FAST OPERATING ELECTROMAGNETIC VALVE

Abstract: A fast operating bistable valve has a movable spherical plug (22) made of magnetic material and a chamber (20) in which the plug is disposed. The chamber has an interior wall shaped to guide the plug along an axis between a first end position and a second end position. A first pole piece (16) made of magnetic material is disposed at the first end position. A first port (24) opens into the chamber such that the plug covers the first port in one end position. A second port (10) opens into the chamber in communication with the first port when the plug is in the other end position. Responsive to a periodic electric current, a first periodic magnetic field of a first given polarity parallel to the axis is generated in the first pole piece to attract periodically the plug to the first end position. The plug is placed in the second end position in the absence of the electric current.

Description: Fast operating electromagnetic valve Background of the Invention This invention relates to fluid control and, more particularly, to a fast operating bistable valve particularly useful in precisely controlling gas flow. There are a number of applications for a valve to control gas flow precisely as a function of the duty cycle of a source of electrical pulses. To respond rapidly to changes in gas flow commands, a fast operating on-off, i.e;, bistable, valve is required. Available solenoid valves are too slow operating and short in life expectancy for a number of precision applications such as respirators. Summary of the Invention According to the invention, a fast operating bistable valve has a movable plug made of magnetic material and a chamber in which the plug is disposed. The chamber has an interior wall shaped to guide the plug along an axis between a first end position and a second end position. A first pole piece made of magnetic material is disposed at the first end position. A first port opens into the chamber such that the plug covers the first port in one end position. A second •-_ port opens into the chamber in communication with the first port when the plug is in the other end position. Responsive to a periodic electric current, a first periodic magnetic field of a first given polarity 5 parallel to the axis is generated in the first pole piece to attract periodically the plug to the first end position. The plug is placed in the second end position in the absence of the electric current. The plug can move rapidly between the first and second end positions 10 responsive to the electric current, thereby permitting rapid change in the gas flow in response to changes in the duty cycle of the command signal. In one embodiment, the plug is placed in the second end position by means of a second pole piece made of ,_ magnetic material at the second end position. Responsive to an electric current, a second magnetic field of a second given polarity parallel to the axis is generated in the second pole piece to attract periodically the plug to the second end position. While generating the 0 second magnetic field in the second pole piece, there is applied to the first pole piece a magnetic field of polarity opposite to the second given polarity and of a magnitude to induce in the plug a magnetic field smaller than the magnetic field induced therein by the second 5 magnetic field. Similarly, while generating the first magnetic field in the first' pole 'piece, there is applied to the second pole piece a magnetic field of polarity opposite to the first given polarity and of a magnitude to induce in the plug a magnetic field smaller than the 0 magnetic field induced therein by the first magnetic field. In each case, the applied magnetic field serves to repel the plug, thereby assisting the attraction of the plug to the other pole piece. A feature of the invention is a spherical plug which discourages binding and facilitates rapid movement 5 between the end positions of the chamber without alignment problems. Brief Description of the Drawings The features of specific embodiments of the best mode contemplated of carrying out the invention are illustrated in the drawings, in which: FIG. 1 is the schematic diagram of one embodiment of the invention; FIG. 2 is a schematic diagram of another embodiment of the invention; FIGS. 3 and 4 are diagrams of the pole pieces and plug, illustrating the attraction-repulsion operation of the valve of FIG. 2; and FIG. 5 is a schematic diagram of still another embodiment of the invention. Detailed Description of the Specific Embodiments In FIG. 1, fluid ports 10 and 12 open into the interior of a tubular, open ended valve body 14, which is made of nonmagnetic material such as aluminum. An end piece 16 made of magnetic material, such as iron, fits in one open end of valve body 14 and an end piece 18 fits in the other open end of valve body 14. In this embodiment, piece 18 is made of nonmagnetic material. The interior end surfaces of end pieces 16 and 18 and the cylindrical interior side surface of valve body 14 together define a chamber 20 within which a freely movable, close fitting spherical plug 22 made of magnetic material, such as iron, can move back and forth along a path defining its stroke. The clearance between plug 22 and the interior surface of valve body 14 is very small, typically of the order of 0.001 to 0.0005 of an inch. The interfaces between end pieces 16 and 18 and the interior surface of valve body 14 are sealed in a conventional manner, for example by 0-rings not shown. In chamber 20, end piece 16 has a distal portion 16a of small diameter and a connecting portion 16b of intermediate diameter between distal portion 16a and the remainder of end piece 16. End piece 18 has a distal portion 18a of small diameter and a connecting portion 18b of intermediate diameter between distal portion 18a and the remainder of end piece 22. Distal portion 18a has a concave semi-spherical seating surface 28 that matches the radius curvature of plug 22. The stroke of plug 22 is much smaller than prior art solenoid values, i.e., typically of the order of several one-thousandths of an inch, which permits rapid switching of valve state between open and closed. A port 24 extends axially along the full length of end piece 18 from chamber 20 to the exterior of valve body 14. Port 12 opens into chamber 20 adjacent to connecting portion 16b and port 10 opens into chamber 20 adjacent to connecting portion 18b. A portion 16c of end piece 16 extends outside valve body 14. An electric coil 32 is wrappped around portion 16c. One end of coil 32 is grounded. The other end of coil 32 is connected through a switch 34 to the positive terminal of a battery 36. The negative terminal of battery 36 is grounded. A resistor 38 is connected in parallel with switch 34 to permit discharge of coil 32 when switch 34 opens. Switch 34 is opened and closed by a switch control circuit 40 under the control of a microprocessor 42. In operation, the described valve is bistable. When switch 34 closes, the current flowing through coil 32 generates a magnetic field that attracts plug 22 to distal portion 16a; in this state, the surface of plug 22 abuts end piece 16 to open the valve and provide a free flow path between ports 10 and 24. End piece 16 thus serves as a magnetic pole piece that attracts plug 22 to one end position in chamber 20 when switch 34 is closed. By virtue of the close fit of plug 22 with the interior side surface of body 14 and the small opening, or no opening, of port 12, the space between end piece 16 and plug 22 has small enough venting to the atmosphere to produce between end piece 16 arid plug 22 a buildup of the pressure of the gas fed to the valve through port 10. When switch 34 opens, gas pressure in chamber 20 between plug 22 and end piece 16 drives plug 22 into abutment with distal portion 18a. In this state, the surface of plug 22 fits snuggly with surface 28 to substantially seal port 24. To permit gas pressure to return plug 22 to seating surface 28 as described, port 12 is either completely closed or has only a very small opening, vis-a-vis, port 24, depending on the pressure of the gas supplied to the valve and the frequency of operation of switch 34. Alternately, instead of gas pressure return, a compression spring could be disposed in chamber 20 between end piece 16 and plug 22, thereby normally urging plug 22 against seating surface 28 of distal portion 18a. Although the described valve has many applications, it serves as a respirator in the embodiment of FIG. 1. The disclosures of U.S. Patents 4,333,453 and 4,259,968 are incorporated fully herein by reference. Specifically, with reference to FIG. 4 of U.S. Patent 4,333,453, issued June 8, 1982, the valve of FIG. 1 is substituted for valve 65. A gas source 44, which supplies oxygen, is connected to port 10. An adjustable needle valve 46 is connected between port 12 and the atmosphere. (Needle valve 46 is opened sufficiently so there is just enough gas pressure to return plug 22 reliably to seating surface 18 when switch 34 is open, thereby minimizing the force required to unseat plug 22 from surface 28 when switch 34 closes.) A patient tube 48 is connected to port 24. The volume of gas supplied from source 44 to a patient through the described valve and patient tube 48 depends upon the duty cycle of switch control circuit 40, which is adjusted on an ongoing basis by microprocessor 42 so as to maintain a desired flow rate. The term "duty cycle" means herein the ratio of pulse duration to pulse period. In general, microprocessor 42 calculates the desired flow rate from data received from one or more sensors such as, for example, a flowmeter and/or a pressure sensor and generates periodic pulses with a duty cycle that varies so as to maintain the desired flow rate. Needle valve 46 provides pressure relief within chamber 20. Needle valve 46 is preferably adjusted without the spring (if used) and without a magnetic field to provide sufficient venting to the atmosphere so plug 22 is suspended y- between distal portions 16a and 18a. This minimizes the magnetic field and spring force required to operate the valve; if needle valve 46 is open too far, plug 22 will abut distal portion 16a and, if open to little, distal portion 18a. In the embodiment of FIG. 2, the components common to the embodiment of FIG. 1 bear the same reference numerals. In this embodiment, there is no spring or pres¬ sure induced plug return. End piece 18 is made of magnetic material and has a portion 18c that extends outside body 14. An electric coil 50 is wrapped around portion 18c in the same direction of rotation as coil 32 viewed from one end of valve body 14. The end of coil 50 adjacent to valve body 14 is grounded. The other end of coil 50 is connected by a switch 52 to the positive terminal of battery 36. A resistor 54 is connected in parallel with switch 52 to permit discharge of coil 50 when switch 52 opens. The direction in which coils 32 and 50 are wound and the direction of current flow therethrough are such that the resulting magnetic field generated by coils 32 and 50 have opposite polarity, i.e., if a north pole is produced at distal portion 16a by coil 32, then a north pole is also produced at distal portion I8a by coil 50. Switch 52 is closed when switch 34 is open, and vice versa. In operation, responsive to switch control ciarcuit 40, switches 34 and 52 alternately open and close. When switch 34 closes and switch 52 opens, the current flowing through coil 32 generates a magnetic field in end piece 16 that attracts plug 22 to distal portion 16a. When switch 34 opens and switch 52 closes, the current flowing through coil 50 generates a magnetic field in end piece 18 that attracts plug 22 to distal portion 18a. Thus, plug 22 shuttles back and forth between distal portion 16a and distal portion 18a at a §TfRiX; OMPI WIrO frequency of as high as 100 to 200 Hz. As in the embodiment of FIG. 1, the volume of gas that reaches patient tube 48 depends upon the switch duty cycle. The greater the percentage of time that switch 34 is closed, vis-a-vis, switch 52, the greater is the vol¬ umetric flow rate through the described valve to the patient from source 44. Precise metering of gas and rapid change in gas flow rate can thus be achieved. Pressure relief to chamber 20 is provided by port 12 in conjunction with needle valve 46, which is adjusted without application of magnetic fields as described in connection with FIG. 1. A feature of the invention incorporated in FIG. 2. is the provision of an assisting magnetic field by the coil (32, 50) associated with the open switch (34, 52). This assisting magnetic field is generated by virtue of the continuing circuit path through the parallel resistor (38, 54) when the corresponding switch (34, 52) is open. Consider first the magnetic field produced by coil 32 when switch 34 closes. In the absence of an assisting magnetic field generated by coil 50, there would be a north pole at distal portion 16a, a south pole induced in the adjacent region of plug 22, a north pole induced in the opposite region of pole 22, and a south pole induced at distal portion 18a, as illustrated in FIG. 3. As a result of the induced magnetism, plug 22 would be attracted to distal portion 18a rather than distal portion 16a, which would inhibit movement of plug 22 into abutment with distal portion 16a. This problem is overcome by the small residual current that flows through resistor 54 into coil 50 when switch 52 opens. Such residual current produces in end piece 18 a magnetic field having a polarity to repel plug 22, thereby assisting its movement into abutment with distal portion 16a, as illustrated in FIG. 4. The magnetic field "fϋRE l OMPI produced in end piece 18 by the residual current is sufficiently small to induce in plug 22 a magnetic field smaller than the magnetic field induced in plug 22 by the magnetic field generated by coil 32. As a result, distal portion 18a and the adjacent region of plug 22 have the same magnetic polarity, e.g., both are north poles, so that plug 22 is repelled by distal por¬ tion 18a. Similarly, when switch 34 opens and switch 52 closes, a residual current flows in coil 32 to assist the movement of plug 22 from distal portion 16a to distal portion 18a. The magnetic field generated by this current is likewise sufficiently small to induce in plug 22 a magnetic field smaller than the magnetic field induced therein by the magnetic field generated in end piece 18 by coil 50. Typically, the residual current is of the order of 5% of the current flowing when the switch (34, 52) is closed. Instead of generating a magnetic field by means of a residual current in one of the coils (32, 50) when its corresponding switch (34, 52) is open, the assisting magnetic field could be produced by permanent magnets. The valve of FIG. 2 is capable of precisely control¬ ling the volumetric gas flow from port 10 to port 24 and responds rapidly to changes in commands issued by microprocessor 42. Typically, the frequency of operation of switch control circuit 40 could be of the order of 100 to 200 Hz because of the small distance of travel of plug 22, typically of the order of several thousandths of an inch between distal portions 16a and 18a. Although it is preferable for the residual current provided by the parallel resistor (38, 54) to be of the same polarity as the actuating current passing through the switch (34, 52), because less energy needs to be stored in the coils (32, 50) and the circuit implementation is simpler, the residual current and OMPI > WIP0 y$ the resulting assisting magnetic field could be of the opposite polarity from the operating current and the resulting magnetic field. The important polarity requirement is between the operating magnetic field of one end piece and the assisting magnetic field of the other end piece, which must be of opposite polarity so as simultaneously to attract and to repel plug 22. In FIG. 5, an embodiment of the invention functions to mix together two different gases from a gas source 60 and a gas source 62. In this embodiment, the components in common with the embodiment of FIG. 2 bear the same reference numerals. A port 64 extends axially along the full length of end piece 16 from chamber 20 to the exterior of body 14. Distal portion 18a has a semi-spherical seating surface 66 matching the curvature of plug 22 where the interior end of port 64 opens into chamber 20. Gas source 60 is connected to port 64 and gas source 62 is connected to port 24. Ports 10 and 12 are coupled by a Y-connection 70 to a patient tube 72 or other gas receiver. The ratio of the gas from source 60 to the gas from source 62 in the gas mixture applied to patient tube 72 depends upon the proportion of the time plug 22 abuts distal portion 16a versus the proportion of the time plug 22 abuts distal portion 18a, which in turn depends upon the duty cycle of switch control circuit 40. The described embodiments of the invention are only considered to be preferred and illustrative of the inventive concept; the scope of the invention is not to be restricted to such embodiments. Various and numerous other arrangements may be deivsed by one skilled in the art without departing from the spirit and scope of this invention. For example, the described valve can be employed to control the flow of liquid instead of gas and can be utilized for many applications other than those disclosed. Although it is preferable for the plug to be spherical so as to provide a single band of contact with the interior surface of valve body 14, which reduces the possibility of the plug binding and reduces friction, the plug could have other shapes such as, for example, cylindrical or tapered at its ends.

Claims: WHAT IS CLAIMED IS: 1. A fast operating, bistable valve comprising: a movable plug made of magnetic material; a chamber in which the plug is disposed, the chamber having an interior wall shaped to guide the plug along an axis between a first end position and a second end position; a first pole piece made of magnetic material at the first end position; a first port opening into the chamber such that the plug covers the first port in one of the end positions; a second port opening into the chamber in communication with the first port when the plug is in the other end position; a source of a periodic electric current having a pulse width and a pulse period; means responsive to the periodic electric current for generating a first periodic magnetic field in the first pole piece of a first given polarity parallel to the axis to attract periodically the plug to the first end position; and means for placing the plug in the second end position in the absence of the electric current. -12a- 2. The valve of claim*l,_in which the means for placing the plug in the second end position comprises: a second pole piece made of magnetic material at the second end position; means responsive to an electric current for generating a second periodic magnetic field in the second pole piece of a second given polarity parallel to the axis; and means while generating the magnetic field in the second pole piece for applying to the first pole piece a magnetic field of polarity opposite to the second given polarity and of a magnitude to induce in the plug a magnetic field smaller than the magnetic field induced therein by the generating means, the valve additionally comprising means while generating the magnetic field in the first pole • piece for applying to the second* pole piece a magnetic field of polarity opposite to the given polarity and of a magnitude to induce in the plug a magnetic field smaller than the magnetic field induced therein by the generating means. 3. The valve of claim 1, additionally comprising means for varying the ratio of the pulse width to the pulse duration of the electric current. 4. The valve of claim 3, in which the means for placing the plug in the second end position comprises a spring urging the plug toward the second end position. -13- 5. The valve of claim 3, in which the means for placing the plug in the second end position comprises: a second pole piece made of magnetic material at the second end position; means responsive to an electric current for generating a second periodic magnetic field in the second pole piece of a second given polarity parallel to the axis; and means while generating the second magnetic field in the second pole piece for applying to the first pole piece a magnetic field of polarity opposite to the second given polarity and of a magnitude to induce in the plug a magnetic field smaller than the magnetic field induced therein by the means for generating a second magnetic field; the valve additionally comprising means while generating the first magnetic field in the first pole piece for applying to the second pole piece a magnetic field of polarity opposite to the first given polarity and of a magnitude to induce in the plug a magnetic field smaller than the magnetic field induced therein by the means for generating a first magnetic field. 6. The valve of claim 5, additionally comprising a gas source connected to one of the ports and a gas receiver connected to the other port. 7. The valve of claim 6, additionally comprising a third port opening into the chamber betv/een the plug and the other end position and an adjustable needle valve coupling the third port to the atmosphere. 8. The valve of claim 7, in which the gas receiver is a patient tube. -14- 9. The valve of claim 5, additionally comprising: a third port opening into the chamber such that the plug covers the third port in the second end position; a fourth port opening into the chamber in communication with the third port when the plug is in the one end position; a first gas source connected to the first port; a second gas source connected to the third port; and a gas receiver connected to the second and fourth ports. 10. The valve of claim 9, in which the gas receiver is a patient tube. 11. The valve of claim 1, in which the plug is spherical and the interior wall of the chamber is cylindrical . 12. A bistable valve comprising: a movable plug made of magnetic material; a chamber in which the plug is disposed, the chamber having an interior wall shaped to guide the plug along an axis between a first end position and a second end position; a first pole piece made of magnetic material at the first end position; a second pole piece made of magnetic material at the second end position; a first port opening into the chamber such that the plug covers the first port in the first end position; a second port opening into the chamber in communication with the first port when the plug is in -15- the second end position; means responsive to an electric current for generating a first magnetic field in the first pole piece of a first given polarity parallel to the axis to attract the plug in the first end position; means while generating the first magnetic field in the first pole piece for applying to the second pole piece a magnetic field of polarity opposite to the first given polarity and of a magnitude to induce in the plug a magnetic field smaller than the magnetic field induced therein by the means for generating a first magnetic field; means responsive to an electric current for generating a second magnetic field in the second pole piece of a second given polarity parallel to the axis; and means while generating the second magnetic field in the second pole piece for applying to the first pole piece a magnetic field of polarity opposite to the second given polarity and of a magnitude to induce in the plug a magnetic field smaller than the magnetic field induced therein by the means for generating a second magnetic field. 13. The valve of claim 12, in which the plug is spherical and the interior wall of the chamber is cylindrical. 14. The valve of claim 13, in which the distal portion of the first pole piece has a semi-spherical seating surface against which the plug abuts in the first end position. 15. The valve of claim 14, in which the first port opens into the chamber at the seating surface of the first pole piece. e**-*" 1 - -16- 1 16. The valve of claim 15, " in which the first pole piece has a distal portion with a small diameter at the first end position and a connecting portion with an intermediate diameter between the distal portion and ' 5 the remainder of the first pole piece. 17. The valve of claim 16, in which the second port opens into the chamber at the interior wall adjacent to the connecting portion of the first pole piece. 10 18. The valve of claim 17, in which the second pole piece has a distal portion with a small diameter at the second end position and a connecting portion with an intermediate diameter between the distal portion 15 and the remainder of the second pole piece. 19. The valve of claim 18, additionally comprising a third port opening into the chamber at the interior wall adjacent to the connecting portion of the second 20 pole piece. 20. The valve of claim 14, in which the distal portion of the second pole piece has a semi-spherical seating surface against which the plug abuts in the 5 second end position. 21. The valve of claim 20, ' in which the second port opens into the chamber at the seating surface of the second pole piece. 0 22. The valve of claim 21, additionally comprising further ports opening into the chamber adjacent to the respective ends of the chamber. 5 -17- 23. A fast operating, bista-ble valve comprising: a movable plug made of magnetic material; a chamber in which the plug is disposed, the chamber having an interior wall shaped to guide the plug along an axis between a first end position and a second end position; a first pole piece made of magnetic material at the first end position; a first port opening into the chamber such that the plug covers the first port in the first end position; a second port opening into the chamber in communication with the first port when the plug is in the second end position; a source of fluid under pressure connected to one port; a fluid receiver connected to the other port; a source of a periodic electric current having a pulse width and a pulse period ; and means responsive to the periodic electric current for generating a ' first periodic magnetic field in the first pole piece of a first given polarity parallel to the axis to attract periodically the plug to the first end position, the space in the chamber between the plug and the second end position having small enough venting to produce a sufficient pressure build up between the plug and the second end position to place the plug in the first end position in the absence of the electric current. 24. The valve of claim 23, in which the receiver is connected to the first port and the source is connected to the second port, the second port being in communication with the space between the plug and the second end position when the plug is in the first end position.

Inventors: RODDER JEROME A, RODDER, JEROME, A.
Applicants: RODDER JEROME A, RODDER, JEROME, A.
Application year: 1984
Main classification: F16K31
IPC codes: A61B5, F16K31