Metal working – Method of mechanical manufacture – With testing or indicating
Reexamination Certificate
2000-12-15
2002-08-06
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
With testing or indicating
C029S407020, C029S434000, C073S862322
Reexamination Certificate
active
06427307
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to a low-hysteresis coupling for a shaft
BACKGROUND OF THE INVENTION
There are many applications which require a coupling to couple a device to a shaft. Often, such couplings allow rotational movement of a shaft to be transferred to a device while not allowing translational movement of the shaft to be transferred to the device. In certain application, the coupling must substantially eliminate hysteresis (which is the lagging of a physical effect on a body behind its cause) in rotational movement of the shaft with respect to the device.
One application of the coupling is a torque sensor device which determines a torque input on a shaft which comprises a torsion bar longitudinally connected to a primary bar. The primary bar is relatively inflexible to a torque input, while the torsion bar torsionally flexes to a torque input. The magnitude of the torque input may be determined by measuring the rotation of the torsion bar relative to the primary bar. One of the difficulties in coupling the torsion bar to the primary bar is that the torsion and primary bar may not be coaxial due to manufacturing tolerances or design requirements. External forces acting perpendicularly to the longitudinal axis of the torsion bar may also cause translation of the torsion bar in an x-y direction of an x-y plane (which is perpendicular to the longitudinal axis of the torsion and primary bar) such that the torsion bar may become temporarily non-coaxial with the primary bar. In addition to connecting with non-coaxial bars, the coupling should transmit the relative rotation of the torsion bar to the torque sensor device without backlash. In other words, the coupling allows rotational movement of the shaft to be transferred to a device while not allowing translational movement of the shaft to be transferred to the device. Thus, the coupling substantially eliminates hysteresis in rotational movement of the primary bar with respect to the torque sensor device.
The torque sensor device may be used to accurately measure the input torque acting on a steering column shaft in an electronic power steering system of an automobile or truck. In this application, an input torque acts on the steering column shaft when an operator turns the steering wheel. The steering column shaft includes the primary bar and the torsion bar. The rotation of the torsion bar relative to the primary bar may be measured with a potentiometer. The torque sensor device may include a coupling which couples the torsion bar to the primary bar so that a sensor brush may slidingly contact a variable resistor as the torsion bar rotates relative to the primary bar. In order to accurately determine the relative rotation of the torsion bar, the coupling should accurately transfer the relative rotation of the torsion bar to the sensor brush with substantially no hysteresis and still allow the translation of the torsion bar in the x-y plane.
Several devices are currently available which couple non-coaxial shafts. However, none of the devices thus far appear to be without problems. One attempt to satisfy the needs discussed above is disclosed in U.S. Pat. No. 3,834,182 (Trask et al.). Referring to
FIGS. 1 and 2
, this patent describes a flexible coupler
20
for connecting nominally coaxial shafts drivingly connected to one another. The coupler
20
permits a limited amount of axial misalignment between the shafts. The coupler
20
comprises three basic elements: an enlarged cylindrical hub
22
fixed to a first shaft, a second smaller cylindrical flange
26
fixed to another shaft
28
in juxtaposition to the hub
22
, and a “floating” annular ring
30
also juxtaposed with the hub
22
about the flange
26
. Loose fitting complementary axial lugs
32
and notches
34
interconnect the hub
22
and ring
30
, and loose fitting complementary radial lugs
36
and notches
38
are interfitted between the ring
30
and flange
26
. The flange
26
and ring
30
are located relative to the hub
22
for axial clearance, permitting limited angular misalignment between the two shafts
24
,
28
. The flange
26
and circumjacent ring
30
form a planar surface juxtaposed with the inner planar surface
40
of the hub
22
. However, due to the loose fitting complementary axial lugs
32
and notches
38
and the loose fitting complementary radial lugs
36
and notches
38
, gaps
42
between the lugs
32
and notches
34
may lead to rotational play between the first and second shaft
24
,
28
.
U.S. Pat. No. 2,956,187 (Wood), U.S. Pat. No. 3,859,821 (Wallace), U.S. Pat. No. 4,357,137 (Brown), and U.S. Pat. No. 4,464,141 (Brown) appear to provide a coupling with less rotational play between a first and second shaft than the Trask patent. These patents describe a flexible coupling for transmitting power from a drive shaft to a driven shaft. The coupling includes a primary coupling member having a hub section for receiving and rotating with a first shaft, a flange section having a resilient insert therein, and a secondary coupling member located centrally within the resilient insert for receiving and rotating with a second shaft. The resilient insert is interference fitted into the primary coupling member, and the secondary coupling is interference fitted into the central region of the resilient insert The resilient insert is adequately flexible to allow for axial misalignments between the shafts. However, a slight rotational play appears to exist between the first and second shafts because the resilient insert flexes to an input torque acting on the shafts.
Another coupling with reduced rotational play is disclosed in U.S. Pat. No. 3,728,871 (Clijsen) which describes a coupling for connecting two approximately registering shafts. Referring to
FIGS. 3 and 4
, the coupling
50
comprises two connecting pieces
52
,
54
respectively connected to a first
56
and second shaft
58
. A loose coupling disc
60
is fitted between the two connecting pieces
52
,
54
and couples the rotary movements of both connecting pieces
52
,
54
to each other and has a limited play in two mutually perpendicular radial directions with respect to the individual connecting pieces
52
,
54
. Play in the direction of rotation is reduced by a resilient C-shaped spring member
62
. One drawback of this coupling
50
appears to be that it is relatively complicated. This may result in an increase in manufacturing time and cost due to the numerous precision shaped components required. It also may result in a less reliable device because the inclusion of more components may translate into a statistically less reliable device.
Another coupling with reduced rotational play is a conventional Oldham coupling.
Referring to
FIG. 5
, the Oldham coupling
100
comprises three basic elements: a first member
102
connected to a first shaft at one end and having an axially extending tongue
104
at the other end, a second member
106
connected to a second shaft at one end and an axially extending tongue
108
at the other end, and a third member
110
positioned between the first member
102
and the second member
106
. The third member
110
has a groove
112
at each end which slidingly mates with the respective tongues
104
,
108
. One drawback of the Oldham coupling
100
is that it appears to be relatively complicated. For the same reasons discussed above in regards to the Clijsen patent, the Oldham coupling may not satisfy certain needs for the torque sensor device.
Thus, there remains a need for a coupling that allows rotational movement of a shaft to be transferred to a device while not allowing translational movement of the shaft to be transferred to the device in an inexpensive, reliable, and rugged manner.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention, a coupling is coupled to a device in a manner that allows rotational movement of a shaft to be transferred to a device while not allowing translational movement of the shaft to be transferred to the device. The coupling is particularly suited for any devic
Hughes S. Thomas
Omgba Essama
Oppenheimer Wolff & Donnelly LLP
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