GB2176344A - Force motor - Google Patents

Abstract

A motor for a servo-valve comprises a circular bottom pole 12 and a top pole 14, an armature 20 positioned between the bottom and top poles, a drive arm assembly 16, a flexure tube 46 supported centrally from the bottom pole and supporting the armature and drive arm assembly for pivotal movement, electromagnet coils 22, 24 sleeved over each end of the armature positioned between the bottom pole and top pole and T-shaped permanent magnets 28, 30 extending between the bottom pole and top pole at the opposite ends of a diameter of the bottom pole and top pole perpendicular to the direction of extent of the armature having stems extending toward each other between the electromagnet coils. <IMAGE>

Description

SPECIFICATION Force motor BACKGROUND OF THE INVENTION Field ofthe Invention The invention relates to force motors for use in electrohydraulicservovalves orthe like and refers more specificallyto aforce motorincluding a flexure tube supporting a drive arm and an armature pivotal in accordance with electrical energy passed to the force motor, a bottom and top pole separated byT-shaped permanent magnets and a pair of electromagnet coils sleeved over the opposite ends ofthe armature for producing pivotal movement of the armature in accordance with the electrical energy passed to the electromagnet coils.

Description of the PriorArt In the past, force motors have been constructed which have been relatively low in cost but which were not operable at low power levels. Other force motors have been constructed which have been operable at low power levels but which have been relatively costly.

Thus, it has in the past often been necessary to make a concious choice between a force motorwhich operated poorly or not at all at low power levels but which was economical and a force motor which operated effectively at low power levels but which was more costly.

Further, such force motors ofthe past have generally been efficient in operation only in certain size ranges thus requiring different size components for different jobs often with the same basic structure thus for example force motors ofthe past have sometimes required different armatures, electromagnet coils or drive arm structures in conjunction with the same pole pieces and permanent magnets for slightly different but similar uses. Inventory requirements for both manufacturers and users offorce motors have thus been larger than necessary.

SUMMARYOFTHE INVENTION In accordance with the present invention a force motor is provided which because ofthe particular shape and arrangement of the elements thereof is efficient in that it operates at particularly low power levels and is particularly inexpensive in that machiningand machinetolerancesarekeptata minimum.

Further, theforce motor ofthe invention is suitablefor use over a large range of input and output requirements thereof.

The force motor ofthe invention includes a substantially circular bottom pole, a circulartop pole positioned in spaced relation to the bottom pole, an elongated armature extending between the top and bottom pole, a drive arm secured to the bottom pole and armature for pivotal movement with pivotal movement ofthe armature. The force motorfurther includes electromagnetic coils sleeved over each end ofthe armature and positioned between the bottom and top pole and T-shaped permanent magnets extending between the top and bottom pole having a stem portion positioned between the electromagnet coilsfor causing movement of the drive arm in accordance with an electrical signal passed to the electromagnet coils.

Also, in accordance with the invention, the armature is shaped to prevent saturation thereof, null adjustment and stop means for adjusting the null position of the armature in relation tothe poles andto limit pivotal movement ofthe armature are provided extending through the top and bottom poles of the force motor into engagement with the opposite ends of the armature. Awire shield is provided in the cover for the force motor to prevent entanglement of the conductors for passing electric energy into the force motor with the armature. Further, in accordance with the invention, the force motor is secured together by attachment screws therefore.

BRIEF DESCRIPTION OF THE DRAWINGS Figure lisa partial elevational view partial longitudinal section view of a force motor constructed in accordance with the invention taken substantially on the line 1-1 in Figure 2 and showing a covertherefore in assembly therewith in total section substantially on the line 1A-1A in Figure 2.

Figure 2 is a bottom viewofthe force motor illustrated in Figure 1, taken in the direction of arrow 2 in Figure 1.

Figure 3 is a longitudinal sectional view of the force motor constructed in accordance with the invention taken substantially on the line 3-3 in Figure 1.

Figure 4 is a transverse cross section ofthe force motor illustrated in Figure 1 taken substantially on the line 4-4 in Figure 1.

Figure 5 is a stepped transverse cross section ofthe force motor illustrated in Figure 1 taken substantially on the line 5-5 in Figure 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in Figure 1, the force motor 10 includes a bottom pole 12 a top pole 14a drive arm assembly 16 secured to the bottom pole 12 bytheflexuretube and an armature 20 secured to theflexure tube and drive arm assembly positioned between the bottom pole 12 and top pole 14. Electromagneticcoils 22 and 24 are sleeved over the opposite ends of the armature 20 and are positioned between the bottom pole 12 and top pole 14for producing pivotal movement of the armature in accordance with an electrical signal passed thereto through electrical conductors 26 and the field oftheT-shaped permanent magnets 28 and 30 having stem portions extending toward each other between the electromagnet coils 22 and 24.

Theforce motorl0furtherincludesthe null adjust structures 32 and 34 extendingthroughthe top pole 14 into contact with the opposite ends 33 and 35 of the armature 20. Stop screws 36 and 38 extend through the bottom pole 12 into spaced relation to the ends 33 and 35 of the armatu re 20 to limit the pivotal movement thereof.

More specifically, the bottom pole 12 as shown best in Figures 2 and 5 iscircularandgenerallyflatand has a flat innersurface 40which may be machined buy a single grinding pass. An axiallyextending circular opening 42 is provided through the bottom pole 1 2to receivethe outer end 44 ofthe flexure tube 46.

Openings 48, SOt 52 and 54two of which,48 and 54, are countersunk are also provided through the bottom pole 12 as shown in Figures2and 5to receive assembly and attachment screws (not shown) extend ing therethrough in opposite direction as will be considered subsequently. Abutments 56 and 58 shaped as shown in Figures 1 and 5 are provided on the bottom pole at each end ofthe diameter shown in FigureS. Recesses 61 and 63 are provided in the bottom ofthe bottom pole 12 as shown best in Figure 2 in which openings66 and 68 are machined through the bottom pole for receiving the stop screws 36 and 38.A location pin 88 extendsfrom the bottom of bottom pole 12 to angularly locate the force motor 10 on a spool I valve orthetube (not shown).

No locking screwsforthestop screws are provided in the bottom pole 12which are locked in adjusted position by an aerobic locking means and the bottom pole is constructed similarto thetop pole to improve the efficiency ofthe force motor 10 by providing better flux paths there through and to improve the symmetry ofth e flux paths nearthe critical working gap between the abutments on the poles and the ends ofthe armature Openings 64,66,68 and 70 extend through thetop pole 14and are aligned with openings52,54,48and 50 in the bottom poleto receive the assembly and attachmentscrews as will be seen subsequently.

Openings 64 and 70 a re counter su nk. Openings 66 and 68 arethreaded. An elongated hexagon shaped -opening 72 extends through the centerofthe tbp pole 14asshown best in Figure 4.

Sartcylindrical shaped recesses 74and 7Bare also provided in the surface 62 of the top pole 14 to receive theannular electromagnet coii structures 22 and 24.

Abutments78 and 80 extend from the surface 62 ofthe top pole 14 atthe opposite ends ofthe diameter 81 thereof as shown best in Figures 1 and 4.

Openings 82 and 84 in the abutments 78 and 80 permit resilient null balance structures 32 and 34 to pass through the top pole 14 and into engagement with the opposite ends ofarmature 20 as shown best in Figure 1.Thetop surface 87 ofthe top pole14is provided with-recesses86 and 89 therein through which electrical conductors 26 pass to the side ofthe force motor 10.

The top pole 14 has a betterflux path than previous top pole structures due to the removal of lock screws used to yock null adjustmentstructures in prior structures. The null adjustment structures 32 and 34 now include a self-locking helical coil insert90for adjusting screw 92 in engagement with spring 93 and spring guide94in each ofthe null adjustment structures 32 and 34 only one of which is shown. Such structure again lowers the cost ofthe force motor 10 and improves the symmetryofthefl ux path nearthe critical working area.

As shown, the armature 20 is shaped to substantial ly eliminate or at least minimize flowsaturation thereof in operation. The shape of armature 20 is shown bestin Figure 5.

As shown, the permanent magnets 28 and 30 are generallyT-shaped in cross section with arcuate cross bar upper surfaces and stems that extend toward each other between the electromagnet coilS22 and 24 as shown best in Figures4and 5. The stem ofthe T-shaped magnets thus serve as a coil separator. The particular shape ofthe permanent magnets also offers a larger magnetic cross section-in the force motor envelope.TheT-shaped permanent magnets also provide additional cost reduction by providing a narrowerwidth structure. TheT-shaped permanent magnets also allowfinish grinding ofthe polefaces in a single pass in place of the two separate operations required to mount permanent magnets in priorforce motor structures.

The drive arm assembly 16 as shown best in Figures 1 and3includestheflappervalve96ontheend ofthe drive arm 98 which drive arm 98 is in turn secured to theupperend 100 oftheflexuretube 46. Damping and inertial structure 102 is provided centralLy of the drive arm 98.

In operation ofthe force motor 10 as in known force motors, as an electrical signal is passed into the electromagnet coils 22 and 24 the electrnmaignets producedthereby cause a magnetic force which in conjunction with the permanent magnets causes the armature 20to pivotaboutthe flexure tube 46 in proportion to the signal and the polarity of the signals received bytheforce motor overtheconductors 26.

Pivoting ofthe armature 20 causes the desired pivoting ofthe drive arm 98 and thus therequirnd positioning oftheflapper 96 as will be understood by those in the art.

In accordance with the invention, a cover 1 is provided forthe force motor 10. The cover 104 is - shaped in section substantially as shown in Figure 1 and includes a deflector portion 106 effective to prnventcontactoftheconductors 26 with the armature 20.

Inassembly, ofthe force motor 1 0,the top and bottom poles 12 and 14 are assembled with the other members ofthe force motor 10 positioned therebetween as shown in Figure 1 and the force motor 10 is secured together by bolts passing from the bottom pole toward the top pole and into engagement with thethreaded openings66and 68 inthetop pole.The assembledforce motor is then attached to a spool valve (not shown) or the like by bolts passing through openings 64 and 70 in the top pole, openings 50 and 52 in the bottom pole and into threaded openings in the spool valve. The cover 104 is secured to the spool valve by bolts passing between the spool valve and flanges (notshown) on the cover 104. An opening 108is provided in the cover 1 04to facilitate null adjustmentwithout removing the cover 104asshown best in Figure 1.

The construction ofthe force motor 10 as setforth above has resulted in low costthrough less machin ing, reduced scrap, reduced partvariationsto cover a performance range and reduced assembly and calibration time in the force motor 10.

In addition, the large magnetic cross section and improved shape, i.e. shorter perimeter and larger cross section ofthe permanent magnets has permitted the use of a single air gap and flexure tube wall thickness combination in the force motor 10 to cover a performance rangethus reducing inventory requirements and also improving performance through lower magnetic hysteresis.

While one embodiment of the present invention has been considered in detail, it will be understood that other embodiments and modifications thereof are contemplated. Itisthe intention to include all embodiments and modifications as are defined by the appended claims within the scope of the invention.

Claims (11)

1. Aforce motorfor an electrohydraulic servovalve orthe like comprising a bottom pole, a top pole positioned in aligned, spaced relation to the bottom pole, an armature positioned between the bottom and top poles in spaced relation thereto, a pair of electromagnet coils sleeved over the opposite ends of the armature and positioned between the bottom and top poles in spaced apart relation to the armature, a flexure tube and drive arm assembly extending centrally th rough and connected to the bottom pole and secured to the armature for pivotal movement with the armature and a pair of permanent magnets extending between the bottom pole and top pole on opposite sides ofthe armature and between the electromagnet coils.

2. Structure as setforth in claim 1, wherein the bottom pole has a substantiallyflatinnersurfaceand abutment portions at the opposite ends of a diameter thereof extending from the flat inner surface toward the ends ofthe armature and the top pole.

3. Structure as setforth inclaim2,whereinthetop pole hasa substantiallyflatinnersurfaceand abutment portions at the opposite ends of a diameter thereof extending from the flat innersurface toward the ends ofthe armature and the abutments on the bottom pole.

4. Structure as set forth in claim 3,wherein an elongated hexagon shaped portion of the center ofthe top pole extending over the armature is removed.

5. Structure as setforth in claim 3, and further including recesses defined by part cylindrical segments adjacent the abutments in the inner surface of the top pole for receiving the electromagnet coils.

6. Structure as set forth in claim 1, wherein the permanent magnets are essentially T-shaped and have a stem portion extending between the electromagnet coils.

7. Structure as setforth in claim 3,whereinthe armature is elongated and substantiallyflat andthe ends thereof extend through the electromagnet coils and between the abutments on the bottom pole and top pole.

8. Structu re as setforth in claim 1, and further including at least one null adjust structure extending through one ofthe poles and into contact with the armature including heli coil structureformaintaining the null adjust structure in an adjusted position without a lock screw.

9. Structu re as set fo rth in claim land further including at least one stop screw extending through one ofthe poles and terminating adjacent the armature for limiting pivotal movement of the armature and an aerobic locking means forsecu ring the stop screw in an adjusted position without a lock screw.

10. Structu re as set forth in claim 1, wherein the force motor is held together at least partly by screws forattaching theforce motorto a spool valve orthe like.

11. Structureassetforth in claim 1, and further including electrical conductors connected to the electromagnet coilsfor providing signals thereto to produce pivotal movementofthe armature and drive arm in accordance with the electrical signal passed to the electromagnet coils and further including a cover for the force motor including a shield for maintaining the electrical conductors in spaced relation to the movable armature.