Solenoid actuator with stationary armature extension

A solenoid actuator including a coil of electrically conductive wire having a central opening, a yoke of magnetic material permanently surrounding the coil, and a stationary armature permanently secured to the yoke and projecting from the yoke into the central opening in the coil. A core tube of non-magnetic material is removably retained within the central opening in the coil, the core tube having a closed end engaging the stationary armature and the core tube being separable from the coil-yoke-armature assembly. A movable armature within the core tube is slidable toward and away from the stationary armature. A stationary armature extension of magnetic material surrounds the exterior of the core tube, the extensions being an element independent of the stationary armature. The extension may be an annular element, coaxial with the core tube, which engages the stationary armature. The extension may be a ring having a wall of uniform or non-uniform thickness along its length. Stationary armature extensions of different lengths are used, depending upon the size of the air gap between the movable armature and the stationary armature when the solenoid coil is deenergized.

This invention relates to solenoid actuators which are used to operate a 
wide variety of devices in response to electrical signals. For example, 
solenoid actuators are commonly used to open and close valves which 
control the flow of fluids. 
Typically, a solenoid actuator includes a coil of electric wire, a steel 
yoke surrounding the coil to define a magnetic circuit, and a plastic 
encapsulation around the yoke and coil. At its center, the encapsulated 
coil has an axial hole for accommodating a core tube which contains a 
stationary armature and a movable armature which moves toward and away 
from the stationary armature in response to electrical signals received by 
the coil. The encapsulated coil is assembled with the core tube by 
slipping the coil over the core tube, so that the core tube extends 
through the hole in the coil. 
An improved solenoid actuator is described and illustrated in copending 
applications Ser. No. 793,208, filed Oct. 31, 1985, now U.S. Pat. No. 
4,683,454, Ser. No. 796,757, filed Nov. 12, 1985, now U.S. Pat. No. 
4,679,767 and Ser. No. 801,466, filed Nov. 25, 1985, now U.S. Pat. No. 
4,658,453, each of these applications being assigned to the assignee of 
the present application. In the improved actuator, the stationary armature 
is located externally of the core tube, and is permanently fixed to the 
yoke. The plastic-encapsulated coil, yoke, and stationary armature unit 
can be slipped over the closed end of the core tube, the opposite end of 
which carries a mounting member for securing the core tube to a device, 
such as a valve, to be controlled by the solenoid actuator. Modules are 
provided which can be plugged into the encapsulated unit, to supply 
electric power to the coil, and the encapsulation is furnished with a 
spring clip for movably securing the encapsulated unit to the mounting 
member. 
A major advantage of the improved solenoid actuator described above is that 
the same encapsulated coil, yoke, and stationary armature unit can be used 
in a wide variety of installations, simply by selection of the appropriate 
module to be used with the encapsulated unit. Consequently, it is not 
necessary to maintain an inventory of different solenoid actuators for 
different purposes. However, a problem is presented when the encapsulated 
unit is to be used with different movable armatures having varying stroke 
lengths. Different devices to be controlled by the solenoid actuator often 
require that the movable armature move through different distances between 
the position which the movable armature occupies when the solenoid coil is 
deenergized and the position which it moves to when the coil is energized. 
Since a standard length core tube is employed, changing the stroke of the 
movable armature is accomplished by using movable armatures having 
different lengths, so that in the deenergized condition of the coil, the 
air gap between the movable armature and the stationary armature is 
greater or lesser, as required. 
When a DC solenoid is used, the amount of magnetomotive force needed to 
move the movable armature increases with increase in the air gap between 
the movable armature and the stationary armature. An increased 
magnetomotive force requirement necessitates energizing the coil with 
higher current, or power. To reduce the power requirement, without 
reducing the length of the movable armature stroke, it is common practice 
to shape the opposing faces of the stationary and movable armatures, so as 
to make them other than flat. For example, these opposed faces are often 
given a conical, or frusto-conical shape, as shown in the three copending 
applications mentioned above. Such shaping can provide a relatively large 
axial distance between the stationary and movable armatures, so as to 
permit a relatively long stroke, while presenting a relatively small 
radial air gap between the two armatures. 
However, different shapes for the opposed armature faces must be used for 
different stroke lengths and other variations in the requirements of an 
actuator for operating a particular device. On the other hand, the major 
benefit sought to be achieved by the encapsulated coil, yoke, and 
stationary armature unit of the three copending applications identified 
above is that the exact same unit can be used in solenoid actuators having 
different requirements. Thus, if such encapsulated units are to be 
employed, a single standard stationary armature already forms a permanent 
part of the unit. Hence, the opportunity for shaping the face of the 
stationary armature is not present, if only a single such unit is to be 
made available. 
It is an object of the present invention to overcome this problem by 
providing such a solenoid actuator, in which a standard stationary 
armature forms a permanent part of the yoke which surrounds the solenoid 
coil, wherein the stationary armature can nevertheless be effectively 
reshaped to maximize the efficiency of the actuator regardless of the 
stroke length of the movable armature. 
It is another object of the invention to provide such a solenoid actuator 
in which the stationary armature face is reshaped by effectively extending 
the stationary armature into the region surrounding the core tube. 
It is a further object of the invention to provide stationary armature 
extensions having different lengths, such extensions being elements 
independant of the stationary armature. 
It is an additional object of the invention to provide such a solenoid 
actuator wherein the extensions themselves can be shaped, such as by 
making the wall thickness of the extension uniform or non-uniform along 
the length of the extension, so as to further improve the efficiency of 
operation of the actuator.

Referring to FIGS. 1 and 2, the solenoid actuator chosen to illustrate the 
present invention includes a coil of electrically conductive wire 10 wound 
upon a spool 11 made of non-electrically and non-magnetically conductive 
material. The two ends of coil 10 are connected to a pair of pins 12, 
respectively, which serve as electrical terminals for the coil. 
The yoke includes a side wall 13 carrying an outwardly projecting boss 14, 
the boss surrounding an internally threaded hole 15 which extends 
completely through the thickness of wall 13. 
The internal dimensions of side wall 13 are sized to completely accommodate 
coil 10 and spool 11. When the coil and spool are inserted into the side 
wall, the side wall is radially spaced from the spool and coil, and pin 
terminals 12 extend outwardly beyond the side wall 13 through a notch (not 
shown) in the side wall. The yoke also includes a top wall 16 and a bottom 
wall 17 both of magnetic material, preferably steel. The side wall 13, top 
wall 16, and bottom wall 17 provide a box-like housing which substantially 
completely encloses coil 10 and spool 11. 
Fixed to, and projecting downwardly from, the center of top wall 16 is a 
cylindrical stationary armature, or plug nut, 20, also formed of a 
magnetic material, such as steel. The upper end 21 of armature 20 is 
reduced in diameter and passes through a hole 22 in top wall 16. The upper 
end 23 of portion 21 is enlarged so as to permanently join together 
stationary armature 20 and top wall 16. The lower face 24 of stationary 
armature 20 may be completely flat, or have any other desired shape. 
Preferably, the bottom face 24 is formed with a peripheral annular ridge 
25, as shown in the drawings. 
After the coil 10 and yoke 13, 16, 17 are assembled, the space between coil 
10 and side wall 13 is filled with a plastic material 28, e.g., an epoxy 
resin. The plastic 28 not only fills the space between coil 10 and side 
wall 13, but also covers the top wall 16. Thereafter, the parts are placed 
into a mold, and another plastic material 29, e.g., nylon, is molded 
around substantially the entire outside of the unit. On its front face, 
encapsulation 29 may be formed with a depression 30 for accommodating an 
electrical connection module (not shown) used to connect coil terminals 12 
to a source of electric power. Threaded hole 15 is adapted to receive a 
threaded bolt for securing the module to the solenoid actuator. 
The solenoid actuator according to this invention may be used to operate a 
wide variety of devices. An example of such devices is the valve 33 shown 
in FIG. 1. Valve 33 includes a valve body 34 having a fluid inlet port 35, 
a fluid outlet port 36, and a valve seat 37 between those ports. A 
mounting member, or bonnet, 38 is threaded into the valve body, the 
mounting member carrying a non-magnetic core tube 39. The core tube is 
closed at its upper end, the upper end wall 40 of the core tube being 
flat, in the present example, so as to meet squarely the flat lower face 
24 of stationary armature 20. Furthermore, the external diameter of at 
least the upper end of core tube 39 is sized to fit snugly within the 
annular ridge 25 projecting downwardly from armature 20. 
Slidable within core tube 39 is a movable armature 43 formed of magnetic 
material, the upper end face 44 of the armature being flat so as to 
conform to the flat surface of upper end wall 40 of core tube 39. If the 
lower face 24 of stationary armature 20 has some shape other than planar, 
core tube end wall 40 and upper end face 44 of the movable armature will 
be similarly shaped. The lower end of movable armature 43 carries a valve 
element 45 of resilient material adapted to cooperate with valve seat 37. 
Surrounding, and preferably fixed to, core tube 39 is a tubular sleeve 46, 
preferably of steel. Sleeve 46 is so located on core tube 39 that when the 
core tube is assembled with the unit encapsulated by plastic 29, the lower 
end of sleeve 46 engages bottom wall 17 of the yoke, as shown in FIG. 1. 
The solenoid actuator is assembled by sliding core tube 39, carrying sleeve 
46, through a central hole 49 in yoke bottom wall 17, and central axial 
opening 50 in spool 11. This movement is continued until upper end wall 40 
of the core tube meets lower face 24 of stationary armature 20. A spring 
clip 51 (FIG. 1), slidable within encapsulation 29, is then moved to 
engage an annular slot 52 (FIG. 2) in mounting member 38 so as to hold the 
solenoid actuator together. Prior to insertion of core tube 39 into spool 
opening 50, mounting member 38 is threaded into valve body 34, so that 
spring clip 51 effectively holds together the solenoid actuator and the 
valve. By manipulating spring clip 51, the interconnection between 
encapsulation 29 and mounting member 38 can be released so as to permit 
disassembly of the parts, as shown in FIG. 2. 
In FIG. 1, coil 10 is deenergized, and hence a spring 53 holds valve disc 
45 against valve seat 37 to close the valve. When coil 10 is energized, 
movable armature 43 rises within core tube 39, to close the gap shown 
between the top end face 44 of the movable armature and the upper end wall 
40 of the core tube, thereby lifting valve disc 45 off valve seat 37 to 
open the valve. 
In cases where only a short stroke of movable armature 43 is required, so 
that only a small air gap is present between end face 44 and end wall 40, 
the solenoid actuator operates satisfactorily and efficiently without any 
need for augmenting stationary armature 20. However, as the required 
stroke of armature 43 increases, so that the air gap between end face 44 
and core tube end wall 40 is larger, when coil 10 is deenergized, the 
magnetomotive force required to attract the movable armature to stationary 
armature 20 increases, thereby increasing the power requirements of the 
actuator to unsatisfactory levels. To avoid this undesirable result, the 
present invention employs stationary armature extensions of various 
lengths, the particular length used depending upon the size of the air gap 
between the armature 43 and the top wall 40 of the core tube. 
In the present example, each stationary armature extension is in the form 
of an annular element, or ring 56 (FIGS. 1 and 2) adapted to fit snugly, 
but slidably, around core tube 39 in coaxial relation therewith. Ring 56 
is placed around core tube 39 before the core tube is inserted through 
hole 49 and opening 50. Preferably, ring 56 is only partially inserted 
upon core tube 39, so that the ring projects slightly above end wall 40. 
Then, as core tube 39 completes its movement into opening 50, the upper 
edge of ring 56 engages the lower edge of ridge 25, so that during the 
final movement of core tube 39 into opening 50, ridge 25 pushes ring 56 
further on to core tube 39. In this way, good contact between ridge 25 and 
ring 56 is assured. 
As shown in FIG. 1, ring 56 effectively extends stationary armature 20 
downwardly along the length of core tube 39. If ring 56 were not present, 
the smallest air gap between movable armature 43 and stationary armature 
20 would be the distance between the upper end of armature 43 and the 
lower end of ridge 25. However, with ring 56 present, the air gap between 
the movable and stationary armatures is only the radial distance between 
armature 43 and ring 56 represented by the thickness of the side wall of 
core tube 39. This reduction in the air gap between the stationary and 
movable armatures, when coil 10 is deenergized, significantly reduces the 
magnetomotive force required to shift the movable armature upwardly to the 
top wall 40 of the core tube, thereby significantly reducing the power 
required to operate the solenoid actuator. 
Armature extension ring 56 has the optimum length for the air gap shown in 
FIGS. 1 and 3B. Where the air gap present, in the deenergized solenoid 
actuator, is smaller than that of FIG. 1, such as is shown in FIG. 3A, a 
stationary armature extension ring 56a will be employed, in place of ring 
56. Ring 56a is identical in diameter to that of ring 56, but is of 
shorter axial length. Likewise, where the air gap between end face 44 and 
core top wall 40 is larger, as shown in FIG. 3C, an armature extension 
ring 56c, longer than ring 56, will be used. 
In general, the longer the stroke of armature 43 and the longer the length 
of stationary armature extension 56, the more the force on armature 43 
decreases as it moves toward stationary armature 20. In an extreme case, 
this force can drop to zero before the movable armature reaches the upper 
end of core tube 39. Consequently, in some arrangements, it is desirable 
to shape the wall thickness of the extension ring so as to ensure 
efficient and proper operation of the solenoid actuator. For example, as 
shown in FIG. 3D, the wall thickness of ring 56d tapers in a direction 
away from stationary armature 20. This may be compared to rings 56, 56a, 
and 56c, in which the wall thickness of each ring is uniform along its 
entire length. The thinner lower end of ring 56d causes the ring to 
magnetically saturate earlier in the upward movement of armature 43, 
thereby leaving sufficient magnetic flux to continue movement of the 
armature until it completes its stroke. 
Thus, it will be appreciated that although different length movable 
armatures 43 may be employed, producing different size air gaps between 
those armatures and top wall 40 of core tube 39, when the actuator is 
deenergized, the very same encapsulated unit, comprising coil 10, yoke 13, 
16, 17, and stationary armature 20, can nevertheless be employed. All that 
need be done is use an appropriate length, or shaped, extension ring 56. 
It may be mentioned that in no case should the lengths of extension 56 and 
sleeve 46 be such that these two elements touch, since a magnetic short 
circuit would then be created detracting from the magnetic flux passing 
through the movable armature. In fact, a minimum distance, e.g., at least 
about one-eighth inch, should always be maintained between extension 56 
and sleeve 46. 
The invention has been shown and described in preferred form only, and by 
way of example, and many variations may be made in the invention which 
will still be comprised within its spirit. It is understood, therefore, 
that the invention is not limited to any specific form or embodiment 
except insofar as such limitations are included in the appended claims.