Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2002-06-06
2004-02-17
Le, N. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207200, C324S207210
Reexamination Certificate
active
06693424
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on Japanese Patent Application No. 2001-174405 filed on Jun. 8, 2001 the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic rotation angle sensor for detecting a rotation angle of a rotor relative to a stator.
2. Description of Related Art
A magnetic sensor can be used for detecting a magnetic flux modulated in accordance with a detection object, such as a rotation angle. However, the magnetic sensor detects not only the modulated magnetic flux but also an external magnetic flux. As a result, the magnetic sensor outputs a detection signal with noise caused by the external magnetic flux.
For example,
FIGS. 6 and 7
show an arrangement of the magnetic sensor for detecting rotation angle. The magnetic rotation angle sensor has a stator and a rotor. One of the stator and the rotor has a magnetic flux modulator that provides a magnetic flux and modulate it in accordance with a relative rotation angle between the rotor and the stator so that the modulated magnetic flux passes through the other one of the stator and the rotor. The other one of the rotor and the stator has a magnetic sensor element for detecting the modulated magnetic flux, and outputs a signal indicative of the rotation angle. For example, the magnetic flux modulator may be provided by cores that vary a direction of the magnetic flux or an amount of the magnetic flux in accordance with a relative rotational position of the rotor and the stator.
In the illustrated case, the magnetic rotation angle sensor has a first portion that has a yoke
13
. The yoke
13
is formed in a substantially cylindrical shape to define an inner cavity. The yoke
13
is made of magnetic material and defines two gaps
11
for receiving magnets
12
respectively. The gaps
11
are located in a diametric relationship on the yoke
13
and separate the yoke
13
into two portions. The magnets
12
are magnetized in tangential directions to a circle defined by the yoke
13
. The magnetized axes D
1
and D
2
are parallel with each other, and directed in the same direction. A second portion that has a core
16
and a magnetic sensor element
15
is disposed inside the first portion. The core
16
is made of magnetic material. The core
16
defines a gap
14
that separates the core
16
into two members at a diametric line. Two magnetic sensor elements
15
are disposed in the gap
14
. Each of the magnetic sensor elements
15
is a molded IC including the Hall effect element. The magnets
12
provide a magnetic flux passing through the yoke
13
, the core
16
and the magnetic sensor element
15
. A relative rotation of the first portion and the second portion changes a relative positional relationship between the yoke
13
and the core
16
. The magnetic flux is modulated in accordance with the relative positional relationship between the yoke
13
and the core
16
. The magnetic sensor element
15
outputs a signal in accordance with the modulated magnetic flux that is indicative of relative rotation angle between the first and second portions. For example, the yoke
13
may rotate as the rotor and the core
16
may be fixed as the stator.
According to the arrangement described above, if the sensor is disposed in an external magnetic field, the sensor is influenced by the external magnetic field. For example, if an external magnetic flux may pass the core
16
in a diagonal direction through a path indicated by a broken line P
4
as shown in
FIG. 6
, an output signal of the magnetic sensor element
15
indicates an incorrect angle.
In a case in which the external magnetic field is applied in a direction perpendicular to a rotation axis of the rotor, the magnetic flux may pass the yoke
13
and the core
16
in a diametric direction through a path indicated by a broken line P
5
as shown in FIG.
7
. In a case of above, the magnetic sensor element
15
also outputs an incorrect signal.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic sensor that is capable of reducing an influence of an external magnetic field.
It is another object of the present invention to provide a magnetic sensor that is capable of detecting a rotation angle accurately.
It is a still another object of the present invention to provide a magnetic sensor that is capable of reducing an influence of an external magnetic field while preventing a short-circuiting leakage of the magnetic flux that is provided by a magnet.
According to a first aspect of the present invention, a magnetic rotation angle sensor for detecting a rotation angle of a rotor relative to a stator comprises a magnet, a yoke, a core, and a magnetic sensor element that detects the magnetic flux modulated by the core. A first means is provided for providing an external magnetic path for an external magnetic flux. The external magnetic path avoids the magnetic sensor element, and has a magnetic resistance lower than that of a magnetic path passing through the magnetic sensor element. Therefore, the external magnetic path guides the external magnetic flux rather than the magnetic path passing through the magnetic sensor element. As a result, the influence of the external magnetic field is reduced. A second means is provided for reducing short-circuiting leakage of the magnetic flux supplied by the magnet. Therefore, the yoke and the core receives sufficient amount of the magnetic flux from the magnet and the magnetic sensor element outputs accurate detection signal.
According to another aspect of the present invention, an additional external magnetic guide provides the external magnetic path. The external magnetic guide provides an axially extending external magnetic path.
According to a still another aspect of the present invention, the magnet is magnetized in an oblique direction so as to provide a shorter gap between the yokes and a longer distance between the poles. This arrangement provides the external magnetic path in the yoke, and provides a sufficient distance between the poles to reduce short-circuiting leakage of the magnetic flux supplied by the magnet.
REFERENCES:
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patent: 5798639 (1998-08-01), McCurley et al.
patent: 6268722 (2001-07-01), Kogure et al.
patent: 6356073 (2002-03-01), Hamaoka et al.
patent: 6414482 (2002-07-01), Mase
patent: 6448762 (2002-09-01), Kono et al.
patent: 6476600 (2002-11-01), Kono et al.
patent: 6501265 (2002-12-01), Nakamura et al.
patent: 6559637 (2003-05-01), Miyata et al.
patent: 11-83422 (1999-03-01), None
Kato Yasunari
Makino Masahiro
Denso Corporation
Kinder Darrell D
Le N.
Nixon & Vanderhye P.C.
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