Patent Application
20050089417
The present invention relates to valve-less positive displacement reciprocating pumps.
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.
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.
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:
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.
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
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 (
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| 60514813 | Oct 2003 | US |
