Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
1999-12-10
2001-11-20
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
Reexamination Certificate
active
06318188
ABSTRACT:
BACKGROUND OF THE INVENTION
1. [Field of the Invention]
The present invention relates to a torque detector for detecting torque without contact when external force is applied to a rotary shaft in a car power steering system or the like.
2. [Description of the Prior Art]
In a car power steering system, it is necessary to detect torque applied to a steering wheel so as to determine the amount of power assist. A torque detector for this purpose is disclosed by Japanese Laid-open Utility Patent No. 1-180737. The structure of this torque detector will be described with reference to FIG.
6
. In
FIG. 6
, reference numeral
1
denotes a first shaft connected to an unshown steering wheel,
2
a second shaft connected to the unshown pinion gear of a steering unit,
3
a torsion bar for elastically connecting the two shafts in a torsion direction,
4
a cylindrical case,
5
a bobbin stored in the case,
6
bearings for fixing the shaft
1
in the case
4
in such a manner that the shaft
1
can rotate freely,
11
and
12
first and second cylinders made from a soft magnetic material and fixed to the first shaft
1
,
13
and
14
third and fourth cylinders made from a soft magnetic material and fixed to the second shaft
2
,
11
a
to
14
a
tooth portions provided on the first to fourth cylinders, and
21
a
to
21
d
first to fourth coils wound in the bobbin
5
.
A description is subsequently given of the operation of this torque detector. When torque is applied to the first shaft
1
from the steering wheel, the torsion deformation of the torsion bar
3
occurs and a relative angular difference is generated between the first shaft
1
and the second shaft
2
. Then, relative displacement between the first cylinder
11
and the third cylinder
13
fixed to the respective shafts occurs in a circumferential direction, and the area forming a magnetic path between the opposite tooth portions
11
a
and
13
a
provided on the respective cylinders is changed, resulting in a variation in the inductance of the first coil
21
a.
The torque can be obtained by detecting this variation in the inductance by means of an unshown detection circuit.
However, as the inductance of the first coil
21
a
is changed not only by torque but also by temperature, the third coil
21
c
whose inductance is changed not by the torsion of the torsion bar but by temperature only in the same manner as the first coil
21
a
is provided and temperature compensation is made by detecting the inductance of the third coil
21
c.
As described above, torque on which temperature compensation has been made can be measured with the first detection set comprising the first and third cylinders and the first and third coils. However, the torque detector of this prior art comprises a second detection set.
Since the second cylinder
12
and the fourth cylinder
14
are fixed to the first shaft
1
and the second shaft
2
, respectively, like the first detection set, they constitute the second detection set with the second and fourth coils, and the second detection set operates in the same manner as the first detection set. Therefore, the torque detector has a double safety function which enable the system to operate with the output of the other detection set when a failure such as disconnection occurs in either one of the detection sets.
SUMMARY OF THE INVENTION
Since the torque detector of the prior art is constituted as described above, the first to fourth cylinders have a complex shape with a large number of tooth portions. Further, since high dimensional accuracy is required for the torque detector, the production cost of the torque detector becomes high.
Since the change rate of magnetic resistance due to a change in the area between the opposite tooth portions caused by relative displacement between the cylinders in a circumferential direction cannot be made so large, it is difficult to improve the sensitivity of the torque detector and the torque detector is readily influenced by error factors such as temperature variations.
Further, since the sensitivity of the torque detector is low, the torsion angle of the torsion bar with respect to given torque must be increased to change the area between the opposite tooth portions, thereby making it impossible to increase the rigidity of the torsion bar. Therefore, when the torque detector is used in a car power steering system, an indefinite and unreliable operation feeling is obtained.
It is an object of the present invention which has been made to solve the above problem to provide a torque detector having a simple structure, high accuracy and high rigidity.
According to a first aspect of the present invention, there is provided a torque detector for detecting torque applied to first and second shafts which are arranged coaxial to each other and whose ends are opposed to each other, which comprises an elastic member which is connected to the first and second shafts and displaced by torque having a torsion direction between the first and second shafts, movable bodies whose both ends are fixed to or supported by the first shaft and the second shaft, which are arched and whose center portions are displaced by a change in the curvature of the arch due to a change in the distance between both fixed ends of the movable bodies according to a relative torsion angle between the first shaft and the second shaft, and means of detecting the displacement of each of the movable bodies.
According to a second aspect of the present invention, there is provided a torque detector wherein the movable bodies are arched along the circumferential directions of the first and second shafts.
According to a third aspect of the present invention, there is provided a torque detector wherein the movable bodies are arched in either one of the longitudinal directions of the first and second shafts.
According to a fourth aspect of the present invention, there is provided a torque detector wherein the movable bodies are made from a magnetic material and means of detecting the displacement of each of the movable bodies magnetically is provided.
According to a fifth aspect of the present invention, there is provided a torque detector wherein the movable bodies are made from a conductive material and means of detecting the displacement of each of the movable bodies with an eddy current generated in the movable body is provided.
According to a sixth aspect of the present invention, there is provided a torque detector wherein the movable bodies are made of an amorphous belt.
According to a seventh aspect of the present invention, there is provided a torque detector wherein the elastic member is shaped like a rod, a cylindrical support member is provided around the elastic member, an end portion connected to the elastic member of the first shaft is extended along the elastic member, the extension portion is inserted into the support member, the support member is fixed to an end portion of the second shaft, one ends of the movable bodies are connected to the extension portion of the first shaft through an opening formed in the support member, and the other ends of the movable bodies are connected to the support member.
According to an eighth aspect of the present invention, there is provided a torque sensor wherein the extension portion is a cylindrical portion located around the elastic member and an end portion of this cylindrical portion is mated with a hole formed in the end portion of the second shaft in such a manner that it can rotate freely.
The above and other objects, features and advantages of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4649341 (1987-03-01), Ulbrich et al.
patent: 5712563 (1998-01-01), Kawagoe et al.
patent: 5831180 (1998-11-01), Tanaka et al.
patent: 1-180737 (1989-12-01), None
Hasegawa Masahiko
Hisaoka Yasushi
Yasui Katsuaki
Fuller Benjamin R.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
Thompson Jewel V.
LandOfFree
Torque detector does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Torque detector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Torque detector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2618281