Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
1999-08-23
2002-04-16
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
C180S444000, C073S862080
Reexamination Certificate
active
06370968
ABSTRACT:
BACKGROUND OF THE INVENTION
1. [Field of the Invention]
The present invention relates to a torque detector for detecting torque when external force is applied to a rotation shaft without contact in a car power steering unit or the like.
2. [Description of the Prior Art]
In a car power steering unit, torque applied to a steering wheel must be detected to determine the amount of assist force. There is known a torque detector disclosed by Japanese Laid-open Patent Application No. 63-65331 as an example of the torque sensor used for this purpose of the prior art. The structure of this device will be described with reference to
FIGS. 10
to
12
.
In these figures, reference symbol
1
A denotes a shaft to be measured,
10
and
11
a pair of electrode bases fixed to the shaft
1
A,
12
and
13
electrodes fixed to the electrode bases
10
and
11
, respectively,
16
a rotary transformer consisting of a rotary core
16
a
and a stationary core
16
b
,
17
a
and
18
a
cores embedded in the rotary core
16
a
, and
17
b
and
18
b
cores embedded in the stationary core
16
b
. As shown in
FIG. 11
, the electrode
12
consists of electrodes
12
a
to
12
d
and the electrode
13
consists of electrodes
13
a
to
13
b
, all of which are shaped like a fan with the center of the shaft
1
A as the center thereof. An overlapped portion between the electrodes
12
a
and
13
a
form a capacitor C
1
, an overlapped portion between the electrodes
12
b
and
13
a
forms a capacitor C
2
, an overlapped portion between the electrodes
12
c
and
13
b
form a capacitor C
3
, and an overlapped portion between the electrodes
12
d
and
13
b
form a capacitor C
4
.
These capacitors are connected to one another to form a Wheatstone bridge circuit as shown in FIG.
12
. The terminals “c” and “d” of the Wheatstone bridge circuit are connected to both ends of the coil
17
a
of the rotary transformer
16
and the terminals “a” and “b” are connected to both ends of the coil
18
a
of the rotary transformer
16
. The coils
17
b
and
18
b
magnetically connected to the coils
17
a
and
18
a
are connected to an unshown detection circuit.
A description is subsequently given of the operation of the torque detector. When torque is applied to the shaft
1
A from the steering wheel, the torsion deformation of the shaft
1
A occurs and relative torsion displacement between the pair of electrode bases
12
and
13
occurs. For example, when the electrodes
13
a
and
13
b
displace in a clockwise direction with respect to the electrodes
12
a
to
12
d
in
FIG. 11
, the areas of the overlapped portions change, whereby the capacitance of each of the capacitors C
1
and C
3
decreases and the capacitance of each of the capacitors C
2
and C
4
increases. Since the Wheatstone bridge circuit is thereby imbalanced, an AC voltage eO is generated between the terminals “a” and “b” by supplying an AC voltage eB between the terminals “c” and “d”. Since this voltage is proportional to the amount of torsion deformation of the shaft and the torque applied to the shaft, the torque is obtained from the voltage between the terminals “a” and “b”.
Since the terminals “a” to “d” are connected to the detection circuit by the rotary transformer
16
without contact, a signal can be transmitted even when the shaft
1
A turns.
SUMMARY OF THE INVENTION
Since the torque detector of the prior art is constituted as described above, to transmit a signal to the fixed detection circuit from a detection unit provided in the turning shaft
1
A, the rotary transformer must be used as in the case above or a slip ring must be used in other known examples with the result that the torque detector becomes complex in structure.
In other torque detector of the prior art, a movable magnetic member is displaced by the twisting of a torsion bar or the shaft caused by torque and this displacement is obtained as a change in the inductance of a coil wound round the shaft.
Since the magnetic characteristics of the magnetic member such as a yoke or movable magnetic member used in the rotary transformer or the coil have temperature characteristics, a torque detection error is easily produced.
It is an object of the present invention which has been made to solve the above problems of the prior art to provide a torque detector having a simple structure and high accuracy.
According to a first aspect of the present invention, there is provided a torque detector for detecting torque which is applied between a first shaft and a second shaft arranged coaxial to each other in such a manner that one end of the first shaft faces one end of the second shaft, wherein the torque detector comprises an elastic member for connecting the first shaft to the second shaft and generating torsion displacement between the first shaft and the second shaft according to the torque between the first and second shafts, a ring-shaped movable electrode attached to the shafts so that it displaces in an axial direction according to a relative torsion angle between the first and second shafts, a fixed electrode installed at a location where its surface is opposed to the surface of the movable electrode and it does not turn together with the shafts, and detecting means for detecting capacitance between the fixed electrode and the movable electrode.
According to a second aspect of the present invention, there is provided a torque detector which comprises first and second fixed electrodes arranged on the same side of the movable electrode and detecting means for detecting capacitance between each of the first fixed electrode and the second fixed electrode and the movable electrode.
According to a third aspect of the present invention, there is provided a torque sensor which comprises a third fixed electrode arranged on a side opposite to the first and second fixed electrodes of the movable electrode.
The above elastic member has a first group of elastic columns which are inclined at a predetermined angle with respect to the first shaft and formed at predetermined intervals on a side where it is fixed to the first shaft and a second group of elastic columns which are inclined at the same predetermined angle in an opposite direction to that of the first group of elastic columns with respect to the second shaft and formed at predetermined intervals on a side where it is fixed to the second shaft. The movable electrode is supported between the first group of elastic columns and the second group of elastic columns directly or indirectly.
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: 2432900 (1947-12-01), Jacobsen
patent: 2737049 (1956-03-01), Waugh
patent: 2754683 (1956-07-01), Waugh
patent: 4676331 (1987-06-01), Iwaki et al.
patent: 5910781 (1999-06-01), Kawamoto et al.
patent: 29 39 620 (1981-04-01), None
patent: 37 08 103 (1987-10-01), None
patent: 38 02 684 (1988-08-01), None
patent: 39 07 707 (1990-09-01), None
patent: 39 18 862 (1991-04-01), None
patent: 40 14 521 (1991-11-01), None
patent: 41 10 280 (1992-10-01), None
patent: 41 10 727 (1992-10-01), None
patent: 41 37 647 (1993-05-01), None
patent: 43 23 960 (1994-01-01), None
patent: 11-030681 (1999-02-01), None
Allen Andre
Fuller Benjamin R.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
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