Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
1998-11-23
2001-05-01
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
Reexamination Certificate
active
06223607
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a torque detector for detecting torque without direct contact when an external force is applied to the rotating shaft of an automobile power-steering mechanism, etc.
2. Description of the Related Art
In an automobile power-steering mechanism, it is necessary to detect the amount of torque being applied to the steering wheel to determine the amount of power assistance required. The torque detector disclosed in Utility Model Laid Open No. 3-285130 is a known example of a conventional torque detector for this purpose. The construction of this device will be explained with reference to FIG.
5
. In the figure, an upper shaft
2
, which is attached to a steering wheel (not shown) and which is supported by a bearing
5
a
so as to be able to rotate freely, and a lower shaft
3
, which is attached to the pinion gear of a steering mechanism (not shown) and which is supported by bearings
5
b
,
5
c
so as to be able to rotate freely, are disposed within a housing
1
. A torsion bar
4
, which is secured at its upper end to the upper shaft
2
by a pin
6
and is supported at its lower end by a bush
7
in the lower end of the upper shaft
2
so as to be able to rotate freely and at the same time is secured to the lower shaft
3
, is disposed within the upper shaft
2
and lower shaft
3
so as to be disposed on the central axis of these shafts and is connected so as to be elastic in the direction of shaft twisting between the upper shaft
2
and lower shaft
3
.
A first cylinder
10
, which is composed of soft magnetic material and is secured to the upper shaft
2
, has tooth portions
12
comprising a plurality of protrusions disposed equidistantly around it. A second cylinder
11
, which is composed of soft magnetic material and is secured to the lower shaft
3
, has tooth portions
13
comprising a plurality of protrusions disposed equidistantly around it. A coil
15
, which detects changes in magnetic resistance between the first cylinder
10
and the second cylinder
11
, is disposed radially outwards from the first cylinder
10
and the second cylinder
11
.
Next, the operation will be explained. When torque is applied to the upper shaft by the steering wheel, torsional deformation occurs in the torsion bar
4
, and angular shear occurs due to relative rotation between the first cylinder
10
and second cylinder
11
, which are attached to the upper shaft
2
and the lower shaft
3
, respectively, that is, relative angular displacement occurs between the upper shaft
2
and the lower shaft
3
. When this happens, the surface area of the overlap which forms a magnetic circuit between the tooth portions
12
and
13
disposed on each of the cylinders changes and thus the magnetic resistance between the first cylinder
10
and the second cylinder
11
changes.
The torque can be determined by detecting this change in the magnetic resistance by means of the coil
15
. However, in practice not only is torque being applied between the upper shaft
2
and lower shaft
3
, but bending forces as well. The torsion bar
4
, which connects the upper shaft
2
to the lower shaft
3
, has little flexural rigidity and cannot withstand the bending forces on its own. For that reason, bending forces are prevented from being applied to the torsion bar by supporting it at both ends by means of the pin
6
and the bush
7
.
Because the conventional torque detector is constructed in the manner described above, the torsion bar
4
requires a certain length and torsional rigidity corresponding to the relative angular displacement occurring between the upper shaft
2
and the lower shaft
3
, but the longer the torsion bar is, the smaller its flexural rigidity becomes. Thus, in order to prevent the magnetic resistance between the first cylinder
10
and the second cylinder
11
from changing due to bending forces, there is a need to increase the rigidity of the upper shaft
2
, the lower shaft
3
, etc., and at the same time to use many supports, such as bushes and bearings. The problem is that increasing the number of supports leads to a loss of torque due to friction in the supports, and making the construction more complicated increases production costs.
SUMMARY OF THE INVENTION
The present invention aims at solving such problems and an object of the present invention is to provide a torque detector of simple construction with little loss of torque.
The torque detector according to the present invention is a torque detector for detecting the torque acting mutually between a first shaft and a second shaft which are arranged end to end on a common axis and comprises: a plurality of elastic rods, which are secured at each end to the facing ends of the first shaft and the second shaft and are each able to twist in response to the torque; at least one movable element with wings, each of which is secured to and spans two of the elastic rods and is displaced radially with respect to the common axis in response to the twisting of the elastic rods; and a detection means, which is disposed so as to face the wings radially to the axis and which generates a magnetic flux in a magnetic circuit which includes the wings and detects radial displacement of the wings as electromagnetic change.
According to the torque detector of the present invention, the elastic rods may be secured to the first shaft and the second shaft by means of a pair of annular members.
The torque detector according to the present invention is also characterized in that each of the movable elements may comprise: a pair of legs composed of elastic bodies, the trunk of one of which is positioned radially outwards from the trunk of the other and whose ends are secured in the securing positions separated from each other axially along the different elastic rods; and a body portion, which is connected to the root of each of this pair of legs; wherein the roots of the wings are connected to the body portion and the tips of the wings extend axially along the elastic rods, and the wings are displaced radially in accordance with changes in the attitude of the body portion in response to changes in the torque.
According to the torque detector of the present invention, each of the body portions may comprise a flat surface positioned at an angle to an imaginary straight line drawn between the securing positions.
According to the torque detector of the present invention, two wings and two detection means may be disposed facing each other for each body portion.
According to the torque detector of the present invention, the entire body of each movable element may be formed from a single sheet of soft magnetic material.
REFERENCES:
patent: 3-285130 (1991-12-01), None
Aw-Musse Abdullahi
Fuller Benjamin R.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
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