Sealed motor driven valve

Disclosed is a motor operated valve including a valve body with an inlet and outlet and a valve seat therebetween. A valve core reciprocates between open and closed positions by threads of the valve core cooperating with threads on a shaft which rotates with the armature of the motor. The armature has a plurality of spaced apart permanent magnets, a bearing assembly, and is enclosed by a magnetically transparent enclosure closed at one end and hermetically sealed at its other end to the valve body. Lying closely outside the enclosure is a drive stator that includes drive windings and plural Hall-effect devices for commutation of the windings.

 

What is claimed is:

1. A motor operated valve including a valve body having at least one inlet and at least one outlet, at least one inlet flow passage and at least one outlet flow passage, at least one valve closing member positioned between said inlet and said outlet passage, at least one valve seating means within said body, said at least one valve closing member mounted for movement between open and closed positions, an armature and a drive member for moving said valve closing member, said drive member and said valve closing member being operatively attached so that rotation of said armature and said drive member cause movement of said valve closing member, said armature having a plurality of spaced apart permanent magnets embedded therein, at least one bearing assembly associated with one of said drive member and said armature, said armature being enclosed by a magnetically transparent enclosure closed at one end and hermetically sealed at its other end to said valve body, and, lying closely outside said enclosure, a drive stator, said drive stator including drive windings and plural Hall-effect devices for commutation of said windings.

2. A motor operated valve as defined in claim 1, wherein said at least one valve closing member comprises a valve core and said valve core seating means comprises an annular tapered valve seat.

3. A motor operated valve as defined in claim 1, wherein said drive member comprises a threaded shaft extending axially beyond a plane transverse to the end of said armature, said threaded shaft having a threaded connection to said valve closing member.

4. A motor operated valve as defined in claim 3, wherein at least one of said threaded shaft and said valve closing member includes at least a surface layer of a lubricous material which includes PTFE.

5. A motor operated valve as defined in claim 1, wherein said magnetically transparent enclosure comprises a stainless steel can having a thickness of from about 0.010 inches to about 0.035 inches.

6. A motor operated valve as defined in claim 1, wherein said armature includes a threaded portion core and wherein said drive member comprises a threaded shaft engaged therewith, said threaded shaft being adapted to move axially as a result of rotation of said threaded core.

7. A motor operated valve as defined in claim 1, wherein said at least one valve closing member comprises a valve core adapted to move axially, and wherein said valve body includes at least two inlets or at least two outlets, wherein at least one valve seating means comprises two valve seating means, and wherein said valve core is movable between said at least two seating means and is further positionable between said seating means so as to constitute said valve a mixing valve or a diverting valve, depending on the direction of flow of fluid therethrough.

8. A motor operated valve as defined in claim 1, wherein said valve closing member comprises a valve core movable at least between open and closed positions, said valve core also including a pilot member able to move substantially independently of fluid forces present in said passages, said pilot member being designed to bring pressure fluid forces to bear on said valve core, said valve core responding by movement in response to pressure fluid forces when said pilot member is moved by rotating said drive member.

9. A motor operated valve as defined in claim 8, wherein said pilot member is arranged for free but limited movement between positions wherein said pilot is seated within said core and a position wherein said pilot allows fluid from a high pressure region to bleed into a region of lower pressure.

10. A motor operated valve as defined in claim 8, wherein said pilot member engages said drive member and is driven thereby and wherein said valve core at least partially surrounds said pilot member.

11. A motor operated valve as defined in claim 10, wherein said core includes a pilot seat and a pilot seat retainer received within said core.

12. A motor operated valve as defined in claim 11, wherein said free but limited movement of said pilot member is restricted by engaging said pilot seat on said valve core in one position, and the pilot seat retainer in another position, thereby positively engaging said core for movement in both directions.

13. A motor operated valve as defined in claim 1, wherein said valve closing member comprises a quarter-turn type valve closing member.

14. A motor operated valve as defined in claim 1, wherein said at least one bearing assembly comprises a bearing assembly including a plurality of roller elements, at least one race for said roller elements, and a cage for said roller elements, said cage comprising a stiff, chemically resistant, lubricous synthetic resinous material.

15. A motor operated valve as defined in claim 14, wherein, in use, said cage engages and supports said roller elements on the upper surface and at least the major portion of two circumferential portions of said elements.

16. A motor operated valve as defined in claim 13 wherein said quarter-turn valve comprises a butterfly-type valve closing member.

17. A motor operated valve as defined in claim 13, wherein said quarter-turn type valve closing member comprises a ball type valve member.

18. A motor operated valve as defined in claim 13, wherein said quarter-turn type valve closing member comprises a plug type valve.

19. A motor operated valve as defined in claim 1, wherein said armature includes a threaded member on the interior thereof, wherein said drive member includes threads engageable with said threaded member, said drive member further including a ferrous armature thereon, said magnetically transparent enclosure also enclosing said ferrous armature, whereby said ferrous armature moves axially with said valve core, and a detector lying outside said magnetically transparent enclosure for detecting the axial position of said ferrous armature from time to time.

20. A motor operated valve as defined in claim 1, wherein said valve closing member includes an axially movable valve core, said motor operated valve including means for preventing rotation of said valve core while allowing said valve core to move axially.

21. A motor operated valve as defined in claim 19, wherein said position detector comprises a linear variable differential transformer.

22. A motor operated valve as defined in claim 19, wherein said position detector comprises at least one displacement sensor.

23. A motor operated valve as defined in claim 19, wherein said position detector comprises a plurality of proximity type sensors having a plurality of home positions.

24. A motor operated valve as defined in claim 1, wherein said valve closing member comprises a quarter-turn closing member, having a stem portion driven by a scotch yoke mechanism.

25. A motor operated valve as defined in claim 1, wherein said drive member includes a threaded element and said valve closing member is the stem of a quarter-turn valve operatively attached to a rotatable wheel having a threaded exterior, whereby rotation of said drive member rotates said wheel and rotation of said wheel opens and closes said valve.

26. A motor operated valve including a valve body having at least one inlet and at least one outlet, at least one inlet flow passage and at least one outlet flow passage, at least one valve closing member positioned between said inlet and said outlet passage, at least one valve seating means within said body, said at least one valve closing member mounted for movement between open and closed positions, an armature and a drive member for moving said valve closing member, said drive member and said valve closing member being operatively attached so that rotation of said armature and said drive member cause movement of said valve closing member, said armature having a plurality of spaced apart permanent magnets embedded therein, at least one bearing assembly associated with one of said drive member and said armature, said armature being enclosed by a magnetically transparent enclosure closed at one end and hermetically sealed at its other end to said valve body, and, lying closely outside said enclosure, a drive stator, said drive stator including drive windings and plural Hall-effect devices for commutation of said windings wherein said at least one bearing assembly comprises a bearing assembly and a bushing, said bearing assembly including a plurality of roller elements, at least one race for said roller elements, and a cage comprising a stiff, chemically resistant, lubricous synthetic resinous material, said bushing being made from a filled graphite material.

27. A motor operated valve as defined in claim 26, wherein said stiff chemically resistant, lubricous synthetic resinous material comprises a PTFE material.

28. A motor operated valve as defined in claim 27, wherein said roller elements are ball bearing elements.

29. A motor operated valve as defined in claim 27, wherein said roller elements are plain roller bearing elements or tapered roller bearing elements.

30. A motor operated valve as defined in claim 27, wherein said cage surrounds said roller elements so as to be in sliding contact therewith over at least 15% of the surface area of said roller elements.

31. A two-position motor operated fluid control valve, comprising a valve body having at least plural passages therein, at least one slide member movable axially and operative to change said fluid flow by making a connection, in one position, between first pairs of passages and another position, between second pairs of passages, said slide member being movable axially by rotation of a drive member which is rotatable with an armature of said motor, said motor armature having a plurality of spaced apart permanent magnets embedded therein, at least one bearing assembly associated with one of said drive member and said armature, said armature being enclosed by a magnetically transparent enclosure closed at one end and hermetically sealed at its other end to said valve body and, lying closely outside said enclosure, a drive stator including drive windings and plural Hall-effect devices for commutation of said windings.

32. A two-position motor operated fluid control valve as defined in claim 31, wherein said at least plural passages comprises four passages, and wherein said slide member moves between positions connecting said first and second passages and said third and fourth passages, to a position wherein said first and fourth passages and second and third passages are connected.

33. A two-position motor operated fluid control valve as defined in claim 31, wherein said at least plural passages comprises six passages, and wherein said slide member moves between a first position connecting said first and second passages, said third and fourth passages, and said fifth and sixth passages and a second position connecting said first and sixth passages, said fourth and fifth passages and second and third passages.

34. A two-position motor operated fluid control valve as defined in claim 31, wherein said slide member is rectangular when viewed along the axis of said drive member.

35. A two-position motor operated fluid control valve as defined in claim 31, wherein said bearing assembly is journaled within a bearing retainer, wherein said enclosure has its said other end received in fluid-tight relation between said bearing retainer and a hold-down member, and said closed end of said enclosure includes a bushing for said armature.

36. A two-position motor operated fluid control valve as defined in claim 31, wherein said valve further includes a second, outer enclosure, said fluid control valve further including drive circuitry, said second, outer enclosure being held over said drive circuitry, said stator, said drive windings and said Hall-effect devices in fluid-tight relation.

37. A method of operating a sealed motor which includes a stator, a plurality of drive windings for said stator, plural Hall-effect devices for commutating said drive windings, and a magnetically transparent enclosure enclosing a rotor including plural permanent magnets therein, said method including periodically energizing said drive windings with plural pulses of current, lowering an average current by periodically interrupting said pulses of said current with relatively great intervals of virtually no current at a time when net movement is desired and periodically allowing said armature to come to a virtual stop during each of said intervals, thereby rotating said armature in increments and avoiding damaging heat buildup in said sealed motor.

38. A method of operating a sealed motor as defined in claim 37, wherein said frequency of each of said intervals of virtually no current is from about 4 Hz to 20 Hz.

39. A method of operating a sealed motor as defined in claim 37, wherein said duration of each of said intervals of virtually no current is from about 5 to about 25 milliseconds.

40. A method of operating a sealed motor as defined in claim 37, wherein said intervals of virtually no current occur about every 150 milliseconds and have a duration of about 15 milliseconds.

41. A method of operating a sealed motor as defined in claim 37, wherein said current pulses peak at from about 2 amps to about 5 amps, and said voltage is about 24 to 48 volts.

42. A method of operating a sealed motor as defined in claim 37, wherein, during said pulses of current, at least most of the inertia of said rotor is overcome, and the back emf generated by said rotor rises substantially, said rotor during said current pulse thereby providing maximum torque.

43. A method of operating a sealed motor as defined in claim 37, wherein said intervals of virtually no current comprise intervals of no current, and allowing said armature to come to a virtual stop comprises allowing said armature to come to a stop.

44. A method of operating a sealed motor as defined in claim 37, said sealed motor being associated in use with a valve which includes a valve body, fluid passages, and a movable valve core, said method including maintaining periodic current pulses even when said valve is seated, and continuing to apply said pulses indefinitely.

45. A motor operated valve including a valve body having at least one inlet and at least one outlet, at least one inlet flow passage and at least one outlet flow passage, at least one valve closing member positioned between said inlet and said outlet passage, at least one valve seating means within said body, said at least one valve closing member being mounted for movement between open and closed positions, said valve closing member comprising a valve cartridge, means associated with said valve cartridge for preventing rotation thereof, a bearing carried by said cartridge, an armature, a threaded drive member guided by said bearings, a threaded valve closing member engaged with said drive member and said cartridge so that rotation of said armature and said drive member cause movement of said valve closing member, said armature having a plurality of spaced apart permanent magnets embedded therein, said armature being closely surrounded by a magnetically transparent enclosure retained in a fluid-tight relation between said cartridge and a hold-down member, and exterior to said enclosure, a drive stator with drive windings therein and plural Hall-effect devices for commutation of said windings.

46. A motor operated valve as defined in claim 45, wherein said drive stator, said drive windings and said plural Hall-effect devices are received within a second, outer enclosure, said outer enclosure being held against said valve body in fluid-tight relation.

47. A motor operated valve as defined in claim 46, wherein said magnetically transparent enclosure includes removable fasteners normally holding said enclosure in a fixed position relative to said valve body and said second enclosure includes removable fasteners normally holding it in a fixed position relative to said valve body.

48. A motor operated valve as defined in claim 45, wherein said magnetically transparent enclosure comprises a stainless steel can of from about 0.010 to 0.035 inches in thickness.

49. A motor operated valve as defined in claim 45, whereby removing said second enclosure exposes said drive stator, said drive windings and said Hall-effect devices for maintenance without disturbing said magnetically transparent enclosure, and wherein removing said magnetically transparent enclosure exposes said armature, said cartridge and said valve closing member for removal from said valve body.

BACKGROUND OF THE INVENTION

The present invention relates to electric motor-driven valves, and particularly, to so-called canned motors preferably using a threaded armature extension to drive the valve core within a valve body and commutated by Hall-effect devices, with the windings and Hall-effect devices ordinarily being enclosed within a second, atmosphere-tight enclosure. The valve housing may comprise a two-way valve, a three-way valve, a pressure-balanced valve or a multi-port valve, as used for example in heat exchange or industrial refrigeration.

The invention also relates to supplying current to the field windings in a unique manner, resulting in a unique armature movement adapted not only to achieve maximum torque in the motor, but also to do so without any thermal overload on the field windings and bearings, whereby the motor may be operated indefinitely without failure.

Still further, and in another aspect, the invention relates to the use in such combination of ball or like bearings wherein the bearings are caged by a PTFE composition capable of furnishing relatively permanent lubrication to the bearings, and thus giving them relative immunity from conditions that would otherwise be detrimental to extended bearing life.

Electric motor-operated valves have heretofore been used in many embodiments, some of which used stem and packing sealing in conjunction with geared, shaded pole or similar motors. This type of valve had its driving motor mounted external to the valve and was connected to the valve core via a stem which incorporated various packing type sealing arrangements designed to contain the fluids within the valve enclosure. Often these sealing arrangements were the first elements to fail in service and leak due to wear, dirt, or corrosion. In some cases, these packings would leak even in new condition. The end result was leakage of fluid from the valve to the atmosphere, or of the atmosphere into the process fluid handled by the valve.

Many valve applications, particularly in the chemical, petroleum, biological, pharmaceutical, industrial refrigeration, or environmental industries cannot tolerate measurable leaks or fugitive emissions from valves in the process loop. Fluid emissions may be dangerous or toxic, or the fluids may simply be precious or sensitive to contamination, for example.

In some valve applications having small torque requirements, an improvement was made in regard to leakage by employing stepping motors mounted wholly within the valve enclosure, thus eliminating the stem and packing and its associated leakage potential. This, however, exposed the rotor, windings and associated wiring to the process fluids. Compatibility between the process fluids and the motor limited the number of fluids acceptable in valves of this type. In those limited applications wherein a stepper motor was compatible with and safe for the process fluids, significant advantages were realized: no stem or packing was required; an increased precision of positioning was available; good motor reliability was obtained at reduced cost and size; and a simple control scheme could be used.

However, entry of control and power wires into the valve-pressurized fluid envelope presented reliability and cost difficulties. Stepping motors have not been able to be applied to control ports larger than about 1/4" in diameter without internal gearing or additional commutation complexity, largely due to the inability of stepping motors to remain stalled under load, and their tendency to lose torque capability if synchronization is lost due to power losses or system forces.

Additionally, the close stator and rotor radial clearances required for small step angle stepper motors prohibits the use of a hermetic, pressure containing magnetically transparent metal can in the magnetic gap. As a practical matter, this then requires the windings to be immersed in the process fluid. This in turn limited the application to those cases wherein the fluid is compatible with the motor windings and currents in question.

A need has therefore developed for a small, compact but high torque motor capable of driving relatively large valve mechanisms to open and close valve ports, wholly or incrementally, and hold the valve mechanisms in a desired position in response to an external control signal.

Additionally, a need has developed for a motor which is able to operate in a hermetically pressure sealed condition to prevent leakage of fluids from a fluid system in which the valve operates, especially at the motor/valve interface. Further, a need has developed for a motor-operated valve for use in a fluid system that is able to operate for longer periods of time without failure when the fluid in the system is corrosive or acts as a solvent to remove material or lubricants from metal, plastic, ceramic or other surfaces that come in contact with the process fluid or with each other within the valve mechanism.

It is therefore, an object of the invention, generally stated, to provide a new and improved motor-driven valve.

Another object of the present invention is to provide a motor-operated valve having a motor producing a higher torque/lower heat relationship than has been heretofore known.

An additional object of the present invention is to provide a motor-operated valve having an operating life which is much longer than that heretofore known.

Yet another object of the invention is to provide a valve having a logical and simplified arrangement of components to provide ease and simplicity of servicing or periodic maintenance.

Still another object of the present invention is to provide a motor having a permanent magnet-containing armature or rotor within a magnetically transparent can, and which includes windings and Hall-effect devices located outside the can, with the field and the Hall-effect devices enclosed within a second can or protective closure which is also sealed to the valve body.

A further object of the present invention is to provide a sealed motor which includes only four electrical conductors passing in a sealed relation through the outermost impervious shell to operate a circuit board located between the shells containing the motor controllers therein.

A still further object of the present invention is to provide a valve core for engaging a seat in the valve body, with the valve core being made from a composite PTFE material or the like and having a valve seating surface made from a hard, wear-resistant material.

An additional object of the present invention is to provide a valve core which is adapted to reciprocate into and out of contact with an annular seat by reason of having threads therein and whose axial motion is insured by a groove and pin arrangement, and whose core is urged axially into and out of registration by a threaded shaft that is secured to said armature and which rotates therewith.

A still further object is to provide a quarter-turn type valve wherein the operator is a canned motor and the valve is turned by the combination of a threaded shaft and a wheel, scotch yoke or other mechanism having a portion attached to the valve.

Another object of the present invention is to provide a motor having a sealed or canned armature and lying within the member comprising the seal, a bearing assembly having an inner and outer race, a plurality of roller elements and a cage securing said bearing elements in position, with the cage comprising a composite PTFE or similar wear-resistant, lubricous material, whereby the bearings have a greatly increased life in relation to other bearings presented to the same environment.

Yet another object of the present invention is to provide a valve operating motor which includes inner and outer leakproof containers, which containers and other elements including the valve core, may be removed in sequence as a matter of maintenance or replacement, without disturbing the valve body.

Still another object of the present invention is to provide a method of controlling a brushless DC motor in operation, which method comprises intermittently furnishing high current pulses to the windings energizing the armature with a relatively long interval between pulses, at which time said armature is not subject to undesirable heat build-up.

A further object of the present invention is to provide a method of operating a brushless DC motor which enables said motor to provide maximum torque indefinitely, yet which is not in danger of failing from excessive thermal overload.

A still further object of the present invention is to provide a sealed motor and a valve core positioning controller wherein the armature and the valve body as well as a position sensing element are surrounded in part by the armature and whereby the armature, the driven rotary shaft and the position indicating element lie within a first sealed housing, and the position sensor, the drivers and the field for the motor lie outside the first housing.

An additional object of the present invention is to provide a motor drive arrangement which includes a rotary screw and a threaded valve core adapted to move within a valve body, with the arrangement of valve components being such that the unit may be adaptable to a number of valve arrangements, including those using single or multiple inlets/outlets.

Another object of the present invention is to provide a sealed motor and valve arrangement wherein the armature is journaled by a graphite containing bearing at one end and by the novel roller/ball bearing at the other end.

Yet another object of the present invention is to provide a motorized valve arrangement wherein the movable portion of the valve core comprises a mixing or diverting valve with a valve core in an intermediate position to allow mixing or diverting of process fluids.

Still another object of the present invention is to provide a sealed motor having a magnetically transparent enclosure for the armature, with the armature having a threaded interior stem portion with a position sensor on one end of the stem and a valve core on the other end of the stem.

The present invention achieves its other objects and advantages which are inherent therein by providing a valve body having at least one inlet and at least one outlet, a valve seat therebetween, and, in several embodiments, at least one valve core which reciprocates between open and closed positions of the valve seat and is moved between positions by threads in the core cooperating with threads on a shaft which rotates with the armature, the armature having a plurality of spaced apart permanent magnets embedded therein, a plurality of drive stator windings and Hall-effect devices commutating the windings, with a sealed, magnetically transparent can between the armature and the stator, and preferably, the entire motor being enclosed within a second housing lying outside the stator and also enclosing the drive circuitry. In other embodiments, the rotary shaft indirectly operates various types of quarter-turn valves.

The manner in which these and other objects and advantages are achieved in practice will become more apparent when reference is made to the following description of the preferred embodiments of the invention and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of a sealed motor-operated two-way valve according to the embodiment of the present invention;

FIG. 1A is an enlarged sectional view of the valve core and related elements of FIG. 1;

FIG. 2 is a vertical sectional view , with portions broken away, of a sealed motor-operated three-way valve according to an alternate embodiment of the present invention;

FIG. 3 is a vertical sectional view of a sealed motor-operated four-way slide valve according to a further embodiment of the present invention;

FIG. 4 is a vertical sectional view of a sealed motor-operated multi-port slide valve according to a still further embodiment of the present invention;

FIG. 5 is a vertical sectional view of a sealed motor-operated, pilot pressure assisted valve according to another embodiment of the present invention;

FIG. 5A is an enlarged sectional view of the pilot-assisted valve of FIG. 5, showing the same in one position of use;

FIG. 5B is a view similar to view FIG. 5A, but showing the pilot-assisted valve in another position of use;

FIG. 6 is a top plan view of an improved bearing assembly designed for running for extended periods whether wet or dry without damage;

FIG. 7 is a perspective view of a bearing cage for the improved bearing;

FIG. 8 is a vertical sectional view of a sealed motor operated valve, including an integral valve member position feedback control according to a still further embodiment of the present invention;

FIG. 9 is a graph illustrating the relationship between motor speed and motor torque for a permanent magnet brushless D.C. motor;

FIG. 10 is a graph illustrating the relationship between motor current and motor heat rise for a permanent magnet brushless D.C. motor utilizing conventional motor drive methods and showing the thermal limit of a conventionally driven motor occurring at a current well below the maximum current;

FIG. 11 is a graph illustrating the full voltage motor current versus time while a permanent magnet brushless D.C. motor utilizing conventional motor drive methods is driven under various loads accelerates from a stopped position to running speed;

FIG. 12 is a graph embodiment of the present invention illustrating the speed versus time while a permanent magnet brushless D.C. motor utilizing conventional motor drive methods is driven under various loads accelerates from a stopped position to running speed;

FIG. 13 is a graph illustrating the motor current versus time while a permanent magnet brushless D.C. motor is subjected under various loads to full voltage for optimally timed pulses according to an embodiment of the present invention;

FIG. 14 is a graph illustrating the motor speed versus time while a permanent magnet brushless D.C. motor is subjected under various loads to full voltage for optimally timed pulses according to an embodiment of the present invention;

FIG. 15 is a graph illustrating the relationship between motor heat rise versus time for a stalled permanent magnet brushless D.C. motor utilizing conventional motor drive methods and utilizing optimally timed pulses according to an embodiment of the present invention;

FIG. 16 is a vertical sectional view of a further embodiment of a motorized valve of the invention, showing the drive unit adapted to turn a socalled quarter turn valve from an open to a shut position;

FIG. 17 is a vertical sectional view of the apparatus of FIG. 16, showing a view of the operative mechanism in end section and showing another view of the manner in which the valve opens and closes;

FIG. 18 is a vertical sectional view of a worm and roller gear used to operate another form of quarter turn valve;

FIG. 19 is a block diagram of a typical motor control used with the present invention; and,

FIG. 20 is a block diagram of a circuit employing a fail-safe, battery backup for operating a valve according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring now to FIG. 1, one embodiment of the present invention is shown to lie in a sealed motor driven valve assembly generally designated 10 which includes a positively driven, pressure balanced valve assembly 10 used to control the flow of fluids. The valve assembly 10 includes a valve body 11 of a flow-through design having an annular inlet flange 12 defining an inlet passage 13 extending centrally thereof into and partially across the valve body 11. On the opposing side of valve body 11 is an annular outlet flange 14 defining an outlet port 15, which extends inwardly partially through the valve body therefrom. The valve body 11 further includes an annular electric motor mounting flange generally designated 16 centrally positioned on top of valve body 11.

In the center portion of the valve body 11 is a dividing wall 20 that separates the inlet port 13 from the outlet port 15. In the center of the dividing wall 20 is a circumferentially extending surface defining an angled valve seat 22 that extends about the passage 21.

Referring now particularly to FIG. 1A, the annular electric motor mounting flange generally designated 16 at the top center of the valve body 11 includes a main central bore 23 extending vertically downwardly thereof, and an enlarged diameter counterbore portion 23a which terminates at the top annular surface 16a of the flange generally designated 16. The counterbore 23a extends from the top surface 16a of the motor mounting flange downwardly and terminates at a shoulder 16b. A generally hollow cylindrical cartridge generally designated 24, is held in the counterbore 23a by an enlarged diameter shoulder portion 24a which includes a groove 28 for receiving an O-ring seal 29. The cartridge 24 also includes a central shaft receiving bore 25, a first, bearing-receiving counterbore 26 and below that a further enlarged second counterbore 27.

A substantially cylindrical valve core generally indicated at 30, is designed to move axially, but not to rotate in the second counterbore 27. The valve core includes a hollow annular bottom portion 31 having a predetermined geometry which, in this case, provides a controlled progression of increase in effective area between the inlet port 13 and the outlet port 15 when the valve core 30 moves upwardly (axially) in the counterbore 27. An annular valve seat insert 33 is positioned on the outside of the valve core 30 to close off the inlet port 13 from the outlet port 15 when the seat insert 33 is matingly engaged with the angled valve seat 22.

The inside diameter portion 30a of the valve core 30 is threadedly engaged with a threaded shaft 43 which is also preferably made from a wear resistant lubricious material 34 such as composite PTFE or similar low-friction, chemically inert material. A pin 36 is retained in the cartridge 24 and engages an axial slot 36a on valve core 30 to prevent rotation of the core when the drive threads 43 are actuated. The valve core 30 has an upper annular surface 35 which engages the shoulder 26a between the bearing-receiving counterbore 26 and the largest counterbqre 27 of the cartridge 24 to stop the upward movement of valve core 30. Pressure balance chamber 62 is sealed from the inlet port 13 by seals 17 and joins the outlet port 15 via a bleed passage 18 which connects the hollow annular bottom portion 31 of valve core 30 to the pressure balance chamber 62.

Referring again to FIG. 1, a brushless D.C. permanent magnet servomotor generally designated 40 is designed to cooperate with the valve generally designated 10. The motor 40 is shown to comprise, beginning from the inside and working toward the outside, a cylindrical rotor 41 in this embodiment having six polar segments which accommodate permanent magnets 42 extend along the vertical sides thereof. Rotor 41 is rotatably mounted between wear resistant lubricious bearing assemblies 59 and 60, which are designed for running wet or dry for extended periods without damage. Referring again to FIGS. 1 and 1A, the rotor 41 has a threaded extension in the form of a shaft 43 which extends from near the bottom end of the rotor 41 through the bores 25, 26 in the cartridge 24, and threadedly engages the valve core 30 as pointed out above. The bushing 59 is preferably made from a lubricous material such as a filled graphite or carbon graphite material affording a lubricous surface and an extended wearing capability. The permanent magnets 42 are retained in the rotor 41 by drawn shell end caps 61.

According to the present invention, a pulse set is used for rotationally positioning the rotor. These pulses are generated by the permanent magnets 42 embedded in the rotor 41 as detected by the Hall-effect sensors 54. The Hall-effect sensors detect the magnetic field surrounding the permanent magnets and switch the field on or off as the magnetic field changes. The present invention utilizes the permanent magnets both as magnetic force generators and as part of the positioning control system.

The rotor 41 is hermetically pressure sealed to the valve body 11 and its internal components by a magnetically transparent stainless steel can 44 that is welded at its top end to a bearing mount 45 and at its bottom end to an annular can flange 47 that is retained on the annular electric motor mounting flange 16 of the valve body 11 by a hold-down flange 46 and bolts 46a. The thickness of the stainless steel can is important to operation of the brushless servo motor 40. Because a thick can requires a longer (therefore weaker) magnetic path to pass there through, and a thin can does not provide the stability needed to rotatably mount the rotor 41 therein, a compromise must be struck. A can having a thickness of 0.015 inches has proved acceptable in at least one case; 0.010 to 0.035 inches seems to be a typical range.

Outside the stainless steel can 44 and mounted on the hold-down flange 46 is a cylindrical housing assembly 50 formed of sheet metal and including a spherical shell end cap 51 welded together and to a removable housing flange 52. The housing assembly 50 is mounted and sealed to the hold-down flange 46 with mounting screws 52a and gaskets. Mounted between the housing assembly and the stainless steel can is an annular stator 48.

The electronic motor drive circuitry shown somewhat diagrammatically in FIG. 1 is mounted on a circuit board generally designated 53 and retained between the bearing mount 45 of the hermetically pressure containing sealed chamber and the housing end cap 51. The electronic circuitry on board generally designated 53 includes sensor wiring extending down to the Hall-effect commutation sensors 54 positioned adjacent but spaced by the thickness of the can 44 from the poles of the magnets 42, and the drive wiring 55 extending from the circuit board 53 to the stator windings 58.

Integrating the driver within the motor envelope reduces the amount of power wiring to be connected by the ultimate user of the valve. Instead of three power wires, there are only two, and all five sensor wires are contained within the valve assembly, thus being eliminated from the user's responsibility. Only two control wires and two power wires are required for motor connection, instead of the eight that are normally required. Control and power wiring from the circuit board extends outwardly of the end cap 51 through a cylindrical conduit 57 specifically designed to hermetically pressure seal the wires using PTFE compression seals 70 and an epoxy resin 71. The housing is cast within with epoxy generally designated 72.

Referring again to FIG. 1, all of the above-enumerated motor components work to turn the rotor 41 inside its hermetically pressure sealed can 44 to turn the threaded shaft 43 on the valve core 30, thus reciprocating the valve member from its closed position to its open position. The valve core 30 may be positioned as desired anyplace between open and fully closed or any intermediate position, as determined by the control commands from the various process sensors.

Referring again to FIG. 1, but also to FIGS. 6 and 7, an area inside the portion of the rotor housing 44 and the valve body 11 that has been found very important to long life of the sealed motor operated valve is the ball or other roller type bearing 60 retained between the cylindrical cartridge 24 and the rotor drive shaft 43.

Referring now specifically to FIGS. 6 and 7, there is shown a bearing assembly, generally designated 60, that includes an outer race 61 and inner race 62, a plurality of ball bearings 63 positioned therebetween and held in place by a cage member, generally designated at 64. Heretofore, most such cage members are believed to have been made of metal. Others are known to be made from plastics, such as polyimides, which are known to lack broad chemical resistance. In the harsh environment of the valve body 11, most process fluids act as de-greasing agents, especially with slow or limited, intermittent, partial rotation. This minimizes or negates the effect of lubricant between the bearing members, i.e., the outer race and the ball bearings, and the inner race and cage. The cage of the present invention, shown at 64, is made of modified polytetraflourethylene (PTFE) or similar chemically resistant, wear-resistant, low friction material. The cage 64 has an annular base 65 and a plurality of nearly spherical cutouts 66 extending inwardly from an upper interrupted annular surface 67 which is thereby divided into a discrete plurality of trapezoid-like surfaces. Each of the ball bearings 63 fits into one of the cutouts 66 and rotates therein, as the outer race 61 is preferably stationary, and the inner race 62 preferably rotates with the drive shaft 43.

It has been found that, by utilizing the PTFE cage, the cage itself acts as a lubricant on a microscopic or molecular level. As the ball bearings 63 rotate in the pocket 66, a microscopic amount of the PTFE is transferred by sacrificial wear to the outer surface of the ball bearings and acts to lubricate the entire ball bearing assembly 60 in the harsh anti-grease or oil lubricant environment normally found within the valve body 11. Tests have shown that the use of the PTFE cage 64 in the ball bearing assembly 60 has provided a bearing life which is up to 50 times or more longer than the bearing life that is expected when a traditional steel cage member is utilized. This in turn significantly contributes to the long operating life of the sealed D.C. brushless servo motor operated, pressure balanced valve assembly of the present invention. It is further thought that the filled PTFE material is particularly effective in view of the stop-start cycling undergone by the armature when the armature is advanced bit by bit in response to pulses of current supplied by the drive windings. Oil and grease lubricants tend not to be as effective as might be thought in this environment. The other end of the rotor is journaled in a bushing typically comprised of graphite or a filled graphite material.

The Magnetic Circuitry

Referring now to FIG. 1, stator windings 58 are constructed of wire length and diameter optimized for a given peak current and voltage in order to deliver an optimum electromagnetic field to the stator iron 48. Stator iron 48 is in close radial proximity to a rotor system including permanent magnets 42, separated by a magnetically transparent, hermetically pressure sealed can 44. Stator iron 48 is optimized in thickness and geometry to deliver the peak electromagnetic field to the permanent magnets 42 across the larger gap (than a conventional motor) required to accommodate the hermetic can. Permanent magnets 42 are optimized in field strength and thickness to react to the peak electromagnetic field with resultant peak torque forces tending to effect motion to the threaded shaft 43 and valve member 30. The permanent magnets 42 are retained to the rotor 41 with magnetically transparent drawn shell end caps 61.

The Electronic Circuitry

Ideally, a motor operator for a control valve needs to deliver strong linear actuation forces, at a relatively slow rate of speed, with low power consumption, in a compact package, with a high reliability, at a low cost. The slow rate is required so that the valve moves from full closed to full open in a time of 6 to 30 seconds, 15 seconds being typical, although other rates are possible, depending on the valve size and other parameters. For a threaded drive application with no additional gearing, the motor would rotate at about 50 revolutions per minute.

In the present invention, prior art problems have been overcome by utilizing low frequency chopped current pulses of full voltage to drive the motor. The frequency of the chopped current is about 8 Hertz, so hysteresis losses are low. The pulse drive operates the motor at a low duty cycle so as to minimize the average current supplied to the motor, thereby allowing higher currents and torque during the on period. Lower average currents reduce the power dissipated by the motor resulting in a reduced temperature rise in the servo motor. Maximum voltage is delivered to the winding regardless of load, and load changes have very little effect on power input and heat rise. Maximum torque is available to the motor, and motor speed remains low. No feedback controls are required, so effective torque and speed control is attained at very little additional cost.

For the improved drive method, the motorized system inertias and frictions are typical of the applications of motor operated valves. Referring to FIG. 1, power and control wiring 73 are connected to the board 53 to supply all power and control commands to the sealed motor operated valve. Hall-effect sensors 54 are positioned outside the can 44 in close radial proximity to the permanent magnets 42 to sense position of the rotor system 41. Signals generated by the sensors are sent to circuit board 53 which are utilized to determine the appropriate windings to energize to rotate the motor. The circuit board 53 contains motor drive circuitry designed to continually deliver on demand peak current periodic pulses through short motor leads 55 to the appropriate stator windings 58 to effect peak torque from the motor. These peak current pulses are optimized in strength, frequency, and length, to effect a simple and improved means to deliver higher torque and control the speed and heat buildup of the motor actuator under widely varying load conditions.

FIG. 9 illustrates the relationship between motor current or torque and speed of a conventional D.C. permanent magnet motor when the motor is driven at a constant voltage. It shows that the highest current and torque possible for a given voltage is when the motor is stalled.

FIG. 10 illustrates the relationship between average current and heat rise for a fully enclosed motor. It shows that increased motor currents produce an increased heat rise, and that the motor has a thermal limit, beyond which thermal breakdown and motor failure will occur.

FIG. 11 illustrates the current verses time for a conventional permanent magnet D.C. motor driven at constant voltage if the motor was allowed to accelerate from a stopped position under various loads. The heaviest load is for a stalled motor where the current reaches a maximum current level in a finite time, a typical value is 15 milliseconds (depending on voltage, inductance, and other factors) and the current remains at that maximum value. The maximum current for the motor subjected to lighter loads is somewhat less, and occurs earlier. As the motor accelerates under these lighter loads, inertial resistance drops and back electromagnetic forces rise, both working to drop the current and torque. As the motor reaches full speed for a given load, the back electromagnetic voltage produced by the motor speed resists and reduces the current input by a function of the motor speed.

FIG. 12 illustrates the speed versus time for a conventional permanent magnet D.C. motor driven at constant voltage if the motor was allowed to accelerate from a stopped position under various loads. The final motor speed is a function of motor load.

FIG. 11 and FIG. 12 illustrate that there are load conditions in which a motor is able to deliver movement under heavy loads, but would not be able to sustain the movement for extended periods without thermal breakdown. They show a limiting factor in conventional motor performance is heat-buildup, not torque. Motors sized only for sufficient torque are usually inadequate for an application due to the probability that the motor will overheat and fail in service. A larger motor would be required if driven conventionally. In an extreme case, as shown in FIG. 15, a motor subjected to stall for extended periods will typically fail within a couple of hours using conventional drive methods.

Heretofore, brushless D.C. motors have not been used for sealed motorized valves partly due to the difficulties in providing slow speed control combined with high torque, without exhibiting thermal runaway or high temperatures. Traditionally, a brushless servomotor driver provides speed control by utilizing a closed loop feedback from Hall-effect sensors and high frequency chopping of the output voltage to the motor. As the motor is started and accelerates to the set speed, the driver chops the full voltage at high frequency effectively to reduce the power to the motor. The method adds cost to the driver and has several disadvantages. Firstly, the frequency of voltage chopping is typically 1,500 Hertz which adds hysteresis losses and heat to the motor. Secondly, during heavy load or stall conditions the motor would overheat as the driver delivered full voltage and current. It is desirable that the motor may be kept running while in a stall condition (such as when the valve is in a closed position), and the heat build up of a motor in such condition using a conventional driver would be intolerable.

A new and improved drive method was developed to utilize maximum motor torque without damaging heat buildup by considering three factors; for a given voltage the current rise time of the stator windings, the rotational inertia of the rotor and driven components, and the back electromagnetic voltage produced by motor velocity. A length of time is chosen based upon these factors where for a given voltage at least enough time for the maximum stalled current would be reached if the motor were stalled, secondarily by no longer a time than necessary for the inertial resistance to drop to a fraction of its initial value and the back electromagnetic force to just become significant if the loads were light. It is important that the armature slows significantly or comes to a stop between cycles. The armature may pass one or two poles if lightly loaded, or less than one pole if heavily loaded, but the armature should come to a virtual stop between each pulse. If a motor is periodically energized for this length of time, individual increments of motion is imparted by the motor producing strong, slow actuation forces which are relatively insensitive to load variations. By applying full voltage to the motor while the armature is stopped, a substantial current is induced, the duration of voltage and current are such that there is a maximum torque production impulse, but little current "wasted" during a period when motor torque would accelerate the load