U.S. patent application number 13/275693 was filed with the patent office on 2013-04-18 for magnetic torque sensor for transmission converter drive plate.
The applicant listed for this patent is Seong-Jae LEE. Invention is credited to Seong-Jae LEE.
Application Number | 20130091959 13/275693 |
Document ID | / |
Family ID | 47263058 |
Filed Date | 2013-04-18 |
United States Patent
Application |
20130091959 |
Kind Code |
A1 |
LEE; Seong-Jae |
April 18, 2013 |
MAGNETIC TORQUE SENSOR FOR TRANSMISSION CONVERTER DRIVE PLATE
Abstract
A magnetic torque sensing device having a disk-shaped member
with a magnetoelastically active region. The magnetoelastically
active region has oppositely polarized magnetically conditioned
regions with initial directions of magnetization that are
perpendicular to the sensitive directions of magnetic field sensor
pairs placed proximate to the magnetically active region. Magnetic
field sensors are specially positioned in relation to the
disk-shaped member to accurately measure torque while providing
improved RSU performance and reducing the detrimental effects of
compassing.
Inventors: |
LEE; Seong-Jae; (Mount
Prospect, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LEE; Seong-Jae |
Mount Prospect |
IL |
US |
|
|
Family ID: |
47263058 |
Appl. No.: |
13/275693 |
Filed: |
October 18, 2011 |
Current U.S.
Class: |
73/862.335 ;
29/428 |
Current CPC
Class: |
Y10T 29/49826 20150115;
G01L 3/10 20130101; G01L 3/1435 20130101 |
Class at
Publication: |
73/862.335 ;
29/428 |
International
Class: |
G01L 3/10 20060101
G01L003/10; B23P 11/00 20060101 B23P011/00 |
Claims
1. A magnetic torque sensing device comprising: a generally
disk-shaped member having opposite generally circular spaced apart
surfaces, and forming a central axis of rotation; first and second
ferromagnetic and magnetorestrictive magnetically conditioned
regions disposed on or in at least a portion of the disk-shaped
member forming a magnetoelastically active region for producing a
magnetic field that varies with a torque applied to the disk-shaped
member, wherein the magnetically active region possesses sufficient
magnetic anisotropy to return the magnetization in the
magnetoelastically active region to an initial state when the
torque applied to the disk-shaped member is reduced to zero; and at
least one pair of magnetic field sensors, each having a sensitive
direction and disposed adjacent to one another and proximate to the
magnetoelastically active region, wherein the sensitive direction
of the first sensor is opposite the sensitive direction of the
second sensor, and perpendicular to the direction of polarization
of the first and second magnetically conditioned regions, wherein
the magnetic field sensors provide an output signal that is
representative of the torque applied to the disk-shaped member, and
wherein variation in the output signal is substantially linear with
respect to variation in the torque applied to the disk-shaped
member.
2. The magnetic torque sensing device, as claimed in claim 1,
wherein the first and second magnetically conditioned regions are
annularly shaped.
3. The magnetic torque sensing device, as claimed in claim 1,
wherein the first and second magnetically conditioned regions are
disposed with no radial gap therebetween.
4. The magnetic torque sensing device, as claimed in claim 1,
wherein the first and second magnetically conditioned regions are
initially polarized in opposite axial directions, and wherein the
sensitive directions of the magnetic field sensors in each pair are
oriented in opposite circumferential directions.
5. The magnetic torque sensing device, as claimed in claim 1,
wherein the first and second magnetically conditioned regions are
initially polarized in opposite circumferential directions, and
wherein the sensitive directions of the magnetic field sensors in
each pair are oriented in opposite axial directions.
6. The magnetic torque sensing device, as claimed in claim 1,
wherein the magnetic torque sensing device comprises at least four
pairs of magnetic field sensors, angularly offset from one
another.
7. The magnetic torque sensing device, as claimed in claim 1,
wherein the magnetic torque sensing device comprises at least eight
pairs of magnetic field sensors, angularly offset from one
another.
8. The magnetic torque sensing device, as claimed in claim 1,
wherein at least one pair of magnetic field sensors comprises a
flux gate sensor.
9. The magnetic torque sensing device, as claimed in claim 1,
wherein at least one pair of magnetic field sensors comprises a
Hall Effect sensor.
10. The magnetic torque sensing device, as claimed in claim 1,
wherein at least a portion of the disk-shaped member is made from
at least AISI 9310 material.
11. The magnetic torque sensing device, as claimed in claim 1,
wherein the magnetoelastically active region is formed on the
disk-shaped member using a pair of permanent magnets arranged with
opposite polarity.
12. The magnetic torque sensing device, as claimed in claim 1,
wherein the disk-shaped member is formed of a material having a
coercivity greater than 15 Oe.
13. The magnetic torque sensing device, as claimed in claim 1,
wherein the disk-shaped member is formed of a material having a
coercivity greater than 20 Oe.
14. The magnetic torque sensing device, as claimed in claim 1,
wherein the disk-shaped member is formed of a material having a
coercivity greater than 35 Oe.
15. The magnetic torque sensing device, as claimed in claim 1,
wherein the disk-shaped member comprises a drive plate.
16. The magnetic torque sensing device, as claimed in claim 1,
further comprising a torque transmitting element directly or
indirectly attached to or forming a part of the disk-shaped member
at the central axis of rotation in such a manner that torque
applied to the torque transmitting element is proportionally
transmitted between the torque transmitting element and the
disk-shaped member.
17. The magnetic torque sensing device, as claimed in claim 16,
wherein the torque transmitting element comprises a crankshaft.
18. A method of manufacturing a magnetic torque sensing device
comprising the steps of: providing a generally disk-shaped member
having opposite generally circular spaced apart surfaces and a
central axis of rotation, wherein the disk-shaped member includes
at least a portion that is both ferromagnetic and
magnetorestrictive, wherein said portion is capable of producing a
magnetic field that varies with a torque applied to the disk-shaped
member, and wherein said portion possesses sufficient magnetic
anisotropy to return the magnetization in said portion to an
initial state when the torque applied to the disk-shaped member is
reduced to zero; positioning a pair of oppositely polarized
permanent magnets proximate to the surface of the disk-shaped
member at a first distance from a surface of the disk-shaped
member; and rotating the disk-shaped member about its central axis
to form two annular, oppositely polarized, magnetically conditioned
regions.
19. The method, as claimed in claim 18, wherein the permanent
magnets forming the pair are positioned with no radial gap
therebetween.
20. The method, as claimed in claim 18, wherein the permanent
magnets forming the pair are arranged such that they are polarized
in opposite axial directions relative to the disk-shaped
member.
21. The method, as claimed in claim 18, wherein the permanent
magnets forming the pair are arranged such that they are polarized
in opposite circumferential directions relative to the disk-shaped
member.
22. The method, as claimed in claim 18, wherein the permanent
magnets forming the pair are rectangular N42 or N45 grade neodymium
iron boron magnets.
23. The method, as claimed in claim 18, wherein the first distance
is between about 0.1 mm and 5 mm.
24. The method, as claimed in claim 18, wherein the first distance
is about 3 mm.
25. A magnetic torque sensing device comprising: a generally
disk-shaped member having opposite generally circular spaced apart
surfaces, and forming a central axis of rotation; a
magnetorestrictive magnetically conditioned region disposed on or
in at least a portion of the disk-shaped member forming a
magnetoelastically active region for producing a magnetic field
that varies with a torque applied to the disk-shaped member,
wherein the magnetically active region possesses sufficient
magnetic anisotropy to return the magnetization in the
magnetoelastically active region to an initial state when the
torque applied to the disk-shaped member is reduced to zero; and at
least one magnetic field sensor unit comprising: a pair of primary
magnetic field sensors disposed adjacent to one another and
proximate to the magnetically conditioned region, each of the
primary sensors having a sensitive direction, wherein the sensitive
direction of the first primary sensor is the same as the sensitive
direction of the second primary sensor, and is perpendicular to the
direction of polarization of the magnetically conditioned region; a
first secondary magnetic field sensor disposed adjacent to the pair
of primary sensors and apart from the magnetically conditioned
region, the first secondary sensor having a sensitive direction
that is opposite the sensitive directions of the first and second
primary sensors; and a second secondary magnetic field sensor
disposed adjacent to the pair of primary sensors, opposite the
first secondary sensor, and apart from the magnetically conditioned
region, the second secondary sensor having a sensitive direction
that is opposite the sensitive directions of the first and second
primary sensors, wherein the primary and secondary sensors,
collectively, provide an output signal that is representative of
the torque applied to the disk-shaped member, and wherein variation
in the output signal is substantially linear with respect to
variation in the torque applied to the disk-shaped member.
26. The magnetic torque sensing device, as claimed in claim 25,
wherein the magnetically conditioned region is annularly
shaped.
27. The magnetic torque sensing device, as claimed in claim 25,
wherein the magnetically conditioned region is initially polarized
in an axial direction, wherein the sensitive directions of the
primary magnetic field sensors are oriented in a first
circumferential direction, and wherein the sensitive directions of
the secondary magnetic field sensors are oriented in a second
circumferential direction opposite the first circumferential
direction.
28. The magnetic torque sensing device, as claimed in claim 25,
wherein the magnetically conditioned region is initially polarized
in a circumferential direction, wherein the sensitive directions of
the primary magnetic field sensors are oriented in a first axial
direction, and wherein the sensitive directions of the secondary
magnetic field sensors are oriented in a second axial direction
opposite the first axial direction.
29. The magnetic torque sensing device, as claimed in claim 25,
wherein the magnetic torque sensing device comprises at least four
magnetic field sensor units, angularly offset from one another.
30. The magnetic torque sensing device, as claimed in claim 25,
wherein the magnetic torque sensing device comprises at least eight
magnetic field sensor units, angularly offset from one another.
31. The magnetic torque sensing device, as claimed in claim 25,
wherein at least one magnetic field sensor unit comprises a flux
gate sensor.
32. The magnetic torque sensing device, as claimed in claim 25,
wherein at least one magnetic field sensor unit comprises a Hall
Effect sensor.
33. The magnetic torque sensing device, as claimed in claim 25,
wherein at least a portion of the disk-shaped member is made from
at least AISI 9310 material.
34. The magnetic torque sensing device, as claimed in claim 25,
wherein the disk-shaped member is formed of a material having a
coercivity greater than 15 Oe.
35. The magnetic torque sensing device, as claimed in claim 25,
wherein the disk-shaped member is formed of a material having a
coercivity greater than 20 Oe.
36. The magnetic torque sensing device, as claimed in claim 25,
wherein the disk-shaped member is formed of a material having a
coercivity greater than 35 Oe.
37. The magnetic torque sensing device, as claimed in claim 25,
wherein the disk-shaped member comprises a drive plate.
38. The magnetic torque sensing device, as claimed in claim 25,
further comprising a torque transmitting element directly or
indirectly attached to or forming a part of the disk-shaped member
at the central axis of rotation in such a manner that torque
applied to the torque transmitting element is proportionally
transmitted between the torque transmitting element and the
disk-shaped member.
39. The magnetic torque sensing device, as claimed in claim 38,
wherein the torque transmitting element comprises a crankshaft.
40. The magnetic torque sensing device, as claimed in claim 25,
wherein the first primary sensor and the second primary sensor are
radially aligned.
41. The magnetic torque sensing device, as claimed in claim 25,
wherein the first primary sensor and the second primary sensor are
circumferentially aligned.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to methods and sensing devices
for automotive transmissions and, more particularly, to
non-contacting magnetoelastic torque sensors for providing a
measure of the torque transmitted radially in a transmission
converter drive plate or similar disk-shaped member.
[0003] 2. Description of the Related Art
[0004] In the control of systems having rotating drive shafts,
torque and speed are fundamental parameters of interest. Therefore,
the sensing and measurement of torque in an accurate, reliable, and
inexpensive manner has long been a primary objective of such
control system designs.
[0005] Previously, torque measurement was accomplished using
contact-type sensors directly attached to a shaft. One such 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 a change in resistance caused by
torque-induced strain is measured by a bridge circuit or other well
known means. However, contact-type sensors are relatively unstable
and of limited reliability due to the direct contact with the
rotating shaft. In addition, they are expensive and are thus
commercially impractical for competitive use in many applications,
such as automotive steering systems, for which torque sensors are
sought.
[0006] Subsequently, non-contact torque sensors of the
magnetostrictive type were developed for use with rotating shafts.
For example, U.S. Pat. No. 4,896,544 to Garshelis, which is
incorporated herein by reference, discloses a sensor comprising a
torque-carrying member, with an appropriately ferromagnetic and
magnetostrictive surface, two axially distinct circumferential
bands within the member that are endowed with respectively
symmetrical, helically-directed residual stress-induced magnetic
anisotropy, and a magnetic discriminator device for detecting,
without contacting the torqued member, differences in the response
of the two bands to forces applied to the torque-carrying member.
Most typically, magnetization and sensing are accomplished by
providing a pair of excitation or magnetizing coils overlying and
surrounding the bands, with the coils connected in series and
driven by alternating current. Torque is sensed using a pair of
oppositely connected sensing coils for measuring a difference
signal resulting from the external magnetic fluxes of the two
bands. Unfortunately, providing sufficient space for the requisite
excitation and sensing coils on and around the device on which the
sensor is used can create practical problems in applications where
space is at a premium. Also, such sensors may be impractically
expensive for use on highly cost-competitive devices, such as in
automotive applications.
[0007] Torque transducers based on measuring the field arising from
the torque induced tilting of initially circumferential remnant
magnetizations have been developed which, preferably, utilize a
thin wall ring ("collar") serving as the field generating element.
See, for example, U.S. Pat. Nos. 5,351,555 and 5,520,059 to
Garshelis, which are incorporated herein by reference. Tensile
"hoop" stress in the ring, associated with the means of its
attachment to the shaft carrying the torque being measured
establishes a dominant, circumferentially directed, uniaxial
anisotropy. Upon the application of torsional stress to the shaft,
the magnetization reorients and becomes increasingly helical as
torsional stress increases. The helical magnetization resulting
from torsion has both a radial component and an axial component,
the magnitude of the axial component depending entirely on the
degree of torsion. One or more magnetic field vector sensors may be
used to sense the magnitude and polarity of the field arising, as a
result of the applied torque, in the space above the magnetically
conditioned regions on a shaft, and provide a signal output
reflecting the magnitude and direction of the torque. Inasmuch as
the peak allowable torque in a ring sensor is limited by slippage
at the ring/shaft interface, concerns have been expressed regarding
distortion arising from slippage at the ring/shaft interface under
conditions of torque overload. This, together with the need for
multiple parts of different materials to minimize the adverse
effects of parasitic fields, has encouraged the investigation of
alternative constructions.
[0008] Magnetoelastic torque transducers have been developed in
which the active, torque sensing region is formed directly on the
shaft itself, rather than on a separate ferromagnetic element which
then has to be affixed to the shaft. See, for example, U.S. Pat.
No. 6,047,605 to Garshelis, which is incorporated herein by
reference. In one form of these so-called "collarless" transducers,
the magnetoelastically active region is polarized in a single
circumferential direction and itself possesses sufficient magnetic
anisotropy to return the magnetization in the region, following the
application of torque to the member, to the single circumferential
direction when the applied torque is reduced to zero. The torqued
shaft is desirably formed of a polycrystalline material wherein at
least 50% of the distribution of local magnetizations lie within a
90-degree quadrant symmetrically disposed around the direction of
magnetic polarization and have a coercivity sufficiently high that
the transducing region field does not create parasitic magnetic
fields in proximate regions of the shaft of sufficient strength to
destroy the usefulness, for torque sensing purposes, of the net
magnetic field seen by the magnetic field sensor. In particularly
preferred forms of such transducers the shaft is formed of a
randomly oriented, polycrystalline material having cubic symmetry
and the coercivity is greater than 15 Oersted (Oe), desirably
greater than 20 Oe and, preferably, greater than 35 Oe.
[0009] More recently, non-contacting magnetoelastic torque sensors
have been developed that provide signals indicative of the torque
transmitted between radially separated locations of disk-shaped
members. U.S. Pat. No. 6,513,395 to Jones, which is incorporated
herein by reference, describes a torque sensor that includes a
disk-shaped member having a magnetoelastically active region that
is polarized in a single circumferential direction. In that patent,
a magnetic field sensor is mounted proximate to the active region,
the sensor sensing the magnitude of a magnetic field resulting from
a torque transferred from a shaft to the disk-shaped member, and
the sensor outputting a signal in response thereto. Such a
configuration may be susceptible to compassing as discussed below.
That patent also describes a disk having dual circumferentially and
oppositely polarized regions, with two sensors positioned along the
same radial line, their sensitive directions oriented radially and
oppositely to permit common mode field cancellation. This placement
of sensors, however, has the undesired result in which the sensors
pick up magnetic field signals that do not change linearly in
response to a change in torque applied to the disk.
[0010] Other prior art describes a torque sensor that includes a
disk-shaped member having a region in which annular magnetically
conditioned regions are separated from one another and spaced in a
radial direction. It is believed, however, that a torque sensor
having a gap between magnetically conditioned regions may exhibit a
large rotational signal uniformity (RSU) signal due to random
magnetic leakage fields between the two annular magnetically
conditioned regions. Ideally, a torque sensor will exhibit a zero
RSU signal, which is defined as no variation in signal output
during the rotation of a member when no torque, or a constant
torque, is applied to the rotating member. In actual practice
however, due to deficiencies in the surface preparation and
magnetization processes, noticeable RSU signals are detected.
Furthermore, a torque sensor having a disk-shaped member with a gap
between magnetically conditioned regions requires additional space,
which is not desirable in applications in which the disk has a
limited amount of flat surface available for magnetically
conditioned regions.
[0011] Because magnetic fields, in the context of their
measurement, are fungible, the sensors taught by the above and
other prior art may be susceptible to other magnetic fields of
exterior origin. In particular, the earth's magnetic field will
cause a phenomenon known as "compassing," in which the measured
field is the sum of the torque induced magnetic field and the
earth's magnetic field. Within the context of this disclosure, the
term "compassing" shall be used to describe any error resulting
from the earth's magnetic field.
[0012] Magnetic fields of external origin can emanate from both far
field and near field sources. A far field source, such as the earth
with its magnetic field, generally has the same effect on each
magnetic field sensor in a torque sensing device having multiple
magnetic field sensors. Near field sources, such as permanent
magnets, magnetized wrenches, motors, solenoids, etc., may create
magnetic fields having significant local gradients, thus having
significantly different effects on the different magnetic field
sensors in a torque sensing device having multiple magnetic field
sensors.
[0013] U.S. Pat. No. 5,520,059 to Garshelis addresses the
compassing issue with respect to far field sources. In that patent,
a shaft is described having two axially distinct magnetoelastically
active regions, polarized in opposite circumferential directions,
with magnetic field sensors having opposite axial polarities
positioned proximate to the active regions and providing output
signals in response to a torque applied to the shaft. By summing
the outputs of the magnetic field sensors, all common mode external
magnetic fields, i.e. far fields, are canceled. In applications
employing such a scheme, the oppositely polarized sensors should be
placed as close to each other as possible to preserve the
efficiency of the common mode rejection scheme. Sensors that are
spaced from one another exhibit reduced common mode rejection
efficiency, as the earth's magnetic field may be significantly
distorted around ferromagnetic parts in and around the torque
sensor.
[0014] U.S. Pat. App. Pub. No. 2009/0230953 to Lee, which is
incorporated herein by reference, describes a torque sensing device
designed to cancel near field magnetic noise from external sources
without canceling a torque-induced magnetic field. That reference
describes a torque sensor including three sets of magnetic field
sensors, axially spaced proximate to a shaft, the shaft having a
magnetoelastically active region that is polarized in a
circumferential direction. Signals received by each of the magnetic
field sensors are adjusted to compensate for the effects of near
field sources.
[0015] In torque sensing devices having ferromagnetic members with
annular magnetoelastically active regions, it is desirable for a
magnetic field sensor placed proximate to the magnetoelastically
active region to pick up a signal that accurately represents the
torque applied to the member, regardless of the angular distance
between the magnetic field sensor and a radius of the member.
Torque sensing devices that demonstrate this characteristic are
said to demonstrate improved rotational signal uniformity (RSU).
Non-uniformities in the depth, width, or magnetic field strength,
about an annular magnetoelastically active region may lead to
noticeable RSU signals and, hence, inaccurate torque measurements.
Improved RSU performance, and a decreased hysteresis effect, may
also be achieved by subjecting the ferromagnetic member to an
appropriate surface hardness process, as is known in the art, prior
to magnetization. Lee, for example describes a torque sensing
device designed to exhibit improved RSU performance by
incorporating a plurality of angularly and axially spaced magnetic
field sensors placed proximate to a circumferential surface of a
rotatable shaft.
[0016] The torque sensing devices described in the prior art are
not specially configured for measuring the torque transmitted
between a shaft and a radially separated portion of a disk-shaped
member, while demonstrating improved RSU performance and reducing
detrimental effects caused by compassing. Accordingly, there exists
a need for such a device.
SUMMARY OF THE INVENTION
[0017] The present invention, as described herein, is generally
applicable to the measurement of torque in any disk-shaped member
that is rotatable about an axis, such as a pulley, gear, sprocket,
or the like.
[0018] It is a principal object of the present invention to provide
a torque sensing device having non-contacting magnetic field
sensors positioned proximate to a disk-shaped member, for measuring
the torque transmitted between a shaft and a radially separated
portion of the disk-shaped member.
[0019] It is another object of the invention to provide a torque
sensing device having magnetic field sensors that output a signal
representative of an applied torque, wherein the output signal
varies linearly with respect to variations in the applied
torque.
[0020] It is another object of the present invention to provide a
torque sensing device having magnetic field sensors placed in
pairs, the magnetic field sensors having their sensing directions
opposite one another, to minimize the detrimental effects of
magnetic noise, including compassing.
[0021] It is another object of the present invention to provide a
torque sensing device with an annular magnetoelastically active
region, having dual, non-separated, oppositely polarized
magnetically conditioned regions to enhance the RSU performance of
the torque sensing device.
[0022] It is another object of the present invention to provide a
torque sensing device with multiple, angularly-spaced magnetic
field sensors that are specially positioned to enhance the RSU
performance of the torque sensing device.
[0023] Briefly described, those and other objects, advantages, and
features of the present invention are accomplished, as embodied and
fully described herein, by a magnetic torque sensing device, which
includes a generally disk-shaped member having opposite generally
circular surfaces and a central axis of rotation; first and second
magnetically conditioned regions disposed on the disk-shaped member
to form a magnetoelastically active region, which is both
ferromagnetic and magnetorestrictive, wherein the
magnetoelastically active region produces a magnetic field that
varies with a torque applied to the disk-shaped member, and wherein
the magnetically active region possesses sufficient magnetic
anisotropy to return the magnetization in the magnetoelastically
active region to an initial state when the torque applied to the
disk-shaped member is reduced to zero; and at least one pair of
magnetic field sensors disposed adjacent to one another and
proximate to the magnetoelastically active region, wherein
sensitive directions of the magnetic field sensors in each pair are
opposite one another and perpendicular to the direction of
polarization of the first and second magnetically conditioned
regions, wherein the magnetic field sensors provide an output
signal that is representative of the torque applied to the
disk-shaped member, and wherein variation in the output signal is
substantially linear with respect to variation in the torque
applied to the disk-shaped member.
[0024] The magnetically conditioned regions of the device may be
annularly shaped with no gap therebetween to increase the accuracy
of the torque sensing device. The device may include multiple pairs
of magnetic field sensors to increase accuracy. The magnetic field
sensors may be circumferentially oriented when magnetically
conditioned regions are axially polarized, and axially oriented
when magnetically conditioned regions are circumferentially
polarized to enhance the linear performance of the device and to
increase accuracy.
[0025] With those and other objects, advantages, and features of
the invention that may become hereinafter apparent, the nature of
the invention may be more clearly understood by reference to the
following detailed description of the invention, the appended
claims and to the several drawings attached herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a perspective view of a disk-shaped member
according to the present invention.
[0027] FIG. 2 is a side elevation view of the disk-shaped member of
FIG. 1, depicting the magnetization of a magnetoelastic active
region, according to an embodiment of the present invention.
[0028] FIG. 3 is a top plan view of the disk-shaped member of FIG.
2, depicting the magnetization of a magnetoelastic active region,
according to an embodiment of the present invention.
[0029] FIG. 4A is a graph illustrating the strengths of the
magnetic fields in the magnetically conditioned regions when the
torque sensing device of the present invention is in a quiescent
state.
[0030] FIG. 4B is a top plan view of a disk-shaped member according
to the present invention, illustrating the relationship between the
disk-shaped member and the graph of FIG. 4A.
[0031] FIG. 5 is a top plan view of a disk-shaped member, showing
illustrative positionings of magnetic field sensors, according to
another embodiment of the present invention.
[0032] FIG. 6 is a top plan view of a disk-shaped member, showing
illustrative positionings of magnetic field sensors, according to
another embodiment of the present invention.
[0033] FIG. 7 is a top plan view of a disk-shaped member, showing
illustrative positionings of magnetic field sensors, according to
another embodiment of the present invention.
[0034] FIG. 8 is a top plan view of a disk-shaped member, showing
illustrative positionings of magnetic field sensors, according to
another embodiment of the present invention.
[0035] FIG. 9 is a top plan view of a disk-shaped member, showing
illustrative positionings of magnetic field sensors, according to
another embodiment of the present invention.
[0036] FIG. 10 is a perspective view of a disk-shaped member
according to the present invention illustrating a change in the
magnetization of the magnetoelastically active region when the
disk-shaped member is subjected to torque.
[0037] FIG. 11 is an exploded view showing an exemplary torque
sensing device according to the present invention for use in an
automotive drive train.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] Several preferred embodiments of the invention are described
for illustrative purposes, it being understood that the invention
may be embodied in other forms not specifically shown in the
drawings. The figures herein are provided for exemplary purposes
and are not drawn to scale.
[0039] Turning first to FIG. 1, shown therein is a perspective
drawing of a generally disk-shaped member 110 in accordance with
the torque sensing device of the present invention. The disk 110 is
formed of ferromagnetic material and is, or at least includes, a
magnetoelastically active region 140. The material selected for
forming the disk 110 must be at least ferromagnetic to ensure the
existence of magnetic domains for at least forming a remnant
magnetization in the magnetoelastically active region 140, and must
be magnetostrictive such that the orientation of magnetic field
lines in the magnetoelastically active region 140 may be altered by
the stresses associated with applied torque. The disk 110 may be
completely solid, or may be partially hollow. The disk 110 may be
formed of a homogeneous material or may be formed of a mixture of
materials. The disk 110 may be of any thickness, and is preferably
between about 3 mm and about 1 cm thick.
[0040] The magnetoelastically active region 140 is preferably flat,
and comprises at least two radially distinct, annular, oppositely
polarized magnetically conditioned regions 142, 144, defining the
magnetoelastically active region 140 of the torque sensing device.
The top and bottom surfaces 112, 114 do not have to be flat,
however, as shown, but could have variable thickness in
cross-section from the center of the disk 110 to the outer edge.
Depending on the application for which the torque sensing device is
desired, it may be impractical to position magnetic field sensors
152, 154 on both sides of the disk 110. Therefore, the present
invention is designed to function in instances where the
magnetoelastically active region 140 is present on only one surface
of the disk 110. However, the magnetoelastically active region 140
may be present on both sides of the disk 110.
[0041] FIG. 2 shows a side view of the disk 110, and illustrates a
process by which the magnetoelastically active region 140 may be
formed on an annular portion of the disk 110. As shown, two
permanent magnets 202, 204, having opposite directions of
magnetization (and thus opposite polarity), are positioned
proximate to the surface of the disk 110 at a distance dl.
Following the positioning of the permanent magnets 202, 204, the
disk 110 may be rotated about its central axis O, resulting in the
formation of two annular, oppositely polarized, magnetically
conditioned regions 142, 144. Alternatively, the magnetically
conditioned regions 142, 144 may be formed by rotating the
permanent magnets about the central axis O, while the disk 110
remains stationary. During creation of the magnetoelastically
active region 140, the speed of rotation about the central axis O,
and the distance dl between the permanent magnets 202, 204 and the
surface of the disk 110, should be kept constant to ensure
uniformity of the magnetoelastically active region 140 and improve
the RSU performance of the torque sensing device. Preferably,
during the creation of the magnetoelastically active region 140,
the permanent magnets 202, 204 are positioned adjacent to one
another, with no gap therebetween, to form magnetically conditioned
regions 142, 144 with no gap therebetween. The absence of a gap
between the magnetically conditioned regions 142, 144 is understood
to result in a torque sensing device with improved RSU
performance.
[0042] In forming the magnetoelastically active region 140, the
strength of the permanent magnets 202, 204, and the distance dl
between the permanent magnets 202, 204 and the disk 110, must be
carefully selected to optimize performance of the torque sensing
device. By using stronger permanent magnets 202, 204, and by
positioning permanent magnets 202, 204 closer to the disk 110, one
can generally produce a magnetoelastically active region 140 that
will provide a stronger, more easily measurable signal, when
employed by a torque sensing device. However, by using permanent
magnets 202, 204 that are excessively strong, or by placing
permanent magnets 202, 204 excessively close to the disk 110, one
can produce a magnetoelastically active region 140 that exhibits
hysteresis, which negatively affects the linearity of the signal
produced by the torque sensing device in response to an applied
torque. Preferably, the magnetoelastically conditioned region 140
is created using rectangular N42 or N45 grade neodymium iron boron
(NdFeB) magnets placed at a distance of between about 0.1 mm and 5
mm from the surface of the disk 110. More preferably, magnets are
placed at a distance of about 3 mm from the surface of the disk
110. Preferably, the width of the magnetoelastically active region
140 is not greater than 13 mm More preferably, the width of the
magnetoelastically active region 140 is about 10 mm.
[0043] FIG. 2 shows an embodiment having permanent magnets 202, 204
with directions of magnetization that are perpendicular to the
plane of the disk 110. This configuration results in magnetically
conditioned regions 142, 144 that are initially polarized in the
axial direction (i.e., perpendicular to the disk surface). In this
configuration, the magnetically conditioned regions 142, 144 are
preferably polarized such that, in the absence of torque applied to
the disk 110 (i.e., when the torque sensing device is in the
quiescent state), the magnetically conditioned regions 142, 144
have no net magnetization components in the circumferential or
radial directions.
[0044] During formation of the magnetoelastically active region
140, the permanent magnets 202, 204 may be positioned, as shown in
FIG. 2, such that the innermost magnetically conditioned region 142
is created with its magnetic north pole directed upward, and the
outermost magnetically conditioned region 144 is created with its
magnetic north pole directed downward. Alternatively, during
formation of the magnetoelastically active region 140, the
permanent magnets may be positioned such that the innermost
magnetically conditioned region 142 is created with its magnetic
north pole directed downward, and the outermost magnetically
conditioned region 144 is created with its magnetic north pole
directed upward.
[0045] FIG. 3 shows a top view of the disk 110, and illustrates an
embodiment in which the magnetoelastically active region 140 is
created with permanent magnets 302, 304 having directions of
magnetization that are parallel to the plane of the disk 110, in
the circumferential direction. This configuration results in
magnetically conditioned regions 142, 144 that are initially
polarized in the circumferential direction of the disk 110. In this
configuration, the magnetically conditioned regions 142, 144 are
preferably polarized such that, in the absence of torque applied to
the disk 110, the magnetically conditioned regions 142, 144 have no
net magnetization components in the axial or radial directions.
[0046] During formation of the magnetoelastically active region
140, the permanent magnets 302, 304 may be positioned, as shown in
FIG. 3, such that the innermost magnetically conditioned region 142
is created with its magnetic north pole having a clockwise
orientation, and the outermost magnetically conditioned region 144
is created with its magnetic north pole having a counter-clockwise
orientation. Alternatively, during formation of the
magnetoelastically active region, the permanent magnets 302, 304
may be positioned such that the innermost magnetically conditioned
region 142 is created with its magnetic north pole having a
counter-clockwise orientation, and the outermost magnetically
conditioned region 144 is created with its magnetic north pole
having a clockwise orientation.
[0047] Turning to FIGS. 4A and 4B, FIG. 4A is a graph illustrating
the strength of the magnetic fields in the magnetically conditioned
regions 142, 144 when the torque sensing device is in the quiescent
state. Values along the vertical axis represent the magnetic field
strength of the magnetoelastically active region 140. The magnetic
fields emanating from the surface of the disk 110 may have their
principle components in the axial direction, as with the disk 110
of FIG. 2, or in the circumferential direction, as with the disk
110 of FIG. 3. Values along the horizontal axis represent distance
along a radius of the disk 110 from the center line O to the outer
edge of the disk 110. Point A corresponds to a point along the edge
of the innermost magnetically conditioned region 142 nearest the
center of the disk 110. Point B corresponds to a point along the
edge of the outermost magnetically conditioned region 144 nearest
the circumferential edge of the disk 110. Point C corresponds to a
point along the boundary between the innermost and outermost
magnetically conditioned regions 142, 144. Point r1 corresponds to
a point within the innermost magnetically conditioned region 142,
at which the magnetic field strength is at a maximum. Point r2
corresponds to a point within the outermost magnetically
conditioned region 144, at which the magnetic field strength is at
a maximum. FIG. 4B shows the disk 110 with points A, B, C, r1, and
r2 corresponding to those points shown in the graph of FIG. 4A.
Points r1 and r2, corresponding to the peak magnetic fields,
indicate the distances from the center of the disk 110 at which
magnetic field sensors 152, 154 should be placed to optimize the
direction of the external magnetic flux, and hence maximize the
performance of the torque sensing device. The units provided in
FIG. 4 are for exemplary purposes and are not limiting on the
present invention.
[0048] Turning to FIG. 5, shown therein is a top plan view of the
disk 110 in the quiescent state, with a magnetoelastically active
region 140 created by permanent magnets 202, 204 as shown in FIG.
2. The magnetoelastically active region 140 includes dual
magnetically conditioned regions 142, 144 that are oppositely
polarized in positive and negative axial directions, respectively.
The dots in FIG. 5 indicate magnetic field lines 546 oriented
perpendicular to the surface of the disk 110, such that the
magnetic field lines 546 are directed out of the page. The X's in
FIG. 5 indicate magnetic field lines 548 oriented perpendicular to
the surface of the disk 110, such that the magnetic field lines 548
are directed into the page.
[0049] A pair of magnetic field sensors 552, 554 is positioned
proximate to the magnetoelastically active region 140, such that
each magnetic field sensor 552, 554 is placed over the portion of
the magnetically conditioned region 142, 144 at a location where
the magnetic field strength is at a maximum. The magnetic field
sensors 552, 554 are oriented such that their sensitive directions
are perpendicular to the direction of magnetization in the
magnetoelastically active region 140. In FIG. 5, arrows indicate
the sensitive directions of the magnetic field sensors 552, 554.
Magnetic field sensors 552, 554 are oriented with their sensitive
directions parallel to the surface of the disk 110 (i.e., in the
circumferential direction), and the magnetically conditioned
regions 142, 144 are polarized perpendicular to the surface of the
disk 110 (i.e., in the axial direction). This configuration ensures
that the representative signals outputted by the magnetic field
sensors 552, 554 vary linearly with respect to variations in the
torque applied to the disk 110.
[0050] Magnetic field sensors 552, 554 are oppositely polarized and
provided in pairs. This placement technique may be referred to as a
common mode rejection configuration. Output signals from each of
the magnetic field sensors 552, 554 in the pair may be summed to
provide a signal representative of the torque applied to the disk
110. External magnetic fields have equal effects on each of the
magnetic field sensors 552, 554 in the pair. Because the magnetic
field sensors 552, 554 in the pair are oppositely polarized, the
summed output of the magnetic field sensors 552, 554 is zero with
respect to external magnetic fields. However, because the
magnetically conditioned regions 142, 144 are oppositely polarized,
as are the magnetic field sensors 552, 554, the summed output of
the magnetic field sensors 552, 554 is double that of each
individual magnetic field sensor 552, 554 with respect to the
torque applied to the disk 110. Therefore, placing magnetic field
sensors 552, 554 in a common mode rejection configuration greatly
reduces the detrimental effects of compassing in the torque sensing
device.
[0051] Turning to the embodiment shown in FIG. 6, the disk 110 is
shown in the quiescent state, and has a magnetoelastically active
region 140 created by permanent magnets 302, 304 as shown in FIG.
3. The magnetoelastically active region 140 includes dual
magnetically conditioned regions 142, 144 that are oppositely
polarized, with magnetic field lines 646, 648, in opposite
circumferential directions. A pair of magnetic field sensors 652,
654 may be positioned proximate to the magnetoelastically active
region 140, such that each magnetic field sensor 652, 656 is placed
over the portion of a magnetically conditioned region 142, 144 at a
location where the magnetic field strength is at a maximum. The
magnetic field sensors 652, 654 are oriented such that their
sensitive directions are perpendicular to the direction of
magnetization in the magnetoelastically active region 140. In FIG.
6, a dot (indicating a direction out of the page) and an X
(indicating a direction into the page) indicate the sensitive
directions of the magnetic field sensors 652, 654. Magnetic field
sensors 652, 654 are oriented with their sensitive directions
perpendicular to the surface of the disk 110 (i.e., in the axial
direction), and magnetically conditioned regions 142, 144 are
polarized parallel to the surface of the disk 110 (i.e., in the
circumferential direction) to ensure that the representative
signals outputted by the magnetic field sensors 652, 654 vary
linearly with respect to variations in the torque applied to the
disk 110. Magnetic field sensors 652, 654 are placed in a common
mode rejection configuration to reduce the effects of compassing in
the torque sensing device.
[0052] Turning to FIG. 7, shown therein is the disk 110 having a
magnetoelastically active region 140 with dual magnetically
conditioned regions 142, 144, which are polarized in opposite axial
directions. Four pairs of magnetic field sensors 552, 554 are
positioned proximate to the magnetoelastically active region 140
with their sensitive directions perpendicular to the magnetization
of the magnetically conditioned regions 142, 144. The four pairs of
magnetic field sensors 552, 554 are evenly spaced about the
magnetoelastically active region 140 with approximately 90 degrees
between each pair. This configuration provides for improved RSU
performance because it allows for representative signals outputted
by the multiple magnetic field sensors 552, 554 to be averaged,
thereby resulting in a more accurate measurement of the torque
applied to the disk 110. Any inaccuracies attributable to a single
magnetic field sensor pair due to non-uniformities in the
magnetoelastically active region 140 are of reduced significance
when the representative signals from multiple magnetic field
sensors 552, 554 are averaged. In torque sensing devices having
magnetoelastically active regions 140 that exhibit a high degree of
uniformity (i.e., RSU signal is substantially zero), as few as one
pair of magnetic field sensors 552, 554 may be used to achieve
sufficient RSU performance. However, due to limitations in material
preparation and magnetization processes, a significant non-zero RSU
signal may be difficult to avoid. In instances in which increased
RSU performance is desired, the number of magnetic field sensor
pairs may be increased. For example, eight pairs of magnetic field
sensors 552, 554, spaced at 45 degrees, may be used.
[0053] Turning to FIG. 8, shown therein is the disk 110 having a
magnetoelastically active region 140 with magnetically conditioned
regions 142, 144 polarized in a single axial direction to form,
essentially, a single magnetically conditioned region. A magnetic
field sensor unit 850 includes four individual magnetic field
sensors 852, 854, 856, 858. Primary magnetic field sensors 852, 854
are positioned proximate to the magnetoelastically active region
140, are aligned in the radial direction, and are similarly
polarized in a direction perpendicular to the magnetization of the
magnetoelastically active region 140. Secondary magnetic field
sensors 856, 858 are positioned on opposite sides of the primary
magnetic field sensors 852, 854, proximate to the disk 110, but
apart from the magnetoelastically active region 140, such that the
secondary magnetic field sensors 856, 858 do not pick up torque
induced signals. The secondary magnetic field sensors 856, 858 are
similarly polarized in a direction opposite that of the primary
magnetic field sensors 852, 854. This configuration may be
advantageous in instances in which a noise source (not shown)
creates a local magnetic field gradient having different effects on
each of the primary magnetic field sensors 852, 854, as discussed
in U.S. Pat. App. Pub. No. 2009/0230953 to Lee, which is
incorporated herein by reference. In such an instance, it may be
assumed that the noise source has the greatest effect on the
secondary magnetic field sensor 856, 858 closest to the noise
source, and the least effect on the secondary magnetic field sensor
858, 856 farthest from the noise source. It may also be assumed
that the effect of the noise source on the primary magnetic field
sensors 852, 854 is between that of its effects on each of the
secondary magnetic field sensors 856, 858. Finally, it may be
assumed that the sum of the noise induced signals picked up by the
secondary magnetic field sensors 856, 858 is equal in value to the
sum of the noise induced signals picked up by the primary magnetic
field sensors 852, 854. Therefore, by summing the signals picked up
by each of the four magnetic field sensors 852, 854, 856, 858, the
effect of magnetic noise on the magnetic field sensor unit 850 is
canceled, and the composite signal picked up by the magnetic field
sensor unit 850 is entirely torque induced.
[0054] FIG. 9 shows a configuration of the disk 110 that may be
advantageous in situations in which the radial space on the disk
110 is limited. The disk 110 has a magnetoelastically active region
140 with a single magnetically conditioned region 143 polarized in
a single axial direction. A magnetic field sensor unit 950 includes
four individual magnetic field sensors 952, 954, 956, 958. Primary
magnetic field sensors 952, 954 are positioned proximate to the
magnetoelastically active region 140, are aligned in the
circumferential direction, and are similarly polarized in a
direction perpendicular to the magnetization of the
magnetoelastically active region 140. Secondary magnetic field
sensors 956, 958 are positioned on opposite sides of the primary
magnetic field sensors 952, 954, proximate to the disk 110, but
apart from the magnetoelastically active region 140, such that the
secondary magnetic field sensors 956, 958 do not pick up torque
induced signals. The secondary magnetic field sensors 956, 958 are
similarly polarized in a direction opposite that of the primary
magnetic field sensors 952, 954. This configuration may be
advantageous in instances in which a noise source (not shown)
creates a local magnetic field gradient having different effects on
each of the primary magnetic field sensors 952, 954, as discussed
in U.S. Pat. App. Pub. No. 2009/0230953 to Lee, which is
incorporated herein by reference. In such an instance, it may be
assumed that the noise source has the greatest effect on the
secondary magnetic field sensor 956, 958 closest to the noise
source, and the least effect on the secondary magnetic field sensor
958, 956 farthest from the noise source. It may also be assumed
that the effect of the noise source on the primary magnetic field
sensors 952, 954 is between that of its effects on each of the
secondary magnetic field sensors 956, 958. Finally, it may be
assumed that the sum of the noise induced signals picked up by the
secondary magnetic field sensors 956, 958 is equal in value to the
sum of the noise induced signals picked up by the primary magnetic
field sensors 952, 954. Therefore, by summing the signals picked up
by each of the four magnetic field sensors 952, 954, 956, 958, the
effect of magnetic noise on the magnetic field sensor unit 950 is
canceled, and the composite signal picked up by the magnetic field
sensor unit 950 is entirely torque induced.
[0055] FIG. 10 provides an illustration of the principle by which
torque applied to the disk 110 is measured by the torque sensing
device. As discussed above, in the quiescent state, the magnetic
fields in the magnetoelastically active region 140 are aligned
either substantially exclusively in the axial direction, as shown
in FIG. 5, or substantially exclusively in the circumferential
direction, as shown in FIG. 6. When torque is applied to the disk
110, magnetic moments in the magnetoelastically active region 140
tend to tilt along the shear stress direction, which forms an angle
of about 45 degrees with respect to the surface of the disk 110, as
indicated by arrows A in FIG. 10. This tilt causes the
magnetization of the magnetoelastically active region 140 to
exhibit a decreased component in the initial direction, and an
increased component in the shear stress direction. The degree of
tilt is proportional to the strength of the torque applied to the
disk 110. The magnetic field sensors 152, 154 are capable of
sensing changes in the strength of magnetic field components along
the sensitive directions of the magnetic field sensors 152, 154.
Therefore, when torque is applied to the disk 110, magnetic field
sensors 152, 154 output representative signals that are
proportional to the applied torque.
[0056] Magnetic field sensors 152, 154 are known in the art and
include magnetic field vector sensor devices such as flux-gate
inductors, Hall Effect sensors, and the like. Preferably, the
magnetic field sensors according to the present invention are
flux-gate inductors having a solenoidal form. In another
embodiment, the magnetic field sensors 152, 154 may be integrated
circuit Hall Effect sensors. Conductors 156, as shown in FIG. 10,
connect the magnetic field sensors to a source of direct current
power, and transmit the signal output of the magnetic field sensors
152, 154 to a receiving device (not shown), such as a control or
monitoring circuit.
[0057] Turning to FIG. 11, shown therein is a perspective, exploded
view drawing of a torque transducer 1100 in accordance with the
present invention. In the exemplary embodiment shown, the torque
transducer 1100 includes a disk 1110, a hub 1120, and a shaft 1130.
The disk 1110, the hub 1120, and the shaft 1130 may be, but are not
necessarily, distinct elements. The disk 1110 may be an axially
thin, generally disk-shaped member, which may be completely flat or
may include contours. The hub 1120 functions by rigidly attaching
the disk 1110 to the shaft 1130. Attachment may be accomplished,
for example, directly or indirectly by any known means which
permits the hub 1120 and the shaft 1130 to act as a mechanical unit
such that torque applied to the shaft 1130 is proportionally
transmitted to the hub 1120 and vice versa. Examples of means of
attachment include pins, splines, keys, welds, adhesives, press or
shrink fits, and the like. The disk 1110 may be attached to the hub
1120 by any appropriate method which permits the disk 1110 and the
hub 1120 to act as a mechanical unit such that torque applied to
the hub 1120 is proportionally transmitted to the disk 1110, and
vice versa. Preferably, holes 1112, 1122 are provided in the disk
1110 and the hub 1120 such that holes 1112 in the disk 1110
correspond to holes 1122 in the hub 1120. Fasteners (not shown),
such as bolts, may be inserted through holes 1112 in the disk 1110
and corresponding holes 1122 in the hub 1120 such that a firm
attachment is formed between the disk 1110 and the hub 1120.
Examples of alternative means of attachment include riveting,
welding, and the like.
[0058] The disk 1110 may be attached to a rim 1160, such that a
portion of the disk 1110 attached to the rim 1160 is radially
distinct from a portion of the disk 1110 attached to the hub 1120.
The rim 1160 may surround the periphery of the disk 1110, or may be
attached to a surface of the disk 1110. The rim 1160 may be an
integral part of the disk 1110. The disk 1110 and the rim 1160 act
as a mechanical unit such that torque applied to the disk 1110 may
be proportionally transmitted to the rim 1160, and vice versa. The
rim 1160 may include force transfer features 1162 for the transfer
of predominately tangential forces to a driving or driven
member.
[0059] An exemplary embodiment of the invention is a torque sensing
device for use in connection with an automobile engine wherein the
disk 1110 includes a drive plate, the shaft 1130 includes a
crankshaft, and the rim 1160 includes a torque converter. It will
be apparent to those skilled in the art to which the invention
pertains, however, that the invention is not limited to any
specific type of automobile configuration, nor is the invention
limited to automotive applications in general.
[0060] The rim 1160 and the hub 1120 are preferably formed of
non-ferromagnetic materials or are magnetically isolated from the
disk 1110 by non-ferromagnetic spacers, such as low permeability
rings (not shown) inserted between the hub 1120 and the disk 1110,
and between the disk 1110 and the rim 1160.
[0061] The magnetoelastically active region 1140 must possess
sufficient anisotropy to return the magnetization to the quiescent,
or initial direction when the applied torque is reduced to zero.
Magnetic anisotropy may be induced by physical working of the
material of the disk 1110 or by other methods. Illustrative methods
for inducing magnetic anisotropy are disclosed in U.S. Pat. No.
5,520,059, incorporated herein by reference.
[0062] Preferably, the disk 1110 is formed from AISI 9310 material.
Examples of alternative materials from which the disk may be formed
are described in U.S. Pat. No. 5,520,059 and U.S. Pat. No.
6,513,395, incorporated herein by reference. The disk 1110 may be
formed of a material having a particularly desirable crystalline
structure.
[0063] In another embodiment of the present invention, the
magnetoelastically active region 1140 may be formed separately from
the disk 1110, and then applied to the disk 1110 by means such as
adhesives, welds, fasteners, or the like, such that torque induced
in the disk 1110 is transmitted to and proportional to torque
induced in the magnetoelastically active region 1140.
[0064] In the operation of the present invention, magnetic fields
arise from the magnetoelastically active region 1140 and these
fields pervade not only the space in which the magnetic field
sensors 1152, 1154 are located but also the space occupied by the
disk 1110 itself. Magnetization changes that take place within
non-active portions of the disk 1110 may result in the formation of
parasitic magnetic fields that may pervade the regions of space
where the magnetic field sensors 1152, 1154 are located. The hub
1120 and the rim 1160 can be formed of non-ferromagnetic materials
to reduce or eliminate parasitic magnetic fields. Thus, in the
interest of not corrupting the transfer function of the
magnetoelastically active region 1140, it is important that the
parasitic fields be very small, ideally zero, in comparison with
the magnetic field arising from the magnetoelastically active
region or, if of significant intensity, that they change linearly
and anhysteretically (or not at all) with applied torque, and that
they be stable with time and under any of the operational and
environmental conditions that the shaft 1130, the disk 1110, and
the magnetoelastically active region 1140 might be subjected to.
Stated otherwise, any parasitic fields which arise must be
sufficiently small compared to the magnetoelastically active region
field such that the net field seen by the magnetic field sensors
1152, 1154 is useful for torque sensing purposes. Thus, in order to
minimize the corrupting influence of parasitic fields, it is
important to utilize a disk material having a coercivity
sufficiently high that the field arising from the
magnetoelastically active region 1140 does not magnetize regions of
the disk 1110 proximate to the magnetoelastically active region
1140 to give rise to such parasitic magnetic fields which are of
sufficient strength to destroy the usefulness, for torque sensing
purposes, of the net magnetic field seen by the magnetic field
sensors 1152, 1154. This may be accomplished, for example, by using
a material in which the coercivity of the disk 1110 is greater than
15 Oe, preferably greater than 20 Oe, and most desirably greater
than 35 Oe.
[0065] In addition to torque, the present invention is capable of
measuring power, energy, or rotational speed, wherein
Power=Torque.times.2.pi..times.Rotational Speed,
and
Energy=Power/Time.
[0066] Although certain presently preferred embodiments of the
disclosed invention have been specifically described herein, it
will be apparent to those skilled in the art to which the invention
pertains that variations and modifications of the various
embodiments shown and described herein may be made without
departing from the spirit and scope of the invention. Accordingly,
it is intended that the invention be limited only to the extent
required by the appended claims and the applicable rules of
law.
* * * * *