Information
-
Patent Grant
-
6597271
-
Patent Number
6,597,271
-
Date Filed
Friday, October 12, 200122 years ago
-
Date Issued
Tuesday, July 22, 200320 years ago
-
Inventors
-
-
Examiners
Agents
- Law Office of Donald D. Mondul
-
CPC
-
US Classifications
Field of Search
US
- 336 178
- 336 83
- 336 212
- 336 165
- 336 134
- 336 233
- 310 178
- 310 218
- 310 258
-
International Classifications
-
Abstract
An electromagnetic apparatus having an adjusting effective core gap includes: (a) an electrical winding; and (b) a ferrous core situated proximal with the electrical winding. The core has a first terminus and a second terminus arranged in spaced relation to establish a gap distance between the termini in a region in substantial register with the termini. The winding and the core cooperate to establish an inductance related with an electrical current applied to the winding. At least one terminus of the termini has a configuration responsive to varying the current by effecting selective local saturation of successive portions of the at least one terminus for successive values of the current. The selective local saturation establishes successive new effective gap distances. Each respective new effective gap distance is appropriate for establishing a successive new optimum inductance for the current value then extant.
Description
BACKGROUND OF THE INVENTION
The present invention is directed to electromagnetic apparatuses that include a core structure. The relationship between inductance and current for an electromagnetic apparatus that includes a core is a measure of the performance of the apparatus. The inductance vs. current relationship varies from apparatus to apparatus as features of the structure change, especially as the core material changes and as the gap in the core changes.
It would be useful to be able to extend the usable current range for a particular core structure and still maintain acceptable inductance vs. current performance of an electromagnetic apparatus that includes the core structure. Such an extension of usable current range for a core structure facilitates handling over-design currents (e.g., transients or high ripple). Such an extension would also facilitate an adapting saturation characteristic of the core to the optimum flat gapped core characteristic at a specific current under normal operating conditions.
The structure of the adjusting effective gap of the present invention is applicable to any gap in any material. It is most useful in ferrite cores where a hard saturation characteristic often prohibits use of such ferrite cores above a proscribed current limit. The adjusting effective gap structure of the present invention is useful for mitigating loss of inductance caused by saturation or by inappropriate gap structure and can be adapted to any core shape and size.
SUMMARY OF THE INVENTION
An electromagnetic apparatus having an adjusting effective core gap includes: (a) an electrical winding; and (b) a ferrous core situated proximal with the electrical winding. The core has a first terminus and a second terminus arranged in spaced relation to establish a gap distance between the first terminus and the second terminus in a region in substantial register with the first terminus and the second terminus. The winding and the core cooperate to establish an inductance related with an electrical current applied to the winding. At least one terminus of the first terminus and the second terminus has a configuration responsive to varying the current by effecting selective local saturation of successive portions of the at least one terminus for successive values of the current. The selective local saturation establishes successive new effective gap distances. Each respective new effective gap distance is appropriate for establishing a successive new optimum inductance for the current value then extant.
It is an object of the present invention to provide an electromagnetic apparatus having an adjusting effective core gap able to extend the usable current range for a particular core structure and still maintain acceptable inductance vs. current performance of the electromagnetic apparatus.
Further objects and features of the present invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings, in which like elements are labeled using like reference numerals in the various figures, illustrating the preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a side elevation schematic view of a first exemplary prior art core structure.
FIG. 2
is a side elevation schematic view of a second exemplary prior art core structure.
FIG. 3
is a side elevation schematic view of a third exemplary prior art core structure.
FIG. 4
is a graphic representation of the relationship of inductance and current for a variety of gap distances for a given core structure.
FIG. 5
is a schematic partial section view of a fourth exemplary prior art core structure having a stepped gap arrangement.
FIG. 6
is a side elevation schematic view of the preferred embodiment of the adjusting effective core structure of the present invention.
FIG. 7
is a schematic top view of the core structure illustrated in
FIG. 6
, taken from viewpoint
7
—
7
in
FIG. 6
, to indicate annuli established when partially saturating the core structure illustrated in FIG.
6
.
FIG. 8
is a side view of the model employed for developing the continuous effective core gap distance variance structure of the present invention.
FIG. 9
is a side profile view of the adjusting effective core gap structure of the present invention illustrating the effect of varying current through an associated winding.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Providing a gap in the core of an electromagnetic device expands the usability of the core to higher currents at the cost of reduced inductance. Adding an air gap increases the reluctance of the magnetic path, thereby reducing the flux density in the core. The result is a reduced effective permeability and inductance at higher currents. Such a result of adding a gap in the magnetic path of an electromagnetic device is regarded as acceptable because the field intensity established by high currents would saturate an ungapped core. However, once the flux in a gapped core exceeds the saturation limit of the core material, the core saturates into an effective air-core. A result of such saturation is an unacceptably drastic reduction in inductance making the electromagnetic device unusable. Such a drastic reduction in inductance is especially likely to occur in ferrite cores where a hard saturation characteristic limits their operational current range.
FIGS. 1-3
are side elevation schematic views of exemplary prior art core structures employing flat gap construction. Flat gapping is introduced into a core by creating a volume of air in the path of the flux at a flat interface surface. For example, in an E-I core construction (FIG.
1
), the flat gap is a volume of air in the center-post. A standard flat-gapped core is limited to a design current range where the inductance is constant. At currents above the design current range, the core begins to saturate. While ferrite cores will usually saturate based on a specific B-H (B: flux density; H: magnetic field intensity) characteristic (such as squareness of a B-H response curve), the current limit for a core is often approximated as a step reduction in inductance. The hard saturation characteristic of a ferrite core makes it unusable at current ranges beyond its maximum design current. This is generally acceptable since core gap selection is limited to constant inductance operation, and intrusion into the saturation mode of the core is considered undesirable when using ferrite cores.
The inductance and current limit of a core can be calculated as
The core and gap reluctances are defined as
where
N
t
: Number of turns.
B
max
: Saturation Flux Density Limit.
R
core
: Reluctance of the core.
R
gap
: Reluctance of the gap.
l
e
: Effective core length.
l
g
: Gap length (height of the gap).
A
e
: Effective core area.
A
g
: Gap area (cross-section of the gap).
μ
r
: Relative permeability of the core material.
μ
o
=4π×10
−7
H/m: Permeability of vacuum.
By varying the gap length l
g
, the core inductance and current limit can be adjusted to a particular application's range.
FIG. 1
is a side elevation schematic view of a first exemplary prior art core structure. In
FIG. 1
, an electromagnetic device
10
includes an E-I core structure
12
with an E-shaped core component
14
and an I-shaped core component
16
. E-shaped core component
14
has a base member
18
and legs
20
,
22
,
24
extending from base member
18
. Legs
20
,
22
,
24
are generally polyhedron-shaped or cylindrically-shaped and are typically integrally formed with base member
18
. A winding structure
26
is arrayed upon E-shaped core component
14
, typically arranged about center leg
22
. A time-varying electrical current is applied to winding structure
26
(details not shown in
FIG. 1
) for establishing an inductance in electromagnetic device
10
. I-shaped core component
16
is situated substantially in register with E-shaped core component
14
resting in an abutting relationship with legs
20
,
24
. E-shaped core component
14
and I-shaped core component
16
establish a magnetic circuit path via legs
20
,
22
,
24
and base member
18
. A gap
28
is established between leg
22
and I-shaped core component
16
. Gap
28
has a gap distance “x
1
” between leg
22
of E-shaped core component
14
and I-shaped core component
16
.
FIG. 2
is a side elevation schematic view of a second exemplary prior art core structure. In
FIG. 2
, an electromagnetic device
40
includes an E-E core structure
42
with a first E-shaped core component
44
and a second E-shaped core component
46
. First E-shaped core component
44
has a base member
48
and legs
50
,
52
,
54
extending from base member
48
. Legs
50
,
52
,
54
are generally polyhedron-shaped or cylindrically-shaped and are typically integrally formed with base member
48
. A winding structure
56
is arrayed upon first E-shaped core component
44
, typically arranged about center leg
52
. A time-varying electrical current is applied to winding structure
56
(details not shown in
FIG. 2
) for establishing an inductance in electromagnetic device
40
. Second E-shaped core component
46
has a base member
49
and legs
51
,
53
,
55
extending from base member
49
. Legs
51
,
53
,
55
are generally polyhedron-shaped or cylindrically-shaped and are typically integrally formed with base member
49
. Second E-shaped core component
46
is situated substantially in register with first E-shaped core component
44
with legs
50
,
51
and legs
54
,
55
in an abutting relationship. Winding structure
56
may be arranged about either center leg
52
,
53
or both of center legs
52
,
53
. First E-shaped core component
44
and second E-shaped core component
46
establish a magnetic circuit path via legs
50
,
51
,
52
,
53
,
54
,
55
and base members
48
,
49
. A gap
58
is established between legs
52
,
53
. Gap
58
has a gap distance “x
2
” between legs
52
,
53
.
FIG. 3
is a side elevation schematic view of a third exemplary prior art core structure. In
FIG. 3
, an electromagnetic device
70
includes a C-shaped core structure
72
with a base member
74
and legs
76
,
78
extending from base member
74
. Legs
76
,
78
are typically integrally formed with base member
74
. Additional legs
80
,
82
extend from legs
76
,
78
toward each other to establish a gap
86
between legs
80
,
82
. Legs
80
,
82
are typically integrally formed with legs
76
,
78
. A winding structure
88
is arrayed upon base member
74
. A time-varying electrical current is applied to winding structure
88
(details not shown in
FIG. 3
) for establishing an inductance in electromagnetic device
70
. The integral structure of electromagnetic device
70
establishes a magnetic circuit path via legs
76
,
78
,
80
,
82
and base member
74
. Gap
86
has a gap distance “x
3
” between legs
80
,
82
.
Alternatively, C-shaped core structure
72
may be fashioned of two U-shaped core structures
71
,
73
, as indicated by dotted line
75
in FIG.
3
. Using such a configuration a magnetic circuit path via legs
76
,
78
,
80
,
82
and base member
74
is still established so long as U-shaped core structures
71
,
73
are in an abutting relationship at dotted line
75
.
FIG. 4
is a graphic representation of the relationship of inductance and current for a variety of gap distances for a given core structure. In
FIG. 4
, a graphic plot
100
plots inductance L for an electromagnetic device (e.g., electromagnetic devices
10
,
40
,
70
;
FIGS. 1-3
) on an axis
106
as a function of peak value of a time-varying current I applied to a winding in the electromagnetic device on an axis
108
. Examples of a time-varying current include an alternating current or a differential current. Several response curves are plotted in
FIG. 4
, as will be explained, indicating a particular representative electromagnetic device having a given core material and other features, indicating responses using different core gaps for the representative device.
FIG. 4
illustrates that inductance L decreases significantly as winding current I increases above a predetermined value. It is at the predetermined value of winding current I that the core in the electromagnetic device represented by the particular response curve saturates, and inductance L of the electromagnetic device precipitously decreases. The response curves illustrated in
FIG. 4
are schematic curves indicating a virtually perpendicular drop in inductance at saturation currents. Actual response curves are often shaped less geometrically, but the geometrically perpendicular curves in
FIG. 4
are illustrative of the pertinent aspects of the present invention for the sake of simplicity of explanation.
A first response curve
101
indicates inductance remaining constant at a level L
1
within a range of currents from zero to I
1
(saturation current). At saturation current I
1
inductance L drops toward zero. Thus, L-I response curve
101
illustrates the L-I characteristic for an electromagnetic device having a particular core and particular configuration including a first core gap distance (e.g., gap distances x
1
, x
2
, x
3
; FIG.
1
-
3
). An optimum L-I value for L-I response curve
101
occurs at an optimum L-I locus
110
.
A second response curve
102
indicates inductance remaining constant at a level L
2
within a range of currents from zero to I
2
(saturation current). At saturation current I
2
inductance L drops toward zero. Thus, L-I response curve
102
illustrates the L-I characteristic for an electromagnetic device having the same particular core and particular configuration associated with L-I response curve
101
, but having a second core gap distance that is larger than the first core gap distance associated with L-I response curve
101
. An optimum L-I value for L-I response curve
102
occurs at an optimum L-I locus
112
.
A third response curve
103
indicates inductance remaining constant at a level L
3
within a range of currents from zero to I
3
(saturation current). At saturation current I
3
inductance L drops toward zero. Thus, L-I response curve
103
illustrates the L-I characteristic for an electromagnetic device having the same particular core and particular configuration associated with L-I response curves
101
,
102
but having a third core gap distance that is larger than the second core gap distance associated with L-I response curve
102
. An optimum L-I value for L-I response curve
103
occurs at an optimum L-I locus
114
.
A fourth response curve
104
indicates inductance remaining constant at a level L
4
within a range of currents from zero to I
4
(saturation current). At saturation current I
4
inductance L drops toward zero. Thus, L-I response curve
104
illustrates the L-I characteristic for an electromagnetic device having the same particular core and particular configuration associated with L-I response curves
101
,
102
,
103
but having a fourth core gap distance that is larger than the third core gap distance associated with L-I response curve
103
. An optimum L-I value for L-I response curve
104
occurs at an optimum L-I locus
116
.
A fifth response curve
105
indicates inductance remaining constant at a level L
5
within a range of currents from zero to I
5
(saturation current). At saturation current I
5
inductance L drops toward zero. Thus, L-I response curve
105
illustrates the L-I characteristic for an electromagnetic device having the same particular core and particular configuration associated with L-I response curves
101
,
102
,
103
,
104
but having a fifth core gap distance that is larger than the fourth core gap distance associated with L-I response curve
104
. An optimum L-I value for L-I response curve
105
occurs at an optimum L-I locus
118
.
The areas under the various response curves
101
,
102
,
103
,
104
,
105
remain constant for the different gap distances, indicating that the flux handling capacity of the core is unchanged. The (L, I) values for the various L-I loci
110
,
112
,
114
,
116
,
118
are determined by the relationship:
L
n
I
max
=K
[5]
where, K=a constant for a given core material, core geometry and number of winding turns;
I
max
=peak current at a particular L-I locus; and
L
n
=inductance at the particular L-I locus.
FIG. 4
illustrates L-I response curves for several core gap distances. Various core gap distances may be appropriate for use with different applications or products. An electromagnetic device having a core that may present a range of effective core gap distances would be advantageous because such a device would be available for use with a variety of products. Such an increased range of applicability for a particular device contributes to greater business efficiency by an ability to manufacture fewer models of an electromagnetic device for use in the same various products that required a greater number of models before. Requiring such a smaller model count to be able to address the same array of applications means business efficiencies, or economies manifested as fewer retooling operations, fewer parts to account for and inventory, fewer components and raw materials to stock for manufacturing the devices and fewer models to track and advertise for sales, marketing, shipping and warranty operations. Other economies may be manifested in various operations including manufacturing, purchasing, inventory, sales, marketing, advertising and other business activities.
In
FIG. 4
, an aggregate L-I response curve
120
illustrates a continuum that includes optimum L-I loci
110
,
112
,
114
,
116
,
118
. An electromagnetic device having a capability to establish a variety of effective core gaps to accommodate a continuum of optimum L-I loci as represented by aggregate L-I response curve
120
would provide significant business economies. A ferrite core with a single flat gap (e.g., electromagnetic devices
10
,
40
,
70
;
FIGS. 1-3
) would not be able to capture the full dynamics of the multi-gap range that would be provided by such an adjusting gap capability.
FIG. 5
is a schematic partial section view of a fourth exemplary prior art core structure having a stepped gap arrangement. The core construction illustrated in
FIG. 5
is an example of an attempt to achieve the capability of providing an adjusting core structure for an electromagnetic device. In
FIG. 5
, a core component
140
includes a first core portion
142
and a second core portion
144
. First core portion
142
includes a base member
150
and a post member
152
. Post member
152
is a substantially polyhedral or cylindrical post integrally formed with base member
150
and extending from base member
150
toward second core portion
144
. Post member
152
is illustrated in
FIG. 5
in section generally along a diameter of post member
152
.
Post member
152
is in spaced relation with second core portion
144
and establishes a first gap distance g
1
between post member
152
and second core portion
144
. Post member
152
is configured with a tiered construction establishing a first level
156
having a first diameter d
1
, a second level
158
having a second diameter d
2
and a third level
160
having a third diameter d
3
. When winding current in a winding associated with post member
152
(e.g., applied to windings
26
,
56
,
88
;
FIGS. 1-3
) rises to an appropriate current level, post member
152
will partially saturate from first level
156
to second level
158
to establish a new effective gap distance g
2
between second level
158
of post member
152
and second core portion
144
. When winding current in the winding associated with post member
152
further rises to a second appropriate current level, post member
152
will further partially saturate from second level
158
to third level
160
to establish another new effective gap distance g
3
between third level
160
of post member
152
and second core portion
144
. This selective saturation of a core component
140
is a crude attempt at adjusting an effective core gap distance that succeeds only in effecting a selection among a few discrete response curves on a plot of the sort described in connection with FIG.
4
. That is, for example, first level
156
of post member
152
may establish an appropriate gap distance g
1
to cause core component
140
to respond according to L-I response curve
101
(FIG.
4
). By way of further example, second level
158
of post member
152
may establish an appropriate effective gap distance g
2
to cause core component
140
to respond according to L-I response curve
103
(FIG.
4
). By way of further example, third level
160
of post member
152
may establish an appropriate effective gap distance g
3
to cause core component
140
to respond according to L-I response curve
105
(FIG.
4
). No true adjustment along a continuum (e.g., aggregate L-I response curve
120
(
FIG. 4
) is effected by the discrete approach provided by core component
140
(FIG.
5
).
In the design of magnetic components, it would be desirable to have a core that can operate at the highest possible L-I level (
FIG. 4
) for a given peak current. Such a core must adapt to increased winding current and its attendant increasing flux by reducing its inductance sufficiently to allow a pre-saturation flux to flow. Such a core would operate as an adjusting core that would be capable of accommodating various winding currents and could handle high current loads without complete failure. One approach to analyzing and designing such an adjusting core would be to introduce multiple step gaps in order to simulate the gradual saturation of the gaps. Such a solution would be constructed using a structure similar to core component
140
(FIG.
5
). A preferred optimal design would capture the full dynamic L-I range of the core to effect true adjustment along a continuum (e.g., aggregate L-I response curve
120
(FIG.
4
).
FIG. 6
is a side elevation schematic view of the preferred embodiment of the adjusting effective core structure of the present invention. In
FIG. 6
, a core component
600
includes a first core portion
602
and a second core portion
604
. First core portion
602
includes a base member
610
and a post member
612
. Post member
612
is a substantially cylindrical post integrally formed with base member
610
and extending from base member
610
toward second core portion
604
. Post member
612
may be configured in a polyhedron-shaped structure or as a substantially planar structure. For ease of explaining the operation of the present invention, post member
612
is illustrated in
FIG. 6
as a cylindrical structure. Post member
612
is illustrated in
FIG. 6
in section generally along a diameter of post member
612
.
Post member
612
is in spaced relation with second core portion
604
and establishes a first gap distance g
1
between post member
612
and second core portion
604
. That is, post member
612
presents a first terminus, or structure, and second core portion
604
presents a second terminus, or structure, to establish first gap distance g
1
between post member
612
and second core portion
604
. Post member
612
is configured with a variable depth construction establishing a first level
614
having a first diameter d
1
. Post member
612
continuously varies its effective diameter to substantially zero along a continuous variance surface
608
to establish a maximum gap distance g
n
when the effective diameter is zero, substantially at center
616
of post structure
604
. The subscript “n” is intended to emphasize that continuous variance surface
608
is not stepped, and an infinite number of gap distances g
n
may be achieved because of that continuous structure.
When winding current in a winding associated with post member
612
(e.g., applied to windings
26
,
56
,
88
;
FIGS. 1-3
) rises to an appropriate current level, post member
612
will locally, or partially saturate from first level
614
to a second level lower than first level
614
. By way of example, post member
612
may continuously vary its effective diameter along continuous variance surface
608
to second level
618
to establish an effective second gap distance g
2
when the effective diameter is d
2
. That is, there is formed in post structure
612
an annulus or ring structure (
FIG. 7
) displaced from second core structure
604
. The annulus structure has a span equal with the distance
It is this annulus structure that establishes magnetic coupling at an effective gap g
2
between post member
612
and second core portion
604
. Given the continuous structure of variance surface
608
(i.e., variance surface
608
is not a stepped structure) any diameter between diameter d
1
and zero diameter, including diameter d
2
, may be established to form respective annuli structures in post member
612
, each respective annulus structure having a respective span
and being separated from second core structure
604
by a respective effective gap distance g
n
without experiencing discrete diameter and effective gap distance changes. Such discrete diameter and effective gap distance changes would be experienced if variance surface
608
were fashioned in a stepped, non-continuous structure. In contrast with prior art attempts at adjusting effective gap core structures (e.g., core component
140
, FIG.
5
), true adjustment along a continuum (e.g., aggregate L-I response curve
120
(
FIG. 4
) is effected by post member
612
continuously varying its effective annular span Δ
n−1
for respective gaps g
n
having respective diameters d
n
along continuous variance surface
608
.
FIG. 7
is a schematic top view of the core structure illustrated in
FIG. 6
, taken from viewpoint
7
—
7
in
FIG. 6
, to indicate annuli established when locally, or partially saturating the core structure illustrated in FIG.
6
. In
FIG. 7
second core portion
604
(
FIG. 6
) is omitted to permit a top view of post member
612
. In
FIG. 7
, a post member
612
is symmetrically oriented about a center
616
. Post member
612
has a diameter d
1
. As described in connection with
FIG. 6
, when winding current in a winding associated with post member
612
(not shown in
FIG. 7
) rises to an appropriate current level, post member
612
will locally saturate from a first level
614
to a second level, for example a level indicated by dashed line
618
that is lower than first level
614
(FIG.
6
). At second level
618
an effective gap distance g
2
is established in an annulus
710
(FIG.
7
). Annulus
710
has a span
A further increase in winding current in a winding associated with post member
612
further locally saturates post member
612
to a level lower than level
618
to establish another annulus (not shown in
FIG. 7
) having a greater span. As explained in connection with
FIG. 6
, the continuous structure of variance surface
608
allows establishment of substantially any diameter between diameter d
1
and zero to form respective annuli structures (e.g., annulus
710
;
FIG. 7
) in post member
612
. Each respective annulus has a respective span
and being separated from second core structure
604
by a respective effective gap g
n
without experiencing discrete changes in diameter and effective gap distances.
Step gaps (e.g., core component
140
,
FIG. 5
) are a simple structure for softening the saturation characteristic of conventional ferrite cores. An optimal adjusting effective gap shape preferably should capture the full dynamic range of the flux capacity curve of a core. In order to achieve this, the core must partially saturate until the inductance has dropped to a point that stops further saturation at the effective gap's effective cross-sectional area (i.e., the area of the annulus structure established in the post member by a given effective diameter).
The first step in modeling the adjusting effective gap is to approximate the effective gap structure as multiple step gaps of finite dimension. The analysis is then extended to determine a desired smooth curve structure.
FIG. 8
is a side view of the model employed for developing the continuous effective core gap distance variance structure of the present invention. In
FIG. 8
, a model air cylinder structure
800
includes cylinders
802
,
804
,
806
,
808
in a substantially concentric nested arrangement. Model air cylinders are used to represent gap volumes in the finished structure. Using such a modeling approach, the finished core structure will include a plurality of core segments that substantially conform with portions of the air gap cylinders that are modeled. Model air cylinder structure
800
has a height and a depth as indicated in FIG.
8
.
The reluctance method of determining inductance and current saturation is employed in the exemplary analytic development, so the same equations introduced above for describing a flat gapped core are applicable for developing the adjusting core gap structure of the present invention (i.e., expressions [1]-[5]). The exemplary core gap chosen to describe the invention is circularly symmetric; a similar design approach may be easily used for other core gap shapes, including polyhedron-shaped core structures and substantially plane core structures. The adjustable effective core structure is therefore modeled as multiple concentric cylindrical air gap components
802
,
804
,
806
,
808
whose effects may be described using the analogy of parallel flux path reluctances.
A shape function ƒ(x) is developed for the analysis. Any function may be used provided that:
0≦
x≦
1
0≦ƒ(
x
)≦1
This general form allows for multiple peaks and troughs between the center and outside radius of the gap. Because the effect of multiple gap peaks can be considered an extension of the effect of a single peak, the gap face curvature is defined for a variation between a single maximum to a single minimum. For this analysis, an exemplary general power function of the form:
is used. When the minimum and maximum positions are set at the center and outer radius of the center-post, the function simplifies to:
ƒ(
x
)=(1
−x
p1
)
p2
[7]
so that the range of possible curvatures can be determined as a function of the two power terms p
1
and p
2
.
The depth of the gap can be defined as a function of radial position:
where
0≦r≦r
max
r
max
: radius of the center-post.
d
o
: minimum gap depth (measured from the center of the core).
d
full
: maximum gap depth (measured from the center of the core).
For this exemplary description of the adjusting core gap structure of the present invention, the gap height is defined as twice the gap depth.
l
(
r
)=2
·d
(
r
) [9]
The cross-sectional area of each cylinder
802
,
804
,
806
,
808
is approximated for a small radial thickness dr:
a
(
r
)=2
πrdr
[10]
Saturation can be determined as a response to the shape function represented by expression [7]. The index “i” is used to denote a saturation level. The gap depth can therefore be represented as:
The reluctance of the adjusting gap can be expressed as the parallel sum of “n” concentric air cylinders:
The first integral in expression [14] is dependent on the shape function f(x); the second integrand is a linear function of radius. The overall effective cross-sectional area of the saturated core gap is expressed as:
C
i
=π(
r
max
2
−r
i
2
) [15]
The inductance and current levels for a particular saturation level “i” may be expressed as:
Using r
i
as the variable indicator of saturation level i, a range of inductance-current (L-I) curves as functions of various inputs may be determined. Varying the depth and shape profile for a particular air gap will produce families of L-I curves (similar to
FIG. 4
) to indicate the best adjustable effective core gap shape. In order to determine the gap shape that captures the dynamic range of the flux capacity curve of the core, the shape function power terms p
1
and p
2
may be varied and a figure of merit for the L-I result may be determined.
In order to determine the optimum combination of powers in the power function employed in design of the adjustable effective core gap structure (e.g., expression [7]) to generate an adjustable effective core gap capable of capturing the flux capacity of the core, combinations of the powers are analyzed and a figure of merit (FOM) is used to determine the optimum shape profile. Since the flux capacity of the core exhibits the highest area under the L-I curve (FIG.
4
), the FOM used may be of the form:
FOM=∫LdI
[18]
There is a family of gap contours that demonstrate optimum adjustable effective core gap performance. Recall that optimum L-I response for a given core for various core gaps may be represented by an aggregate optimum L-I response curve, such as curve
120
in FIG.
4
. The shapes determined by the family of gap contours for the exemplary adjustable effective cylindrical gap structure have been determined by the inventors to all exhibit a sharp indentation or “dimple” gap. By determining the peak FOM point using expression [18], one can ascertain the power factors (p
1
, p
2
) that are required for producing the optimum design for the adjusting core gap. Nonlinear effects may also affect the desired gap profile. Further refinement of the apparatus of the present invention may be able to improve even further upon the performance of a core structure.
Finite element analysis may be carried out to allow the inclusion of fringing field effects in considering an adjusting core gap design. Because of the gradual saturation of the adjusting core gap, fringing fields would be highly dependent on the current level applied to the core. At low currents, most of the gap would be enclosed by ferrite (e.g., proximal locus
614
; FIG.
6
). However, at higher current levels an adjusting core gap may be less enclosed by unsaturated ferrite (e.g., at depth
618
;
FIG. 6
) and fringing fields would begin to grow as a function of the gap shape until the gap saturated to an effective flat gap (e.g., at depth
620
; FIG.
6
).
FIG. 9
is a side profile view of the adjustable effective core gap structure of the present invention illustrating the effect of varying current through an associated winding. In
FIG. 9
, a core component
900
includes a first core portion
902
and a second core portion
904
. First core portion
902
includes a base member
910
and a post member
912
. Post member
912
is a substantially cylindrical post integrally formed with base member
910
and extending from base member
910
toward second core portion
904
. Post member
912
may be configured in a polyhedron-shaped structure or as a substantially planar structure. For ease of explaining the operation of the present invention, post member
912
is illustrated in
FIG. 9
as a cylindrical structure. Post member
912
is illustrated in
FIG. 9
in partial section generally along a diameter of post member
912
.
Post member
912
is in spaced relation with second core portion
904
and establishes a first gap distance g
1
between post member
912
and second core portion
904
. That is, post member
912
presents a first terminus, or structure, and second core portion
904
presents a second terminus, or structure, to establish first gap distance g
1
between post member
912
and second core portion
904
. Post member
912
is configured with a variable depth construction establishing a first level
914
having a first diameter d
1
. Post member
912
continuously varies its effective diameter to substantially zero along a continuous variance surface
908
to establish a maximum effective gap distance g
n
when the effective diameter is zero, substantially at center
916
of post structure
604
.
When winding current in a winding associated with post member
912
(e.g., applied to windings
26
,
56
,
88
;
FIGS. 1-3
) rises to an appropriate current level, post member
912
will locally saturate from first level
914
to a second level lower than first level
914
. By way of example, post member
912
may continuously vary its effective diameter along continuous variance surface
908
to second level
916
to establish a second effective gap distance g
2
when the effective diameter is d
2
. That is, there is formed in post structure
912
an annulus or ring structure (
FIG. 7
) displaced from second core structure
904
. The annulus structure has a span
It is this annulus structure that establishes magnetic coupling at an effective gap g
2
between post member
912
and second core portion
904
.
A higher winding current will cause post member
912
to further locally saturate to a level lower than second level
916
, such as third level
918
to establish a third effective gap distance g
3
when the effective diameter is d
3
. That is, there is formed in post structure
912
an annulus or ring structure (
FIG. 7
) displaced from second core structure
904
. The annulus structure has a span
It is this annulus structure that establishes magnetic coupling at an effective gap g
3
between post member
912
and second core portion
904
.
A still higher winding current will cause post member
912
to still further locally saturate to a level lower than third level
918
, such as fourth level
920
to establish a fourth effective gap distance g
n
when the effective diameter is d
n
. That is, there is formed in post structure
912
an annulus or ring structure (
FIG. 7
) displaced from second core structure
904
. The annulus structure has a span
It is this annulus structure that establishes magnetic coupling at an effective gap g
n
between post member
912
and second core portion
904
. The subscript “n” is intended to emphasize that continuous variance surface
908
is not stepped, and an infinite number of gap distances g
n
may be achieved because of that continuous structure.
Given the continuous structure of variance surface
908
(i.e., variance surface
908
is not a stepped structure) any diameter between diameter d
1
and zero diameter, including diameter d
2
, may be established to form respective annuli structures in post member
912
, each respective annulus structure having a respective span
and being separated from second core structure
904
by a respective effective gap distance g
n
without experiencing discrete diameter and effective gap distance changes. Such discrete diameter and effective gap distance changes would be experienced if variance surface
908
were fashioned in a stepped, non-continuous structure. In contrast with prior art attempts at adjusting effective gap core structures (e.g., core component
140
, FIG.
5
), true adjustment along a continuum (e.g., aggregate L-I response curve
120
(
FIG. 4
) is effected by post member
912
continuously varying its effective annular span Δ
n−1
for respective gaps g
n
having respective depths d
n
along continuous variance surface
908
.
As mentioned earlier, the power function (expression [7]) is described herein as an exemplary function by which to develop the requisite continuous variance surface
908
of the present invention. As mentioned earlier herein, any function may be used provided that:
0≦
x≦
1
0≦ƒ(
x
)≦1
The important point is to develop a continuous variance surface for an adjusting effective gap structure for a ferrous core structure that will yield performance substantially conforming with the appropriate aggregate L-I response curve for the electromagnetic device being produced (e.g., aggregate L-I response curve
120
; FIG.
4
). Providing a continuous variance surface is also advantageous because it is amenable to a variety of manufacturing techniques for its creation, including but not limited to stamping, molding, swaging and other techniques for shaping and manipulating material.
It is to be understood that, while the detailed drawings and specific examples given describe preferred embodiments of the invention, they are for the purpose of illustration only, that the apparatus and method of the invention are not limited to the precise details and conditions disclosed and that various changes may be made therein without departing from the spirit of the invention which is defined by the following claims:
Claims
- 1. An improved core apparatus for a magnetic device; the core apparatus having a first terminus and a second terminus; said first terminus and said second terminus cooperating to establish a gap across an expanse between said first terminus and said second terminus; said gap having a gap distance; said magnetic device including an inductive winding structure; said inductive winding structure cooperating with the core apparatus to establish a magnetic circuit having inductance; said inductance being variable with current applied to said inductive winding structure; said magnetic device having an optimum inductance-current locus for each said gap distance; respective said optimum inductance-current loci for selected said gap distances being expressible by an inductance-current curve; the improvement comprising: at least one terminus of said first terminus and said second terminus being configured to effect variance of effective said gap distance across said expanse; said variance effecting selective local saturation of successive portions of said at least one terminus; said selective local saturation establishing successive new effective gap distances; said successive new said effective gap distances establishing successive new optimum inductance-current loci closely approximating said inductance-current curve.
- 2. An improved core apparatus for a magnetic device as recited in claim 1 wherein said at least one terminus is one terminus of said first terminus and said second terminus.
- 3. An improved core apparatus for a magnetic device as recited in claim 2 wherein said first terminus presents a substantially planar first face segment to said zone and said second terminus is said at least one terminus; said successive portions being generally annular portions substantially parallel with said first face segment.
- 4. An improved core apparatus for a magnetic device as recited in claim 1 wherein said variance of said effective gap distance is a substantially continuous variance.
- 5. An improved electromagnetic apparatus; the apparatus including an inductive winding and a ferrous core; said core having a first terminus and a second terminus arranged in spaced relation to establish a gap distance between said first terminus and said second terminus in a region in substantial register with said first terminus and said second terminus; said winding and said core cooperating to establish an inductance; said inductance being related with an electrical current applied to said winding; the improvement comprising: at least one terminus of said first terminus and said second terminus having a configuration to effect variance of effective said gap distance across said region; said configuration responding to varying said current by effecting selective local saturation of successive portions of said at least one terminus for successive values of said current; said selective local saturation establishing successive new effective gap distances; each respective said new effective gap distance being appropriate for establishing a successive new optimum inductance for said current value then extant.
- 6. An improved electromagnetic apparatus as recited in claim 5 wherein said at least one terminus is one terminus of said first terminus and said second terminus.
- 7. An improved electromagnetic apparatus as recited in claim 6 wherein said first terminus presents a substantially planar first face segment to said region and said second terminus is said at least one terminus; said successive portions being generally annular portions substantially parallel with said first face segment.
- 8. An improved electromagnetic apparatus as recited in claim 5 wherein said variance of said effective gap distance is a substantially continuous variance.
- 9. An electromagnetic apparatus comprising:(a) an electrical winding; and (b) a ferrous core situated proximal with said electrical winding; said core having a first terminus and a second terminus arranged in spaced relation to establish a gap distance between said first terminus and said second terminus in a region in substantial register with said first terminus and said second terminus; said winding and said core cooperating to establish an inductance; said inductance being related with an electrical current applied to said winding; at least one terminus of said first terminus and said second terminus having a configuration responsive to varying said current by effecting selective local saturation of successive portions of said at least one terminus for successive values of said current; said selective local saturation establishing successive new effective gap distances; each respective said new effective gap distance being appropriate for establishing a successive new optimum inductance for said current value then extant.
- 10. An electromagnetic apparatus as recited in claim 9 wherein said at least one terminus is one terminus of said first terminus and said second terminus.
- 11. An electromagnetic apparatus as recited in claim 10 wherein said first terminus presents a substantially planar first face segment to said region and said second terminus is said at least one terminus; said successive portions being generally annular portions substantially parallel with said first face segment.
- 12. An electromagnetic apparatus as recited in claim 9 wherein said variance of said effective gap distance is a substantially continuous variance.
US Referenced Citations (5)