Electricity: electrical systems and devices – Control circuits for electromagnetic devices – Systems for magnetizing – demagnetizing – or controlling the...
Reexamination Certificate
2001-02-20
2003-05-27
Strecker, Gerard R. (Department: 2862)
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
Systems for magnetizing, demagnetizing, or controlling the...
C324S174000, C324S207220, C335S306000, C384S448000, C029S593000
Reexamination Certificate
active
06570751
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic encoder applied to a bearing having a function of detecting a rotational frequency or the direction of rotation, a wheel bearing having the magnetic encoder and a method of manufacturing a magnetic encoder.
2. Description of the Background Art
A magnetic encoder for detecting a rotational frequency or the like has such a structure that a magnetic member is circumferentially formed on an annular member and multipolarly magnetized in the circumferential direction. The magnetic encoder is rotated with a rotator so that a magnetic sensor closely opposed to the magnetic member detects the rotation thereby detecting the rotational frequency.
In general, the magnetic member of such a magnetic encoder is magnetized by one-shot magnetization or index magnetization.
FIG. 17
is a diagram for illustrating a method of performing one-shot magnetization on a magnetic member of a magnetic encoder. Referring to
FIG. 17
, a magnetic encoder
103
consisting of a metal ring
102
forming an annular member and a magnetic member
101
provided on the outer peripheral surface of the metal ring
102
is prepared. A magnetization yoke
111
supporting a plurality of exciting coils
112
is so arranged that the exciting coils
112
are opposed to the surface of the magnetic member
101
of the magnetic encoder
103
. In this state, a current is fed to the exciting coils
112
in a prescribed direction, thereby magnetizing the magnetic member
101
and multipolarly magnetized in the circumferential direction.
FIG. 18
is a diagram for illustrating a method of performing index magnetization on a magnetic member of a magnetic encoder. Referring to
FIG. 18
, a magnetic encoder
203
consisting of a metal ring
202
forming an annular member and a magnetic member
201
provided on the outer peripheral surface of the metal ring
202
is prepared. A pair of tooth profiles of a magnetization yoke
211
having an exciting coil
212
wound thereon are closely arranged on the outer peripheral surface of the magnetic encoder
203
. In this state, a current is fed to the exciting coil
212
for generating a magnetic flux passing through the magnetization yoke
211
in a prescribed direction, and the magnetic flux passing through the clearance between the tooth profiles magnetizes the magnetic member
201
for obtaining a pair of N and S poles. Thereafter a step of rotating the magnetic encoder
203
by a prescribed angle and magnetizing the same is repeated thereby multipolarly magnetizing the overall periphery of the magnetic member
201
in the circumferential direction. This method is hereinafter referred to as surface layer magnetization.
In the one-shot magnetization shown in
FIG. 17
, however, the magnetization pitch is disadvantageously largely irregularized depending on the manufacturing accuracy for each magnetic pole or the way of winding the coil when the pitch is reduced to not more than a pole width of about 1.5 mm, although high magnetization strength is attained.
In the surface layer magnetization shown in
FIG. 18
, the magnetization yoke
211
has a pair of tooth profiles and hence magnetization pitch accuracy is improved when attaining indexing accuracy of a spindle for rotating a workpiece. In this method, however, only the surface layer of the magnetic member
201
can be magnetized, disadvantageously leading to small magnetization strength.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetic encoder having high magnetization strength similar to that in one-shot magnetization and a small magnetization pitch error similar to that in surface layer magnetization.
Another object of the present invention is to provide a wheel bearing having a magnetic encoder having high magnetization strength and a small magnetization pitch error.
A magnetic encoder according to the present invention comprises an annular member and a magnetic member circumferentially provided on the annular member and multipolarly magnetized in the circumferential direction, and is characterized in that a magnetization pitch error of the magnetic member is not more than 3% and surface magnetization strength per unit magnetic pole is at least 30 mT/mm.
Then, surface magnetization strength per unit magnetic pole is a value obtained by dividing a maximum surface magnetization strength in one magnetic pole by the magnetic pole width.
Thus, it is possible to obtain a magnetic encoder having a small magnetization pitch error of not more than 3% similarly to that obtained in surface magnetization and high surface magnetization strength of at least 30 mT/mm similarly to that obtained in one-shot magnetization. Thus, the magnetic encoder can detect a rotational frequency or the like with higher accuracy.
In the aforementioned magnetic encoder, the annular member preferably consists of a magnetic substance, and the magnetic member preferably consists of an elastomer mixed with magnetic powder.
The annular member consists of a magnetic substance as described above, so that leakage of a magnetic flux can be suppressed in magnetization of the magnetic member and magnetization strength of the magnetic member is improved.
A wheel bearing according to the present invention rotatably supporting a wheel has a rotating member provided with the aforementioned magnetic encoder, and is characterized in that the rotating member is so arranged that the magnetic encoder is closely opposed to a magnetic sensor for detecting the speed of rotation of the wheel.
Thus, a wheel bearing provided with a magnetic encoder capable of rotating the speed of rotation of a wheel in high accuracy can be obtained.
The aforementioned wheel bearing preferably has a fixed member rotatably supporting the rotating member, and the magnetic encoder preferably forms a sealing apparatus sealing an annular space between the rotating member and the fixed member.
Thus, the magnetic encoder can also serve as the sealing apparatus, whereby increase of the number of components can be prevented.
In the aforementioned wheel bearing, the sealing apparatus preferably has a sealing member mounted on the fixed member to be capable of coming into sliding contact with the annular member of the magnetic encoder.
Thus, it is possible to prevent leakage of oil from the bearing or penetration of foreign matter of moisture from outside the bearing.
A method of manufacturing a magnetic encoder according to the present invention, circumferentially providing a magnetic member on an annular member and magnetizing the magnetic member, arranges a magnetization yoke passing a magnetic flux for magnetizing the magnetic member to hold the magnetic member and the annular member so that the magnetic flux passes through and magnetizes the magnetic member in the portion held by the magnetization yoke for successively magnetizing the magnetic member along the circumferential direction thereby multipolarly magnetizing the magnetic member in the circumferential direction.
The magnetization yoke thus holds the magnetic member and magnetizes the same so that the magnetic flux passes through the magnetic member, whereby magnetization strength can be increased similarly to that obtained by one-shot magnetization. Further, the magnetic member is magnetized every magnetic pole, whereby a magnetization pitch error can be reduced similarly to that obtained in surface layer magnetization so far as indexing accuracy of a spindle can be attained.
Preferably, the aforementioned method of manufacturing a magnetic encoder makes magnetization conditions variable in N pole magnetization and S pole magnetization of the peripheral surface of the magnetic member
1
.
Thus, N and S poles can be controlled to reach substantially identical magnetization strength by varying the magnetization conditions.
Preferably, the aforementioned method of manufacturing a magnetic encoder varies the value of a current fed to a coil wound on the magnetization yoke with the N pole magnetization and the S pole magnetizat
Inokuchi Kazuyuki
Iwamoto Ken-ichi
Koike Takashi
NTN Corporation
Strecker Gerard R.
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