U.S. patent application number 11/018308 was filed with the patent office on 2005-05-19 for integrating fluxgate for magnetostrictive torque sensors.
This patent application is currently assigned to DELPHI TECHNOLOGIES, INC.. Invention is credited to Fuller, Brian K., Heremans, Joseph Pierre, Naidu, Malakondaiah, Nehl, Thomas Wolfgang, Smith, John R..
Application Number | 20050103126 11/018308 |
Document ID | / |
Family ID | 32989754 |
Filed Date | 2005-05-19 |
United States Patent
Application |
20050103126 |
Kind Code |
A1 |
Naidu, Malakondaiah ; et
al. |
May 19, 2005 |
Integrating fluxgate for magnetostrictive torque sensors
Abstract
A torque sensing apparatus for picking up a magnetic field of a
magnetostrictive material disposed on a shaft, comprising: a first
integrating ring; a second integrating ring; a first fluxgate
return strip and a second fluxgate return strip each being
connected to the first integrating ring at one end and the second
integrating ring at the other end; an excitation coil; and a
feedback coil; wherein the first integrating ring and the second
integrating ring are configured to be positioned to pick up flux
signals along the entire periphery of the ends of the
magnetostrictive material.
Inventors: |
Naidu, Malakondaiah; (Troy,
MI) ; Heremans, Joseph Pierre; (Troy, MI) ;
Nehl, Thomas Wolfgang; (Shelby Township, MI) ; Smith,
John R.; (Birmingham, MI) ; Fuller, Brian K.;
(Rochester Hills, MI) |
Correspondence
Address: |
Scott A. McBain
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: |
32989754 |
Appl. No.: |
11/018308 |
Filed: |
December 21, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11018308 |
Dec 21, 2004 |
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10402620 |
Mar 28, 2003 |
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6871553 |
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Current U.S.
Class: |
73/862.331 |
Current CPC
Class: |
G01L 3/105 20130101;
G01L 3/102 20130101 |
Class at
Publication: |
073/862.331 |
International
Class: |
G01L 003/02 |
Claims
1. A torque sensing apparatus for picking up a magnetic field of a
magnetostrictive material disposed on a shaft, comprising: a first
integrating ring; a second integrating ring; a first fluxgate
return strip and a second fluxgate return strip each being
connected to said first integrating ring at one end and said second
integrating ring at the other end; an excitation coil comprising a
first coil and a second coil, said first coil being wound about
said first fluxgate return strip and said second coil being wound
about said second fluxgate return strip and said first and said
second coil are connected in series to provide a measurement flux;
and a feedback coil wound about said excitation coil; wherein said
first integrating ring, said second integrating ring, said first
fluxgate return strip and said second fluxgate return strip provide
a low reluctance closed loop flux path and are disposed on a
cylindrical member being configured to allow said shaft to be
rotatable received therein.
2. The torque sensing apparatus as in claim 1, wherein said first
integrating ring, said second integrating ring, said first fluxgate
return strip and said second fluxgate return strip are constructed
out of a high-permeable material.
3. The torque sensing apparatus as in claim 1, wherein said first
integrating ring and said second integrating ring are configured to
pick up magnetic flux along the periphery of the magnetostrictive
material.
4. (canceled)
5. (canceled)
6. (canceled)
7. The torque sensing apparatus as in claim 1, wherein said first
integrating ring and said second integrating ring are configured to
be positioned to pick up flux signals along the entire periphery of
the ends of the magnetostrictive material.
8. The torque sensing apparatus as in claim 1, wherein said first
integrating ring, said second integrating ring, said first fluxgate
return strip and said second fluxgate return strip are constructed
out of a high-permeable material and said first integrating ring
and said second integrating ring are configured to pick up magnetic
flux along the periphery of the magnetostrictive material and the
torque sensing apparatus further comprises a pickup coil.
9. The torque sensing apparatus as in claim 8, wherein the
application of a torque to the shaft will provide an induced
voltage in the pickup coil, the induced voltage contains a 2.sup.nd
harmonic component which is extracted by a means of a lock-in
amplifier and rectified and fed, as current, to the feedback coil
via a voltage to current converter to nullify the 2.sup.nd harmonic
component, wherein the 2.sup.nd harmonic voltage is proportional to
the torque to the shaft.
Description
TECHNICAL FIELD
[0001] This disclosure relates to torque sensing apparatus and, in
particular, an apparatus and method for sensing the torque applied
to a rotating shaft.
BACKGROUND
[0002] In systems having rotating drive shafts it is sometimes
necessary to know the torque and speed of these shafts in order to
control the same or other devices associated with the rotatable
shafts. Accordingly, it is desirable to sense and measure the
torque applied to these items in an accurate, reliable and
inexpensive manner.
[0003] Sensors to measure the torque imposed on rotating shafts,
such as but not limited to shafts in vehicles, are used in many
applications. For example, it might be desirable to measure the
torque on rotating shafts in a vehicle's transmission, or in a
vehicle's engine (e.g., the crankshaft), or in a vehicle's
automatic braking system (ABS) for a variety of purposes known in
the art.
[0004] One application of this type of torque measurement is in
electric power steering systems wherein an electric motor is driven
in response to the operation and/or manipulation of a vehicle
steering wheel. The system then interprets the amount of torque or
rotation applied to the steering wheel and its attached shaft in
order to translate the information into an appropriate command for
an operating means of the steerable wheels of the vehicle.
[0005] Prior methods for obtaining torque measurement in such
systems was accomplished through the use of contact-type sensors
directly attached to the shaft being rotated. For example, one such
type of sensor is a "strain gauge" type torque detection apparatus,
in which one or more strain gauges are directly attached to the
outer peripheral surface of the shaft and the applied torque is
measured by detecting a change in resistance, which is caused by
applied strain and is measured by a bridge circuit or other
well-known means.
[0006] Another type of sensor used is a non-contact torque sensor
wherein magnetostrictive materials are disposed on rotating shafts
and sensors are positioned to detect the presence of an external
flux which is the result of a torque being applied to the
magnetostrictive material.
[0007] Such magnetostrictive materials require an internal magnetic
field which is typically produced or provided by either
pre-stressing the magnetostrictive material by using applied forces
(e.g., compressive or tensile) in either a clockwise or counter
clockwise to pre-stress the coating prior to magnetization of the
pre-stressed coating in order to provide the desired magnetic
field. Alternatively, an external magnet or magnets are provided to
produce the same or a similar result to the magnetostrictive
material.
[0008] To this end, magnetostrictive torque sensors have been
provided wherein a sensor is positioned in a surrounding
relationship with a rotating shaft, with an air gap being
established between the sensor and shaft to allow the shaft to
rotate without rubbing against the sensor. A magnetic field is
generated in the sensor by passing electric current through an
excitation coil of the sensor. This magnetic field permeates the
shaft and returns back to a pick-up coil of the sensor.
[0009] The output of the pick-up coil is an electrical signal that
depends on the total magnetic reluctance in the above-described
loop. Part of the total magnetic reluctance is established by the
air gap, and part is established by the shaft itself, with the
magnetic reluctance of the shaft changing as a function of torque
on the shaft. Thus, changes in the output of the pick-up coil can
be correlated to the torque experienced by the shaft.
[0010] As understood herein, the air gap, heretofore necessary to
permit relative motion between the shaft and sensor, nonetheless
undesirably reduces the sensitivity of conventional
magnetostrictive torque sensors. As further understood herein, it
is possible to eliminate the air gap between a shaft and a
magnetostrictive torque sensor, thereby increasing the sensitivity
of the sensor vis-a-vis conventional sensors. Moreover, the present
disclosure recognizes that a phenomenon known in the art as "shaft
run-out" can adversely effect conventional magnetostrictive torque
sensors, and that a system can be provided that is relatively
immune to the effects of shaft run-out.
SUMMARY
[0011] It is an object of the present disclosure to provide a
torque sensor that is sufficiently compact for use in applications
where space is at a premium, such as in automotive
applications.
[0012] A torque sensing apparatus for picking up a magnetic field
of a circumferentially magnetized magnetostrictive material
disposed on a shaft, comprising: a first integrating ring; a second
integrating ring; a first fluxgate return strip and a second
fluxgate return strip each being connected to the first integrating
ring at one end and the second integrating ring at the other end;
an excitation coil comprising a first coil wound about the first
fluxgate return strip and a second coil wound about the second
fluxgate return strip wherein the first and second coils of the
excitation coil are connected in series so that the net excitation
flux circulates between the flux gate strips via a first
integrating ring and a second integrating ring; and a feedback coil
wound about the first fluxgate return strip and the second fluxgate
return strip, wherein the first integrating ring and the second
integrating ring are configured to be positioned to pick up flux
signals along the entire periphery of the ends of the
magnetostrictive material.
[0013] A method for determining the applied torque to a shaft,
comprising: collecting flux a first end of a magnetostrictive
material disposed on the shaft via a first integrating ring;
collecting flux at a second end of the magnetostrictive material
disposed on the shaft via a second integrating ring; providing a
measurement flux in a first flux gate winding and a second flux
gate winding positioned about said magnetostrictive material;
providing a low reluctance closed loop flux path from the first
flux gate winding to the second flux gate winding; and measuring an
applied torque to the shaft by using a null detection scheme on the
low reluctance closed loop flux path.
DESCRIPTION OF THE FIGURES
[0014] FIG. 1 is a perspective view of a magnetostrictive material
disposed on a shaft;
[0015] FIG. 2 is a perspective view of an integrating flux gate of
the present disclosure disposed about a shaft having a
magnetostrictive material;
[0016] FIG. 3 is a perspective schematic view of an integrating
flux gate of the present disclosure;
[0017] FIG. 4A is a graph of the BH curve of the integrating flux
gate of the present disclosure with no torque;
[0018] FIG. 4B is a graph of the BH curve of the integrating flux
gate of the present disclosure with torque;
[0019] FIGS. 5 and 6 are graphs of illustrating the time dependence
of the voltage across the excitation coil and the feedback coil for
no applied torque and applied torque, respectively;
[0020] FIGS. 7A-7B are graphs illustrating the rectified second
harmonic voltage signals as input to voltage to current converters
feeding feedback coils;
[0021] FIG. 8 illustrates an integrating fluxgate with five coils
(excitation C1, C2, connected in series; pickup C3, C4, connected
in series; and Cfb);
[0022] FIG. 9 shows the measured current waveform when a sinusoidal
voltage is applied to the excitation coil (C1) in the presence of a
torque flux;
[0023] FIG. 10 illustrates the voltage measured across pick up coil
(C3) under the same excitation as illustrated in FIG. 9 and in the
presence of a torque flux;
[0024] FIG. 11 illustrates the voltage measured across feedback
coil (Cfb) under the same excitation as illustrated in FIG. 9 and
in the presence of no torque flux;
[0025] FIG. 12 illustrates the voltage measured across pickup coil
(C3) under the same excitation as illustrated in FIG. 9 and in the
presence of no torque flux;
[0026] FIG. 13 is a schematic illustration of an exemplary circuit
for use with the integrating flux gate of the present
disclosure;
[0027] FIG. 14 is a schematic illustration of an alternative
exemplary circuit for use with the integrating flux gate of the
present disclosure;
[0028] FIG. 15 is a graph illustrating a plot of the output voltage
on the feedback coil (Cfb) versus an applied torque;
[0029] FIG. 16 is another graph illustrating a plot of the output
voltage on the feedback coil (Cfb) versus an applied torque in an
ascending and descending torque direction;
[0030] FIG. 17 is a schematic illustration of another alternative
exemplary circuit for use with the integrating flux gate of the
present disclosure; and
[0031] FIG. 18 is a schematic illustration of yet another
alternative alternative exemplary circuit for use with the
integrating flux gate of the present disclosure.
DETAILED DESCRIPTION
[0032] Referring now to FIGS. 1-18 exemplary embodiments of a
torque sensing apparatus 10 are illustrated. In an exemplary
embodiment and referring in particular to FIG. 1, the
torque-subjected member is in the form of a cylindrical shaft 12.
However, the present disclosure is not intended to be limited to
the specific configurations illustrated in FIG. 1. The shaft
comprises a non-magnetic material, such as a stainless steel or
aluminum. Disposed on the surface of shaft 12 is a magnetostrictive
material 14. The magnetostrictive material is coated on or applied
to the shaft in a manner that will produce a flux signal when the
torque is applied to the shaft. The same signal is collected by the
integrating fluxgate for measuring the torque applied to the shaft.
An example of the magnetostrictive material is of the type
disclosed in U.S. Pat. No. 6,645,039, the contents of which are
incorporated herein by reference thereto. Of course, other types of
magnetostrictive materials are contemplated to be used in
accordance with the present disclosure.
[0033] The magnetostrictive material is magnetically polarized to
have a circumferential moment in the direction of arrow 16. Of
course, the magnetostrictive material may be magnetically polarized
in a direction opposite of arrow 16. Upon receipt of an applied
torque (arrow 18) a longitudinal magnetic flux (arrow 20) or torque
flux leaves the magnetostrictive material. This flux is
proportional to the torque that will be picked up by the device and
method of the present disclosure.
[0034] Torque 18 is shown as being in a clockwise direction looking
at the visible end of shaft 12, but obviously can be applied to
rotate the shaft in either or both directions depending on the
nature of the machine incorporating shaft 12.
[0035] Referring now in particular to FIGS. 2 and 3 an integrating
fluxgate 22 is disposed about magnetostrictive material 14. As will
be described herein integrating fluxgate 22 is adapted to measure
the torque flux of shaft 12. Integrating fluxgate 22 is mounted on
a cylindrical member 24. Member 24 is constructed of a
non-conductive material such as plastic, nylon or polymer of
equivalent properties, which is lightweight and easily molded or
manufactured. Member 24 is configured to allow shaft and
magnetostrictive material 14 to be rotatably received therein. In
addition, member 24 is secured to a structure (not shown) that is
stationary with respect to rotating shaft member 12 accordingly;
shaft member 12 is capable of rotation within member 24. In
addition, and in order to prevent the device of the present
application from being affected by external magnetic fields (e.g.,
the Earth's magnetic field) the entire device will be received with
a shield capable of protecting the torque sensing apparatus for
being adversely affected by such magnetic fields.
[0036] Disposed on member 24 is a first integrating ring 26 and a
second integrating ring 28. Integrating rings 26 and 28 are
constructed out of a high-permeable material such metalglass or
permalloy of mumetal, or other materials having equivalent
characteristics. As will be discussed herein the configuration of
integrating rings 26 and 28 allow integrating fluxgate 22 to pick
up torque flux signals anywhere along the periphery of
magnetostrictive material 14. The torque flux signals are sensed by
the integrating flux gate using a variety of coil configurations.
In one embodiment, a three-coil configuration (C excitation, C
pickup and C feedback) is used, in another embodiment a three-coil
configuration is used (C excitation (C1 and C2 connected in series)
and C feedback), is used, in yet another embodiment a two-coil
configuration is used (C excitation and C feedback), in still
another embodiment a single-coil configuration is used (wherein the
coil is used as C excitation and C feedback) and in still another
embodiment a five-coil configuration is used (C excitation (C1 and
C2 connected in series), C pickup (C3 and C4 connected in series)
and C feedback). These configurations and schemes for measuring
torque using the fluxgate will be discussed herein.
[0037] Referring now to FIG. 3 an integrating fluxgate with a
three-coil arrangement is illustrated. Here a feedback coil 30
(Cfb) is disposed about the other two coils. Disposed between
integrating rings 26 and 28 is a first fluxgate return strip 32 and
a second fluxgate return strip 34 as shown in FIG. 3. First
fluxgate return strip 32 and second fluxgate return strip 34 are
constructed out of the same material as the integrating rings.
[0038] A first flux gate winding 36 (C1) is wound about first
fluxgate return strip 32 and a second flux gate winding 38 (C2) is
wound about second fluxgate return strip 34. As discussed above,
and in one embodiment the integrating fluxgate of the present
disclosure is able to measure the torque flux of the
magnetostrictive material through the use of three coils, namely,
C1, C2 and Cfb. In an exemplary embodiment coils C1 and C2 are
connected in series and coil Cfb is disposed about coils C1 and C2.
Thus, a device is created wherein the external magnetic field of
the magnetostrictive material is measured. In particular, the
external magnetic field is collected along the periphery of the
ends of the magnetostrictive material through the use of
integrating rings 26 and 28.
[0039] However, it is noted that the integrating fluxgate can
measure the torque flux through the use of a five coil arrangement,
shown in FIG. 8, comprising of coils C1, C2, C3, C4 and Cfb. The
excitation coils (C1 and C2) are connected in series while the
pick-up coils (C3 and C4) are also connected in series. In
addition, and in accordance with an exemplary embodiment of the
present disclosure the number of coils used are reduced. For
example, and in one embodiment three coils are used (C excitation,
C pickup and C feedback), or in another three coil arrangement
wherein the pickup coil is eliminated C excitation (coils C1 and C2
connected in series) and C feedback is used, in another embodiment
two coils are used (C excitation and C feedback) and in yet another
embodiment one coil is used for both excitation and feedback, in
the later three embodiments the pickup coil is completely
eliminated.
[0040] In the three-coil arrangement (C excitation, C pickup and C
feedback), the induced voltage in the pickup coil contains the
2.sup.nd harmonic component upon application of a torque to the
shaft. This 2.sup.nd harmonic voltage is extracted by a means of a
lock-in amplifier and rectified and fed, as current, to the
feedback coil via a voltage to current converter to nullify the
2.sup.nd harmonic component. This 2.sup.nd harmonic voltage is
proportional to the torque to the shaft.
[0041] In an exemplary embodiment and as illustrated in FIG. 3,
first flux gate winding 36 and second flux gate winding 38 are
connected in series to provide an excitation flux and the
integrating flux gate 22 (integrating rings 26 and 28 and fluxgate
return strips 32 and 34) provides a low reluctance closed loop flux
path 40 from first flux gate winding 36 to second flux gate winding
38.
[0042] As shown, the apparatus is disposed in a surrounding
relationship with the shaft to sense the torque imposed on the
shaft. In one exemplary embodiment, the shaft is a rotating shaft
within a vehicle. For instance, the shaft can be an ABS shaft,
engine shaft, or transmission shaft, although it is to be
appreciated that the principles set forth herein apply equally to
other vehicular and non-vehicular rotating shafts.
[0043] It is being understood that in the embodiment where the
pickup coil is eliminated the first and the second flux gate
windings are connected in series are excited by a high frequency
sinusoidal voltage to generate magnetic flux. This would also be
the case in the five-coil arrangement. The excitation voltage and
the frequency are adjusted such that the passing flux through the
two flux gate strips and integrating rings such does not cause
saturation without torque flux. The excitation current and
frequency are adjusted such that the flux gate material is just
below the saturation limit of the flux gate core.
[0044] For illustration purposes flux density (B) can be determined
through use of the following formula:
B=E.times.10.sup.8/4Anf; wherein
[0045] E=Input or Output Voltage, in volt (rms)
[0046] A=Cross Sectional Area, in cm.sup.2
[0047] f=Switching frequency, in H.sup.z
[0048] N=Number of Turns
[0049] In addition, and for illustration purposes, the
magnetization force or H can be determined through the following
formula:
H=0.4.pi.NI/l; wherein
[0050] N=No. of turns
[0051] I=Current in Amps
[0052] l=Magnetic Path Length in cm.
[0053] In addition, the second flux gate winding is configured to
receive magnetic flux from the shaft. Thus, the apparatus of the
present disclosure is capable of maintaining the flux gate material
out of magnetic saturation wherein an applied torque will create a
torque flux that will be picked up by the device. When the flux
material is out of saturation (e.g., no torque applied and no
torque flux measured) there is no 2.sup.nd harmonic waveform
(current or voltage). Thus, and in accordance with an exemplary
embodiment of the present disclosure the device uses the 2.sup.nd
harmonic waveform (current or voltage) to provide a signal that is
used to provide a nullifying current to the feedback coil. The
skilled artisan will appreciate that the flux defines a flux path
from the excitation coil to its respective pickup coil or in the
embodiment wherein the pickup coil is removed the flux defines a
flux path from the excitation coils connected in series.
[0054] As discussed above when shaft 12 is presented with an
applied torque (arrow 18) a longitudinal magnetic flux leaves the
coating of magnetostrictive material, the integrating fluxgate of
the present disclosure provides this flux with a return path. The
produced or excitation flux and torque flux, if existing, is picked
up by integrating ring 26, passes through fluxgate return strips 32
and 34 and integrating ring 28 to the other side of the
magnetostrictive material 14. The torque flux adds or subtracts to
the excitation flux produced by C1 and C2 in a three-coil
arrangement or C excitation in a three, two or single coil
arrangement as discussed in the various embodiments of the present
disclosure. The signals are then interpreted by the torque sensing
apparatus of the various embodiments of the present disclosure in
various ways so that the applied torque is capable of being
measured.
[0055] FIGS. 4-6 illustrate the principle operation of the fluxgate
of the present disclosure. FIGS. 4A and 4B illustrates a BH curve
of the core material with and without torque. FIGS. 5 and 6 show
the time dependence of the voltage across the excitation coils and
feedback coil (with and without an applied flux or torque). FIGS.
7A and 7B are graphs which show the rectified 2.sup.nd harmonic
voltage of the pickup coil (e.g., a three coil arrangement C
excitation, C pickup and C feedback) as an input to the feedback
coil (with and without an applied torque flux).
[0056] Therefore, the passing of the torque flux through both
return strips of the fluxgate causes early magnetic saturation in
one direction and then in the other direction while the excitation
frequency is sweeping the fluxgate core material in both
directions.
[0057] This saturation causes 2.sup.nd harmonic voltages in the
feedback coil or pickup coil, depending on the embodiment being
implemented as well as DC offset in the excitation current.
Therefore, and in one embodiment, the applied torque is
proportional to the rectified 2.sup.nd harmonic voltage of the
feedback coil or pickup coil, which is fed as current input to the
feedback coil to nullify the core saturation. In another
embodiment, the torque is proportional to the DC offset current in
the excitation coil, which is fed as input to the feedback coil to
nullify the core saturation caused by external torque flux.
[0058] In addition, and due to the circular configuration of
integrating rings the flux gate is capable of integrating the
magnetic flux about the entire periphery of the magnetostrictive
material. Accordingly, the torque moment is measured about the
entire periphery of the magnetostrictive material by integrating
along the circumference at either end of the magnetostrictive
material. This allows the integrating fluxgate of the present
disclosure to measure the torque moment of the shaft regardless of
angle at which the shaft is positioned. In addition and by
integrating along the circumference at either end of the
magnetostrictive material, the integrating fluxgate is
self-correcting or is not susceptible to measurement anomalies
associated with shaft wobble or irregularities in the surface of
the shaft or magnetostrictive material disposed on the shaft. Thus,
the integrating fluxgate of the present disclosure measures the
torque leakage along the entire end of the magnetostrictive
material.
[0059] The output waveforms of various embodiments of the
integrating fluxgate of the present disclosure are shown in FIGS.
8-12. FIG. 8 illustrates an integrating fluxgate constructed with
five coils (C1, C2, C3, C4, and Cfb) where the excitation coils C1
and C2 are connected in series and the pickup coils C3 and C4 are
connected in series. However, as discussed above and as will be
shown herein only three coils (C1, C2 and Cfb) or less are
necessary to measure the applied torque in accordance with the
various embodiments of the present disclosure as the pickup coil
and others can be removed while still providing a device for
measuring and nullifying torque flux.
[0060] When a sinusoidal voltage is applied to the excitation coil
(C1 or C1 and C2 connected in series) and the current waveform is
measured in the presence of a torque flux, FIG. 9 shows that the
current waveform has a distortion that consists of a second
harmonic signal and asymmetry with respect to the x-axis.
Accordingly, the integrating fluxgate of the present disclosure can
use the following properties to diagnose the presence of a torque
flux: the second harmonic voltage, or a non-zero D.C. value of the
time-averaged integral of the excitation current.
[0061] Referring now to FIGS. 10 and 11 and under the same
excitation as illustrated in FIG. 9, the voltage is measured across
the pick up coil (C2). As illustrated, a second harmonic signal is
also seen when a torque flux is present (FIG. 10) and disappears
when the torque flux is zero. Accordingly, the voltage of pick up
coil (C2) can also be used to diagnose the presence of a torque
flux.
[0062] Referring now to FIG. 12 and under the same excitation, the
waveform of the voltage on the feedback coil (Cfb) is also shown.
This waveform also has a strong second harmonic signal. If the
structure had been perfect, and the two fluxgate strips absolutely
symmetric, no contribution of the fundamental waveform would have
been measured on the feedback coil (Cfb). Therefore, the feedback
coil can also use the second harmonic signal as a diagnostic of the
torque flux.
[0063] During operation of the integrating fluxgate of the present
disclosure and regardless of how many coils are used or implemented
a D.C. current is sent into the feedback coil to counterbalance the
torque flux. To accomplish this a feedback loop (FIGS. 13, 14, 17
and 18) is required and accordingly, a D.C. current is sent into
the feedback coil, such that either the second harmonic
contribution on the feedback coil (Cfb) or the DC offset current in
the excitation coil are nul, or in other words the integral of the
current waveform into excitation coil is zero or nul, This feedback
ensures that the entire structure is out of magnetic saturation.
This DC current fed back to the feedback coil nullifies the
saturation due to torque flux since it is proportional to the
applied shaft torque.
[0064] A signal relating to the DC current sent to the feedback
coil is also sent to a microprocessor, controller or equivalent
means having a look up table or other means for determining the
applied torque, which is used in any vehicular or other control
system requiring torque readings.
[0065] FIG. 13 illustrates an embodiment of a three coil
(excitation coils AC1, AC2 connected in series and a feedback coil
DC1) flux gate torque sensing circuit for determining the amount of
torque being applied to the shaft by looking at the rectified
second harmonic voltage of the voltage waveform of the feedback
coil (DC1). In this embodiment AC1 is wound about one of the flux
gate strips and AC2 is wound about the other while the feedback
coil DC1 is wound about the two excitation coils AC1 and AC2.
[0066] The circuit is contemplated for use with an integrating flux
gate as illustrated in FIGS. 2 and 3. The integrating flux gate
comprises two integrating rings, two flux strips, two coils (AC1 or
C1) and (AC2 or C2) connected in series and the feedback coil (DC1
or Cfb). In this embodiment AC1 comprises 50 turns of 32 gage wire
and AC2 comprises 50 turns of 32 gage wire while the feedback coil
DC1 comprises 72 turns of 25 gage wire. Of course, and as
applications require the gage of the wire and number of turns may
vary. In the illustrated embodiment, an AC voltage of 1.8 volts at
a frequency of 49 kilohertz is applied to the excitation coils (AC1
and AC2, connected in series). In addition, this voltage is also
applied to a frequency doubler 44 that doubles the frequency and
applies a 98 kilohertz frequency as a reference input into a
lock-in amplifier 46, which is used as a bandpass filter.
Accordingly, only voltages at the reference frequency (98 khz, i.e.
double the excitation frequency) will be picked up. Of course, and
as applications require the frequency and the magnitude of
excitation voltage may vary depending on the design of the flux
gate.
[0067] The feedback coil voltage is passed through the lock-in
amplifier to extract the rectified second harmonic voltage signal,
which is then inputted into a voltage to current converter 48. This
converted voltage is then inputted as DC current in the feedback
coil DC1 to nullify the flux gate core saturation caused by the
torque flux. The rectified 2.sup.nd harmonic voltage is
proportional to the applied shaft torque.
[0068] In this embodiment the integrating fluxgate is measuring the
applied torque by using a null detection scheme wherein the
fluxgate is measuring the applied torque by picking up the 2.sup.nd
harmonic rectified DC voltage of the feedback coil, converting it
into a current, and feeding into the feedback coil to nullify the
core saturation due to torque flux.
[0069] Referring now to FIG. 14, an alternative circuit for
determining the amount of torque that is being applied to the shaft
in a three coil (C1, C2, Cfb) flux gate torque sensor circuit by
looking at the second harmonic of the current waveform of the
excitation coil (C1 and C2 connected in series). The circuit is
contemplated for use with an integrating flux gate as illustrated
in FIGS. 2 and 3. The integrating flux gate comprises two
integrating rings, two flux strips, two coils (AC1 or C1) and (AC2
or C2) connected in series and the feedback coil (DC1 or Cfb). In
this embodiment AC1 comprises 50 turns of 32 gage wire and AC2
comprises 50 turns of 32 gage wire while the feedback coil DC1
comprises 72 turns of 25 gage wire. Of course, and as applications
require the gage of the wire and number of turns may vary. In the
illustrated embodiment, an AC voltage of 1.8 volts at a frequency
of 49 kilohertz is applied to the coils AC1 and AC2.
[0070] The excitation frequency is also applied to a frequency
doubler 44 that doubles the frequency (98 kilohertz) and used as a
reference frequency signal to the lock-in amplifier 46. This
lock-in amplifier takes the voltage proportional to the excitation
current across the shunt 50 as input, shown in FIG. 14, and
extracts the 2.sup.nd harmonic content. It also rectifies and
filters the 2.sup.nd harmonic voltage and provides a DC voltage
signal to the voltage to current converter.
[0071] In an exemplary embodiment, resistor 50 has a value in the
range of 10-100 ohms; of course, other values greater or less than
the aforementioned range are contemplated for use with the present
disclosure.
[0072] As illustrated, only currents at the reference frequency,
double the excitation frequency (98 khz) will be picked up. Of
course, and as applications require the frequency and magnitude of
the excitation voltage may vary to values greater or less than 49
khz and 1.8 volts respectively. The measured voltage across the
resistor, which is proportional to the current in the resistor, is
fed into the lock-in amplifier, the DC output voltage signal of the
lock-in amplifier is fed to the feedback coil through a voltage to
current converter wherein the current applied to the feedback coil
nullifies core saturation caused by the torque flux. The output of
DC voltage of the lockin amplifier is proportional to the applied
shaft torque.
[0073] In this embodiment the integrating fluxgate is measuring the
applied torque by using a null detection scheme wherein the
fluxgate is measuring the applied torque by picking up the 2.sup.nd
harmonic current in the excitation coil (C1) and drive it to zero
by feeding the current into the feedback coil to nullify the core
saturation caused by the torque flux.
[0074] FIG. 15 is a graph illustrating a plot of the output voltage
on the feedback coil (Cfb) versus an applied torque and FIG. 16 is
another graph illustrating a plot of the output voltage on the
feedback coil (Cfb) versus an applied torque.
[0075] FIG. 17 is a schematic illustration of an alternative
embodiment of the present disclosure wherein a two coil (excitation
and feedback) torque sensor circuit is used to measure the applied
torque. In this embodiment a single coil is used to provide the
excitation flux and receive the torque flux through the integrating
rings and flux gate return strips of the present disclosure. The
circuit of this embodiment comprises an oscillator 60 it can be
square wave or sine wave or any periodic function of time, a
differential amplifier 62, a second order filter 64, a voltage
controlled current source 66, and an output amplifier 68.
[0076] In this embodiment the flux strips of the closed loop
reluctance path are maintained just below the magnetic saturation
point when only excitation current flows through the single
excitation coil (with no torque flux). When an applied torque is
encounter or applied to the shaft the flux strips are magnetically
saturated in one direction then in the other direction when the
excitation frequency is sweeping the core in both positive and
negative directions. The saturation causes DC offset in the
excitation waveform, the voltage proportional to the excitation
current obtained by measuring the voltage across the series
resistor connected in the excitation coil is fed to the
differential amplifier 62. The output of the differential amplifier
62 is fed to second order active filter 64 to extract DC voltage
proportional to the offset DC current in the excitation coil. The
voltage is fed to the voltage to current converter (voltage control
current source 66) and fed back to the feedback coil to nullify the
flux gate core saturation due to torque flux.
[0077] FIG. 18 is a schematic illustration of another alternative
exemplary circuit for use with the integrating flux gate of the
present disclosure. Here a single coil is used as both the
excitation and feedback coil. In this embodiment the flux strips of
the closed loop reluctance path are maintained just below their
magnetic saturation point when the excitation current is flowing
through the coil. When an applied torque is encountered or applied
to the shaft the flux strips are magnetically saturated in one
direction then in the other direction when the excitation frequency
is sweeping the core in both positive and negative directions. The
saturation causes DC offset in the excitation waveform, the voltage
proportional to the excitation current obtained by measuring the
voltage across the series resistor connected in the coil is fed to
the differential amplifier 62. The output of the differential
amplifier 62 is fed to second order active filter 64 to extract DC
voltage proportional to the offset DC current in the coil. The
voltage is fed to the voltage to current converter (voltage control
current source 66) and fed back to the coil to nullify the flux
gate core saturation due to torque flux.
[0078] 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 invention 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.
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