Valves and valve actuation – Electrically actuated valve – Including solenoid
Reexamination Certificate
2001-07-13
2003-08-12
Revill, John (Department: 3753)
Valves and valve actuation
Electrically actuated valve
Including solenoid
C251S129170, C335S281000, C335S297000
Reexamination Certificate
active
06604726
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to solenoid-operated fluid control valves of the type described in the '425 application and the '033 and '947 Patents, which may be used in precision fluid flow regulation systems, such as those that require precise control of the rate of fluid flow, including but not limited to pneumatic and hydraulic regulation. The invention is particularly directed to a modification of the configuration of the magnetic pole piece, that obviates the need for an alignment and support element of non-magnetic material, thereby reducing the complexity and cost of manufacturing.
BACKGROUND OF THE INVENTION
As described in the above-referenced '425 application and the '033 and '947 patents, precision fluid flow control devices commonly employ a solenoid-operated valve for controlling fluid flow substantially proportional to the current applied to the solenoid. It is also desirable that hysteresis in the flow rate versus control current characteristic (which creates an undesirable dead band in the operation of the valve) be maintained within some minimum value. A standard practice for reducing hysteresis has been to physically support the solenoid's moveable armature within the bore of its surrounding drive coil by means of low friction bearings, such as Teflon rings. However, even with the use of such a low friction material, there is still significant ‘dead band’ current (e.g. on the order of forty-five milliamps), which limits the operational precision of the valve.
One proposal to deal with this physical contact-created hysteresis problem is to remove the armature support mechanism from within the bore of the solenoid coil (where the unwanted friction of the armature support bearings is encountered) to an end portion of the coil, and to support the armature for movement within the bore by means of a spring mechanism located outside of the solenoid coil. An example of such a valve configuration is described in the U.S. Pat. to Everett, No. 4,463,332, issued Jul. 31, 1984.
According to this patented design, the valve is attached to one end of an armature assembly supported for axial movement within the cylindrical bore of the solenoid coil and having a permanent ring magnet surrounding the solenoid. One end of the solenoid contains a ring and spring armature support assembly, located substantially outside the (high flux density) solenoid bore, and whose position can be changed, so as to adjust the axial magnetic flux gap within the bore and thereby the force applied to the valve.
Unfortunately, this type of support structure requires a magnetic flux booster component which, in the patented design, is a permanent magnet. Namely, even though the objective of the Everett design is to adjust magnetic permeance and maintain linearity, the overall solenoid structure and individual parts of the solenoid, particularly the ring spring armature assembly (which itself is a complicated brazed part), and the use of a permanent booster magnet, are complex and not easily manufacturable with low cost machining and assembly techniques, resulting in a high price tag per unit. In another prior art configuration, described in the U.S. Pat. to Nielsen, No. 4,635,683, the movable armature is placed outside the bore by means of a plurality of spiral spring-shaped bearings adjacent to opposite ends of the solenoid structure.
Advantageously, the linear motion proportional solenoid assembly described in U.S. Pat. No. 4,954,799 (hereinafter referred to as the '799 patent) entitled: “Proportional Electropneumatic Solenoid-Controlled Valve,” improves on the above designs by using a pair of thin, highly flexible annular cantilever-configured suspension springs, to support a moveable armature within the bore of solenoid, such that the moveable armature is intimately coupled with its generated electromagnetic field (thereby eliminating the need for a permanent magnet as in the Everett design).
In order to make the force imparted to the movable armature substantially constant, irrespective of the magnitude of an axial air gap between the armature and an adjacent magnetic pole piece, the device detailed in the '799 Patent places an auxiliary cylindrical pole piece region adjacent to the axial air gap. This auxiliary cylindrical pole piece region has a varying thickness in the axial direction, which serves to ‘shunt’ a portion of the magnetic flux that normally passes across the axial gap between the armature assembly and the pole piece element to a path of low reluctance. By shunting the flux away from what would otherwise be a high reluctance axial path through a low reluctance path, the auxiliary pole piece region effectively ‘linearizes’, the displacement vs. current characteristic over a prescribed range.
The proportional solenoid structure described in the '298 Patent and diagrammatically shown in FIGS. 1 and 2, reduces the structural and manufacturing complexity of the implementation of the structure described in the '799 Patent by locating a moveable, ferromagnetic (or simply magnetic) armature
10
adjacent to one end of a fixed pole piece
12
made of ferromagnetic (magnetic) material that protrudes outside a solenoid coil bore
14
, and configuring this moveable armature
10
to provide two, relatively low reluctance magnetic flux paths
21
and
22
. (For a description of additional details of the solenoid-actuated valve structure shown in FIGS. 1 and 2, attention may be directed to the '298 Patent, proper.)
Now even though the proportional solenoid structure described in the '298 Patent operates extremely well in relatively small and larger sized hardware configurations, for very small (e.g., micro-valve) applications and using reasonable priced industry standard materials, it is possible for one or more components of the assembly may become distorted, particularly those parts that are very small and dimensionally thin (such as the moveable armature's support springs). Namely, for very small dimension applications, what would otherwise be a negligible axial magnetic flux component accompanying the dominant radial flux component bridging the variable geometry radial air gap
32
between the saturated tapered rim portion
34
of the moveable armature
10
and the inwardly projecting tapered portion
36
of the solenoid assembly housing
30
becomes significant.
In particular, the non-radially directed magnetic flux in the variable geometry air gap
32
can overcome the mechanical rigidity of the material (e.g., beryllium copper) of the armature support springs
41
and
42
, and cause the springs to warp or twist from their intended shape, and deviate from their intended axial cantilever axial flexing.
This unwanted distortion of the armature support springs is particularly likely where there are nontrivial departures from dimensional tolerances in the manufacturing of the parts of the solenoid assembly. Because of the variable geometry gap inherently tends to provide some degree of play between the armature and the housing, distortion of the armature support springs can cause an unbalanced physical engagement of the tapered rim portion of the moveable armature with the inwardly projecting tapered portion of the housing, thereby preventing proper operation of the proportional solenoid assembly.
The invention disclosed in the '425 application and the '033 and '947 Patents (diagrammatically illustrated in FIGS. 3 and 4 as comprising a valve unit
100
coupled with a valve-control solenoid unit
200
) remedies this component distortion problem by modifying the configuration of the moveable armature to eliminate the variable geometry annular air gap between the radially projecting, tapered rim portion of the moveable armature and the inwardly projecting tapered portion of the solenoid assembly housing, while still retaining their flux control functionality. (For a description of additional details of the solenoid-actuated valve structure shown in FIGS. 3 and 4, attention may
Revill John
Teknocraft, Inc.
The Bilicki Law Firm P.C.
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