US20050089417A1

US20050089417A1 - Positive displacement pump

Info

Publication number: US20050089417A1
Application number: US10/974,227
Authority: US
Inventors: Lalit Chordia; John Davis
Original assignee: Thar Technologies Inc
Current assignee: Thar Technologies Inc
Priority date: 2003-10-27
Filing date: 2004-10-27
Publication date: 2005-04-28

Abstract

The present invention provides a novel method of actuation for valve-less positive displacement reciprocating pumps. It also allows for variation of pumping volume by altering the speed of the motor, typically by adjusting the voltage. Use of the valve-less piston allows for compact design and it simplifies the construction, thereby ensuring reliable service.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from the U.S. provisional patent application of the same title, which was filed on Oct. 27, 2003 and was assigned U.S. patent application Ser. No. 60/514,813, teachings of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to valve-less positive displacement reciprocating pumps.

BACKGROUND OF THE INVENTION

The pumping chamber of the present invention makes use of a notched piston that normally occludes either the inlet or outlet of the cylinder. For short instances of a pumping cycle, however, the piston blocks both the inlet and the outlet at the same time so as to ensure that at no time is the inlet open to the outlet. The piston rotates as it moves up and down in the axial direction. Said occlusions occur whenever the notch in the piston is in a rotational position that faces it away from an opening.
This type of pump has, until now, been practiced with an articulated piston: the rotational movement of the motor is transmitted to the piston by means of a ball joint, the angle of which helps determine the stroke distance of the piston inside the pump cylinder. To vary the flow rate of the pump, the angle is adjusted mechanically.
There are several disadvantages to this arrangement. For one thing, any adjustment to flow rate means that the body of the pump changes shape. The pump and motor are no longer in the same position relative to each other. If the operator desires to fix the motor in a stationary position, then the pump chamber must be allowed to swing at an angle from the motor-shaft axis. This in turn necessitates the use of flexible tubing for the inlet and outlet. For another thing, such a pump-motor combination cannot be enclosed in a single hermetic case. The ball-joint must always be placed on the pump end, preventing the use of a magnetic coupling because the pump shaft changes its angular orientation relative to the motor shaft. Examples of articulated shaft movement are provided by Pinkerton, H. (U.S. Pat. Nos. 3,168,872, 4,008,003, 4,941,809) and Pinkerton, D. (U.S. Pat. No. 5,020,980), who attach the piston to the inside of a ring that is fixed to and concentric with the shaft.

BRIEF SUMMARY OF THE INVENTION

The present invention improves upon the above-identified shortcomings by fixing the motor and piston along the same axis. Flow rate is controlled by varying the motor speed. No mechanical intervention is needed to change the flow rate. The straight-line configuration saves space and makes it possible to seal the pump and the motor in a hermetic case, thereby opening up new applications that prohibit leakage of pumped fluid. There would be no shaft seal that might leak pumped fluid to the environment.
Putting the motor and pump shaft on the same axis, which is referred to a straight-line actuation, requires careful attention to mechanical constraints, particularly those that incur excessive friction. The piston must be carefully aligned so as to allow radial and axial movement. A means must be provided to convert radial forces from the motor to axial forces for piston movement, without excessive friction. The ball joint of earlier designs overcame this problem, but with the major disadvantage of requiring articulated movement. The current invention does away with articulated movement, with the result that the pump and motor can be sealed together, or at least connected in a more compact configuration that does not change shape with every change in flow rate capacity.
One embodiment of the present invention provides for a positive displacement piston pump in which the piston moves axially while rotating on the same axis as the motor shaft. The reciprocating action of the rotating piston is actuated by means of a ramp, which causes the piston to move up and down.
In one embodiment of the present invention, the pump piston is connected to a motor by means of a sliding coupler that allows for the reciprocating motion of the piston. The entire pump-motor combination may be encased hermetically. The angle formed between the plane of the ramp and a plane perpendicular to the piston is less than 45 degrees. The piston and cylinder are preferably composed of ceramic material.

BRIEF DESCRIPTION OF THE DRAWINGS

For the present invention to be easily understood and readily practiced, the invention will now be described, for the purposes of illustration and not limitation, in conjunction with the following figures, wherein:
FIG. 1 shows one embodiment of the present invention having a typical pump configuration with motor attached along the same axis as the pump itself;
FIG. 2 shows the pump portion of one embodiment of the present invention, specifically a spring-loaded ramp valveless pump, in cross-section;
FIG. 3 shows more detail of one embodiment of the pump in cross-section, with an outline of the attached motor; and
FIG. 4 shows one embodiment of the notched piston used in the pump according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the present invention provides a novel method of actuation for positive displacement pumps that are based on the principle of a valve-less, rotating piston. This method provides for reciprocal piston displacement and rotation along a single axis, thereby enabling compact construction. It also allows for variation of pumping volume by altering the speed of the motor, typically by adjusting the voltage. Pumps made according to this method can be small enough to be suitable for small-device cooling or refrigeration, including but not limited to electronic devices such as computers, lasers and remote sensing equipment, and can be used in analytical and laboratory equipment, medical devices, kitchen utensils, portable coolers, table-top heating/refrigeration surfaces, aquariums, and various other apparatuses that require fluid pumping.
FIG. 1 shows an outer view of one embodiment of a complete assembly (1) of the pump (11) according to the current invention, with motor (12). Inlet and outlet ports (not shown) are typically at the end of the pump body (13). In another embodiment of the present invention, inlet and outlet ports can be located at the side of the pump casing; or, either the inlet or the outlet can be located at the case end while the other port is on the side. The choice of port locations is not important to the operation of the pump (11), but rather is important mainly to the installation and application of the pump (11). FIG. 1 demonstrates an important feature of one embodiment of the current invention: the motor (12) and the pump (11) are coupled on the same axis, or at least parallel axes. If a gear is employed between the motor (12) and the pump (11), then the axes might not coincide, although they would still be parallel as a requirement of the current disclosure.
FIG. 2 presents a cross-sectional view of one embodiment of the pump (2), wherein the outer case is in two parts (21) and (24) and contain components essential to the pumping activity of one embodiment of the invention. The upper case (24) features a motor-mount surface (241) for attachment of the motor (12) (not shown). The piston (23) is forced to move axially as it rotates because of the movement of a flattened ball (26) against flat ramp (25) that is cut on an angle of up to 45 degrees from perpendicular to the axis of the piston (23). The ramp (25) is a separate piece and is mounted just above the pump cylinder (22). A spring (28) forces the ball (26) against the surface of the ramp (25). Meanwhile, rotational movement from the motor (12) (not shown) is transferred to the piston (23) by means of a loose coupling effect between a motor coupler (29), which is attached to the motor shaft (not shown), and a piston collar (27). The collar (27) serves multiple purposes. First, it holds the piston (23). Secondly, the collar (27) holds the flattened ball (26), preventing it from escaping from the collar (27) but allowing it to precess within an angular range that is at least as large as the angle of the cylinder ramp (25) relative to perpendicular to the piston (23). Thirdly, the collar (27) features a protruding member on its top surface, which points in an opposite direction from the cylinder ramp (25) and toward the motor (12) (not shown). This protrusion can take any of several forms as long as its shape is symmetrical relative to the axis of the piston (23). In a preferred embodiment of this disclosure, the protrusion is shaped as a flat vane. Fourthly, the collar (27) may contain ventilation holes to permit the flow of liquid or air in an axial direction, so as to relieve hydraulic resistance to its axial movement.
FIG. 3 presents another embodiment of the pump-motor (1) in cross-sectional view as a pump-motor assembly (3). In this embodiment, the pump case (31) is a single unit and not split between upper and lower cases (24 and 21, respectively) as in FIG. 2. The cylinder (32) is nearly identical to cylinder (22), the only exception being that in this embodiment incorporates the ramp (35) on the end that faces to the interior of the pump assembly, thereby eliminating the need for a separate ramp insert (25). In other respects, the components are essentially unchanged from the design shown in FIG. 2. The piston (33) is fixed inside a well that is bored into the collar (37). The collar (37) may contain vent hoses. A flattened ball (36) is also held by the collar (37). The ball (36) is allowed to precess within the collar (37) only to the extent of the angle cut into the cylinder (32) end. A spring (38) forces the flattened ball (36) onto the ramp (35) surface at all times. The collar (37) contains a protrusion that fits within a slot cut into the motor coupler (39), such that a limited amount of axial movement is permitted as the motor shaft rotates. This connection is referred to as a sliding coupler: The vane protrusion of the collar (37) slides inside the slot that is cut into the motor shaft. The extent of movement is limited to the movement, in the axial direction, of the flattened ball (36) as is rotates about the cylinder ramp (35). The distance is identical to the stroke length of the piston (33). The motor assembly (391) is shown in outline form for the purpose of demonstrating the in-line nature of the motor/pump assembly (3). Inlet and outlet ports (311) go out through the end of pump case (31), but as is in the example depicted in FIG. 2, these can be re-located to the sides of the pump case (31) at a point directly opposite the ports (312) that are bored into the cylinder (32).
FIG. 4 details one embodiment of the piston (4) that is common to both of the embodiments described by FIGS. 2 and 3, showing the notch (41). At each revolution of the piston (4), this notch (41) is open to either the inlet or outlet port, but never both at the same time. In this way, it acts as a valve, permitting fluid to flow into the pump as the piston is driven toward the motor by the action of the flattened ball against the cylinder ramp, and flowing out of the pump during the down stroke, under the force of the spring. The piston should fit snugly inside the cylinder, preferably without the use of piston rings to seal the pump cavity from the ramped actuator. This will further help reduce friction while at the same time providing bearing surfaces to ensure axial alignment. In the preferred embodiment, close tolerance between the piston and cylinder can best be achieved from fabricating them out of ceramic materials.
A pump according to the present invention is capable of handling a variety of flow rates because it is not limited by the mechanical constraints of an articulated piston. In cases where a fluid is being passed through microchannels, such as the cooling of hot electronic parts such as integrated logic and memory chips, the pump may generate sufficient pressure head to ensure fluid circulation through such microchannels. The pump may be fabricated for low and high-pressure applications, including those utilizing a supercritical fluid. Because there is no outward change in shape in low- or high-flow rate applications or low- or high-pressure applications, the pump can be sealed away inside the casing of the system in which it operates. In the case of computer cooling, the pump could draw small amounts of power from on-board power sources, and it would operate quietly.
The means for achieving straight-line actuation is the ramp, over which a fixed appendage from the piston must move during its rotation with the piston. Said appendage is demonstrated in FIGS. 2 and 3 as flattened balls (26) and (36), but other forms are possible. Among these is a flat pad that is held loosely within the collar and is backed by a ball that is itself held between the pad and the collar. This “tilted pad” configuration, the bearing surface, or pad, tilts at an angle determined by the angle of the ramp, as in the case of the flattened ball. The ramp is in the form of an ovate path about the piston. The difference in the height of the ramp, from its lowest point to its highest in the axial direction, determines the stroke length. The angle formed between the plane of the ramp and a plane perpendicular to the piston must be less than 45 degrees in order to limit frictional losses but is preferably less than 10 degrees.
In one embodiment of the present invention, lubrication may be supplied by the pumping fluid, a small amount of which passes through the gap between the piston and cylinder. Said fluid is prevented from leaking outside of the pump by either (1) a seal on the motor shaft where it penetrates the pumping chamber, or (2) a hermetic casing that mechanically isolates the pump from the motor. In (2), isolation is practiced by placing a magnetic rotor on an extension of the piston. This rotor rotates with the motor shaft and reacts magnetically with either the corresponding permanent magnet of a magnetic coupling, , or—in the case of a “canned” motor—the rotor reacts magnetically with the stator coil of the motor. In either of these hermetic options, the casing that surrounds the rotor also encases the pump's internal components. Thus, the present invention encompasses at least two basic configurations: The spring-loaded ramp actuator of axial motion (FIGS. 2 and 3), with either a shaft-sealed motor or a hermetic pump that contains shaft mounted magnetic.
In some embodiments of the present invention having the canned motor configuration, the casing is extended upwards, enveloping the permanent-magnet rotor. The casing is thinned at this point to a thickness that is enough to contain the internal pressure of the pump but not so much as to weaken the magnetic attraction between the motor rotor and its fixed stator. The stator is mounted just outside the case. This stator-rotor combination constitutes a brushless motor, which may be controlled with Hall sensors or in sensorless fashion, according to established art for brushless permanent-magnet motors. Bearing support for the motor end must be provided separately, by means of an extension to the casing beyond the rotor. Said extension is made long enough to allow up-and-down motion of the piston, but is machined to a close tolerance to the piston diameter. Bearing support for the pump end of the piston is provided by the pump cylinder.
In some embodiments of the present invention using the magnetic coupling configuration, the fixed stator is replaced by the corresponding permanent magnetic of a rotating coupling. Either canned motor or magnetic coupling version of the hermetic configuration further allows for the possibility of replacing the mechanical ramp actuator with a non-mechanical linear magnetic actuator. In such an embodiment, additional components would be mounted on the integral pump-piston and motor-shaft. These would add to the inertial load, although frictional losses from an otherwise mechanical actuator would be avoided.
In a preferred embodiment of this invention, the pump employs a mechanical ramp in a hermetic configuration. The angle formed between the plane of the mechanical ramp and a plane perpendicular to the piston is less than 10 degrees and the type of bearing used against the ramp is of the “tilted pad” type. The pump would not need additional lubrication beyond that which is provided by the fluid and it would be fabricated of ceramic materials. Because the motor and pump are fixed on the same axis—or at least parallel axes is a gear is employed—the pump can be hermetically sealed. There is never any change in the angular orientation of the pump to the motor. This allows for very compact design. Use of the valve-less piston is also important to compact design, and it simplifies the construction, thereby ensuring reliable service. These features make the pump ideal for high-reliability, small-scale applications, such as found in electronic cooling and many types of medical devices.

A pump according to the present invention may utilize a wide variety of fluids, including but not limited to organic fluids, such as water, hydrocarbons or carbon dioxide, or synthetic fluids, such as newer refrigerants. Furthermore, the pump may handle a fluid at a pressure and temperature above its critical point. Fluids corrosive to metals may also be handled.

REFERENCES

U.S. PATENT DOCUMENTS

NUMBER	DATE	INVENTOR	REFERENCE

3,168,872	Feb. 9, 1965	Pinkerton, H.	103/157
4,008,003	Feb. 15, 1977	Pinkerton, H.	417/250
4,941,809	Jul. 17, 1990	Pinkerton, H.	417/500
5,020,980	Jun. 4, 1991	Pinkerton, D.	417/500

Claims

1. A positive displacement piston pump in which said piston moves axially while rotating on the same axis as a motor shaft.

2. The pump as described in claim 1 in which the axial movement of said piston is actuated by a ramp.

3. The pump as described in claim 1 in which said piston is connected to said motor by a sliding coupler.

4. The pump as described in claim 1 in which said piston has a motor rotor directly mounted onto it.

5. The pump as described in claim 4 wherein said piston-and-motor rotor combination is encased hermetically.

6. The pump as described in claim 2 wherein the angle formed between said ramp and a plane perpendicular to said piston is less than 45 degrees.

7. The pump as described in claim 1 formed from ceramic materials.

8. The pump as described in claim 1 wherein said pump is hermetically-sealed from a motor.