Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
2002-08-20
2004-01-06
Strecker, Gerard R. (Department: 2862)
Measuring and testing
Dynamometers
Responsive to torque
C324S207160, C324S207250, C324S233000, C073S862331
Reexamination Certificate
active
06672175
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rotation sensor attached to a shaft or other object for assembly experiencing an offset of the angle of relative rotation at different positions in the axial direction and detecting by a non-contact method the difference in angle of relative rotation of the object for assembly and a measurement circuit using the rotation sensor and relates to a rotation sensor for detecting by a non-contact method the angle of rotation (position) of the object for assembly in addition to the angle of relative rotation.
BACKGROUND ART
To detect the rotational torque acting on the steering wheel shaft of an automobile comprising a drive shaft and a driven shaft coupled via a torsion joint, sometimes a rotation sensor is used as a relative rotation angle detector for detecting the angle of relative rotation of the steering wheel shaft. As an example of such a rotation sensor, Japanese Examined Patent Publication (Kokoku) No. 63-45528 discloses a configuration forming notches at predetermined positions in the longitudinal direction of two conductive members comprised of cylindrical shapes, rotating a shaft attached with a conductive member relatively so as to change the area of the conductive member cutting across the magnetic field and generate an eddy current in the conductive member and thereby change the inductance of a coil, and detecting the amount of offset of the angle of relative rotation at the shaft by a non-contact method.
According to this configuration, since the area of the conductive member cutting across the magnetic field is changed by the change in relative position of two conductive members, in order to accurately detect the amount of offset of the angle of rotation of the shaft, it is necessary to make the amount of offset of the angle of the rotation of the two shafts and the magnitude of the eddy current occurring in the conductive members proportional. Structurally, the area of a conductive member cutting across the magnetic field is proportional to the amount of offset, but what is necessary is to make the intensity of the magnetic field cut across by the two conductive members constant.
The magnetic field generated from the coil is however distributed substantially uniformly in the circumferential direction, while the distribution of the magnetic field on the rotation axis direction or radial direction of the coil is not uniform. Therefore, to ensure sensing with good linear characteristics, the two conductive members have to be assembled to overlap without a clearance. To improve the detection precision of the angle of rotation of the shaft, there is the problem that assembly precision continues to be strictly required.
Further, in a conventional measurement circuit of a rotation sensor, an AC current flows to an excitation coil provided at a stationary core and electrically connected to an oscillation circuit. The impedance of the coil changes depending on the angle of relative rotation of the first and second rotors. Further, the oscillation frequency of the oscillation circuit fluctuates in accordance with the change in the impedance of the excitation coil. Therefore, in this measurement circuit, the practice has been to count the pulse signals generated from the oscillation circuit by a pulse counter so as to detect the oscillation frequency and to measure the angle of relative rotation of the first rotor and the second rotor.
In this measurement circuit, however, the oscillation frequency of the oscillation circuit fluctuates in the range of 98 kHz to 108 kHz with respect to a change in the impedance of the coil. The circuit normally measured the number of pulses by a resolution for counting the pulse signals in a time of 5 ms. Therefore, if this measurement circuit is used to detect the torque acting on for example the steering wheel shaft of a vehicle, there was the problem that time was taken for counting the pulses by a pulse counter and the response became poor. For example, when the oscillation frequency of the oscillation circuit fluctuates from 100 kHz to 105 kHz due to this resolution, the number of pulses becomes measured by a fluctuation from 500 pulses to 525 pulses, that is, by an amount of fluctuation of 25 pulses. Further, in this measurement circuit, if the time for counting pulses of the pulse counter is shortened to improve the response, the amount of fluctuation of the number of pulses becomes smaller and the resolution falls, so there is the problem that detection of fluctuation of the oscillation frequency becomes difficult.
On the other hand, the rotation sensor shown in
FIG. 53
is comprised of a stationary magnetic member
1
having a coil and a magnetic material rotor
2
having irregularities on its outer circumference between which is arranged, in a predetermined gap, a metal rotor
3
having a plurality of metal teeth
3
a.
This rotation sensor has the plurality of metal teeth
3
a
arranged at equal intervals in the circumferential direction and generates an eddy current in the metal teeth
3
a
when the metal teeth
3
a
cut across the AC magnetic field with the irregular distribution due to the relative rotation of the two rotors
2
and
3
. This eddy current fluctuates due to the angle of relative rotation between the two rotors
2
and
3
. Therefore, the rotation sensor detects the angle of relative rotation of the two rotors
2
and
3
, that is, the angle of relative rotation between two relatively rotating members, by measuring the change in the impedance of the coil caused due to the fluctuation in the eddy current induced inside the members.
A rotation sensor using such an irregular distribution AC magnetic field, however, is governed in characteristics by two parameters, that is, the fluctuation &Dgr;B of the magnetic
10
flux density and the boundary area &Dgr;&thgr; of the intensity of the magnetic field in the distribution produced as shown in
FIG. 54
showing the fluctuation in magnetic flux density in the circumferential direction in the gap. That is, the rotation sensor has a higher sensitivity of detection of the angle of rotation the larger than fluctuation &Dgr;B of the magnetic flux density and has a good linearity of detection output the smaller the boundary area &Dgr;&thgr; of the distribution of the magnetic field.
The rotation sensor, however, suffers from the following problem if making the degree of irregular distribution of the AC magnetic field due to the size of the gap larger.
As is well known, in a magnetic circuit, fluctuations of the effective specific magnetic permeability due to the size of the gap deviate from a linear characteristic. That is, in a magnetic circuit, the smaller the gap, the larger the fluctuation of the effective specific magnetic permeability. Since the metal rotor
3
is arranged in the gap in this way, if considering the manufacturing precision and rotational precision of the rotor, normally in the rotation sensor, the gap G
1
is desirably set to at least 1 rom as shown in FIG.
53
. An amount of change of the gap of several millimeters is required in order for the rotation sensor to obtain a suitable detection sensitivity. That is, the rotation sensor has to be of a size giving an amount &Dgr;G of change of the gap (=G
2
−G
1
) accompanying irregularity of the magnetic material rotor
2
of several millimeters.
On the other hand, in the rotation sensor shown in
FIG. 53
, the thickness of the magnetic material rotor
2
is changed cyclically corresponding to the plurality of metal teeth
3
a
along the circumferential direction. Therefore, since the gap formed in the circumferential direction between the fixed magnetic member
1
and magnetic material rotor
2
is step-like in shape, when magnetic flux flows from the core material with the high magnetic permeability into the air with the low magnetic permeability, it characteristically concentrates at the corner portions of the core material. Therefore, due to the magnetic flux concentrating at the corner portions, in this rotation sensor, there was
Abe Fumihiko
Jin Dongzhi
Tanaka Kengo
Strecker Gerard R.
The Furukawa Electric Co. Ltd.
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