U.S. patent application number 10/961945 was filed with the patent office on 2005-03-24 for non-contact magnetically variable differential transformer.
This patent application is currently assigned to DELPHI TECHNOLOGIES, INC.. Invention is credited to Nicholson, Warren Baxter.
Application Number | 20050062573 10/961945 |
Document ID | / |
Family ID | 33097903 |
Filed Date | 2005-03-24 |
United States Patent
Application |
20050062573 |
Kind Code |
A1 |
Nicholson, Warren Baxter |
March 24, 2005 |
Non-contact magnetically variable differential transformer
Abstract
A magnetically variable differential transformer, comprising: a
primary winding; a first secondary winding; a second secondary
winding; a non-movable permeable core disposed within the primary
winding, the first secondary winding and the second secondary
winding; and a movable magnet configured for movement about the
primary winding, the first secondary winding and the second
secondary winding, wherein movement of the movable magnet causes
magnetic saturation of portions of the non-movable permeable
core.
Inventors: |
Nicholson, Warren Baxter;
(El Paso, TX) |
Correspondence
Address: |
Jimmy L. Funke
DELPHI TECHNOLOGIES, INC.
Legal Staff - Mail Code: 480-410-202
P.O. Box 5052
Troy
MI
48007-5052
US
|
Assignee: |
DELPHI TECHNOLOGIES, INC.
|
Family ID: |
33097903 |
Appl. No.: |
10/961945 |
Filed: |
October 8, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10961945 |
Oct 8, 2004 |
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10423151 |
Apr 25, 2003 |
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6803758 |
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Current U.S.
Class: |
336/126 |
Current CPC
Class: |
H01F 21/00 20130101;
G01D 5/2291 20130101 |
Class at
Publication: |
336/126 |
International
Class: |
H01F 027/02 |
Claims
1. A magnetically variable differential transformer, comprising: a
primary winding; a first secondary winding; a second secondary
winding; a non-movable permeable core disposed within said primary
winding, said first secondary winding and said second secondary
winding and wherein said primary winding said first secondary
winding, said second secondary winding and said non-movable
permeable core are sealed within a non-magnetic housing; and a
movable magnet, comprising a pair of magnets, encased in a ring of
plastic having an inner opening configured to allow said
non-magnetic housing to pass therethrough in a non-contacting
manner and wherein movement of said movable magnet causes magnetic
saturation of portions of said non-movable permeable core.
2. (Cancelled)
3. The magnetically variable differential transformer as in claim
1, wherein said first secondary winding and said second secondary
winding are connected to each other and have induced voltages which
cancel each other out when said movable magnet is in a center
position with respect to said non-movable permeable core and said
primary winding is connected to a source of excitation.
4. (Cancelled)
5. The magnetically variable differential transformer as in claim
1, wherein said movable magnet is secured to a connecting member
adapted to translate movement to said movable magnet.
6. The magnetically variable differential transformer as in claim
5, wherein said connecting member depends away from said movable
magnet in a direction that is not parallel to the direction of
movement of said movable magnet.
7. The magnetically variable differential transformer as in claim
5, wherein said connecting member depends away from said movable
magnet in a direction that is orthogonal to the direction of
movement of said movable magnet.
8. The magnetically variable differential transformer as in claim
1, wherein said non-movable permeable core is a ferrite
material.
9. A method for tracking the movement of a movable object with a
variable differential transformer, comprising: providing an
excitation to a primary winding disposed between a first secondary
winding and a second secondary winding, said primary winding, said
first secondary winding and said second secondary winding are each
disposed about a non-moveable permeable core and are each sealed
within a non-magnetic housing along with the non-moveable permeable
core, wherein said first secondary winding and said second
secondary winding are connected to each other and provide an output
corresponding to voltages induced within said first secondary
winding and said second secondary winding by said primary winding;
and coupling a movable magnet to the movable object by a connecting
member that depends away from said movable magnet in a direction
that is not parallel to the direction of movement of said movable
magnet, wherein said movable magnet is configured to move about
said non-magnetic housing in a non-contacting manner, and wherein
said movable magnet saturates portions of said non-moveable
permeable core thereby modifying the output corresponding to
voltages induced within said first secondary winding and said
second secondary winding by said primary winding.
10. (Cancelled)
11. The method as in claim 9, wherein said connecting member
depends away from said movable magnet in a direction that is
orthogonal to the direction of movement of said movable magnet.
12. (Cancelled)
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a variable differential
transformer for measuring the movement of an object.
BACKGROUND
[0002] The linear variable differential transformer (LVDT) is one
of the oldest electronic methods known to accurately measure the
linear displacement of a body. The LVDT is a differential
transformer which consists of a primary winding and two secondary
windings and a movable coupling core.
[0003] As shown in FIGS. 1-3 a LVDT device 10 of the prior art
(e.g., movable coupling core) is shown. Here LVDT device 10
comprises a primary winding 12, a first secondary winding 14, a
second secondary winding 16 and a movable core 18. As is known in
the related arts the core is connected to a sine wave excitation
source for inducing voltages in the secondary windings.
[0004] When the movable core is at a center point of travel (FIG.
1) the core equally overlaps the two secondary windings, which
results in equal voltages being induced in the secondary windings.
The two secondary windings are connected in such a way that the two
voltages are opposite in phase and cancel each other out resulting
in a zero output. This is illustrated schematically in graph
20.
[0005] As the core moves to the maximum point of travel in one
direction (FIG. 2) the induced voltage reaches a maximum with a
phase illustrated in graph 22. This is because the core, which is
of a high permeability material couples more magnetic flux into
secondary winding 14 and very little into secondary winding 16. The
difference between secondary winding 14 and secondary winding 16
results in a maximum amplitude and phase graph 22, which is similar
to the excitation. Positions of the core between the center of
travel illustrated in FIG. 1 and the maximum illustrated in FIG. 2
will have a lower amplitude but similar phase.
[0006] As the core moves to the position illustrated in FIG. 3, the
amplitude of the induced voltage reaches a maximum (graph 24), with
a phase that is 180 degrees opposite to the phase of graph 22. FIG.
4 schematically illustrates a LVDT 10. As illustrated in FIG. 4,
the windings and the movable core are housed with a structure and
movement of the movable core is facilitated by an actuating member
28 that is secured to the movable core at one end and the item
whose movement is to be tracked or sensed at the other end. In
order to allow for movement of the movable core the actuating
member must pass through a sealing device or bearing that allows
for movement of the actuating member while protecting the interior
of the LVDT from contamination, such as moisture or salt or other
contaminants which may affect performance of the LVDT.
[0007] Examples of such LVDTs are disclosed in U.S. Pat. Nos.
3,546,648 and 4,808,958 the contents of which are incorporated
herein by reference thereto.
[0008] There are two shortcomings of the LVDTs of the prior art
that are overcome by the present disclosure. First, the length of
the LVDT device is twice the designed length of travel since the
actuating member must have a length outside of the housing that is
long enough to provide the movement illustrated in FIGS. 1-3 (e.g.,
movement of the core within the housing). And secondly, the
actuating member or rod, which is secured to the movable core and
the body to be measured, must pass through the housing of the LVDT
which means a sealing means is required.
[0009] In vehicular applications these two problems are exacerbated
as real estate for such devices is typically at a premium and
sealing means which are subject to constant movement may curtail
the life expectancy of such a device.
SUMMARY
[0010] A magnetically variable differential transformer,
comprising: a primary winding; a first secondary winding; a second
secondary winding; a non-movable permeable core disposed within the
primary winding, the first secondary winding and the second
secondary winding; and a movable magnet configured for movement
about the primary winding, the first secondary winding and the
second secondary winding, wherein movement of the movable magnet
causes magnetic saturation of portions of the non-movable permeable
core.
[0011] A magnetically variable differential transformer,
comprising: a primary winding disposed on a center portion of a
bobbin having a central opening, the bobbin being formed out of a
non-magnetic material; a first secondary winding disposed on one
side of the bobbin adjacent to the primary winding; a second
secondary winding disposed on another side of the bobbin adjacent
to the primary winding; a non-movable permeable core being disposed
in the central opening and being disposed within the first
secondary winding, the primary winding and the second secondary
winding; and a movable magnet disposed about the primary winding,
the first secondary winding and the second secondary winding,
wherein movement of the movable magnet causes magnetic saturation
of portions of the non-movable permeable core.
[0012] A magnetically variable differential transformer,
comprising: a primary winding disposed about a center portion of a
non-movable permeable core; a first secondary winding disposed on
one side of the primary winding and being disposed about a first
portion of the non-movable permeable core; a second secondary
winding disposed on another side of the primary winding and being
disposed about a second portion of the non-movable permeable core;
and a movable magnet being configured to magnetically saturate one
of the first portion, the second portion or the center portion of
the non-movable permeable core as the movable magnet moves with
respect to the non-movable permeable core.
[0013] A method for tracking the movement of a movable object with
a variable differential transformer, comprising: providing an
excitation to a primary winding disposed between a first secondary
winding and a second secondary winding, the primary winding, the
first secondary winding and the second secondary winding are each
disposed about a non-moveable permeable core, wherein the first
secondary winding and the second secondary winding are connected to
each other and provide an output corresponding to voltages induced
within the first secondary winding and the second secondary winding
by the primary winding; and coupling a movable magnet to the
movable object wherein the movable magnet saturates portions of the
non-moveable permeable core thereby modifying the output
corresponding to voltages induced within the first secondary
winding and the second secondary winding by the primary
winding.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present disclosure will now be described, by way of
example, with reference to the accompanying drawings, in which:
[0015] FIG. 1 is a schematic illustration of a linear variable
differential transformer (LVDT) of the prior art in a first
position or center of travel;
[0016] FIG. 2 is a schematic illustration of a linear variable
differential transformer (LVDT) of the prior art in a second
position or a limit of travel in one direction;
[0017] FIG. 3 is a schematic illustration of a linear variable
differential transformer (LVDT) of the prior art in a third
position or a limit of travel in another direction;
[0018] FIG. 4 is a cross-sectional view of a linear variable
differential transformer (LVDT) of the prior art;
[0019] FIG. 5 is a cross-sectional view of a magnetically variable
differential transformer (MVDT) of the present disclosure in a
first position or center of travel;
[0020] FIG. 6 is a cross-sectional view of a magnetically variable
differential transformer (MVDT) of the present disclosure in a
second position or a limit of travel in one direction;
[0021] FIG. 7 is a cross-sectional view of a magnetically variable
differential transformer (MVDT) of the present disclosure in a
third position or a limit of travel in another direction; and
[0022] FIG. 8 is a perspective view of a sensor assembly a
magnetically variable differential transformer (MVDT) of the
present disclosure.
DESCRIPTION OF THE EMBODIMENTS
[0023] Disclosed herein is a non-contact magnetically variable
differential transformer (MVDT) wherein a movable magnet is
disposed about the housing of the MVDT and the core of the MVDT is
stationary. Movement of the magnet will change the induced voltages
in the secondary windings. Thus, the need for a sealing means is
negated as there is no requirement for an actuating member to move
the core. Also the length of the device is reduced as the body
whose movement is to be monitored is mechanically connected to the
movable magnet is direction which allows the required space for the
MVDT to be reduced.
[0024] Referring now to FIG. 5, a non-contact magnetically variable
differential transformer (MVDT) 32 of the present disclosure is
illustrated. Here MVDT 32 comprises a non magnetic housing 34 which
is configured to encase a primary winding 36, a first secondary
winding 38 and a second secondary winding 40 disposed about a
non-movable core 42, which extends through the entire length
between primary winding 36 and first secondary winding 38 and
second secondary winding 40 which are disposed on either side of
the primary winding. In other words the non-movable core may be
referred to as comprising three portions, a center portion disposed
within primary winding 36, a first end portion disposed within
first secondary winding on one side of the center portion and a
second end portion disposed within second secondary winding at the
other side of the center portion.
[0025] In an exemplary embodiment, the non-movable core is high
permeable material such as ferrite or steel or equivalents thereof
that is easily magnetically saturated. Therefore the core will lose
it high permeability when it is magnetically saturated by a magnet,
which in essence converts it from a material that efficiently
transfers flux to a material that has permeability characteristics
similar to air.
[0026] In accordance with an exemplary embodiment the core is not
movable and extends completely through the windings or completely
through an opening of a bobbin 41 upon which the windings are
placed. The bobbin and the housing comprise a non-magnetic material
such as plastic, which is also easily molded into a preferred
configuration. In addition, and in order to assist with the
placement of the windings on the bobbin the bobbin is configured to
have partitions which separate the area for the primary winding
from the areas for the secondary windings. The bobbin may also
comprise end portions, which are located at the center of the
bobbin. Of course, the bobbin may be configured without end
portions and partitions. Once the windings are in place and the
non-movable core is disposed therein, the entire assembly is sealed
within housing 34 thereby providing a moisture or contaminant
resistant housing. The only items that leave housing 34 are the
terminations for the windings to provide the excitation and measure
the induced voltages.
[0027] Disposed about the housing of MVDT 32 is a movable permanent
magnet 44, which is configured to pass magnetic flux into the core
as it is moved with respect to the housing and saturate local areas
of the core as it is moved with respect to the core. Movement of
the movable magnet in the directions indicated by arrows 46 is
facilitated by a mechanical connection 48 between movable magnet 44
and a body 50 (illustrated schematically) whose movement is to be
tracked.
[0028] In an exemplary embodiment movable magnet comprises two
magnets 45 each having the appropriate pole configuration to
saturate the portions of the core disposed within the area between
the magnets. In this embodiment, the two magnets are encased in a
ring of plastic wherein the ring is configured to be disposed about
housing 34 and allow housing 34 to move within movable magnet 44.
In other words, the ring is configured to move along the length of
the housing in a non-contacting manner. The ring of plastic is then
secured to connection 48 or alternatively connection 48 may be
integrally molded with the ring of plastic having the magnets
sealed therein.
[0029] Of course, other configurations are contemplated to be
within the scope of the present disclosure. For example, a ring
magnet may be used or a plurality of ring magnets may be used. In
essence and in accordance with an exemplary embodiment the movable
magnet comprises an item capable of magnetically saturating
relevant portions of the core material while also being connected
to a movable member whose movement is to be tracked. This
connection is facilitated in a manner which allows the overall
length of the MVDT to be reduced, as compared to an LVDT.
[0030] As illustrated in FIG. 5 mechanical connection 48 depends
away from housing 34 in the direction of arrow 52. This allows MVDT
32 to be positioned adjacent to or in a parallel relationship with
regard to the body whose movement is to be tracked. This in turn
allows the overall length of MVDT 32 to be shorter than the LVDT of
the prior art, as the latter requires a length of an actuating
member at least as long, if not longer, to depend away from one end
of the device. The reduced size of the MVDT is particularly useful
in vehicular applications wherein high resolution sensitivity is
required and there is very little space for moving parts. An
example of such an application is a "steer by wire" sensor. Of
course, many other uses are contemplated to be within the scope of
the present disclosure.
[0031] Of course, it is contemplated that the angular
configurations of mechanical connection 48 with respect to magnet
44 and/or body 50 may vary to configurations other than those shown
in FIG. 5. Also, and since movable magnet 44 is disposed outside
the housing of MVDT 32, there is no need for a sealing means at the
end of the device. Thus, the device can be hermetically sealed.
[0032] FIG. 5 illustrates the movable magnet of MVDT 32 at a center
point of travel with respect to the core of the MVDT. At this
point, the position of the movable magnet induces lines of flux 54
to pass through the core, which magnetically saturates the central
portion of the core thereby results in equal voltages being induced
in the secondary windings.
[0033] The two secondary windings are connected to each other in a
manner similar to that illustrated schematically in FIG. 3, which
results in the two induced voltages to be opposite in phase and
thus cancel each other out. This results in a zero output. This is
illustrated schematically in graph 56.
[0034] It is, of course, noted that the configuration of movable
magnet 44, core 42, primary winding 36 and the secondary windings
38 and 40 are provided such that the centering of the movable
magnet saturates the portion of the core disposed within primary
winding 36 while the induced voltages in the unsaturated portions
of the core disposed within the two secondary windings are equal in
amplitude but in opposite phase.
[0035] Referring now to FIG. 6, which illustrates the movable
magnet of MVDT 32 at a maximum point of travel in one direction or
left as illustrated in the figure. At this position the induced
voltage in the second secondary winding reaches a maximum with a
phase illustrated in graph 58. This is because the position of the
magnet couples more magnetic flux 60 into the portion of the
non-movable core disposed with first secondary winding 38 and very
little or no flux into the portion of the non-movable core disposed
within second secondary winding 40. Therefore, the portion of the
core disposed within first secondary winding 38 becomes
magnetically saturated. The difference in the induced voltages
between first secondary winding 38 and second secondary winding 40
with the movable magnet at this position results in a maximum
amplitude and phase of the voltages induced in the second secondary
winding (e.g., the non-magnetically saturated portion of the core)
which is illustrated by graph 58. It is also noted that the signal
illustrated by graph 58 is out of phase with the excitation. Note
this graph 58 has a phase similar to the phase to graph 24 (FIG. 3)
wherein a movable core is used.
[0036] Of course, positions between of the movable magnet between
the center of travel illustrated in FIG. 5 and the maximum
illustrated in FIG. 6 will result in induced voltages having a
lower amplitude but similar phase.
[0037] As the movable magnet is moved to the position illustrated
in FIG. 7, which illustrates the movable magnet of MVDT 32 at a
maximum point of travel in another direction or right as
illustrated in the figure. At this position the induced voltage
reaches a maximum with a phase illustrated in graph 62. The phase
in graph 62 is 180 degrees opposite to the phase of graph 58.
[0038] Here more magnetic flux 64 is coupled into the portion of
the non-movable core disposed within second secondary winding 40
and very little into portion of the core disposed within first
secondary winding 38. Therefore, the portion of the core disposed
within second secondary winding 40 becomes magnetically saturated.
The difference in the induced voltages between first secondary
winding 38 and second secondary winding 40 with the movable magnet
at this position results in a maximum amplitude and phase of the
voltages induced in the first secondary winding (e.g., the
non-magnetically saturated portion of the core) which is
illustrated by graph 62. It is also noted that the signal
illustrated by graph 62 has a phase similar to the phase of graph
22 (FIG. 2) wherein a movable core is used.
[0039] Accordingly, and by using known technologies to measure the
output or induced voltage of the MVDT, the position of a body or
movement of a body is determined by coupling the body to the
movable magnet. Thus, wherein a very accurate high resolution
sensor is provided that utilizes much less length (approximately
1/2) of a LVDT to measure the movement of the same item. In
addition, the entire structure is capable of being sealed thereby
making it moisture proof.
[0040] The MVDT of the present disclosure operates similar to a
LVDT, the device comprises a primary and two secondary windings
however, the core now extends along the entire length of the sensor
and is not movable. The non-movable core, which comprises a high
permeable material (as compared to air), such as ferrite or
equivalents thereof, transmits large amounts of magnetic flux to
the secondary coils from the primary excitation coil and the
movable magnet is used to saturate relevant portions of the
non-movable permeable core effectively nullifying its capability to
transfer magnetic flux.
[0041] The stationary core material exhibits high permeability
until the maximum flux density for the core material is reached and
wherein the permeability drops to about 1 or that of air when flux
saturation occurs. In accordance with an exemplary embodiment of
the present disclosure, the movable permanent magnet provides the
extra flux required to saturate the core material. Thus, movement
of the magnet saturates relevant portions of the core while the
other unsaturated portions allow higher induced voltages to be
generated in the secondary windings disposed about the unsaturated
portions of the core.
[0042] It is noted that the particular configuration of the
windings (primary and secondaries), the movable magnet and the core
material are such that when the movable magnet is in center
position illustrated in FIG. 5, the induced voltages (in the
secondary windings) are symmetrical in amplitude but in opposite
phase. In addition, the secondary windings are connected in such a
manner that when the movable magnet is in the center position
illustrated in FIG. 5, the symmetrically induced voltages are
opposite in phase and thus, cancel each other out.
[0043] In an exemplary embodiment, the MVDT is used in a
displacement sensor assembly wherein the MVDT is configured to
provide outputs that correspond to the position of an item being
sensed by the displacement sensor assembly.
[0044] FIG. 5 shows the displacement sensor at the center of travel
where the core material disposed at the center of the assembly is
saturated however, symmetry between the windings 38 and 40 is
preserved and the voltages in the secondary windings are equal and
opposite in phase thus, they cancel each other out and provide a
zero output. As the magnet is moved to a limit of travel to the
left (FIG. 6) the core material disposed inside first secondary
winding 38 is saturated resulting in a low voltage introduced into
first secondary winding 38. However, second secondary winding 40
has a full unsaturated core disposed therebetween as the magnet has
been moved to the position in FIG. 6, which results in a large
induced voltage in second secondary winding 40. The result is a
large amplitude signal of opposite phase with respect to the
excitation (graph 58) at the output.
[0045] When the magnet is moved to its maximum range illustrated in
FIG. 7, which is as far as possible from the position illustrated
in FIG. 6, the core material disposed inside second secondary
winding 40 is saturated which results in a low voltage outlet from
second secondary winding 40 and a large voltage output from first
secondary winding 38. This output is now at a maximum amplitude and
in phase with the excitation (graph 62)
[0046] In addition, since the housing no longer requires a seal for
a movable rod connected to the core there is no chance for external
contaminants to infiltrate into the sensor and cause permanent
damage. For example, water may act as a conductor and salt can
cause corrosion in the windings or the wires of the device. The
connection to the movable body to be measured can be connected to
the sensor at a right angle to the axis of the sensor, which makes
for a sensor of minimum length. This method of connection will also
eliminate hysterisis problems which are a by product of an O-ring
sealing means used in the actuation to movable core connection
illustrated in FIGS. 1-4, such hysterisis is caused by wear in the
O-ring or sealing means which will provide variable resistance
between the rod and the O-ring as it moves therein.
[0047] Referring now to FIG. 8, a perspective view of a possible
MVDT assembly is illustrated. Here movable magnet 36 is a ring
plastic having at least two magnets 45 encased therein. The movable
magnet is secured to the body whose movement is to be tracked and
housing 34 is supported at one end by a structure 70 that allows
the movable magnet to be in a non-contact relationship with respect
to the housing. Of course, other means for supporting housing 34
within movable magnet 36 are contemplated to be within the scope of
the present disclosure.
[0048] Also, structure 70 may provide a means for connecting the
primary to a source of excitation 72 while also providing a means
for connecting the outputs of the induced voltages of the secondary
windings to a controller 74 (e.g., wires housed within structure
70). It is of course, noted that the structures are for purposes of
providing an example and/or illustration and the present disclosure
is not intended to be limited to the specific embodiments disclosed
therein.
[0049] While the invention has been described with reference to an
exemplary embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the present disclosure not be
limited to the particular embodiment disclosed as the best mode
contemplated for carrying out this invention, but that the
invention will include all embodiments falling within the scope of
the appended claims. Furthermore, no element, component, or method
step in the present disclosure is intended to be dedicated to the
public regardless of whether the element, component, or method step
is explicitly recited in the claims.
* * * * *