer in the first
pressing stroke is similar to that in a pump without a hydraulic
buffer, except the pressure rises upon a higher check valve
threshold 504, which includes two check valve thresholds (e.g. the
thresholds of check valves 104 and 405). In a suction stroke,
different from that in a pump without hydraulic buffer, instead of
dropping sharply, under the pressure provided by the piston and
spring, the pressure downstream from the hydraulic buffer just
drops (almost linearly but slower) when liquid flows out. And after
another pressing stroke starts, the pressure downstream from the
hydraulic buffer follows the driving pressure in the hydraulic
buffer once the force provided by the piston and spring is
overcome.
[0045] The pressure drop in the hydraulic buffer 400 is affected by
the suction stroke time. In applications where only low pressure
fluctuation is allowed, the suction stroke time has to be short or
a large hydraulic buffer is required. To further decrease pressure
drop and continuously control driving pressure, two air-driven
pumps can be used together to have the driving pressure controlled
by at least one pump during working time. As depicted in FIG. 6,
two pumps 610 and 620 and a hydraulic buffer 630 work together to
provide a liquid flow with controlled pressure. A two-way
air-intake solenoid 601 with its outlet fluidly connected to the
pump 610 has its inlet fluidly connected to a side port of a Tee
connector 603, through an air passage 602. The other side port of
the Tee connector 603 is fluidly connected to the inlet of another
two-way air-intake solenoid 606, the outlet of which is fluidly
connected to the pump 620. The center port of the Tee connector 603
is connected to a compressed air supply. In the same way, the
outlets of air releasing solenoids 605 and 611 of the pumps 610 and
620 are fluidly connected together through a Tee connector 608, the
center port of which can be connected to a muffler 609 to decrease
air releasing noise. In the liquid path, a passage 613 fluidly
connects the liquid supply port of the pump 610 to a side port of a
Tee connector 614, the other side port of which is fluidly
connected to the liquid supply port of the pump 620 through a
passage 615. The center port of the Tee connector 614 is connected
to a liquid supply. In the same way, the liquid output ports of the
pump 610 and 620 are fluidly connected to the two side ports of a
Tee connector 618 separately through passages 616 and 617. The
center port of the Tee connector 618 is fluidly connected to the
liquid supply port of a hydraulic buffer 630. A pressure sensor 619
positioned inside the hydraulic buffer 630 is electrically
connected to a controller 640, which also electrically controls the
solenoid valves 601, 605, 606, and 611.
[0046] Liquid flows out of the hydraulic buffer 630 under a driving
pressure controlled by the controller 640. Referring to FIG. 7, in
which curves 701 and 702 show the changes in control mode of pumps
610 and 620 respectively, a control starts with triggering a
suction stroke in the pump 610. When the suction stoke completes, a
pressing stroke starts, during which driving pressure is
established in the hydraulic buffer 630 and then pressure feedback
control is enabled. At the same time when the pump 610 starts the
suction stroke, a suction stroke is triggered for the pump 620.
When the suction stroke of the pump 620 completes and the pressure
feedback control in the pump 610 goes to steady, i.e., Mode 1
(keeping air in the pump) is triggered at a moment 711, the pump
620 goes into Mode 3 for a certain time positioning for driving
pressure control. The Mode 3 duration time of the pump 620 is
calculated using the Mode 3 and Mode 0 time of the pump 610 before
its Mode 1 is triggered and after its suction stroke completes.
Once the next suction stroke for the pump 610 is triggered at a
moment 712, the pump 620 enters pressure feedback control
continuing controlling the driving pressure in the hydraulic buffer
630. Once the pressure control goes to Mode 1 at a moment 713, the
total time in Mode 3 and Mode 0 in the control of the pump 620
starting from the moment 711 is recorded, and a Mode 3 thereafter
is set at moment 714 for the pump 610 with a suction stroke
triggered for the pump 620. The Mode 3 duration time for the pump
610 is calculated using the recorded total time in Mode 3 and Mode
0 for the pump 620. In this way, the pump 610 and 620 work
alternately to provide uninterrupted driving pressure control.
[0047] In the pressure control, the idling pump (e.g the pump 610)
starts a pressing stroke (Mode 3) after the working pump (e.g. the
pump 620) enables pressure feedback control. Therefore, there is a
period of overlap time in which both of the pumps are in pressing
stroke, e.g. between the moments of 711 and 712. During the overlap
time, the working pump is in pressure feedback control, while
pressure in the other one is not controlled though the pump is
pressurized. Pressurizing the idling pump is to reduce the
transition time after pump control is switched. The pressure in the
idling pump should be close to but lower than the threshold (e.g.
the upper limit of the predetermined pressure control range) above
which the working pump goes into Mode 0 releasing air, since liquid
in the idling pump cannot flow into the working pump, and high
pressure in the idling pump could firstly cause a peak of driving
pressure in the hydraulic buffer and then a valley due to feedback
control in the working pump. The air filling time (Mode 3 duration
time) of the idling pump is calculated using the net air filling
time of the working pump, which is a function of the total air
filling time (Mode 3 duration time) and the total air releasing
time (Mode 0 duration time) of the working pump before its pressure
control goes steady. The net air filling time of working pump is a
reference. The calculated air filling time for the idling pump
should be shorter than the net air filling time.
[0048] Although the apparatus and method of the invention are
described herein in relation to the preferred embodiments shown in
FIGS. 1-7, certain design alternations and modifications will
become apparent to those of ordinary skill in the art upon reading
this disclosure in connection with the accompanying drawings. For
example, the pump 100 shown in FIG. 1 can be used in the structure
illustrated in FIG. 4 and FIG. 6; the pump 100 in FIG. 1a has two
ports, one dedicated for air releasing and another one for air
supply; and in FIG. 4, a solenoid valve in between the ports 102
and 408 can further be used to fine control the pressure in the
buffer 400. It is intended, however, that the scope of the
invention be limited only by the appended claims.
* * * * *