Note: Descriptions are shown in the official language in which they were submitted.
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INTRODUCTI ON
~ he present invention relates generally to
transducers having input and output members which
measure applied forces therebetween and, more
particularly, to torque-responsive devices for
controlling the power steering of a vehicle.
BACKG~OUND OF THE INVENTION
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Automotive vehicles commonly are provided
with power-assist systems to facilitate the steering
of the vehicle. Typically, servo motors or other
operator input sensitive devices are coupled with the
steering linkage or the steerable wheels of the
vehicle and are operated in response to rotation of
the steering wheel shaft.
Electrical power-assist steering units are
often employed in vehicles having motors as prime
movers such as electric lift trucks, electric
passenger vehicles and the like. Such units employ a
transducer for monitoring the operator applied torque
in the steering shaft and generating an output signal
in response thereto. Such a device is disclosed in
U.S. Patent 4,173,265 to Kremer which describes a
device for measuring the torque in a shaft. The
Kremer device employs two rotatable parts of a shaft
which are coupled together through an elastic body
for the transmission of torque therebetween. A
permanent magnet is carried on one of the rotatable
parts in rotational alignment with a differential
field plate sensor responsive to the position of the
magnet for generating an analog output signal
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representing torque e~erted between the parts of the
shaft. In the unloaded condition, the magnet lies
opposite the center of the differential field plate
sensor.
Devices of the type disclosed by Kremer,
although having enjoyed some commercial success,
suffer from several shortcomings. Typically such
transducers are relatively mechanically complex,
requiring frequent servicing and having a short
useful life. Expense is a corollary to such
mechanical complexity. Specifically, certain
components such as Hall effect sensors and permanent
magnets have become unduly costly in recent years and
thus are not well-suited to high-volume, low-cost
applications.
Another shortcoming common in some prior
art devices resides in the fact that electrical
sensory elements are disposed on rotating shafts or
other components requiring the use of slip rings,
wrapped wire umbilicals or the like, which tend to
quickly corrode, become intermittent and deteriorate
the performance of the transducer. Additionally,
many prior art devices exhibit poor sensitivity
through an entire range of operation and are
therefore limited in accuracy, repeatability, and the
ability to provide the vehicle operator with any kind
of "feel" for the vehicle.
It will be apparent from a reading of the
Specification that the present invention may be
advantageously utilized in many different
applications, both mobile and fixed, requiring the
precise monitoring of applied forces in general and
torques in particular. However, the invention is
especially useful when applied to an electric power
steering system for an electric vehicle and will be
described in connection therewith.
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BRI~F DESCRIPTION OF THE INVENTION
The present invention overcomes many of the
above described shortcomings of the prior art by
providing a transducer which monitors mechanical
forces and generates a signal representative
thereof. The present invention includes a transducer
having two members mounted for relative displacement,
a coil or inductor energized to estab'ish an
electrical field and a field shunt which engages the
members for selective positioning within the field as
a function of their relative displacement to effect
generation of the member condition signal. This
arrangement has the advantage of providing a
mechanical force transducer constructed of simple,
inexpensive parts and whose performance is not prone
to rapid deterioration over time and use.
According to a preferred embodiment of the
invention, a torque transducer is described including
concentric input and output shafts mounted for
relative rotational displacement and which generates
a signal representative of torque applied to the
input shaft in response to relative rotational
displacement of the shafts. This arrangement
provides the advantage of a torque transducer which
can be inserted in line with a vehicle steering
system or the like.
According to another aspect of tlle present
invention, a frame or housing is provided to retain
the shafts in an axially fixed relationship as well
as to hold the inductor(s) while permitting the
shafts to ~ointly continuously rotate. This
arrangement has the advantage of positioning all
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electrical components in a fixed relationship with
the frame, thereby eliminating the need for slip
rings, umbilical connections and the like.
Accorcling to another aspect of the
invention, two magnetically isolated inductors are
provided which are energized to establish two
distinct electromagnetic fields. An electromagnetic
Lield shunt assembly is provided within each field,
each shunt assembly engaging the shafts for
selective, complementary positioning within the
electromagnetic fields in response to relative
rotational displacement of the shafts. This
arrangement, by virtue of the differential action
which eliminates common mode drift and other
undesirable effects in the transducer and electronic
circuitry, has the advantage of providing a usable
repeatable, stable output signal through ~he full
range of operation of the torque transducer.
According to still another aspect of the
invention, in one embodiment the shunt assemblies
comprise first and second pairs of adjoining rotary
vanes, each disposed within one of the
electromagnetic fields and operable to selectively
shunt substantially all of its associated
electromagnetic field. In another embodiment, the
shunt assemblies comprise a generally cylindrical
carrier disposed concentrically with one of the
shafts which simultaneously complementarily shunts
the electromagnetic fields by selectively axially
shuttling between two fixed limits of travel. This
arrangement provides two species of the present
invention, each of which have particular advantages,
depending upon the specific application comtemplated.
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These and other aspects and advantages of
this invention will become apparent upon reading the
following Specification, which, along with the patent
drawings, describes and discloses a preferred and an
alternative embodiment of the invention in detail.
A ~-~etailed description of the Embodiments
of the Invention makes reference to the accompanying
drawings.
BRIEF D~SCRIPTION OF THE DRA~ GS
FIGURE 1, is a cross-sectional view of the
preferred embodiment of the inventive torque
transducer;
FIGURE 2, is a cross-sectional view taken
on line 2-2 of FIGURE l;
FIGURE 3, is a cross-sectional view taken
on line 3-3 of FIGURE l;
FIGURE 4, is a cross-sectional view taken
on line 4-4 of FIGURE l;
FIGURE 5, is a cross-sectional view taken
on line 5-5 of FIGURE 1,
FIGURE 6, is a broken perspective view of
one of the inductor and field shunting assemblies of
the torque transducer of FIGURE l;
FIGURE 7, is a side cross-sectional view,
~5 partly in relief, of the torque transducer of
FIGURE l;
FIGURE 8, is a schematic diagram of a logic
circuit employed with the torque transducer of
FIGURE l;
FIGURE 9, is a graphical illustration of
the applied torque versus relative rotation
(mechanical degrees) characteristic of the torque
transducer of FIGURE l;
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FIGURE 10, is a graphical presentation of
the phase shift (electrical degrees) versus relative
rotation characteristic of the torque transducer of
FIGURE 1, and
FIGURE 11, is a cross-sectional view
(partly in broken relief~ of an alternative
embodiment of the invention.
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DETAILED DESCRIPTION OF lHE PREFERRED AN~ ALTERNATIVE
EMBODIMENTS OF T~E INVENTION
Referring to FIGURES 1 through 5, a
preferred embodiment of a torque transducer assembly
(hereinafter referred to as torque sensor) is
illustrated. Torque sensor 10 is intended for use as
an electric torque sensor for a vehicle electric
power steering system. Sensor 10 is adapted for
in-line insertion with a vehicle's steering linkage
to sense torque applied at the steering wheel by an
operator and to generate a system controlling torque
demand signal to provide a power steering assist in
lift truck type vehicles (by way of example).
Torque sensor 10 comprises an input shaft
or member 12, an output shaft or member 14 and a
frame or housing assembly shown generally at 16.
Output shaft 14 is loosely telescopingly disposed
within a rightwardly (as viewed in FIGURE 1) opening
bore 18 within input shaft 12. This arrangement
maintains concentricity of shafts 12 and 14 while
permitting relative rotation therebetween. Frame
assembly 16 comprises an input shaft mounting
block 20 mounted to a frame member 22 by bolts 24 or
the like and an output shaft mounting block 26
mounted to frame member 22 through an intermediate
spacing block 28 by additional bolts 25 or the like
Thus, frame assembly 16 forms a single rigid
structure which, in application, would be affixed to
the vehicle with which torque sensor 10 is associated.
Input shaft 12 passes through an
aperture 30 within input shaft mounting block 20 and
is supported radially by an intermediate sleeve
bearing 32 press fit within aperture 30. A first
thrust washer 34 is carried by input shaft 12 and
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abuts the left-hand most surface of input shaft
~ounting block 20. Washer 34 is held in place by a
snap ring 36 residing in a circumferential slot 38
formed in input shaft 12. Likewise, a second thrust
washer 40 is carried by input shaft 12 and abuts the
right-hand most surface of mounting block 20. A
second snap ring 42 disposed within a circumferential
slot 44 prevents washer 40 from righward axial
displacement. Snap rings 36 and 42 coact to hold the
assembly of washers 34 and 40 and sleeve bearing 32
in the illustrated position whereby input shaft 12 is
radially and axially supported by frame assembly 16
but allowed to freely rotate therein.
Input shaft 12 extends leftwardly from
mounting block 20 and terminates in a threaded
portion 45 which is intended, in application, to
receive a steering wheel or other suitable input
linkage whereby shaft 12 receives operator applied
torque in the process of steering the associated
vehicle.
Output shaft 14 extends rightwardly from
its point of emergence from bore 18 within input
shaft 12, passing through an aperture 46 within
output shaft mounting block 26. Output shaft 14
loosely fits within aperture 46 and is thus free to
rotate therein but is prevented from radial
displacement thereby. It is contemplated that a
bearing could be provided to support output shaft 14
as in the case of input shaft 12. Output shaft 14
extends rightwardly from output shaft mounting block
26 and, in application, is mechanically linked to a
load such as the steered wheels of the associated
vehicle through interconnecting linkage 48. Linkage
48 is secured for rotation to output shaft 14 by an
-35 anchor pin or dowel 50 which passes through
registering radially directed bores therein.
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As can best be seen in FIGURE 3, input and
output shafts 12 and 14 are linked to provide limited
relative rotation by a dowel 52 press fit within a
radial bore 54 within output shaft 14. Dowel 52
extends radially outwardly in both directions through
registering apertures 56 within input shaft 12.
Apertures 56 are circumferentially elongated to
permit limited relative rotation of + 22.5 from a
nominal centered position (illustrated). Thus, when
torque is applied to input shaft 12, it will freel~
rotate without affecting output shaft 14 through the
first 22.5 of rotation in either direction. At +
22.5 of relative rotation, the radially outward most
ends of dowel 52 will contact input shaft 12 and thus
applied tor~ue will be transmitted to output shaft
14. Thereafter, shafts 12 and 14 are permitted to
jointly continuously rotate. Dowel 52 serves an
additional function of preventing relative axial
displacement between input and output shafts 12 and
14.
Dowel pin 52 extends radially outwardly of
the outer surface of input shaft 12 for reasons that
will become apparent herein below. Additionally, a
second dowel pin 52' passing through a bore 54'
within output shaft 14 and circumferentially
elongated registering apertures 56' within input
shaft 12 is provided (refer FIGURE 1) at a point
axially displaced from pin 52, which functions as
described in connection wi~h the description of pin
52 hereinabove and in concert therwith. The need for
pin 52' will become apparent in the description
herein below.
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Input shaft 12 has a radially outwardly
extending annular flange 58 affixed at the right-hand
most (as viewed in FIGURE 1) extent thereof. An
anchor pin 60 is press fit within an aperture 62 in
~lange 58 and extends rightwardly therefrom.
A second radially outwardly extending
annular flange 64 is carried by output shaft 14 at a
point rightwardly spaced from flange 58. Flange 64
includes an integral hub portion 66. A press fit
dowel pin 68 (as is best viewed in FIGURE 5) passes
through registering apertures 67 and 65 in output
shaft 14 and hub portion 66, respectively, to secure
flan~e 64 to output shaft 14 for rotation therewith.
A second anchor pin 70 is press fit within an
aperture 72 at the radially outward most extent of
flange 64 which extends leftwardly therefrom. As is
best illustrated in FIGURE 2, anchor pin 70 is
located radially outwardly of anchor pin 60 to
provide rotational clearance therebetween. Anchor
pins 60 and 70 are positioned in flanges 58 and 64,
respectively, so as to be in angular alignment when
input and output shafts 12 and 14 are in their
nominal centered position. A coil spring 74 is
loosely carried on output shaft 14 intermediate
~5 flanges 58 and 64. The ends 74a of coil springs 74
are directed radially outwardly and extend beyond
anchor pin 70 in a generally parallel spaced
fashion. Ends 74a are positioned to simultaneously
straddle anchor pins 60 and 70 and to bear
thereagainst whenever shafts 12 and 14 are in other
than their nominal centered position. Restated,
spring 74 acts to bias input and output shafts 12
and 14 into their nominal centered position and will
do so whenever torque is being applied to input shaft
12.
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Spring 74, anchor pins 60 and 70 and
flanges 58 and 54 therefore comprise resilient means
which, during the first +22.5 of relative rotation
between input and output shafts 12 and 14 transmit
~orce (torque) therebetween. Once 22.5~ of relative
rotation is realized, dowels 52 and 52' take over to
directly transmit force (torque) between input and
output shafts 12 and 14. By its arrangement, spring
74 acts bidirectionally to urge shafts 12 and 14 back
into their nominal centered position.
Two electromagnetic field shunt assemblies
designated 76 and 78 generally are disposed between
input shaft mounting block 20 and flange 58. The
details of construction of shunt assemblies 76 and 78
are identical, and thus for sake of brevity only one
will be described in detail. The detailed operation
of shunt assemblies 76 and 78 is best understood by
simultaneous reference to drawing FIGURES 1, 3, 4, 6,
and 7. Each electromagnetic field shunt assembly 76
and 78 comprises an electrical coil or inductor 80
mechanically supported by a plastic carrier 82 backed
by an aluminum shield washer 84, a first vane
assembly 86 and a second vane assembly 88, all
concentrically disposed about input and output shafts
25 12 and 14.
Coil 80 is mounted to carrier 82 which, in
turn, is secured from all but axial displacement to
input shaft ~nounting block 20 b~ two diagonally
opposed elongated cover mounting screws 90. Carrier
82 is square in cross-section as best seen in FIGURE
. 2 and screws 90 pass through two of its diagona]
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corners for reasons which will become apparent herein
helow. Vane assemblies 86 and 88 as well as coil 80
are generally of circular cross~section so as not to
interfere with mounting screws 90 during operation of
torque sensor 10. Input shaft 12 passes through a
relatively large passageway 92 in carrier 82 so as
not to contact same. First vane assembly 86
comprises four circumferentially spaced vanes or
segments 86a depending radially outwardly from an
annular root portion 86b. Root portion 86b
integrally transitions into an axially directed hub
portion 86c. The radially innermost surface of hub
portion 86c forms a guide surface 86d which
circumferentially rests on input shaft 12 and is
restrained from radial displacement thereby but is
free for axial displacement therealong. Vane
assembly 86 is secured for rotation with input
shaft 12 by a small dowel pin 94 press fit within a
radially outwardly opening blind hole 95 within input
shaft 12. Dowel pin 94 extends radially outwardly
through an axially elongated registering slot 86e in
hub portion 86c of vane assembly 86. Slot 86e is
best illustrated in FIGURE 7. Each vane 86a defines
an angular segment of approximately 45.
Second vane assembly 88 is constructed
similarily to first vane assembly 86, including four
circumferentially spaced vanes 88a depending radially
outwardly from a root portion 88b. The radially
innermost portion of root portion 88b transitions
into axially aligned hub portion 88c. The radially
innermost surface of hub portion 88c defines a
support surface 88d which rides upon the
circumferential surface of input shaft 12. The
radially outwardmost extent (ends) of dowel 5~ reside
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within axially elongated registering notches 88e in
second vane assembly 88. Accordingly, second vane
assembly 88 i5 prevented from radial displacement by
input shaft 12 but is linked for rotational
displacement wi~h output shaft 14 through dowel 52.
The individual vanes 88a of second vane assembly 88
define approximate 45 angular segments.
Vanes 86a and 88a are positioned so that
when shafts 12 and 14 are in their nominal centered
position, overlaying corresponding vanes are 22.5~
out-of-phase as illustrated in FIGURE 6. Thus, in
the centered condition four 22.5 segments of coil 80
are exposed or remain uncovered by electromagnetic
field shunt assembly 76. Electromagnetic field shunt
assembly 78 illustrated in FIGURE 6 is simplified to
illustrate the relative relationship of vane
assemblies 86 and 88 with respect to coil 80 in the
nominally centered position.
The structure of electromagnetic field
shunt assembly 78 is substantially as depicted herein
above.
Two axially aligned electromagnetic field shunt
assembly biasing springs 96 carried on bolts 90 tend
to bias assemblies 76 and 78 apart from one another.
Springs 96 tend to bias shield washer 84 of
assembly 76 leftwardly abutting carrier 82 and
coil 80. Coil 80 is then, in turn, biased against
the right-hand most surface of the vanes 86a of vane
assembly 86 (through an intermediate milar washer if
desired). The left-hand most surface of vane
assembly 86 is then biased against the right-hand
- most surface of vane assembly 88 (through an
intermediate optional milar washer). The left-hand
most limit of travel of vane assembly 88 and thus the
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entire assembly 76 is reached when notch 88e contacts
dowel 52. Likewise, electromagnetic field shunt
- assembly 78 is biased by springs 96 rightwardly until
notch 88e' in hub portion 88c' of second vane
assembly 88' abuts dowel 52'. The applicant notes
that FIGURE 7 has been simplified somewhat in
selected areas to simplify understanding of the
present Specification.
The arrangement of shunt assemblies 76 and
78 is intended to insure intimate contact between
coils 80 (80') and their associated vane
assemblies 86 and 88 ~86' and 88'). The biasing
effect of springs 96 also compensates for wear over
extended use of torque sensor 10. Finally, for
reasons which should become apparent herein below,
the present arrangement provides adequate spacing to
insure th~t energization of coils 80 and 80' will
generate two substantially discreet or independent
electromagnetic fields. By way of definition,
isolated electromagnetic fields means fields spaced
or shielded so that any magnetic coupling
therebetween is incidental and has an insignificant
effect upon overall operation of sensor 10.
Cover mounting screws 90 extend rightwardly
(in FIGURE 1) from electromagnetic field shunt
assembl~ 78 and secure a cup-shaped cover housing 91
to input shaft mounting block 20. Mounting block 20
and housing 91 coact to completely enclose
electromagnetic field shunt assemblies 76 and 78 with
suitable sealing means (not illustrated).
The operation of torque transducer 10 is
best illustrated by reference to FIGURES 6, 8, 9, and
10. Coils 80 and 80' are electrically energized to
form separate, isolated axially aligned fields. Vane
assemblies 86 and 88 coact to define shutters which
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selectively shunt the electromagnetic field
associated therewith as a function of the portion of
the coil 80 covered thereby. As can be seen in
FIGURE lO, the amount of mechanical rotation for each
set of vane assemblies 86 and 88 i5 linearly directly
correlatable to the electrical phase shift of the
voltage impressed across coil 80. This mechanical
rotation to electrical phase shift relationship can
be expressed in a relative rotation to torque applied
on input shaft 12 relationship as e~pressed in FIGURE
9. Referring again to FIGURE 6, as vane assemblies
86 and 88 are rotated with respect to one another
from the nominal centered position illustrated, more
or less of coil 80 will be exposed and thus more or
less of the field generated thereabout will be
shunted. At one extreme of relative rotation,
substantially all of the surface area of coil 80 will
be covered and at the other extreme o relative
rotation, the 45 vane segment 86a and 88a will be in
alignment whereby only one-half of the total surface
area of coil 80 will be covered. The input/output
shafts, housing and frame, 12, 14, 91, and 16
respectively, are constructed of steel. Vane
assemblies 86 and 88 are constructecl of aluminum.
However, it is contemplated that other diamagnetic
materials as well as paramagnetic and ferrous metals
could be employed to provide the shunting function as
should be obvious to those of ordinary skill in the
art in light of the present Specification.
Vane assemblies of shunt assemblies 76 and
78 are oriented to provide complementary operation.
By way of definition, such operation entails the
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closing of one shutter with the simultaneous opening
of another. When in the nominally centered position
illustrated in EIGURE 6, both shunt assemblies
exhibit a 22.5 offset. When a relative rotation of
22.5 is achieved (the limit) one of the pairs of
vane assemblies 86 and 88 totally covers its
respective coil for maximum shunting effect while the
other pair are in register for the minimum shunting
effect. This arrangement effectively doubles the
usable signal available to the control circuit
described herein below.
Operation of torque sensor 10 is best
understood by referring to a schematic diagram in
FIGURE 8 illustrating a control circuit designated 98
employed therewith. Electromagnetic field shunt
assemblies 76 and 78 effectively operate as air core
transformers. When coils 80 and 80' are excited with
a high-frequency AC signal, vane assemblies 86 and 88
act as short-circuited secondary coils. As a greater
area of coils 80 and 80' are covered by the metal
vane assemblies 86 and 88, electrically more and more
"secondary transformer coils" are effectively shorted
and thereby more magnetic flux is captured and
absorbed via generation of eddy-currents.
Referring to FIGVP~E 8, a high-frequency
oscillator 100 provides an AC signal to a divider or
flip-flop 102 which outputs two square wave signals
which are 90 out-of-phase. Oscillator 100 is
operating at 450 khz. Divider 102 is a 4013 CMOS.
The outputs from divider 102 pass through
current-limiting resistors 104 and 106 and feed the
- points of common connection between a capacitor 108
and inductor 80, and a capacitor 110 and inductor
80', respectively. Capacitor 108 and coil 80 form a
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tan~ circuit having a sine wave output. Likewise,
capacitor 110 and coil 80' form a second independent
tank circuit having a sine wave output. The
frequency of oscillator 100 is selected to drive the
tank circuits at or near resonance. The sine wave
outputs ~rom the tank circuits have a phase
relationship determined by the relative angular
displace~ent between input and output shafts 12 and
14. As vanes 86a and 88a (86a' and 88a')
collectively overlay more or less of coils 30 and 80'
and thus shunt more or less of the electromagnetic
fields associated therewith, the resonant frequency
of the tank circuits will shift as will the relative
phase relationship of their sine wave outputs. The
output of the tank circuit associated with resistor
104 is fed to a high gain amplifier 112 and the
output of tank circuit associated with resistor 106
is fed to a second high gain amplifier 114.
Amplifiers 112 and 114 are employed to permit
comparison of the phase relationship (zero crossing)
of the signals from the tank circuits. The gain of
amplifiers 112 and 114 is relatively large and will
cause the signal to saturate, resulting in a square
wave output from each. Type 4069 inverter packages
were employed in open loop configuration.
The outputs of amplifiers 112 and 114 are
fed to the inputs of an exclusive-or gate 116. Gate
116 will generate an output when and only when there
is a difference between the signals at the two
inputs. As a result, the output of gate 116 is a
pulse whose width is modulated by the amount of phase
shift present. These pulses can be from very low to
almost 100~ duty cycle. If for example, at the
nominal centered posltion, a S0~ duty cycle is
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realized, that can be established as a norm for the
steering center and as the steering wheel is turned
left or right, the duty cycle will become less or
more, which can be subsequently recognized as a
demand for left steer or right steer.
The output of gate 116 represents torque
demand and is passed through a filter 118 as a DC
level. In practice, filter 118 is of the RC type
having an output which is an average DG voltage
whereby if the incoming pulse becomes longer, the
voltage level increases and if the pulse becomes
shorter, the voltage level decreases. The torque
demand signal is then processed by passing it into an
amplifier stage 120 and then through gating 122 to
generate appropriate clockwise or counterclockwise
control signals for a power switching circuit 124. A
power supply 126 feeds switching circuit 12~ which,
depending upon the gating control signal received
will drive a motor 128 in a clockwise or
counterclockwis~ orientation. The motor 128, in
turn, is mechanically linked to a load 130 which, in
the intended application, comprises the steered wheel
and its associated linkage mechanisms. Transducer 10
is mechanically interconnected to load 130 by linkage
48 as well as to an operator manipulated steering
wheel 160 by input shaft 12.
Referring to FIGURE 11, an alternative
embod~ment of the present invention (torque sensor
131) is illustrated which operates substantially as
the preferred embodiment of the invention described
hereinabove. A steel input shaft 132 is loosely
disposed within a bore 134 within a steel output
shaft 136 for relative rotation therein. An aluminum
cylinaric carrier 138 is disposed concentrically
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externally of output shaft 136. Finally, a
non-metallic cylindric bobbin housing, generally
designated 140, is disposed externally of carrier 138
and supports two inductors or coils 142 and 144 in an
axially spaced relationship. When energized
electrically, inductors 142 and 144 established
distinct, isolated electromagnetic fields
thereabout. Carrier 138 is prevented from radial
displacement by virtue of its telescoping
relationship between output shaft 136 and housing
140. ~wo dowel pins 144 are press fit within
outwardly opening blind bores 146 within output shaft
136, and pass radially outwardly through registering
axially elongated slots 148 in carrier 138. Dowel
pins 144 prevent relative rotation between
carrier 138 and output shaft 136. Carrier 138 is
otherwise free for relative axial displacement with
respect to shafts 132 and 136 between two limits of
travel defined by the points at which dowel pins 144
bottom out in slots 148. FIGURE 11 illustrates
carrier 138 in its nominal centered position in which
it nominally overlays half of the inner surfaces of
coils 142 and 144. A dowel pin 150 is press fit
within a radially outwardly opening blind bore 152
within input shaft 132 which passes radially
outwardly through a circumferentially elongated
slot 154 within output shaft 136 and a skewed
elongated slot 156 in carrier 138.
In the nominal centered position, pins 146
and 150 are in rotational alignment, causing
carrier 138 to assume a central position between
inductors 142 and 144. Whenever shafts 132 and 136
are rotated relative with one another, pins 146 and
152 will likewise be angularly displaced. Such
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angular displacement will cause pln 150 to cam
agaiI~st the Surfaces of carrier 138 r~efining slot
156, causing axial displacement in one direction or
the other. Such displacement will occur through a
limited travel. At one limit of travel, carrier 138
will completely overlay the inner surface of
inductor 142 while totally exposing the inner surface
of inductor 144, and at the other limit of travel,
will totally overlay the inner surface of
inductor 144 and expose inductor 142. This
arrangement will result in the same operation as was
described in detail hereinabove when torque sensor
131 is combined with or includes a logic circuit such
as that described in connection with FIGURE 8.
A detailed logic circuit description has
not been included in the description of the
alternative embodiment of the invention for the sake
of brevity. However, for completeness, the circuit
of FIGURE 8 could substitute inductors and 80 and 80'
with 142 and 144 with substantially identical
results. Finally, carrier 138 as well as the system
of dowel pins 144 and 150 and slots and notches 148,
154 and 156 comprise an electromagnetic field
shunting assembly shown generally at 158.
It is to be understood that the invention
has been described with reerence to specific
embodiments which provide the features and advantages
previously described, and that such specific
embodiments are susceptible to modification, as will
be apparent to those within the art. Accordingly,
the foregoing description is not to be construed in a
limiting sense.
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