US3460081A - Electromagnetic actuator with permanent magnets - Google Patents

Description

Aug. 5, 1969 A. TILLMAN 3,460,081

ELECTROMAGNETIC ACTUATOR WITH PERMANENT MAGNETS Filed May 51. 1967 ATTORNEYS.

United States Patent 9 Claims ABSTRACT OF THE DISCLOSURE A bi-stable electrically operated actuator suitable for use with valves, switches, or any other device that must be moved between positions at opposite ends of a stroke, and that must be held in position, selectively, at either end of the stroke. The actuator has two permanent magnets, one for holding it in each position, and it has electromagnetic windings that are temporarily energized to shift the movable element of the actuator from one position to the other. The movable element is a plunger which is made of material that is attracted by a magnet, but it is not itself a permanent magnet and it does not carry any of the windings. The preferred embodiment operates without requiring any reversal of the polarity of any of the magnetic poles of the actuator.

Brief description of the invention The invention is an improved bi-stable solenoid of the type which has a plunger that is held, selectively, at either end of its stroke by permanent magnets; and that requires energization only during the time that the plunger is moving between different ends of its stroke.

The plunger is not itself a magnet, but it is made of material which is attracted by magnets. There is a different electromagnetic coil for moving the plunger in each direction. Although the permanent magnets are located at opposite ends of the plunger stroke, the stroke is long enough so that the distance from the disengaged magnet is sufiicient to prevent that magnet from adversely affecting the holding power of the permanent mag net by which the plunger is held at any particular time The actuator is constructed so that the permanent magnets do not have direct contact with the plunger and are not subject to direct shocks resulting from snap action of the plunger.

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

Brief description of the drawing In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views:

FIGURE 1 is a sectional view through :an actuator made in accordance with this invention; and

FIGURES 2 and 3 are sectional views, on a reduced scale, taken on the lines 2-2 and 3-3, respectively, of FIGURE 1.

Detailed description of the invention FIGURE 1 shows an actuator including a housing which comprises a core 12 with a cylindrical opening 14 extending throughout the full length of the core and preferably coaxial with the core. There is a pole piece 16 in the left-hand end of the cylindrical opening 14; and a corresponding pole piece 18 in the right-hand end of the cylindrical opening. Each of these pole pieces 16 and 18 is preferably a press fit in the core 12; and each "ice of the pole pieces may have a cylindrical bearing surface 20, coaxial with the opening 14.

The movable element of the actuator is a plunger 22 which slides freely in the cylindrical opening 14 between confronting end faces 24 of the pole pieces 16 and 18. The plunger 22 contacts with the end face of the pole piece 16 at one end of the stroke of the plunger, and with the end face 24 of the pole piece 18 at the other end of the stroke. Thus the stroke of the actuator 10 is determined by the spacing of the pole pieces 16 and 18 from one another.

The end faces of the plunger 22 are of complementary contour to the end faces 24 of the pole pieces 16 and 18. In the construction illustrated, these faces are frustoconical, but it will be understood that they can be flat or stepped, depending upon the desired shape of the power curve of the actuator.

There is an actuator shaft 28 connected with one end of the plunger 22. The drawing shows the shaft 28 with threads 30 that screw into the plunger 22. This is merely representative of a connection between the shaft and plunger, and these parts can be of one piece construction, if desired. The actuator shaft 28 slides axially in the pole piece 16.

At the other end of the plunger 22, the drawing shows another actuator shaft 28', which is connected with the plunger 22 in the same way as the actuator shaft 28, and which slides axially in the pole piece 18. If the actuator is intended for a use requiring only one actuator shaft, the other actuator shaft 28 or 28' can be omitted. The plunger 22 is shown with a uniform diameter between its end faces, but this is not essential, and the mid portion of the plunger 22 can be of reduced diameter to decrease the friction surface, or the plunger can be made in two portions connected together by a threaded element.

The core 12 has circumferentially extending cut-out portions in which electromagnetic windings 32 and 34 are located. Beyond these coils or windings 32 and 34 there are annular permanent magnets 36 and 38, respectively. In the construction shown, the magnets 36 and 38 are beyond the outer circumference of the coils 32 and 34 with the poles of each magnet axially spaced from one another, but these magnets can be beyond the ends of the coils with their poles in radial relation to one another. The core 12, pole pieces 16 and 18, and the plunger 22 are made of ferrous material, or other material which is a good conductor of magnetic flux.

The annular permanent magnets 36 and 38 are preferably of one-piece construction. There is preferably a ring 46, also of one-piece annular construction, for holding the magnets 36 and 38 in spaced relation to one another. An end ring 48 is preferably pressed over the end of the core 12 to hold the magnets 36 and 38, and the ring 46 against axial displacement.

The rings 46 and 48 are preferably of ferrous material so as to constitute a part of the magnetic circuit of the core 12. The electromagnetic windings 32 and the permanent magnet 36 are located so that their poles are effectively at opposite sides of the gap between the plunger 22 and the end face 24 of the pole piece 16 when the plunger is at the right-hand end of its stroke. Similarly, the electromagnetic windings 34 of the permanent magnet 38 effectively span the gap between the other end of the plunger 22 and the end face 24 of the pole piece 18 when the plunger 22 is at the left-hand end of its stroke.

In order to spread the magnetic flux and to concentrate it in the confronting faces of the plunger and pole pieces 16 and 18, there are sections of non-magnetic material 52 inserted in the core 12 adjacent to the gaps between these confronting faces. The sections 52 preferably span the gaps.

With the parts in the position shown in FIGURE 1,

the plunger 22 is held in contact with the end face 24 of the pole piece 18. When winding 34 is not energized, the magnetic circuit is from the permanent magnet 38, through ring 48 (if used), through core 12, pole pieces 18, plunger 22, through ring 46 (if used) and the other end of magnet 38. Although there is a similar magnetic circuit at the other end of the plunger, the gap between the plunger and the pole piece 16 is sufficient to weaken this other magnetic circuit so that it does not detract substantially from the holding power of the magnetic flux at the right-hand end of the plunger 22.

The plunger 22 will remain in this position without expenditure of any electrical energy, until the winding 32 is energized to move the plunger toward the left. When this winding 32 is energized, it adds so much additional flux to the magnetic circuit of the magnet 36 that the combined pull of the magnet 36 and the electromagnet formed by the windings 32 is sufficient to overcome the holding power of the permanent magnet 38, and the plunger 22 is moved to the left-hand end of its stroke. The supply of energy to the windings 32 is then shut off, but the plunger 22 remains in position at the right end of its stroke as a result of the attraction of the permanent magnet 36.

Return movement of the plunger 22 to the right end of its stroke can be effected at any time by energizing the winding 34 which adds to the pull of the magnet 38 sufliciently to overcome the holding power of the permanent magnet 36.

In the construction illustrated, the plunger 22 has direct contact with the end faces of the pole pieces 16 and 18; but non-magnetic gaskets or facing can be used to produce a small magnetic gap between the ends of the plunger and the end faces of the pole pieces 16 and 18, if desired, while still leaving the end faces as the ultimate mechanical stops for limiting the stroke of the plunger 22.

From the description of the operation, it will be apparent that the plunger 22 moves with snap action. This is highly desirable for operating either valves or switches. The shock of the plunger in striking the stops, provided by the faces 22, at each end of the stroke, is not a direct shock on the permanent magnets 36 and 38. This protects the magnets and is an advantage over constructions which require that the plunger be a permanent magnet, or that the plunger strike against permanent magnets. The invention provides a bi-stable solenoid-operated actuator which is firmly held in position at either end of its stroke and without requiring the energizing of the actuator coils at any time except when the plunger is being moved.

The apparatus can also be operated by Supplying current to the magnet coil at the end of the apparatus at which the plunger 22 is in contact with the pole piece 16 or 18 and with the current in a direction to set up an opposing flux that nullifies the fiux of the permanent magnet so that less force is required to move the plunger. In some designs the permanent magnet at either end can be made strong enough to shift the plunger when the flux of the permanent magnet at the other end is nullified by its associated coil 32 or 34.

The preferred embodiment of the invention has been illustrated and described, and the invention is defined in the claims.

What is claimed is:

1. In a bi-stable electromagnetic actuator including a core having an axial opening therein, a plunger that slides back and forth in the opening as a bearing, stops in said opening at opposite ends of the plunger for limiting the reciprocating movement of the plunger to a predetermined stroke, the core, plunger and stops being made of magnetizable material, and an electromagnetic winding surrounding the opening near each end of the plunger, the improvement which comprises a shell around the outside of the core, plunger and stops, at least a portion of the shell comprising permanent magnets axially spaced from one another and carrying the flux in the shell including that produced by the excitation of the winding, a different one of the permanent magnets also surrounding the core at each end of the plunger.

2. The electromagnetic actuator described in claim 1 characterized by the electromagnetic winding being divided between two separate elcctromagnets, one at each end of the plunger, the permanent magnets also including one at each end of the plunger, and magnetic insulating material between the magnets at one end of the Plunger and those at the other end thereof.

3. The electromagnetic actuator described in claim 1 characterized by the core having confronting shoulders axially spaced from one another, the shell being held between the shoulders, one of the permanent magnets being located with one of its pole faces in contact with one of the shoulders, the other of the permanent magnets being located with its opposite pole face in contact with the other of said shoulders.

4. The electromagnetic actuator described in claim 2 characterized by each of the permanent magnets being of annular cross section and surrounding the outside of a different one of the electromagnets along most of the axial length of said permanent magnet and effectively spanning the locations at which there is a gap between the plunger and each end stop when the plunger is in contact with the other stop.

5; The electromagnetic actuator described in claim 1 characterized by the opening in the core having magnetic insulation in the side walls thereof at the locations where there are gaps between the plunger and each of the stops when the plunger is in contact with the stop at the other end of the stroke of the plunger.

6. The electromagnetic actuator described in claim 1 characterized by the stops being elements inserted into the opening in the core at opposite ends of said opening, and one of the elements having an opening therethrough of substantially smaller diameter than the plunger, and a shaft connected to the plunger and movable as a unit with the plunger, the shaft extending through the opening in the element that has the opening therein and being slidable in said element as a bearing.

7. The electromagnetic actuator described in claim 6 characterized by both of the stops having similar openings therein coaxial With the axis of the opening in the core, and shafts extending from both ends of the plunger through the openings in the stop for connection with apparatus that is to be operated by said actuator.

8. The electromagnetic actuator described in claim 1 characterized by the confronting faces of the plunger and stops being complementary and at least a pair of one of the faces having a projecting portion that fits into a recess in the confronting face to influence the force curve of the actuator.

9. The electromagnetic actuator described in claim 2 characterized by the permanent magnets and parts of the core being rings that fit around the other parts of the core and around the electromagnets and that stack on the core to form the shell of the actuator assembly.

References Cited UNITED STATES PATENTS 3,022,450 2/1962 Chase 335--229 XR 3,040,217 6/1962 Conrad 335234 3,139,565 6/1964 Levine 335-230 3,202,886 8/1965 Kramer 335234 3,381,181 4/1968 Weathers 335-230 XR GEORGE HARRIS, Primary Examiner US. Cl. X.R. 335-268 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Ltent No. 3,460,081 August 5, 1965 Alfred Tillman It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 51, "pair" shouid read part Signed and sealed this 21st day of April 1970.

1rd M. Fletcher, Jr.

WILLIAM E. SCHUYLER, JR sting Officer Commissioner of Patents

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