Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2000-06-09
2002-11-19
Sherry, Michael (Department: 2829)
Electricity: measuring and testing
Magnetic
Displacement
C324S207200, C324S207210, C324S207240
Reexamination Certificate
active
06483296
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon Japanese Patent Application Nos. Hei. 11-171650 filed on Jun. 17, 1999, Hei. 11-171651 filed on Jun. 17, 1999, and Hei. 11-244306 filed on Aug. 31, 1999, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to angular position detection apparatuses, and in particular to an angular position detection apparatuses containing a permanent magnet which is magnetized so that lines of magnetic force are parallel with each other.
2. Related Art
In an angular position detection apparatus, which detects for example an opening degree of a throttle valve (an opening degree of a throttle) of an internal combustion engine, as shown in
FIG. 22
, a stator core
12
is concentrically arranged at an inner side of a cylindrical rotor core
11
, which integrally rotates with throttle valve (not-shown). Two permanent magnets
13
having circular arc are fixed to the inner side of the rotor core
11
so as to confront each other with sandwiching the stator core
12
. Each of the permanent magnets
13
is radially magnetized so that all of lines of magnetic force in the permanent magnets
13
are set to a radial direction. Here, in
FIG. 22
, directions of lines of magnetic forces in each of parts are illustrated by arrows (→). Incidentally, a magnetic flux detection gap portion
14
having a constant width is formed at a center portion of the stator core
12
so as to open along a diametral direction. A magnetic detection element
15
such as a Hall IC is provided in the magnetic flux detection gap portion
14
.
According to this structure, as shown in
FIG. 24
, since a magnetic flux density going through the magnetic flux detection gap portion
14
of the stator
12
(magnetic flux density crossing the magnetic detection element
15
) changes in proportion to the angular position of the rotor core
11
, and since output of the magnetic detection element
15
changes in proportion to the magnetic flux density, the angular position of the rotor core
11
(angular position of the throttle valve) is detected based on the output of the magnetic detection element
15
.
In the above-described structure, the output of the magnetic detection element
15
for detecting the angular position of the rotor core
11
changes in proportion to the magnetic flux density in the magnetic flux detection gap portion
14
. Therefore, if the magnetic flux in the magnetic flux detection gap portion
14
linearly changes in proportion to the angular position of the rotor core
11
, since an output characteristic of the magnetic detection element
15
regarding the angular position becomes linear, a detection characteristic of the angular position is improved.
However, according to the conventional structure discussed above, since the permanent magnets
13
are radially magnetized, it is impossible to secure a wide range in which magnetic flux in the magnetic flux detection gap portion
14
linearly changes in proportion to angular position of rotor core
11
. Therefore, since linear output with respect to angular position can be obtained over only a relatively narrow range, detection accuracy of the angular position decreases. For example, as shown in
FIG. 24
, a range, in which the magnetic flux in the magnetic flux detection gap portion
14
linearly changes in proportion to the angular position of the rotor core
11
, is at most approximately 80° (degrees). Therefore, when the angular position exceeds 80° (degrees), it is impossible to obtain linear output with respect to angular position, and detection accuracy of the angular position decreases.
Furthermore, since the permanent magnets
13
are arranged so as to confront with an outer surface of the stator core
12
, an outer size of the rotor core
11
for fixing the permanent magnets
13
and therefore an outer size of the angular position detection apparatus becomes bulky.
Moreover, in order to uniformly radially magnetize the permanent magnets
13
, a density of the inner side of the permanent magnet
13
needs to be dense and a density of the outer side thereof needs to be coarse. Therefore, strength of the permanent magnet
13
is likely to decrease due to a difference in density.
SUMMARY OF THE INVENTION
This invention has been conceived in view of the background thus far described and its first object is to provide an angular position detection apparatus in which a linearity of an output characteristic with respect to an angular position can be improved so as to improve a detection accuracy of the angular position.
Its second object is to improve strength of a permanent magnet.
Its third object is to downsize an outer size of the angular position detection apparatus.
According to one aspect of the present invention, a permanent magnet is fixed to a side portion of a rotor core, so that the permanent magnet does not confront with an outer surface of a stator core. Thus, an outer size of the rotor core and therefore an outer size of the angular position detection apparatus can be downsized.
In this case, it can be thought of as an axial gap in which a gap toward an axial direction (shaft direction) between the permanent magnet and the stator core exists, so that magnetic flux goes through the gap along the axial direction. However, one needs to form the air gap toward the axial direction between the permanent magnet and the stator core uniform and small, in order to improve linearity of the output characteristic of a magnetic detection element. In this case, it needs to precisely control a ratio of flatness and a ratio of the parallelism of confronted surfaces of the permanent magnet (rotor core) and the stator core, and therefore it is hard to manufacture.
According to this structure, although the permanent magnet is fixed to the side portion of the rotor core, the angular position detection apparatus is not formed as an axial gap type, but is formed as the radial gap type in which a cylindrical portion formed at the outer portion of the rotor core is closely confronted with the outer surface of the stator core, so that the magnetic flux goes through the air gap between the cylindrical portion and the stator core along the radial direction. As a result, when the axis between the rotor core and the stator core can be accurately controlled to be coaxial, the dimensional accuracy of the air gap can be also controlled. Furthermore, since the permanent magnet is fixed to the side portion of the rotor core, the permanent magnet can be formed in a flat plate shape, and therefore it can facilitate manufacture of the permanent magnet.
Moreover, in this structure, the permanent magnet is magnetized so that lines of the magnetic force in the permanent magnet are parallel with respect to each other (parallel magnetization). Thus, it can expand the range in which the magnetic flux density in the magnetic flux detection gap portion of the stator core linearly changes in proportion to rotation of the permanent magnet, compared to the radial magnetization in the related art. As a result, it can obtain linear output with respect to angular position over a wider range compared to the related art, and it can improve the detection accuracy of angular position. Furthermore, parallel magnetization can make the density of the permanent magnet uniform, so that the strength of the permanent magnet can be increased.
Incidentally, for example, in an electric throttle system, a throttle valve is rotated by an actuator such as a motor via a reduction mechanism, and angular position of the actuator is detected by an angular position apparatus to detect the angular position of the throttle valve (throttle opening degree). However, in this structure, since the throttle opening degree is calculated by dividing detected notation of the actuator by the reduction ratio of the reduction mechanism, detection error of the throttle opening becomes greater due to variation in the reduction ratio or backlash (backlash) between gears.
To
Hamaoka Takashi
Kubota Takamitsu
Nanba Kunio
Shimazu Akira
Tanaka Kunio
Denso Corporation
Nguyen Trung
Nixon & Vanderhye P.C.
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