Patent Application
20050042111
Some patients that require supplemental oxygen for breathing are able to conduct their daily activities by transporting a portable pressurized oxygen tank with them. Such oxygen tanks typically contain oxygen that is pressurized to about 2200 psi. Patients who live at home must be able to replace the tanks or have a means for refilling the tanks when the tanks become depleted.
Embodiments of the present invention include a pump that is capable of pumping fluid under pressure in an efficient manner and is suitable for refilling oxygen tanks in a home setting.
One particular embodiment includes a pump that can have a housing and a first piston positioned within a first chamber in the housing. The first chamber can have a first inlet and a first outlet. A second piston can be positioned within a second chamber in the housing and secured to the first piston. The first and second pistons each have a diameter, with the diameter of the first piston being larger than the diameter of the second piston. The second chamber has a second inlet and a second outlet. The second inlet can be in communication with the first outlet of the first chamber.
A drive system reciprocates the first and second pistons in unison within the first and second chambers such that when the first piston is moving in an expansion stroke, fluid can be drawn into the first chamber through the first inlet. At the same time, the second piston is moving in a compression stroke where fluid can be expelled from the second chamber through the second outlet. When the first piston is moving in a compression stroke, the second piston is moving in an expansion stroke where fluid can be expelled from the first chamber through the first outlet and into the second chamber through the second inlet.
In particular embodiments, a connecting member can secure the first and second pistons together in a spaced apart manner along a common axis and extends between the first and second chambers. The connecting member can include a threaded screw. The drive system can include a rotatable nut engaged with the threaded screw and a reversible motor for alternately rotating the nut in opposite directions to cause reciprocating linear translation of the connecting member and pistons. The rotatable nut can be a ball screw nut.
A check valve system can be included for preventing back flow through the pump so that fluid flows in one direction. The check valve system can include a first check valve for preventing fluid from exiting the first chamber through the first inlet, a second check valve for preventing fluid from exiting the second chamber through the second inlet, and a third check valve for preventing fluid from entering the second chamber through the second outlet.
A piston position sensing system can be included for sensing piston position. In addition, pressure within the first chamber can be sensed by a first pressure sensor, and pressure of fluid expelled from the second chamber can be sensed by a second pressure sensor. The diameters of the first and second pistons can have a difference in size of about a 3.5 to 1 ratio. In one embodiment, the diameter of the first piston can be about 4 inches, the diameter of the second piston can be about 1.127 inches, and the stroke of the first and second pistons can be about 6 inches. A pump with such dimensions is capable of pumping about 0.5 in.3 of gas at about 2200 psi per cycle.
In embodiments of the pump, using a drive system with a low friction ball screw, reciprocating the pistons in unison, and pumping the gas in two stages for increasing pressure, allows gases such as oxygen to be pumped under pressure into a tank with the use of a relatively small motor which minimizes the use of power and the generation of heat.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
Referring to
The pump 10 includes a first stage piston 14 which reciprocates within a first stage chamber 12, and a second stage piston 18 which reciprocates within a second stage chamber 16. The first stage piston 14 and chamber 12 are larger in diameter than the second stage piston 18 and chamber 16. The first 14 and second stage 18 pistons are secured to each other by a threaded screw 38 and positioned in line with each other along a longitudinal stroke axis A. The threaded screw 38 is connected to a drive system 45 having a rotating ball screw nut 42 which drives the threaded screw 38 in alternating directions for reciprocating the first 14 and second 18 stage pistons in unison within the first 12 and second stage 16 chambers. The drive system 45 is controlled by a controller 62 in electrical communication thereto. The threaded screw 38 extends along axis A between the first 12 and second 16 stage chambers and passes through a connecting passage 44 that extends between chambers 12 and 16.
The first stage chamber 12 has a first inlet 27 for allowing gas to enter chamber 12. A first check valve 24 of a check valve system is positioned upstream of inlet 27 in close proximity thereof to prevent gas from exiting the first stage chamber 12 through inlet 27. An inlet pressure sensor 26 that is in communication with controller 62 is included between inlet 27 and check valve 24 for sensing the entering gas pressure. The first stage chamber 12 also has a first outlet 28 which is communication with the second stage chamber 16 through a second inlet 58 by a passage 30 extending therebetween. A second check valve 32 of the check valve system is positioned upstream from the inlet 58 in close proximity thereof for preventing gas from exiting the second stage chamber 16 through inlet 58. The second stage chamber 16 has a second outlet 60 through which gas exits the chamber 16. A third check valve 48 of the check valve system is positioned downstream from the outlet 60 to prevent gas that is pumped therethrough from reentering the second stage chamber 16 through outlet 60. An outlet pressure sensor 50 that is in communication with controller 62 is positioned downstream from check valve 48 for sensing the exiting gas pressure.
When pumping oxygen such as in the configuration shown in
The motor drive 45 then drives the pistons 14 and 18 in unison in the reverse or opposite direction (to the right) so that the second stage piston 18 moves in a compression stroke toward outlet 60, decreasing the volume therein and forcing the oxygen from the second stage chamber 16 (
When the first stage piston 14 is in the open position, controller 62 can be programmed to reactivate drive system 45 for another cycle only if the inlet pressure sensor 26 detects a sufficient amount of oxygen. When the outlet pressure sensor 50 senses that the oxygen within tank 52 has reached a desired predetermined level, controller 62 can be programmed to deactivate drive system 45 so that the full tank 52 can be disconnected from the pump 10. An empty or partially empty tank 52 can then be connected to pump 10 for filling with oxygen.
Pump 10 is now described in further detail. Typically, chambers 12 and 16 are in a housing 11. Housing 11 can include hollow cylindrical members forming chambers 12 and 16 or can include one or more blocks with bores formed therein to form chambers 12 and 16. The threaded screw 38 forms a connecting member for securing the first stage piston 14 to the second stage piston 18 and can be fully threaded, or alternatively, partially threaded. In the embodiment shown, drive system 45 includes a reversible drive motor 40 which rotates ball screw nut 42 about threaded screw 38 and around axis A. The ball screw nut 42 is constrained to a fixed position along axis A so that rotation of ball screw nut 42 drives the threaded screw 38 longitudinally or linearly along axis A. The ball screw nut 42 has friction reducing balls which engage the threads of threaded screw 38 in a rolling manner, thereby reducing friction forces between the ball screw nut 42 and the threaded screw 38. This minimizes power losses when the rotational motion of the ball screw nut 42 is converted into linear motion of the threaded screw 38, and also minimizes the generation of heat therebetween.
Typically, the motor 40 is connected to the ball screw nut 42 by a power transmission 41 which converts rotational motion provided by motor 40 into rotational motion of ball screw nut 42. The power transmission 41 can be any suitable power transmission, such as a low backlash gear set, a timing belt/pulley set, etc. The motor 40 is typically a reversible electric motor. The stroke S (
The size and rotational speed of motor 40, the transmission ratio of the power transmission 41 between the motor 40 and the ball screw nut 42, the threads per inch or thread pitch of the threaded screw 38, and the piston sizes and stroke lengths, can be selected to provide the desired pumping speed, power consumption and overall size of pump 10, depending upon application at hand. Embodiments of pump 10 are typically more efficient then prior pumps because less energy is lost to friction, and therefore can use substantially less power, run cooler, and can be much quieter than prior pumps. In addition, the use of a ball screw for reciprocating the pistons 14 and 18 makes use of a high degree of mechanical advantage so that a relatively small motor 40 can be used which further uses less power and generates less heat. Since the gas pumped by pump 10 can increase in pressure in two stages, a much smaller motor can be used in comparison to a pump that only has one stage.
In the embodiment shown in
Although pump 10 has been described and shown in
Although
While this invention has been particularly shown and described with references to particular embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
For example, although some dimensions have been given as examples in one embodiment of pump 10, it is understood that a variety of different dimensions are possible, depending upon the application at hand. In particular, the diameters of the pistons 14 and 18 can be varied. In addition, the diameter ratio of pistons 14 and 18 can be varied as well as the stroke length. The inlets and outlets to the first 12 and second stage 16 chambers can be positioned on the sides of the chambers and/or the axial ends, as desired. Passage 30 between the first 12 and second stage 16 chambers can be formed in the housing 11 or can be tubing extending between the two chambers. A passage between the first 12 and second stage 16 chambers can also be formed longitudinally through pistons 14 and 18 with a check valve positioned along the longitudinal passage. In other embodiments both sides of the pistons 14 and 18 can be employed for pumping so that each piston when moving, can simultaneously perform an expansion stroke on one side of the piston and a compression stroke on the other side. In such embodiments, additional appropriately positioned passages and check valves can be used as needed. Although the drive system 45 has been described as being connected to the threaded screw 38, the threaded screw 38 can be considered part of the drive system 45. Furthermore, although two pistons have been shown in
This application claims the benefit of U.S. Provisional Application No. 60/445,358, filed Feb. 5, 2003. The entire teachings of the above application are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60445358 | Feb 2003 | US |
