Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2001-01-26
2002-11-05
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250
Reexamination Certificate
active
06476600
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to an improved structure of a device for measuring an angular position of an object using a magnetic detector and magnets, and more particularly to a compact and high-accuracy angular position measuring device.
2. Background Art
U.S. Pat. No. 5,861,745 (Japanese Patent First Publication No. 2920179, PCT:WO98/080601) discloses an angular position measuring device using a magnetic detector such as a Hall element and magnets.
FIG. 19
shows one example of conventional angular position measuring devices designed to measure an opened position of a throttle valve of an internal combustion engine. The device includes a cylindrical rotor core (i.e., a yoke)
11
rotating along with the throttle valve (not shown) and a stator core
12
disposed coaxially within the rotor core
11
. Disposed between the rotor core
11
and the stator core
12
are two arc-shaped magnets
13
which are diametrically opposed to each other. Each of the magnets
13
is so magnetized that all lines of magnetic force are oriented in a radius direction of the magnet
13
. A magnetic gap
14
is formed in the stator core
12
which has a constant width and extends through the center of the stator core
12
in a diameter direction. A magnetic detector such as a Hall IC is disposed at the center of the magnetic gap
14
.
The density of a magnetic flux through the magnetic gap
14
in the stator core
12
changes as a function of an angular position of the rotor core
11
. The magnetic detector
15
produces an output as a function of the magnetic flux density. Specifically, the angular position of the rotor core
11
, or the opened position of the throttle valve is determined using the output of the magnetic detector
15
.
The arc-shaped magnets
13
are, as described above, magnetized radially. Uniformly magnetizing the magnets
13
requires decreasing the magnetic flux density in an outer peripheral portion of the magnets
13
, while increasing the magnetic flux density in an inner peripheral portion of the magnets
13
. Such magnets are, however, difficult to produce and may have a great variation in quality. The variation in quality will lead to an error in an output of the magnetic detector
15
.
Additionally, the installation of the magnets
13
between the rotor core
11
and the stator core
12
will result in an increase in diameter of the rotor core
11
, thereby leading to an increase in overall size of the angular position measuring device.
SUMMARY OF THE INVENTION
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide a compact angular position measuring device capable of determining an angular position of a rotary object with high accuracy.
According to one aspect of the invention, there is provided an angular position measuring device which comprises: (a) a stationary member; (b) a rotatable member rotatable following rotation of an object to be measured in angular position; (c) a plurality of magnets installed in one of the stationary member and the rotatable member so that the same poles are opposed magnetically to produce a repellent force in magnetic fields of the magnets; and (d) a sensor element installed in the other of the stationary member and the rotatable member, the sensor element being responsive to a change in density of magnetic flux produced by the magnets to provide an output as a function of an angular position of the object.
In the preferred mode of the invention, each of the magnets is made of one of a plate and a cylindrical member whose ends are magnetized.
The rotatable member is made of a hollow cylindrical yoke having installed therein the magnets. The stationary member is made of a stator core having installed therein the sensor element and disposed inside the cylindrical yoke. A sensor gap is formed in the stator core within which the sensor element is disposed.
The cylindrical yoke may have air cavities formed in an inner surface thereof which open to the magnets for avoiding a short of the magnetic flux between each pole of the magnets and the stator core.
The magnets may be so arranged as to define two magnetic paths along which the magnetic fluxes produced by the magnets pass. The magnetic paths extend symmetrically through the stationary member and the rotatable member.
The stator core is made of three or more parts which are so fabricated as to define air gaps one of which is the sensor gap within which the sensor element is disposed.
The air gaps extend radially in the stator core at a regular angular interval. The magnets are arranged at an angular interval identical with the angular interval of the air gaps.
The stator core may be circular in cross section. The one of the air gaps employed as the sensor gap is longer than a radius of the stator core.
The one of the air gaps as employed as the sensor gap is longer than the other air gaps.
The stator core may have formed in at least one of ends of the sensor gap a greater air cavity which serves to concentrate the magnetic flux at the sensor gap.
An air gap may be defined between the inside of the cylindrical yoke and the outside of the stator core. The air gap is defined by an interval between the inside of the cylindrical yoke and the outside of the stator core which varies in a circumferential direction of the inside of the cylindrical yoke.
The interval may be maximized at each of the poles of said magnets.
The cylindrical yoke defines therein an oval chamber in which the stator core is disposed.
REFERENCES:
patent: 5528139 (1996-06-01), Oudet et al.
patent: 5789917 (1998-08-01), Oudet et al.
patent: 5861745 (1999-01-01), Herden
patent: 6043645 (2000-03-01), Oudet et al.
patent: 6130535 (2000-10-01), Herden et al.
patent: 19634281 (1998-02-01), None
patent: 19726691 (1999-01-01), None
patent: 1065473 (2001-01-01), None
patent: 2842482 (1998-10-01), None
patent: 11-83422 (1999-03-01), None
patent: 2920179 (1999-04-01), None
patent: WO 98/08060 (1998-02-01), None
Aoki Tetsuya
Fukitsuke Takuya
Hamaoka Takashi
Kono Yoshiyuki
Kubota Takamitsu
Lefkowitz Edward
Zaveri Subhash
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