Actuator

Information

  • Patent Grant
  • 6182942
  • Patent Number
    6,182,942
  • Date Filed
    Thursday, March 12, 1998
    26 years ago
  • Date Issued
    Tuesday, February 6, 2001
    23 years ago
Abstract
An electromagnetic actuator has an armature assembly including a pair of spaced plate springs to locate the magnetic core radially. The springs are formed from concentric rings interconnected by radial bridges so that flexure of the spring does not cause radial displacement. A single coil or double coil may be used and each coil is supported on a pair of bobbins. One bobbin overlies the core and the other has a recess to receive part of the core to maintain a uniform air gap between the core and bobbin.
Description




BACKGROUND OF THE INVENTION




The present invention relates to an electromagnetic actuator.




It is well known to utilize electromagnetic actuators, commonly referred to as solenoids, to control the operation of ancillary devices such as hydraulic valves. The principle of operation is well known and utilizes the magnetic field produced by a coil to cause displacement of a magnetizable core.




One such arrangement is shown in U.S. Pat. No. 5,513,832 to Becker in which a hydraulic valve is controlled by an armature mounted within a coil. The armature includes a magnetizable core supported on a central pin. The pin is guided for movement at one end in a conventional bearing. At the opposite end, a fluid-tight diaphragm is provided that includes a plate spring to provide a return force on the armature.




The accurate control of the ancillary device depends upon the repeatability of the response to a given input signal and the proportionality of that response. As such, the mechanical systems utilized to support an armature within the actuator have a significant effect upon the performance of the actuator and the device upon which it is acting. The coil not only imparts axial forces to the armature but also imparts radial forces. Conventional bushings of the type shown in the Becker patent are therefore susceptible to increased friction forces, particularly as the actuator wears, and radial misalignment that affects the proportionality of the response from given inputs.




It is therefore an object of the present invention to provide an actuator in which the above disadvantages are obviated or mitigated.




SUMMARY OF THE INVENTION




In general terms, therefore, the present invention provides an electromagnetic actuator having a body, an armature movable within the body, and a pair of supports extending between the body and the armature at longitudinally spaced locations to support the armature. A coil assembly is located in the body to encompass the armature. Each of the supports includes a resilient plate member extending normal to the longitudinal axis and secured to the body. Each plate member is arranged to flex in the direction of the longitudinal axis upon application of an electromagnetic force between the coil and the armature and thereby provide a bias to the armature.




Preferably the plate member is provided by a plurality of concentric rings interconnected by bridging members. The bridging members are circumferentially displaced to provide circumferentially extending beams between adjacent rings that allow for flexure of the plate upon application of an axial force.











BRIEF DESCRIPTION OF THE DRAWINGS




Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which





FIG. 1

is a sectional view of an actuator;





FIG. 2

is an exploded view of the actuator shown in

FIG. 1

;





FIG. 3

is a sectional view of an alternative double-acting actuator; and





FIG. 4

is an exploded view similar to

FIG. 2

of the actuator shown in FIG.


3


.











DESCRIPTION OF THE PREFERRED EMBODIMENTS




Referring therefore to

FIG. 1

, an electromagnetic actuator


10


is connected to a hydraulic valve


12


shown in ghosted outline. In this embodiment, the valve


12


has an operating member


14


connected to the actuator


10


as will be described below. The form of the valve


12


and the operating member


14


may be one of many known types in which axial translation of the spool


14


provides control of hydraulic fluid flowing through the valve


12


. Those skilled in the art will appreciate that the exact form of the valve


12


may be chosen to suit particular requirements and need not be described further.




The actuator


10


includes a body


16


formed from a pair of nested housings


18


,


20


. The housing


18


has an internal screw thread


22


to receive a complementary external screw thread


24


on the housing


20


. An end cap


21


is provided in the housing


18


and carries a button


23


that is slidable relative to the end cap. A vent screw


25


is also provided in the end cap


21


for initial bleeding of the actuator. Housing


20


has a threaded boss


26


for connection to the valve


12


with an O ring


27


to provide a seal between the valve and the actuator.




A coil assembly


28


is located within the body


16


and includes a coil


30


and a pair of bobbins


32


,


34


. The coil


30


is centre-wound so as to be reversible within the body


16


. Power is supplied to the coil


30


by a pair of leads


36


that extend along the housing


18


to an opening


38


. The opening


38


is sealed with mastic


40


.




Each of the bobbins


32


,


34


is formed from a non-magnetic material, typically aluminum with an anodized surface coating, and includes a radial flange


42


and an axial shoulder


44


to support the coil


30


. The flanges


42


extend radially to the interior of the housings


18


,


20


where they are sealed by O rings


46


.




The bobbin


32


includes an axial bore


33


having radially inwardly directed watts


35


and the bobbin


34


has a smaller diameter axial bore


37


. The coil assembly


28


is located axially within the body


16


by means of a spacer washer


48


in the housing


18


and an end plate


50


located in the housing


20


. The housings


18


,


20


are screwed together to trap the bobbins and coil between the washer


48


and end plate


50


and thereby axially locate the coil assembly


28


.




A pair of plate springs


52


,


54


are axially spaced within the body


16


to support an armature


56


. The plate spring


52


is interposed between the washer


48


and the bobbin


32


and the plate spring


54


similarly interposed between the end plate


50


and the bobbin


34


. The marginal periphery of the plate springs


52


,


54


is thus held adjacent the body


16


to prevent axial movement of the plate springs.




The form of the plate springs can best be seen in FIG.


2


and as each is identical, only one need be described.




The plate spring


52


is formed from a plurality of concentric rings


58


,


60


,


62


,


64


and


66


. The rings


58


,


60


,


62


,


64


,


66


are interconnected by radial bridges


68


,


70


,


72


and


74


which connect respective adjacent pairs of the rings


58


-


66


. The ring


58


is connected to ring


60


by a pair of diametrically aligned bridges


68


and the ring


60


is in turn connected by a pair of diametrically aligned bridges


70


to the ring


62


. It will be noted that the bridges


68


,


70


are circumferentially staggered by 90° so that the quadrant of the ring


60


between the bridges


68


,


70


forms a curved beam member. The ring


60


can thus be considered to be formed from four beams interconnected at the bridges


68


,


70


. The rings


62


,


64


are similarly connected by bridges


72


which in turn are staggered relative to the bridge


70


. Likewise, rings


64


and


66


are connected by bridges


74


which in turn are staggered relative to the bridges


62


. An axial force applied to the centre of the plate spring


52


with the outer ring


58


held stationery will thus cause flexure of each of the beam members in each ring to allow axial displacement of the centre relative to the periphery.




An aperture


76


is provided at the centre of each of the plate springs


52


,


54


to receive a respective one of pin members


78


,


80


. Each of the pin members


78


,


80


has an enlarged head


82


and a shank


84


that may pass snugly through the aperture


76


. The shank


84


is dimensioned to be a press fit within a tube


86


that extends between the plate springs


52


,


54


. The tube


86


is non-magnetic and maintains the plate springs in spaced relationship. The tube


86


passes freely through the bore


37


in the bobbin


34


to allow flexure of the plates


52


,


54


.




The tube


86


carries a magnetizable core


90


that is generally cylindrical in cross-section and is formed from soft iron or similar magnetizable material. The core


90


is located within bore


33


in the bobbin


32


and is dimensioned to be freely movable within the bore


33


and maintained a small distance from the walls


35


of the bore.




The core


90


is a press fit on the tube


86


and upon insertion of the pin


78


, the tube


86


is expanded radially to secure the core


90


to the tube. The core


90


and tube


86


are thus connected for unitary motion relative to the coil assembly


28


.




The tube


86


also carries a non-magnetic spacer


94


which limits movement of the core


90


toward the bobbin


34


. The spacer


94


is received within a counterbore


96


located in a radial face of the bobbin


34


. The counterbore


96


is dimensioned so as to receive one end of the core


90


so that a predetermined clearance is provided between the radially outer surface of the core


90


and the radially inner surface of the counterbore


96


. This clearance is less than the spacing provided by the spacer


94


so that a constant air gap and an enhanced proportionality is obtained.




The head


82


of the pin


80


is slotted to receive the end of operating member


14


and thus provide a direct connection between the armature


56


and the member


14


. The connection is preferably such as to permit relative rotation between the spool


14


and the armature


56


about the longitudinal axis but any suitable form of connection can be utilized.




It will be appreciated that the tube


86


, pins


78


,


80


and bobbins


32


,


34


are formed from non-magnetic material. In operation, therefore, the plate springs


52


,


54


support the armature


56


for movement along the longitudinal axis of the actuator


10


and radially locate the armature. Upon energization of the coil, an electromotive force is applied to the core


90


that induces movement along the longitudinal axis. That movement is opposed by the plate springs and results in deflection of the plate springs


52


,


54


into a conical configuration. The deflection is accommodated by flexure of the beams forming the concentric rings but because of the symmetrical arrangement of the bridges, the armature remains centrally located. Upon termination of the current or modulation of the current to the coil, the resilience of the plates biases the armature toward the at rest position.




The radial face


98


of the core


90


co-operates with the counterbore


96


to provide a uniform air gap during axial displacement and thereby enhance the proportionality of the actuator. As the current is modulated, the axial position of the armature relative to the housing will similarly be modulated and the operating member


14


associated with the valve moved to a corresponding position. Obviously the current may be modulated by any suitable control system to achieve the required control function in the valve.




Button


23


provides a manual override or reset to act through the armature upon the operating member if necessary in the event a control signal is not available.




A further embodiment of spool is shown in

FIGS. 3 and 4

and like numerals will be used to denote like components with the suffix “a” or “b” added for clarity of description.




In the embodiment of

FIGS. 3 and 4

, a pair of coil assemblies


28




a


,


28




b


are utilized and each co-operates with a respective armature


56




a


,


56




b


mounted on a common tube


86




a


. A non-magnetic spacer


100


maintains the cores


90




a


,


90




b


in spaced relationship to maintain the separate magnetic circuits.




The bobbin


32




a


is interposed between a pair of end bobbins


34




a


,


34




b


and supports each of the coils


30




a


,


30




b.






Plate springs


52




a


,


54




a


support the armature


56




a


for movement along the longitudinal axis.




The provision of the pair of coil assemblies


28




a


,


28




b


permits the actuator


10




a


to be double-acting and may thus move to either side of the neutral at rest position shown in the drawings.




It will be noted in the embodiment of

FIGS. 3 and 4

that pin


78




a


is provided with a magnetic insert


102


that is positioned adjacent a Hall effect sensor


104


. Movement of the armature


56




a


relative to the body


16




a


may therefore be monitored by the Hall effect sensor


104


to provide a control signal indicative of the position of the operating member


14




a.






The Hall effect sensor


104


is shielded from the magnetic field of the coils by an internal cap


21


a located within the housing


18




a


. the cap


21


a also includes a vent screw


25




a


to permit initial venting of the valve assembly during installation.



Claims
  • 1. An electromagnetic actuator comprising a body, an armature movable within said body for reciprocation along a longitudinal axis, a pair of supports extending from said body to said armature at longitudinally spaced locations to support said armature and a coil assembly located in said body and encompassing said armature, each of said supports including a resilient plate member extending normal to said longitudinal axis and secured to said body, said plate member flexing in a direction of said longitudinal axis upon application of an electromagnetic force between said coil assembly and said armature, wherein said plate members include a plurality of concentric rings interconnected to one another by a plurality of radial bridges for inhibiting relative torsional displacement of said armature with respect to said body.
  • 2. An actuator according to claim 1, wherein said radial bridges are staggered circumferentially to provide a flexible beam between adjacent ones of said concentric rings.
  • 3. An actuator according to claim 2 wherein said adjacent concentric rings are interconnected by diametrically opposed said radial bridges.
  • 4. An actuator according to claim 3 wherein radially adjacent ones of said radial bridges are staggered 90°.
  • 5. An actuator according to claim 1 wherein said armature includes a tube extending between said plate members and secured thereto by pins passing through said plate members and into said tube.
  • 6. An actuator according to claim 5 wherein said pins are an interference fit in said tube.
  • 7. An actuator according to claim 5, wherein said tube is non-magnetic.
  • 8. An actuator according to claim 1 wherein said coil assembly includes a coil and a pair of bobbins located at opposite ends of said coil, said bobbins extending between said coil and said body to locate said coil axially and having an axially extending shoulder to support said coil radially.
  • 9. An actuator according to claim 8 wherein said shoulder of one of said bobbins extends between said armature and said coil.
  • 10. An actuator according to claim 9 wherein another of said bobbins has a radial end face directed to an end face on said armature, said radial end face of said armature including a recess to receive said armature upon displacements along said longitudinal axis.
  • 11. An actuator according to claim 10 wherein a spacer is located between said armature and said other bobbin to maintain said radial face of said armature in spaced relationship with an end wall of said recess.
  • 12. An actuator according to claim 8 wherein said coil assembly includes a pair of coils axially spaced along said body and each of which is supported by a pair of bobbins, and said armature includes a pair of magnetizable cores spaced apart from one another and associated with respective ones of said coils.
  • 13. An actuator according to claim 12 wherein said cores are supported on a non-magnetic tube extending between said plate members and maintained in spaced relationship by a non-magnetic spacer.
  • 14. An electromagnetic actuator comprising a body, an armature moveable within said body for reciprocation along a longitudinal axis, a pair of supports extending from said body to said armature at longitudinally spaced locations to support said armature and a coil assembly located in said body and encompassing said armature, each of said supports including a resilient member extending normal to said longitudinal axis and secured to said body, said resilient member flexing in a direction of said longitudinal axis upon application of an electromagnetic force between said coil and said armature, thereby providing a bias to said armature, said armature including a magnetizable core mounted on a tube extending between said members and secured thereto by pins passing through said members and into said tube, wherein said pins expanding said tube radially for securing said core to said tube.
  • 15. An actuator according to claim 14, wherein said tube is non-magnetic.
  • 16. An actuator according to claim 14, wherein each of said resilient members includes a plurality of concentric rings interconnected to one another by a plurality of radial bridges, said radial bridges being staggered circumferentially to provide a flexible beam between adjacent ones of said concentric rings.
  • 17. An actuator according to claim 16 wherein said adjacent concentric rings are interconnected by diametrically opposed said radial bridges.
  • 18. An actuator according to claim 17 wherein radially adjacent ones of said radial bridges are staggered 90°.
  • 19. An electromagnetic actuator comprising a body, an armature moveable within said body for reciprocation along a longitudinal axis, a pair of supports extending from said body to said armature at longitudinally spaced locations to support said armature and a coil assembly located in said body and encompassing said armature, each of said supports including a resilient member for locating said armature radially with respect to said body, said resilient member extending normal to said longitudinal axis and secured to said body, said member flexing in a direction of said longitudinal axis upon application of an electromagnetic force between said coil and said armature thereby providing a bias to said armature, said coil assembly including a coil and a pair of bobbins located at opposite ends of said coil, said bobbins extending between said coil and said body to locate said coil axially and having an axially extending shoulder to support said coil radially, wherein said resilient member and said axially extending shoulder facilitate a radially fixed spatial relationship between said armature and said coil assembly.
  • 20. An actuator according to claim 19 wherein said shoulder of one of said bobbins extends between said armature and said coil.
  • 21. An actuator according to claim 20 wherein another of said bobbins has a radial end face directed to an end face on said armature, said radial end face of said armature including a recess to receive said armature upon displacements along said longitudinal axis.
  • 22. An actuator according to claim 21 wherein a spacer is located between said armature and said other bobbin to maintain said radial face of said armature in spaced relationship with an end wall of said recess.
  • 23. An actuator according to claim 19 wherein said coil assembly includes a pair of coils axially spaced along said body and each of which is supported by a pair of bobbins, and said armature includes a pair of magnetizable cores spaced apart from one another and associated with respective ones of said coils.
  • 24. An actuator according to claim 23 wherein said cores are supported on a non-magnetic tube extending between said plate members and maintained in spaced relationship by a non-magnetic spacer.
Parent Case Info

This U.S. application is a Continuation in Part of U.S. Ser. No. 566,058 filed on Dec. 1, 1995, now issued as U.S. Pat. No. 5,806,565 on Sep. 15, 1998.

US Referenced Citations (9)
Number Name Date Kind
3900822 Hardwick et al. Aug 1975
4396037 Wilcox Aug 1983
4494098 Haneda et al. Jan 1985
4635683 Nielsen Jan 1987
4988074 Najmolhoda Jan 1991
5234032 Kline et al. Aug 1993
5513832 Becker et al. May 1996
5787915 Byers et al. Aug 1998
5806565 Kadlicko Sep 1998
Continuation in Parts (1)
Number Date Country
Parent 08/566058 Dec 1995 US
Child 09/041508 US