Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TRANSDllCER COUPL I NG
The present invention relates to torque sensors
and more particularly to a sensor which produces an
electrical signal as a function of the torque applied
thereto and simultaniously provides mechanical coupling
between two rotatable members.
Torque transducers which generate an electrical
signal as a function of the torque applied thereto, are
well known. For example, such a torque transducer is
disclosed in U. S. Patent No. 4,415,054, to Gilbert H.
Drutchas and assigned to TRW, Inc. Typically, this
general type of torque transducer includes an input
member and an output member which are connected one to
the other by a torsion beam. When torque is applied to
the input member, this torque is applied to the output
member through the torsion beam thereby providing both a
mechanical coupling between the input and output members
and imposing a strain on the torsion beam. Various
sensing devices such as strain gauges, Hall effect
geneeators, and the like are affixed to the beam or to
the beam and related members to produce an electrical
signal whose magnituder frequency, etc. is a function of
the strain and, accordingly, the torque applied to the
torsion beam. In these structures, it has been the
common practice to provide the torsion beam dimensions
and configuration such that it functions both as a
mechanical coupling between the input and output members
and as a deformable element the deformation of which can
be sensed to provide the desired electrical torque
signal. Because the torsion beam must function both as a
mechanical coupling and a deformable element the designer
must select a suitable compromise between the strength
and mechanical reliability of the torsion member and a
member which will exiblt sufficient strain under normal
loads to provide the desired electrical signal.
In one application of such torque sensors
particularly relevant at the present invention, the
sensor is utilized as a coupling member in an electrical
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power steering mechanism, the torq~le sensor providing a
signal indicative of steering forces being applied to the
mechanism by a driver. In this application, it will be
recogni~ed that the torque sensor, because it also
provides mechanical coupling between the steering wheel
and the steered wheels of a vehicle, must not fail.
Simultan~ously, in this application the normal torsion
loads applied to the torsion beam may be substantially
exceeded in circumstances such as the driver forcing the
steering wheel against its stops, the vehicle striking a
curb, and the like. When the torsion beam is subjected
to such excessive loads, it is essential that the beam be
protected against excess strain which could cause damage
to the beam and/or the associated transducers af~ixed
thereto. Simultaneously, it is essential that the
torsion beam exibit a sufficient amount of strain under
normal loads to produce an electrical signal of
sufficient definition to enable precise and predictable
control of the vehicle.
There exists therefore a need for a torque
transducer coupling which simultaniously provides a
positive and reliable coupling between an input member
and an output member, produces an electrical signal of
sufficient magni/tude and definition to enable precise
control of related mechanisms, and which insures that the
torsion beam wVll not be subjected to excessive stress
and strain which could damage the beam and/or its
associated transducer elements.
It is also desirable that such a transducer
coupling provide a coupling havinc3 little or no backlash
and which can be easily serviced or replaced.
In its broader aspects, the invention is a
torque transducer coupliny which comprises an input and
an output member co-axially journaled ~or relative
rotational movement. A torsion member connects the input
and output members and a lost motion mechanism or
coupling means connects the input and output members in
response to a predetermined angular movement
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therebetween. The lost motion coupling includes co-operatively
connected portions of the input, output and torsion members. Such
connected portions of the input and output member portions each have
slots therein with the torsion member portion being ~ixedly secured
in one of the slots and engaging the other of the slots in response to
the predetermined angular movement. Strain sensing means are fixed to
the torsion member for generating an electrical signal as a function of
the strain.
More specifically, the transducer coupling is provided with a
torsion member or beam which is fixedly secured at its opposite ends to
the input and output members and a portion of the torsion beam
positively keys the input to the output member at predetermined angular
displacements therebetween whereby strain of the torsion beam is limited
to such predetermined angular displacement and the input and output
members are resiliently coupled by the torsion beam For relative angular
movement having a displacement of less than said predetermined limit.
It is therefore an object of the invention to provide an
improved torque sensor coupling.
It is a further object of the invention to provide such a
transducer coupling particularly well suited to use in electrically power
assisted steering systems.
Another object of the invention is to provide a transducer
coupling in which the transducer torsion beam provides a positive
deformable coupling between an input and output member between predeter-
mined limits of angular displacement but which positively locks the
input of the output member to limit strain of the torsion beam.
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These and other objects, features and aspects of
the invention will be more fully understood and better
described in view of the following specification taken in
conjunction with the appended drawings wherein:
Figure 1 is an axial cross-section of a
transducer coupling in accordance with the invention
incorporated in a rack and pinon steering assembly:
Figure 2 is an exploded perspective view showing
key components of the invention;
Figure 3 is an axial cross-section of the
transducer coupling shown adapted to a recirculating ball
steering ~echanism;
Figures 4a and 4b are diagramatic illustrations
useful in explaining operation of the invention; and
Figure 5 is a perspective drawing of an electric
; power assisted rack and pinion steering assembly
; incorporating the transducer coupling of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, there is shown in
Figure 1 a torque transducer coupling indicated generally
at 10 mounted in a housing 12 of a rack and pinion
steering gear 14. The transducer coupling 10 comprises
generally cylindrical input member 16, output member 18,
and a torsion member 20. Input member 16 is provided
with an axially extending bore or cavity 22 of stepped
diameter extending from its end 24. Output member 18 is
provided with an end portion 26 of reduced diameter,
which is rotatably received in end portion 25 of the bore
22 by reason of a smooth bearing fit therebetween.
In the illustrated embodiment, the transducer
coupllng is incorporated in a rack and pinion steering
assembly 14 and, accordingly, the input member 16 is
shown provided with a splined end 30 adapted to be
coupled to the steering wheel of a vehicle through
appropriate mechanisms (not shown in Figure 1) and the
output member 18 is provided with a pinion gear portion
32 operatively engaged with a rack gear 34 which is in
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turn coupled to steerable portions of a vehicle in the
conventional manner. Input and output members 16, 18 are
further journaled by means of suitable bearings as at 36,
38, 40, seals, retainers and end caps 44, 46, again, in
conventional manner. The housing 12 includes rack
housing 52, transducer housing 54, and an end cap 56. It
is to be understood that these latter elements are
adapted for application of the invention to a steering
gear assembly. The transducer coupling of the invention
may, however, be used in a variety of applications and
the housing 12 may be either modified for the particular
application or, in some cases, be eliminated.
Output member 18 closes the cavity 22 and, as
explained in more detail below, the torsion member 20 is
coupled between the end 60 of the cavity 22 and the end
26 of the output member 18.
AS can best be seen in Figures 1 and 2, end 60
of input member 16 is provided with a slot 62 contiguous
with a diameter thereof. A similar slot 64 is provided
in the output member 18 in axially spaced registry with
slot 62. The torsion member 20, as best seen in Figure
2, is elongated, and flat with a central portion 66 of
reduced lateral dimension. The end portions 68, 70
tFigu~e 2 only) define ears as at 72, 74 and the member
is interlockingly engaged with the slots 62, 64.
Preferably, torsion member 23 is further provided with an
axially extending tab portion ~ which has a lateral
dimension which engages the interior of the cavity 22.
Input member 16 is further provided with
longitudinally extending slots as at 76 having width and
length dlmensions such that the torsion member 20 can be
inserted laterally therethrough, and moved axially
towards the output~member 18 to the effect engagement of
the tab portion ~ with the interior wall of cavity 22.
As can best be seen in Figure 2, the end of the
torsion member 20 which engages the output member 18 ls
provided with a chamfer as at 80. Member 18 is provided
with a recess 86 adjacent the center of slot 64 in which
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is secured a rubber plug 88 having a slot lOZ which is radially displaced
from its axis. When the torsion member 20 is inserted through the slots
76 into engagement with the slot 62 of input member 16, and input member
16 and torsion member 20 are axially engaged with the output member 1~,
: the offset in the slot 102 in conjunction with the rubber plug ~8, effects
a positive lash-free engagement therebetween.
The torsion member 20 is further secured to the input member 16
by means of a press-fitted pin 90 which is inserted ~hrough registered
holes 89 in input member 16 and torsion member 20.
~ Lastly, a suitable strain sensitive element such as a strain
gauge 94 is fixedly secured to one of the surfaces of the torsion member
20 in conventional manner. In the case of a steering assembly, because
the number of revolutions of the unit that can occur is limited,
electrical connection to the strain gauge is effected by means of a
helically wound flexible conductor cable 96 which extends outwardly
throuyh the slots 76 to a suitable control unit 98 (Figure 5 only).
As can be seen in reference to Figures 4a and ~b the end
portions 100 of slots 76 have a circumferential dimension that provides
: a predetermined clearance between the tab portions 72, 74 of the torsion
member 20 and the walls of the slot end portions 100.
The unit is assembled by first inserting the torsion member 20
through one of the slots 76 to engage the portion 70 thereof with the
slot 62 of input member 16. The torsion member 20 is moved forwardly
to engage the tab portion 77 with the walls of cavity 22 and secured
; in position by means of pin 90. The input member 16 and torsion member
20 are then axially mo~ed into engagement with the output member 18.
lhe chamfer 80 facilitates this assembly. The offset slot 102 of the
plug 88 is preferably dimensioned for a tight pressfit with the tab
portion 77 such that there is substantially no play between the input
and output members.
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Disassembly is effected in reverse order. Accordingly, it is seen to be
simple and easily performed even in the field.
It will now be seen that torque applied to the input member 16
will produce direct mechanical coupling of the torque to the output member
1~ through the torsion member 20. This torque will further effect strain
in the torsion member 20 which is a function of the torque applied there-
through. This torque is converted to an electrical signal by means of
of the strain gauge or other strain sensing elements 94, this signal being
sent to an appropriate controller as required in the application. The
input and output members are journaled, one to the other, and accordingly,
relative rotational movement can occur therebetween as the tors;on melnber
20 Flexes. However, when strain of the torsion member 20 reaches a
predetermined angular value, the tab portions 72, 74 will come into direct
physical engagement with the slot end portions lO0. This is best seen in
Figures 4a and 4b in which the position of the torsion member 20 relative
to the slot end portions 100 is shown in an unstressed and a stressed
condition. Further increases in the torque applied to the input member
will be communicated by a direct mechanical linkage from the input member
16, to the tab portions 72, 74, to the slot 64 and the output member 18.
Accordingly, it will be seen that the tab portions 72, 74 function as
keys for effecting a positive mechanical linkage that is totally
independent of the torsion member 20 itself. It will also be observed
that this linkage is bi-directional.
In a working embodiment, the torsion member 20 normally
experiences torque loads of zero to forty pound inches. The clearance
between the tab portions 72, 74 and slot end portions lO0 is designed to
accommodate a torque value of plus or minus 60 pound inches at which time
the tabs will positively engage the slot end portions lO0. These tab
portions are normally tested for up to lO0 foot pounds of torque.
Accordingly, it will be seen that the
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transducer coupling of the present invention provides a
sensitive torque sensing element in normal opeeating
ranges of the device. Simultaneously, the unique
mechanical linkage between the input and output members
effected through what is, in effect, a lost-motion
mechanism comprising slot portion 100, slot 64, and tab
portions 72, 74, prevents overstressing of the torsion
member 20 thereby obviating damage or destruction. It
will further be seen that even when the assembly is
~0 subjected to very high torques, the assembly will return
to a totally normal state upon release of the torque as a
res~lt of the limitation of the strain on the torsion
member. In a working embodiment, engagement occurs after
3 degrees of relative rotation.
Referring now to Figure 3, the transducer
coupling 10 is shown installed in an electric power
assisted steexing mechanism of the recirculating ball
variety. In this embodiment, like components are
identified by like primed numerals. It will be seen that
in this embodiment, the output member 18' also comprises
the recirculating ball pinion shaft for the mechanism.
The housing 14l is further modified for adaptation to
this type of a stee~ing mechanism. It furthee will be
seen that the steering mechanism is assisted by means of
an electric motor 104 which operates through a plurality
of gears 106, 108, 110 to apply torque to the output
member 18'. It will be observed that the torque is
applied to the output member such that it does not apply
a torque to the torque sensor 10 but rather reduces the
torque that must be applied to the input member 16.
Referring now to Figure 5, a rack and pinlon
steering mechanism which includes electrlc power assist
is shown generally at 112. The steering mechanlsm
incorporates a mechanism substantially as shown in
Figure 1. It further will be observed that the electric
motor 114 again applies torque to the output me~ber via a
gear train (not shown) enclosed within the housing
portion 116, this torque being applied to the end 118 of
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the output member 18 (Figure l only). The rack gear 34
(not shown in Figure 5) i5 coupled in the conventional
manner to tie rods as at 122 and ball joints 124 to the
wheels of the vehicle. The motor control is, again,
indicated at 98, the control being coupled to sense or
otherwise receive the signal from the strain gauge
elements 94 to apply a signal to the motor 114 via
conductors 126.
In other applications, not illustrated, it will
be recognized that the torque sensor could also be
applied between a motor and a driven load such as a
generator, machine or the like. In such an appplication,
alternative sensors may be substituted for the strain
gauge 94 in view of the continuous rotation of the input
and output members. Such sensors, are of course well
known to those skilled in the art.
Furthermore, it is contemplated that one skilled
in the art could make many modifications and/or changes
to the invention as described herein without deviation
from the essence thereof. As such these modifications
and/or changes are intended to fall within the scope of
the appended claims.
