Rotation detector

Details Rotation detector Rotation detector

2001-03-26

2003-05-27

Gutierrez, Diego (Department: 2859)

Geometrical instruments

Miscellaneous

Light direction

C033S708000, C033S0010DD, C033S706000

Reexamination Certificate

active

06568093

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a rotation detector, and more particularly, to a rotation detector that includes a magnetic sensing element.
The applicant has proposed a rotation detector, or a rotation position sensor
51
, as illustrated in FIG.
15
. The rotation position sensor
51
has an iron rotating plate
52
and a sensor body
53
. The rotating plate
52
, which is in the shape of disk, is secured to a steering shaft
54
of a vehicle. The rotating plate
52
rotates together with the steering shaft
54
about the axis of the steering shaft. Extending from the peripheral edge of one surface of the rotating plate
52
, a plurality of arcuate iron magnetic path changing pieces
55
are formed. Each piece
55
is coaxial with the shaft
54
.
The sensor body
53
is located outside of and close to the magnetic path changing pieces
55
. The sensor body
53
includes a plurality of magnetic sensing bodies
56
encapsulated by a resin molding material
57
and fixed to a fixing member, not shown. Each of the magnetic sensing bodies
56
includes a bias magnet
56
b,
which is opposite to the rotating plate
52
and oriented in a predetermined direction, and a magneto-resistive element
56
a,
which detects magnetic flux of the bias magnet
56
b.
The direction of the magnetic flux of each bias magnet
56
b
is changed when the associated magnetic path changing piece
55
passes a position corresponding to the magnetic sensing body
56
as the rotating plate
52
is rotated. The magneto-resistive element
56
a
detects changes in the direction of the magnetic flux of the associated bias magnet
56
b.
In this way, rotation is detected.
In the rotary position sensor
51
thus formed, however, if a disturbance source G such as a coil exists nearby, as indicated by broken lines in
FIG. 15
, disturbance magnetic flux m may be generated from the disturbance source G. Thus, when detecting the presence or absence of a magnetic path changing piece
55
between the bias magnet
56
b
and the axis of the shaft
54
, the disturbance magnetic flux m may affect the rotating plate
52
and the magnetic path changing piece
55
and adversely affect the magnetic sensing bodies
56
.
Specifically, even though a magnetic path changing piece
55
is located between the bias magnet
56
b
and the axis, the associated magneto-resistive element
56
a
may detect magnetic flux having a direction substantially similar to that of the flux in existence when the magnetic path changing piece
55
is not between the bias magnet
56
b
and the axis. Conversely, the magneto-resistive element
56
a
may detect magnetic flux having a direction substantially similar to that of the flux in existence when the associated magnetic path changing piece
55
is between the bias magnet
56
b
and the axis although the magnetic path changing piece
55
is not between the bias magnet
56
b
and the axis.
SUMMARY OF THE INVENTION
Accordingly, it is an objective of the present invention to provide a rotation detector that is capable of eliminating the influence of disturbance on magnetic sensing of a magnetic sensing element even if a disturbance source is positioned near the rotation detector.
In order to achieve this object, in accordance with the present invention, there is provided a rotation detector comprising: a circular rotating member; magnetic path changing pieces formed at predetermined intervals in a circumferential direction of the rotating member, each of the magnetic path changing pieces being made of a magnetic material; a magnetic sensing element for detecting magnetic flux of a magnet located in a predetermined orientation to the rotating member; and a shielding member covering at least a portion of the magnet and the magnetic sensing element, wherein the shielding member is made of a magnetic material.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.


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