Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
2002-08-30
2004-07-20
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
C073S862334, C073S862335, C336S020000, C336S030000, C336S115000
Reexamination Certificate
active
06763733
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotational angle detecting device for detecting a rotational angle of a rotating member, a torque detecting device for detecting a rotational torque applied to a rotating shaft, and an automobile steering apparatus provided with the rotational angle detecting device and the torque detecting device.
2. Description of Related Art
An electric power steering apparatus which is constructed to drive an electric motor for assisting steering on the basis of a detection result of a steering torque applied to a steering wheel for steering to transmit a rotating force of the electric motor to a steering mechanism for assisting steering has an advantage in that the assisting power characteristics can be easily controlled in accordance with the running state such as high and low speed of the automobile, the frequency of steering, and the like as compared with a hydraulic pressure power steering apparatus using a hydraulic pressure actuator as a generation source of a steering assisting power. As a consequence, the scope of application of an electric power steering apparatus has tended to expand in recent years.
In such an electric power steering apparatus, a steering torque is detected at an intermediate portion of a steering shaft for connecting the steering wheel and a steering mechanism by detecting the rotational angle at two positions separated in the shaft length direction. That is, on the steering shaft which is operated for steering, torsion is generated with an action of the steering torque which is applied to the steering wheel. This torsion corresponds to a difference in the detection angle at two positions described above, so that the rotational torque (steering torque) applied to the steering shaft can be determined by using this difference.
Furthermore, in actuality, the steering shaft is constructed in such a manner that a first shaft (an input shaft) on the steering wheel side and a second shaft (an output shaft) on the steering apparatus side are separated, and these two shafts are coaxially connected via a torsion bar having a small diameter as a torsion element, so that a large relative angle deviation is generated with the torsion of a torsion bar between the first shaft and the second shaft at the time of action of the above steering torque. Consequently, the torque is detected with a high degree of accuracy on the basis of a difference in the detection angle.
Furthermore, in the electric power steering apparatus, it is necessary to detect the rotational angle of the steering shaft, namely the steering angle from the mid-point of the steering angle in order to use the drive control of the electric motor for assisting the steering. In the torque detecting device described above, the steering angle can be detected by the rotational angle detected at two positions of the steering shaft.
The applicant of the present invention proposed in Japanese Patent Application Laid-Open No. 2002-107112 a detecting device which can be preferably used in the detection of the rotational angle and the rotational torque as described above. In the schematic view of
FIG. 1
, a construction of the rotational angle and torque detecting device is shown.
These conventional rotational angle and torque detecting device, as shown in
FIG. 1
, is provided with target plates (rotating members)
30
and
40
both having a disc-like shape which are externally fitted onto and fixed to both the first shaft
1
and the second shaft
2
in the vicinity of a connection portion of the first shaft
1
and the second shaft
2
coaxially connected via a torsion bar T. MR (magnetic resistance effect) sensors
50
and
60
as detecting means are fixed and arranged so as to be positioned opposite to the outer circumferencial surface of these target plates
30
and
40
.
On the outer circumferential surface of the target plates
30
and
40
where MR sensors
50
and
60
are positioned opposite to each other, targets
30
a
and
40
a
are provided as detection targets. These targets
30
a
and
40
a
are, as shown in
FIG. 1
, protrusions made of a magnetic member constructed as a partially helical continuous member whose inclination direction with respect to an axial direction is cyclically changed, and is present as a magnetically discontinuous portion with respect to the peripheral portion. Such targets
30
a
and
40
a
reciprocate in an axial direction in accordance with the rotation of the target plates
30
and
40
when viewing the fixed position of the MR sensors
50
and
60
as a reference. Then, the MR sensors
50
and
60
are constructed so as to generate a sine wave-like output which changes cyclically in accordance with the axial direction deviation of the targets
30
a
and
40
a.
FIG. 2
is a view for explaining an operation of detecting rotational angle with the conventional rotational angle and torque detecting device described above. As shown in
FIG. 2
, the MR sensor
50
is constructed in such a manner that a pair of MR (magnetic resistance effect) elements
50
a
and
50
b
having a characteristic of changing the electric resistance with the action of the magnetic field are connected in series, and an internal magnet
50
c
is arranged so as to allow an equally magnetic field to act on one side of the pair of MR elements
50
a
and
50
b
. With such a construction, an electric potential, when a predetermined voltage is applied to a series circuit of the MR elements
50
a
and
50
b
, can be taken out as an output.
FIG. 2
is a view showing a state in which the target
30
a
provided on an outer circumference of the target plate
30
is developed on a plane. The MR sensor
50
which is constructed in a manner as described above is arranged, so that the other side (the opposite side of internal magnet
50
c
) of MR elements
50
a
and
50
b
is positioned approximately at the center of the deviation area of the above-described target
30
a
. When the target plate
30
is rotated in this state, the MR sensor
50
relatively changes its position in a circumferential direction along the outer circumference of the target plate
30
and the target
30
a
on the outer circumference of the target plate
30
is deviated in the direction of a parallel arrangement of MR elements
50
a
and
50
b.
Here, since the target
30
a
is made of a magnetic member, the magnetic field formed by the internal magnet
50
c
is deviated to either one of the MR elements
50
a
and
50
b
in accordance with a deviation of the target
30
a
. That is, in the case where the MR sensor
50
is positioned at point A in
FIG. 2
, the magnetic field formed by the internal magnet
50
c
is deviated to the MR element
50
a
side which relatively comes close to the target
30
a
, so that the resistance of the MR element
50
a
becomes larger while the resistance of the other MR element
50
b
becomes small. Consequently, the output taken out between both MR elements
50
a
and
50
b
becomes minimum. On the other hand, in the case where the MR sensor
50
is positioned at point B in
FIG. 2
, the magnetic field formed by the internal magnet
50
c
is deviated to the MR element
50
b
side which comes relatively close to the target
30
a
so that the resistance of the MR element
50
b
increases while the resistance of the other MR element
50
a
decreases, so that the output taken between both MR elements
50
a
and
50
b
becomes maximum.
In this manner, the output of the MR sensor
50
becomes an output having a sine wave-like form which cyclically changes between the minimum output at the point A and the maximum output at the point B in accordance with the target
30
a
caused by the rotation of the target plate
30
. Consequently, this output is taken in at a predetermined sampling cycle to calculate an accumulated value of output change from the previous sampling time, so that the rotational angle of the target plate
30
and the first shaft
1
are obtained.
Also, at the MR sensor
60
arranged opposite to the target plate
40
on
Ellington Alandra
Koyo Seiko Co. Ltd.
Lefkowitz Edward
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