Solenoid

Abstract

A solenoid assembly is provided. The solenoid assembly includes a plunger of magnetic material, the plunger being guided along a rectilinear path from a first end of the path to a second end of the path when a coil surrounding the path is energized. A first member of magnetic material is provided which partially encircles a first part of the circumference of the path near the second end of the path. A second member of magnetic material partially encircles a second part of the circumference of the path near the second end of the path. The extent of circumferential encirclement of the first member and the second member increases in a direction from the first end of the path to the second end of the path.

Description

The present invention relates to a solenoid assembly including a solenoid and a plunger. More particularly, the present invention is directed to a solenoid assembly whereby the force-distance characteristics of the solenoid assembly are controlled.

Solenoid assemblies comprising a solenoid and a plunger are well-known. The solenoid assembly includes an elongated tubular magnetic coil which is adapted to be excited by an external current source, a hollow guidance tube arranged coaxially within the tubular magnetic coil and a plunger of magnetic material arranged slidably in the guidance tube. Usually a spring is associated with the solenoid assembly which tends to guide the plunger outwardly from the end of the guidance tube to a rest position.

When the coil is energized, the plunger becomes magnetized and mutual attraction takes place between the coil and the plunger. The plunger then moves within the hollow guidance tube until the net opposing mechanical forces balance each other. This occurs when the mutual opposing polarities of the coil and the plunger coincide. The net force exerted upon the plunger by the opposing mechanical forces is at a minimum at the time just after the coil is energized. The force gradually increases with the distance moved by the plunger and is usually at a maximum at or near the end of the plunger stroke. This force-distance relationship is represented by curve A of FIG. 5. Because of the large force generated at or near the end of the plunger stroke, a hammer blow occurs at the end of the stroke. The hammer blow is undesirable in that it is both noisy and tends to result in premature solenoid failure. It would be desirable to control the force-distance characteristics which occur during the travel of the plunger within the solenoid coil. Ideally, the force-distance characteristic would be modified so that the force is at a maximum shortly after the plunger movement is initiated and levels off or decreases near the end of the plunger stroke. This ideal condition is represented by curve B of FIG. 5.

Many devices have been proposed for modifying and controlling the force-distance characteristics of solenoid assemblies. Toggles, cams, bellcranks and levers have been used in connection with electromagnets in order to obtain force-distance characteristics different from those exhibited by the electromagnet alone. Other methods for altering the force-distance characteristics involve the shaping and proportioning of coils, plungers, armatures, or air gaps. Such known methods for modifying the force-distance characteristics have not been wholly successful in that they introduce inherently complicated mechanical arrangements or involve expensive assembly, machining or shaping operations during the manufacture of the solenoid assemblies. It would be desirable to provide a simple means for modifying the force-distance characteristics of solenoid assemblies and to provide a solenoid assembly with a substantially uniform force throughout the distance of travel of the plunger.

Accordingly, it is a principal object of the present invention to provide a solenoid assembly with modified force-distance characteristics. It is another object of the present invention to provide a solenoid assembly which has a substantially uniform force exerted upon the plunger throughout the distance of travel of the plunger. It is a further object of the present invention to provide a solenoid assembly with modified force-distance characteristics and yet which is simple to manufacture.

Generally, in accordance with various features of the present invention, a solenoid assembly is provided. The solenoid assembly comprises a plunger of magnetic material, the plunger being guided along a rectilinear path from a first end of the path to a second end of the path when a coil surrounding the path is energized. A first member of magnetic material is provided which partially encircles a first part of the circumference of the path near the second end of the path. A second member of magnetic material is also provided and the second member partially encircles a second part of the circumference of the path near the second end of the path. The extend of circumferential encirclement of the first member and the second member increases in a direction from the first end of the path to the second end of the path.

The novel features which are considered to be characteristic of the invention are set forth below in particular in the appended claims. The invention, however, both as to its construction and its method of operation together with additional objects and advantages is best understood from the following descrption of specific embodiments when read in combination with the accompanying drawings in which:

FIG. 1 is a view, partially in section of a solenoid assembly in accordance with an embodiment of the invention;

FIG. 2 is a view, partially in section, of FIG. 1 revolved 90.degree.;

FIG. 3 is a cross-sectional view of the solenoid assembly of FIGS. 1 and 2 taken along the line 3--3 of FIG. 2;

FIGS. 4 and 4A is a top view and an end view of one of the magnetic members of the invention, prior to shaping the member; and

FIG. 5 is a graph showing various force-distance characteristics for various solenoid assemblies.

FIG. 6 is a view, broken away and partially in section, of a solenoid assembly in accordance with an alternate embodiment of the invention;

FIG. 7 is a view, broken away and partially in section of FIG. 6 revolved 90.degree..

Referring now to the drawings, a solenoid assembly 11 is shown in FIGS. 1 and 2. The solenoid assembly includes a bobbin or guidance tube 13 of non-magnetic material having a first flanged end 15 and a second flanged end 17. Arranged coaxially within the guidance tube 13 is a slideable plunger 19. The plunger 19 is provided with a flange 20 at one end. An electromagnetic coil 23 is helically wound around the guidance tube 13 between the first flanged end 15 and the second flanged end 17. A spring 21 is mounted around plunger 19 and urges plunger 19 into a rest position when the coil 23 is unenergized. The coil 23 is adapted to be connected to a switched external electrical source (not shown) by means of terminals 24 shown in FIG. 2. As shown in FIGS. 1 and 2 the coil is in an energized state and the plunger 19 is drawn within the guidance tube 13, thus compressing spring 21. An enclosure (not shown) of magnetic or other material may be placed around the solenoid assembly in accordance with the known practice.

A first member 25 of magnetizable material partially encircles guidance tube 13. A second magnetizable member 27 also partially encircles guidance tube 13. The shape of the first member and the second member is such that the circumferential encirclement of a first portion of each member is constant in a direction along the path of travel of the plunger 19 and the circumferential encirclement of a second portion increases in a direction corresponding to the path of travel of the plunger 19 when the coil 23 is energized. The first portion of constant circumferential encirclement of the first member and the second member may extend a total distance corresponding to from zero to one half of the total length of the first member and the second member, the total length being measured in the direction of travel of the plunger 19.

It has been discovered that the presence of the first and second magnetizable member alters the force-distance characteristics of the solenoid assembly. In this connection, the force-distance characteristics of the solenoid assembly with the first and second magnetizable member in position are generally as shown by curve C of FIG. 5. The solenoid assembly of the invention including the first magnetizable member and the second magnetizable member is particularly suitable for improving the force-distance characteristics of a solenoid energized by a D.C. electrical source so that it resembles an A.C. solenoid characteristic. However, improvements in the force-distance characteristics of solenoids energized by A.C. electrical source may also be provided by the solenoid assembly of the invention.

The first and second members are constructed from any suitable magnetizable material. As best seen in FIG. 4, the member 25 and the member 27 may be constructed from a flat sheet of magnetizable material. The flat sheet is cut into a suitable shape and is then formed into a suitable configuration to encircle the path of the plunger 19, and is placed around the guidance tube 13 prior to winding the coil 23.

The first member 25 and the second member 27 may comprise a section or part of the guidance tube 13.

It is also contemplated that a shape corresponding to the shape of members 25 and 27 can be imprinted upon the guidance tube 13 by use of magnetizable ink or by deposition of magnetic particles.

The thickness of the members 25 and 27 is not critical, but the effect on the force-distance characteristics of the solenoid assembly are related to the thickness of the magnetized members 25 and 27. In one embodiment of the invention found to be suitable, the members 25 and 27 have a thickness of about 0.048 inches.

The gaps 29 and 30 between the first member 25 and the second member 27 are not critical, but the effect on the force-distance characteristics of the solenoid assembly are related to the extent of the gaps 29 and 30. Generally, in one embodiment of the invention found to be suitable, each of the gaps 29 and 30 extends about 7 percent of the circumference of the guidance tube 13.

The rate of increase of circumferential encirclement of the members 25 and 27 in the direction of travel of the plunger 19 is not critical. Also, the increase in circumferential encirclement may be uniform, as shown in the drawings, or may be stepwise. However, the effect on the force-distance characteristics of the solenoid assembly is related to the rate of increase of the circumferential encirclement and the total distance along the path of travel of the plunger over which the increase in circumferential travel occurs. The distance between the second end of the path of travel of the plunger 19 and forward terminus of the first member 25 or the second member 27 from the first end is preferably at least one quarter of the total distance of travel of the plunger 19.

As shown in FIG. 2, the first member 25 and the second member 27 are overlapping in a direction corresponding to the direction of travel of the plunger 19. Also, as shown in FIG. 2 the first member 25 and the second member 27 are adjacent to and abut the second flanged end 17 of the guidance tube 13. Such overlapping and abutting position is preferred but is not essential for operation for the solenoid assembly in accordance with the invention to alter the force-distance characteristics of the solenoid.

While the invention has been illustrated and described as embodied in a particular solenoid assembly, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing from the spirit of the present invention as set forth in the appended claims.

Claims

What is claimed is:

1. A solenoid assembly comprising a plunger of magnetic material, said plunger being guided along a rectilinear path from a first end of said path to a second end of said path, a first member of magnetic material partially encircling a first part of the circumference of said path at said second end of said path and a second member of magnetic material partially encircling a second part of the circumference of said path at said second end of said path, the circumferential encirclement of said first member and said second member increasing in a direction from said first end of said path to said second end of said path.

2. A solenoid assembly in accordance with claim 1 wherein said first member and said second member overlap in a direction along said rectilinear path.

3. A solenoid assembly in accordance with claim 1 wherein there is a gap between said first and said second member.

4. A solenoid assembly in accordance with claim 1 wherein said increase of said circumferential encirclement of said first member and said second member is uniform.

5. A solenoid assembly in accordance with claim 1 wherein said increase of said circumferential encirclement of said first member and said second member is stepwise.

6. A solenoid comprising a guidance tube of non-magnetic material having a first end and a second end, a plunger of magnetic material extending through an aperture in said first end and coaxially with said guidance tube, a first member of magnetic material partially encircling said guidance tube at the second end thereof, and a second member of magnetic material partially encircling said guidance tube at the second end thereof, the circumferential encirclement of said first member and said second member increasing in a direction from said first end of said path to said second end of said path.

7. A solenoid assembly in accordance with claim 6 wherein said first member and said second member overlap in a direction along said rectilinear path.

8. A solenoid assembly in accordance with claim 6 wherein there is a gap between said first and said second member.

9. A solenoid assembly in accordance with claim 6 wherein said increase of said circumferential encirclement of said first member and said second member is uniform.

10. A solenoid assembly in accordance with claim 6 wherein said increase of said circumferential encirclement of said first member and said second member is stepwise.

11. A solenoid in accordance with claim 6 wherein said first end and said second end of said guidance tube are flanged.

12. A solenoid in accordance with claim 11 wherein said first member and said second member abut said flange of said second end.