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.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

Not Applicable

Not Applicable

FIELD OF THE INVENTION

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.

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

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.

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.

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.

A further object is to provide controls means to avoid the effects of the suction stroke in controlling driving pressure.

SUMMARY

In accordance with the present invention, a hydraulically actuated pumping apparatus with driving pressure controlled within a predetermined range is provided.

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.

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.

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.

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

FIG. 1a depicts an air-driven hydraulic pump system with two two-way solenoid valves and a pump without piston;

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;

FIG. 2 is a flow chart of a control algorithm for controlling strokes and pressure;

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;

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;

FIG. 5 illustrates a timing chart of pressure changes in systems with and without a hydraulic buffer;

FIG. 6 depicts a system with two hydraulic pumps working together to control driving pressure within a predetermined range;

FIG. 7 is timing chart of control mode changes in a system shown in FIG. 6

DETAILED DESCRIPTION

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.

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 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

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.

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.

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.

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.

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.

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 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

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.

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.

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=V0−K*t   (1)

, where V is the current liquid volume inside the pump; V0 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=V0∫t0tC√{square root over (P)}dt   (2)

where C is a constant; P is the driving pressure at moment t, and t0 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), V0 and t0 are, respectively, the liquid volume and the time moment when the solenoid valve starts to open.

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 = - (

Download full PDF for full patent description/claims.




You can also Monitor Keywords and Search for tracking patents relating to this Air-driven hydraulic pump with pressure control patent application.
###


Other recent patent applications listed under the agent :