U.S. patent number RE40,523 [Application Number 10/797,702] was granted by the patent office on 2008-09-30 for non-contact rotational position sensor and throttle valve assembly including non-contact rotational position sensor.
This patent grant is currently assigned to Hitachi Car Engineering Co., Ltd., Hitachi, Ltd.. Invention is credited to Masanori Kubota, Kenji Miyata, Satoshi Shimada, Fumio Tajima, Toshifumi Usui.
United States Patent |
RE40,523 |
Miyata , et al. |
September 30, 2008 |
Non-contact rotational position sensor and throttle valve assembly
including non-contact rotational position sensor
Abstract
A non-contact sensor for sensing a rotational position of a
rotating object is provided. A ring-shaped permanent magnet
magnetized in the axial direction is sandwiched between two pairs
of magnetic plates from above and below. Two pairs of upper and
lower protruded magnetic substance portions are provided between
the upper and lower magnetic plates at opposite outer ends thereof.
Magnetic sensitive devices are inserted in air gaps between the two
pairs of upper and lower protruded magnetic substance portions. A
magnetic flux generated from the ring-shaped permanent magnet is
substantially concentrated to the protruded magnetic substance
portions and passes the magnetic sensitive devices. The amount of
magnetic flux passing each magnetic sensitive device is
substantially proportional to the rotational angle of the
ring-shaped permanent magnet. The rotational position of the
ring-shaped permanent magnet and hence the rotational position of a
rotating shaft supporting the ring-shaped permanent magnet can be
sensed in a non-contact manner as a signal output from the magnetic
sensitive device. Since the magnetic flux is effectively
concentrated to positions where magnetic sensitive devices are
attached, a non-contact rotational position sensor having high
accuracy and high sensitivity can be obtained.
Inventors: |
Miyata; Kenji (Hitachinaka,
JP), Shimada; Satoshi (Hitachi, JP),
Tajima; Fumio (Taga-gun, JP), Usui; Toshifumi
(Tokyo, JP), Kubota; Masanori (Hitachinaka,
JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
Hitachi Car Engineering Co., Ltd. (Hitachinaka-shi,
JP)
|
Family
ID: |
18870607 |
Appl.
No.: |
10/797,702 |
Filed: |
March 10, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
09820327 |
Mar 29, 2001 |
06559637 |
May 6, 2003 |
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Foreign Application Priority Data
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Jan 10, 2001 [JP] |
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2001-002045 |
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Current U.S.
Class: |
324/207.2;
123/406.52; 324/207.25 |
Current CPC
Class: |
G01D
5/145 (20130101) |
Current International
Class: |
G01B
7/30 (20060101) |
Field of
Search: |
;324/207.2,207.21,207.25,207.22,174 ;123/406.52,617 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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199 44 019 |
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Mar 2000 |
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DE |
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0 798 541 |
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Oct 1997 |
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EP |
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0798541 |
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Oct 1997 |
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EP |
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1 065 473 |
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Jan 2001 |
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EP |
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1065473 |
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Jan 2001 |
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EP |
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08-126380 |
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May 1996 |
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JP |
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2842482 |
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Jun 1996 |
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JP |
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2920179 |
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Aug 1998 |
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JP |
|
2842482 |
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Oct 1998 |
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JP |
|
2920179 |
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Apr 1999 |
|
JP |
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2000-097606 |
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Apr 2000 |
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JP |
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WO 97/43602 |
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Nov 1997 |
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WO |
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Primary Examiner: Patidar; Jay M
Attorney, Agent or Firm: Crowell & Moring LLP
Claims
What is claimed is:
1. A non-contact rotational position sensor comprising: a permanent
magnet having a circular or arc-shaped outer circumference; a shaft
for supporting and fixing said permanent magnet; upper and lower
magnetic plates sandwiching said permanent magnet from above and
below, at least one of said upper and lower magnetic plates being
horizontally separated from each other with an air gap formed
therebetween; .[.at least one protruded magnetic substance portion
disposed between said upper and lower magnetic plates; and.]. a
magnetic sensitive device disposed on a protruded surface of
.[.said.]. .Iadd.a .Iaddend.protruded magnetic substance portion,
said permanent magnet and said shaft constituting a rotor which is
rotatable relative to said upper and lower magnetic plates
vertically spaced from each other, said permanent .[.magnetic.].
.Iadd.magnet .Iaddend.being magnetized substantially in the
direction of a rotating axis, whereby the amount of magnetic flux
passing said magnetic sensitive device is varied with rotation of
said permanent magnet, wherein said upper and lower magnetic plates
sandwiching said permanent magnet from above and below are
.[.formed of.]. magnetic plates each having protruded portions at
opposite ends .[.instead of providing said protruded magnetic
substance portion on at least one of said upper and lower magnetic
plates.]. , said protruded portions being bent to .[.form pairs
of.]. .Iadd.comprise .Iaddend.upper and lower .[.protruded
portions.]. .Iadd.pairs.Iaddend., and said magnetic sensitive
device is .[.inserted.]. .Iadd.arranged .Iaddend.in an air gap
formed between .[.protruded.]. surfaces of every two .Iadd.of said
.Iaddend.upper and lower .Iadd.pairs of .Iaddend.protruded
portions.[...]. .Iadd.; .Iaddend. .Iadd.said upper magnetic plate
is comprised of a first upper magnetic plate and a second upper
magnetic plate; said lower magnetic plate is comprised of a first
lower magnetic plate and a second lower magnetic plate; said
permanent magnet consists of two permanent magnets, in which the
first of the permanent magnets is magnetized in one direction, and
the second of the permanent magnets is magnetized in a direction
opposite to the one direction; a first area in which the magnetic
field of the first permanent magnet has the one direction and a
first area in which magnetic field of the second permanent magnet
has the opposite direction being positioned between said first
upper magnetic plate and said first lower magnetic plate; and a
second area in which the magnetic field of the first permanent
magnet has the one direction and a second area in which the
magnetic field of the second permanent magnet has the opposite
direction being positioned between said second upper magnetic plate
and said second lower magnetic plate; whereby the first upper
magnetic plate and the first lower magnetic plate thus form a
linear magnetic circuit between the permanent magnet and the
protruded magnetic substance portion independent of a rotating
position of said permanent magnet, and the second upper magnetic
plate and said second lower magnetic plate thus form a linear
magnetic circuit between said permanent magnet and the protruded
magnetic substance portion independent of the rotating position of
the permanent magnet..Iaddend.
2. A non-contact rotational position sensor comprising: a rotating
axis; an annular or semi-annular magnet fixed to said rotating
axis; magnetic substance assemblies arranged in opposing relation
to sandwich said magnet therebetween with a spacing greater than a
thickness of said magnet left between said magnetic substance
assemblies in .[.the.]. .Iadd.an .Iaddend.axial direction of said
rotating axis, such that a uniform air gap is formed between said
magnet and a surface of each of said magnetic substance assemblies
.[.confronting.]. .Iadd.facing .Iaddend.said magnet; a pair of
small air gaps .[.formed in.]. .Iadd.defined by .Iaddend.said
magnetic substance assemblies and being smaller than said
.Iadd.uniform .Iaddend.air gap; and a magnetic sensitive device
disposed in .Iadd.each .Iaddend.said small air gap, wherein said
magnetic substance assemblies comprise a pair of
rectangularly-shaped magnetic plates, and at least one of said pair
of rectangular magnetic plates .[.has a split.]. .Iadd.is divided
by a separating .Iaddend.air gap .[.formed along an imaginary
plane.]. passing .[.an axial center line of.]. .Iadd.through
.Iaddend.said rotating axis.[., said air gap splitting said
rectangular magnetic plate into two parts.]. .Iadd.; the at least
one pair of magnetic plates comprising upper and lower magnetic
plates in which the upper magnetic plate is comprised of a first
upper magnetic plate and a second upper magnetic plate, the lower
magnetic plate is comprised of a first lower magnetic plate and a
second lower magnetic plate, the magnet is comprised of two magnets
with the first of the being magnetized in one direction, and the
second of the magnets being magnetized in a direction opposite to
the one direction; a first area in which a magnetic field of the
first magnet has the one direction and a first area in which a
magnetic field of the second magnet has the opposite direction
being positioned between first upper magnetic plate and the first
lower magnetic plate; and a second area in which the magnetic field
of the first magnet has the one direction and a second area in
which the magnetic field of the second magnet has the opposite
direction being positioned between second upper magnetic plate and
the second lower magnetic plate; whereby the first upper magnetic
plate and the first lower magnetic plate thus form a linear
magnetic circuit between the magnet and the protruded magnetic
substance portion independent of the rotational position of the
magnet, and the second upper magnetic plate and the second lower
magnetic plate thus form a linear magnetic circuit between said
magnet and a protruded magnetic substance portion independent of
the rotational position of the magnet.Iaddend..
3. A non-contact rotational position sensor comprising: a rotating
axis; an annular or semi-annular magnet fixed to said rotating
axis; magnetic substance assemblies arranged in opposing relation
to sandwich said magnet therebetween with a spacing greater than a
thickness of said magnet .[.left.]. .Iadd.arranged .Iaddend.between
said magnetic substance assemblies in .[.the.]. .Iadd.an
.Iaddend.axial direction of said rotating axis, such that a uniform
air gap is formed between said magnet and a surface of each of said
magnetic substance assemblies .[.confronting.]. .Iadd.facing
.Iaddend.said magnet; a pair of small air gaps .[.formed in.].
.Iadd.defined by .Iaddend.said magnetic substance assemblies and
being smaller than said .Iadd.uniform .Iaddend.air gap; and a
magnetic sensitive device disposed in .Iadd.each .Iaddend.said
small air gap, wherein said pair of small air gaps are formed in
symmetrical positions with respect to said rotating axis situated
therebetween.Iadd., the at least one pair of magnetic plates
comprising upper and lower magnetic plates in which the upper
magnetic plate is comprised of a first upper magnetic plate and a
second upper magnetic plate, the lower magnetic plate is comprised
of a first lower magnetic plate and a second lower magnetic plate,
the magnet is comprised of two magnets with the first of the being
magnetized in one direction, and the second of the magnets being
magnetized in a direction opposite to the one direction; a first
area in which a magnetic field of the first magnet has the one
direction and a first area in which a magnetic field of the second
magnet has the opposite direction being positioned between first
upper magnetic plate and the first lower magnetic plate; and a
second area in which the magnetic field of the first magnet has the
one direction and a second area in which the magnetic field of the
second magnet has the opposite direction being positioned between
second upper magnetic plate and the second lower magnetic plate;
whereby the first upper magnetic plate and the first lower magnetic
plate thus form a linear magnetic circuit between the magnet and
the protruded magnetic substance portion independent of the
rotational position of the magnet, and the second upper magnetic
plate and the second lower magnetic plate thus form a linear
magnetic circuit between said magnet and a protruded magnetic
substance portion independent of the rotational position of the
magnet.Iaddend..
4. A non-contact rotational position sensor according to claim 3,
wherein said pair of small air gaps are each formed between
confronting surfaces of a pair of protrusions protruded from said
magnetic .[.plate.]. .Iadd.substance .Iaddend.assemblies in
directions in which said protrusions come closer to each other.
5. A throttle valve assembly comprising: an annular or semi-annular
magnet attached to one end of a throttle valve; a resin cover
attached to a body in which said throttle valve is mounted; an
auxiliary .[.caver.]. .Iadd.cover .Iaddend.attached to said resin
cover; magnetic path forming members attached to said resin cover
and said auxiliary cover, respectively, and forming magnetic paths
with said annular or semi-annular magnet situated therebetween; a
magnetic flux converging portion formed in each of said magnetic
paths and concentrating a magnetic flux passing said magnetic path
to a .[.particular.]. .Iadd.predetermined .Iaddend.position; and a
magnetic sensitive device attached to said magnetic flux converging
portion and detecting change of the magnetic flux in said magnetic
flux converging portion caused upon rotation of said throttle
valve.Iadd., the magnetic path members comprising upper and lower
magnetic plates in which the upper magnetic plate is comprised of a
first upper magnetic plate and a second upper magnetic plate, the
lower magnetic plate is comprised of a first lower magnetic plate
and a second lower magnetic plate, the magnet is comprised of two
magnets with the first of the being magnetized in one direction,
and the second of the magnets being magnetized in a direction
opposite to the one direction; a first area in which a magnetic
field of the first magnet has the one direction and a first area in
which a magnetic field of the second magnet has the opposite
direction being positioned between first upper magnetic plate and
the first lower magnetic plate; and a second area in which the
magnetic field of the first magnet has the one direction and a
second area in which the magnetic field of the second magnet has
the opposite direction being positioned between second upper
magnetic plate and the second lower magnetic plate; whereby the
first upper magnetic plate and the first lower magnetic plate thus
form a linear magnetic circuit between the magnet and the protruded
magnetic substance portion independent of the rotational position
of the magnet, and the second upper magnetic plate and the second
lower magnetic plate form a linear magnetic circuit between said
magnet and a protruded magnetic substance portion independent of
the rotational position of the magnet.Iaddend..
6. A throttle valve assembly according to claim 5, further
comprising: a motor for driving said throttle valve; and a magnetic
substance arranged between said motor and said magnetic paths.
7. A throttle valve assembly according to claim 6, wherein said
magnetic substance is in the form of a gear for transmitting
rotation of said motor to a rotating shaft of said throttle valve,
or in the form of a rotating shaft of said gear.
8. A throttle valve assembly according to claim 5, wherein said
resin cover has a hole for insertion of a rotating shaft provided
with said throttle valve fitted thereon; said magnetic path forming
member attached to the side of said resin cover has a hole formed
at the center thereof and having a diameter greater than a diameter
of said rotating shaft, but smaller than a diameter of said annular
or semi-annular magnet; and said annular or semi-annular magnet is
detachably attached to an end of said rotating shaft inserted
through said hole in said magnetic path forming member.
.Iadd.9. A non-contact rotational position sensor comprising: two
permanent magnets having a circular or arc-shaped outer
circumference; a shaft for supporting and fixing said permanent
magnet; upper and lower magnetic plates sandwiching said permanent
magnet from above and below, at least one of said upper and lower
magnetic plates being horizontally separated from each other with
an air gap formed therebetween; at least one protruded magnetic
substance portion disposed between said upper and lower magnetic
plates; and a magnetic sensitive device disposed on a protruded
surface of said protruded magnetic substance portion, said
permanent magnet and said shaft constituting a rotor which is
rotatable relative to said upper and lower magnetic plates
vertically spaced from each other, said permanent magnet being
magnetized substantially in the direction of a rotating axis,
whereby the amount of magnetic flux passing said magnetic sensitive
device is varied with rotation of said permanent magnet, said upper
magnetic plate is comprised of a first upper magnetic plate and a
second upper magnetic plate; said lower magnetic plate is comprised
of a first lower magnetic plate and a second lower magnetic plate;
the first of the permanent magnets being magnetized in one
direction and the second of the permanent magnets being magnetized
in a direction opposite to the one direction; a first area in which
a magnetic field of the first permanent magnet has the one
direction and a first area in which a magnetic field of the second
permanent magnet has the opposite direction being positioned
between said first upper magnetic plate and said first lower
magnetic plate; and a second area in which the magnetic field of
the first permanent magnet has the one direction and a second area
in which the magnetic field of the second permanent magnet has the
opposite direction being positioned between said second upper
magnetic plate and said second lower magnetic plate; whereby the
first upper magnetic plate and the first lower magnetic plate thus
form a linear magnetic circuit between the permanent magnet and the
protruded magnetic substance portion independent of a rotating
position of said permanent magnet, and the second upper magnetic
plate and said second lower magnetic plate thus form a linear
magnetic circuit between said permanent magnet and the protruded
magnetic substance portion independent of the rotating position of
the permanent magnet..Iaddend.
.Iadd.10. A non-contact rotational position sensor according to
claim 9, wherein said permanent magnet is in the form of a
ring..Iaddend.
.Iadd.11. A non-contact rotational position sensor according to
claim 9, wherein said permanent magnet is in the form of an arc
having a certain width in the radial direction..Iaddend.
.Iadd.12. A non-contact rotational position sensor according to
claim 9, wherein said permanent magnet is in the form of a
disk..Iaddend.
.Iadd.13. A non-contact rotational position sensor according to
claim 9, wherein each of air gaps between said permanent magnet and
said upper and lower magnetic plates has a width of not less than
0.5 mm..Iaddend.
.Iadd.14. A non-contact rotational position sensor according to
claim 9, wherein the magnetic flux density in at least the magnetic
plates is not higher than 0.5 T..Iaddend.
.Iadd.15. A non-contact rotational position sensor according to
claim 9, wherein said magnetic sensitive device is a Hall device or
a Hall IC..Iaddend.
.Iadd.16. A non-contact rotational position sensor according to
claim 9, wherein said magnetic plate and a member for fixing said
magnetic plate are comprise a one-piece resin-molded
unit..Iaddend.
.Iadd.17. A non-contact rotational position sensor according to
claim 9, wherein at least one hole is formed in said magnetic plate
near said protruded magnetic substance portion..Iaddend.
.Iadd.18. A non-contact rotational position sensor comprising: a
permanent magnet having a circular or arc-shaped outer
circumference; a shaft for supporting and fixing said permanent
magnet; magnetic plates sandwiching said permanent magnet from
opposite outer sides in the radial direction; a magnetic circuit
having a portion for converging a magnetic flux generated from said
permanent magnet; an air gap formed at a fore end of the magnetic
flux converging portion of said magnetic circuit; and a magnetic
sensitive device disposed in said air gap, said permanent magnet
and said shaft constituting a rotor which is rotatable relative to
said magnetic plates arranged outwardly of said permanent magnet in
the radial direction, said permanent magnet being magnetized
substantially in the radial direction, whereby the amount of
magnetic flux passing said magnetic sensitive device is varied with
rotation of said permanent magnet the at least one pair of magnetic
plates comprising upper and lower magnetic plates in which the
upper magnetic plate is comprised of a first upper magnetic plate
and a second upper magnetic plate, the lower magnetic plate is
comprised of a first lower magnetic plate and a second lower
magnetic plate, the magnet is comprised of two magnets with the
first of the being magnetized in one direction and the second of
the magnets being magnetized in a direction opposite to the one
direction; a first area in which a magnetic field of the first
magnet has the one direction and a first area in which a magnetic
field of the second magnet has the opposite direction being
positioned between first upper magnetic plate and the first lower
magnetic plate; and a second area in which the magnetic field of
the first magnet has the one direction and a second area in which
the magnetic field of the second magnet has the opposite direction
being positioned between second upper magnetic plate and the second
lower magnetic plate; whereby the first upper magnetic plate and
the first lower magnetic plate thus form a linear magnetic circuit
between the magnet and the protruded magnetic substance portion
independent of the rotational position of the magnet, and the
second upper magnetic plate and the second lower magnetic plate
thus form a linear magnetic circuit between said magnet and a
protruded magnetic substance portion independent of the rotational
position of the magnet..Iaddend.
.Iadd.19. A non-contact rotational position sensor comprising: a
rotating axis; an annular or semi-annular magnet fixed to said
rotating axis; magnetic substance assemblies arranged in opposing
relation to sandwich said magnet therebetween with a spacing
greater than a thickness of said magnet left between said magnetic
substance assemblies in an axial direction of said rotating axis,
such that a uniform air gap is defined between said magnet and a
surface of each of said magnetic substance assemblies confronting
said magnet; a pair of small air gaps defined between said magnetic
substance assemblies and being smaller than said uniform air gap;
and a magnetic sensitive device disposed in said small air gap, the
magnetic substance assemblies comprising upper and lower magnetic
plates in which the upper magnetic plate is comprised of a first
upper magnetic plate and a second upper magnetic plate, the lower
magnetic plate is comprised of a first lower magnetic plate and a
second lower magnetic plate, the magnet is comprised of two magnets
with the first of the being magnetized in one direction and the
second of the magnets being magnetized in a direction opposite to
the one direction; a first area in which a magnetic field of the
first magnet has the one direction and a first area in which a
magnetic field of the second magnet has the opposite direction
being positioned between first upper magnetic plate and the first
lower magnetic plate; and a second area in which the magnetic field
of the first magnet has the one direction and a second area in
which the magnetic field of the second magnet has the opposite
direction being positioned between second upper magnetic plate and
the second lower magnetic plate; whereby the first upper magnetic
plate and the first lower magnetic plate thus form a linear
magnetic circuit between the magnet and the protruded magnetic
substance portion independent of the rotational position of the
magnet, and the second upper magnetic plate and the second lower
magnetic plate thus form a linear magnetic circuit between said
magnet and a protruded magnetic substance portion independent of
the rotational position of the magnet..Iaddend.
.Iadd.20. A non-contact rotational position sensor according to
claim 19, wherein said pair of magnetic plates are each rectangular
in shape..Iaddend.
.Iadd.21. A non-contact rotational position sensor according to
claim 19, wherein: at least one of said pair of magnetic plates has
a split air gap formed along an imaginary plane passing an axial
center line of said rotating axis, said air gap splitting said
magnetic plate into two parts; and said pair of small air gaps are
formed in symmetrical positions with respect to said split air gap
situated therebetween..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotational position sensor for
detecting the rotational position of a rotating axis of a throttle
valve used in an internal combustion engine, for example, and more
particularly to a non-contact rotational position sensor.
The present invention also relates to a throttle valve assembly
including the non-contact rotational position sensor.
2. Description of the Related Art
Conventional rotational position sensors of the above-mentioned
type are disclosed in Japanese Patent Nos. 2842482 and 2920179 and
U.S. Pat. Nos. 5,528,139, 5,789,917 and 6,137,288.
Those prior-art sensors are based on the fact that, taking the
permanent magnet side as a rotor, the circumferential magnetic flux
density in a stator is linearly distributed relative to the
rotating direction of the rotor. To avoid as perfect as possible a
magnetic field distribution in the stator from being affected by
the rotational position of the rotor to which the magnet is
attached, confronting surfaces of the rotor and the stator are
shaped such that their lengths are even in a direction
perpendicular to the rotating direction of the rotor.
Because of such a limitation imposed on shapes of the confronting
surfaces of the rotor and the stator, the conventional rotational
position sensors have a problem that flexibility in design is low
when the sensors are designed to be adapted for target equipment to
which the sensors are attached.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a
non-contact rotational position sensor which is able to operate
with satisfactory performance even when confronting surfaces of
magnetic paths on the stator side and the rotor side are not shaped
such that their lengths are even in a direction perpendicular to
the rotor rotating direction.
To achieve the above object, according to one aspect of the present
invention, part of a stator-side magnetic path is formed by, e.g.,
a pair of magnetic plates arranged to sandwich an annular or
semi-annular permanent magnet therebetween, which constitutes a
rotor. A magnetic flux converging portion serving as a portion to
concentrate a magnetic flux is provided midway a closed magnetic
path formed through the stator-side magnetic path. A magnetic
sensitive device is disposed in the magnetic flux concentrating
(converging) portion.
According to another aspect of the present invention, an annular or
semi-annular permanent magnet is attached to an end of a rotating
shaft of a throttle valve, and a pair of magnetic substance
assemblies sandwiching the permanent magnet therebetween to form
magnetic paths are attached to a resin cover which is in turn
attached to a body of the throttle valve. A magnetic flux
converging portion is provided in each of the magnetic substance
assemblies, and a magnetic sensitive device is disposed in the
magnetic flux converging portion.
More specifically, the annular or semi-annular permanent magnet is
detachably attached to the rotating shaft, and at least one of the
magnetic substance assemblies has a hole formed at the center
thereof and having a diameter greater than a diameter of the
rotating shaft, but smaller than an inner diameter of the permanent
magnet.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an external appearance of a non-contact rotational
position sensor according to a first embodiment of the sent
invention;
FIG. 2 shows an internal structure of the non-contact rotational
position sensor according to the first embodiment of the present
invention;
FIG. 3 shows a magnetization distribution of a ring-shaped
permanent magnet as one component of the non-contact rotational
position sensor according to the first embodiment of the present
invention;
FIG. 4 shows a distribution of magnetic flux density vectors in the
non-contact rotational position sensor according to the first
embodiment of the present invention;
FIG. 5A is a representation for explaining the principle of
operation of the non-contact rotational position sensor according
to the first embodiment of the present invention, and FIG. 5B is a
conceptual sectional view taken along line Y--Y in FIG. 5A;
FIG. 6 shows an external appearance of a non-contact rotational
position sensor according to a second embodiment of the present
invention;
FIG. 7 shows an internal structure of the non-contact rotational
position sensor according to the second embodiment of the present
invention;
FIG. 8 shows a magnetization distribution of a ring-shaped
permanent magnet as one component of the non-contact rotational
position sensor according to the second embodiment of the present
invention;
FIG. 9 shows a distribution of magnetic flux density vectors in the
non-contact rotational position sensor according to the second
embodiment of the present invention;
FIG. 10 shows an external appearance of a non-contact rotational
position sensor according to a third embodiment of the present
invention;
FIG. 11 shows an external appearance of a non-contact rotational
position sensor according to a fourth embodiment of the present
invention;
FIG. 12 shows an internal structure of a non-contact rotational
position sensor according to a fifth embodiment of the present
invention;
FIG. 13 shows an internal structure of a non-contact rotational
position sensor according to a sixth embodiment of the present
invention;
FIG. 14 shows an internal structure of a non-contact rotational
position sensor according to a seventh embodiment of the present
invention;
FIG. 15 shows shapes of magnetic plates before machining, which are
used in a non-contact rotational position sensor according to an
eighth embodiment of the present invention;
FIG. 16 shows an internal structure of the non-contact rotational
position sensor according to the eighth embodiment of the present
invention;
FIG. 17 shows an internal structure of a non-contact rotational
position sensor according to a ninth embodiment of the present
invention in a state of being attached to an actual apparatus;
FIG. 18 shows an internal structure of a non-contact rotational
position sensor according to a tenth embodiment of the present
invention in a state of being attached to an actual apparatus;
FIG. 19 is a conceptual view (showing components that have the same
functions as actual ones, but are not exactly coincident in
dimensions, shapes and positional relationship with the actual
ones) taken along line X--X in FIG. 20; and
FIG. 20 is an exploded perspective view showing one embodiment of a
throttle valve assembly to which the non-contact rotational
position sensor of the present invention is attached.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A first embodiment of the present invention will be described with
reference to FIGS. 1 to 4.
FIG. 1 shows an external appearance of a non-contact rotational
position sensor 100 according to this first embodiment, and FIG. 2
shows an internal structure of the sensor. As shown FIGS. 1 and 2,
in this embodiment, a rotor comprises a ring-shaped (annular)
permanent magnet 10 and a shaft (rotating axis) 15 for supporting
the ring-shaped permanent magnet 10. The ring-shaped permanent
magnet 10 is sandwiched between vertically spaced pairs of magnetic
plates (magnetic substance assemblies) 11, 12, 13 and 14 from above
and below.
The magnetic plates 11, 12 are arranged to be apart from each other
in the horizontal direction. Air gaps (a1, a2, b1 and b2) are
therefore formed between the magnetic plates 11, 12. Also, air gaps
are similarly formed between the magnetic plates 13, 14.
The magnetic plates 11, 12, 13 and 14 are provided respectively
with protruded magnetic substance portions 16, 17, 18 and 19 that
serve as magnetic flux concentrating (converging) portions. A Hall
device (magnetic sensitive device) 21 is arranged between the
protruded magnetic substance portions 16 and 17, and a Hall device
(magnetic sensitive device) 22 is arranged between the protruded
magnetic substance portions 18 and 19.
The protruded magnetic substance portions 16, 17, 18 and 19 serving
as the magnetic flux concentrating (converging) portions are formed
in horizontally symmetrical positions with the air gaps a1, a2, b1
and b2 situated between pairs 16, 18; 17, 19, and they are located
at an outer periphery of the magnet 10. While the protruded
magnetic substance portions 16, 17, 18 and 19 serving as the
magnetic flux concentrating (converging) portions are formed
integrally with the magnetic plates 11, 12, 13 and 14 in this
embodiment, they may be formed separately and then fixed to the
respective magnetic plates by bonding or welding.
A front view of the non-contact rotational position sensor of this
embodiment is shown in FIG. 5B.
The pairs of magnetic plates 11, 13; 12, 14 are arranged to face
each other in parallel with a uniform gap G1 left therebetween.
A small gap g1 is formed between the magnetic plates 11, 12 and an
upper surface of the magnet 10, and a small gap g2 is formed
between the magnetic plates 13, 14 and a lower surface of the
magnet 10.
As a result, the gap G1 has a size determined by the sum of a
thickness t1 of the magnet 10 and the two small gaps g1, g2.
Also, gaps between one pair of protruded magnetic substance
portions 16, 17 and between the other pair 18, 19 are each smaller
than the thickness t1 of the magnet 10.
An insertion hole 51 formed at the center of the two magnetic
plates 13, 14 for insertion of the shaft 15 therethrough has a
diameter d set to be equal to or smaller than an inner diameter D
of the magnet 10.
The diameter d of the insertion hole 51 is required to be at least
smaller than an outer diameter D0 of the magnet 10, but how small
should be the diameter d of the insertion hole 51 is determined
depending on conditions of magnetic paths.
Note that a hole 52 at the center of the two magnetic plates 11, 12
and the small gaps a1, a2, b1 and b2 between them may be dispensed
with. An embodiment corresponding to such a modification will be
described later.
The diameters d, d0 of the holes 51, 52 formed at the centers of
the pairs of magnetic plates (11, 12; 13, 14) are determined
depending on whether the rotating shaft 15 is utilized as part of
the magnetic paths. When the rotating shaft 15 is made of a
non-magnetic substance, a noticeable change in performance is not
resulted from setting the diameters d, d0 of the holes 51, 52,
which are formed at the centers of the pairs of magnetic plates, to
be smaller than the inner diameter D of the magnet 10. On the other
hand, when the rotating shaft 15 is made of a magnetic substance,
the magnetic flux at positions, where the magnetic sensitive
devices 21, 22 are attached, is affected by the magnetic flux
leaking through the rotating shaft 15. Therefore, the diameters d,
d0 of the holes 51, 52 formed at the centers of the pairs of
magnetic plates (11, 12; 13, 14) are determined in consideration of
such an effect.
In the case of positively utilizing the magnetic flux passing the
rotating shaft 15, the diameters d, d0 of the holes 51, 52 formed
at the centers of the pairs of magnetic plates (11, 12; 13, 14) are
set to smaller values. Conversely, in the case of avoiding an
effect of the magnetic flux passing the rotating shaft 15, the
diameters d, d0 of the holes 51, 52 formed at the centers of the
pairs of magnetic plates (11, 12; 13, 14) are set to larger values.
However, if the hole diameters d, d0 are set to be greater than the
outer diameter D0 of the magnet 10, air gaps between the magnet 10
and the magnetic plates (11, 12; 13, 14) would be too increased,
thus resulting in the reduced amount of basic magnetic flux. For
this reason, upper limits of the diameters d, d0 of the holes 51,
52 formed at the centers of the pairs of magnetic plates (11, 12;
13, 14) are each preferably set to the outer diameter D0 of the
magnet 10.
By setting the shapes and layouts of the respective magnetic
members (11 to 14, 16 to 19, and the rotating shaft) and the
dimensional relationships among the gaps (g1, g2, G1 and G2) as
described above, the magnetic flux generated from the magnet is
concentrated and converged to the two air gaps G2 where the
magnetic sensitive devices 21, 22 are attached.
The leakage magnetic path passing the rotating shaft 15 is utilized
to adjust the magnetic flux so that extreme saturation of the
magnetic flux will not occur at the protruded magnetic substance
portions 16, 17, 18 and 19.
Although the non-contact rotational position sensor functions with
only one of the Hall devices 21, 22, two Hall devices are disposed
in this embodiment for the purpose of backup in the event of a
failure or diagnostic check of a failure.
As indicated by arrows in FIG. 3, the ring-shaped permanent magnet
10 is magnetized substantially in the axial direction of the
rotating shaft. The direction in which the ring-shaped permanent
magnet 10 is magnetized is upward in one angular region covering
1800 in the rotating direction, and it is downward in the other
angular region.
In this state, magnetic flux density vectors are distributed as
schematically shown in FIG. 4. Magnetic fields generated by the
ring-shaped permanent magnet 10 are shunted to the upper and lower
magnetic plates 11, 12, 13 and 14, and then pass the protruded
magnetic substance portions 16, 17, 18 and 19 and the Hall devices
21, 22. The direction and intensity of the magnetic field passing
the Hall devices 21, 22 are changed depending on the rotational
position of the ring-shaped permanent magnet 10.
The relationship between the rotational position of the ring-shaped
permanent magnet 10 and the amount of magnetic flux passing the
Hall device 21 will now be described with reference to FIG. 5A. The
directions of the magnetic fields generated by the ring-shaped
permanent magnet 10 are shown in FIG. 5A.
At the rotational position illustrated, a region a and a region b
cover the same circumferential (opening) angle, and the direction
of the magnetic fields in these regions are opposite to each other.
Therefore, the magnetic flux generated from the region a is
canceled by the magnetic flux generated from the region b. Because
the magnetization is actually weakened near the boundary between
the region a and a region c at which the direction of the
magnetization distribution is reversed, the magnetic fluxes from
the two regions a and b are not exactly canceled in the strict
sense, but they can be regarded as being substantially canceled in
the practical point of view.
Accordingly, most of the magnetic flux generated from the remaining
region c passes the protruded magnetic substance portions 16, 17.
The amount of magnetic flux passing the protruded magnetic
substance portions 16, 17 is proportional to the area of the region
c.
Also, the area of the region c is proportional to the rotational
angle of the ring-shaped permanent magnet 10. The magnetic flux
density detected by the Hall device 21 is therefore substantially
proportional to the rotational angle of the ring-shaped permanent
magnet 10. As a result, by sensing the magnetic flux density
detected by the Hall device 21, it is possible to detect the
rotational angle of the ring-shaped permanent magnet 10, i.e., the
rotational angle of the shaft 15.
In this embodiment, the gaps a1, a2, b1 and b2 between the magnetic
plates 11 and 12, shown in FIG. 1 are set to satisfy a1=a2=b1=b2.
However, the present invention is not limited to such an
arrangement, and the gaps may be set to satisfy a1>b1 and
a2>b2. Preferably, the relationships of a1=a2 and b1=b2 are
satisfied. Setting the gaps to satisfy a1>b1 and a2>b2
contributes to weakening the magnetic coupling between magnetic
plates 11 and 12, and hence to improving linearity in the
relationship between the magnetic flux density detected by the Hall
device 21 and the rotational angle of the ring-shaped permanent
magnet 10.
The pairs of upper and lower magnetic plates 11, 13; 12, 14 are
arranged to face each other in parallel with the uniform gap G1
left therebetween. Also, the pairs of upper and lower magnetic
plates 11, 13; 12, 14 are arranged to face the permanent magnet 10
such that the uniform gaps g1 (upper gap) and g2 (lower gap) are
kept with respect to the upper and lower surfaces of the permanent
magnet 10. The gap G1 is greater than the thickness t1 of the
permanent magnet 10 by the sum (g+g2) of the gaps g1, g2. On the
other hand, a gap g3 between the protruded magnetic substance
portions 16, 17 and a gap g4 between the protruded magnetic
substance portions 18, 19 are smaller than the thickness t1 of the
permanent magnet 10. This arrangement enables the magnetic flux of
the permanent magnet 10 to be converged to the protruded magnetic
substance portions 16, 17, 18 and 19. From this point of view, the
protruded magnetic substance portions 16, 17, 18 and 19 serve as
magnetic flux concentrating portions. Thus, the basic principle of
the present invention resides in that the protruded magnetic
substance portions 16, 17, 18 and 19 are provided between the pairs
of magnetic plates 11, 13; 12, 14 to form portions allowing the
magnetic flux to easily pass therethrough, whereby the magnetic
flux is condensed to those portions.
Considering that the attachment accuracy of each component is on
the order of .+-.0.2 mm when the non-contact rotational position
sensor is produced at a low cost, an effect of attachment errors
upon characteristics of the sensor can be reduced in this
embodiment by setting each of the air gaps between the ring-shaped
permanent magnet 10 and the upper and lower magnetic plates 11, 12,
13 and 14 to be not less than 0.5 mm, preferably approximately 1
mm. This point is similarly applied to other embodiments described
below.
Magnetic materials have varying degrees of magnetic hysteresis
characteristic. Generally, when the degree of magnetic hysteresis
exceeds 0.5 T or 1 T, the magnetic hysteresis effect becomes
noticeable in a gradually increasing manner. To obtain a high
accuracy in detection of the rotational position sensor, therefore,
it is preferable that the magnetic hysteresis is held in a range as
small as possible in operation of the sensor. For this reason, the
magnetic flux density in magnetic materials, typically represented
by the magnetic plates 11, 12, 13 and 14, is preferably held to be
not higher than 0.5 T. This point is also similarly applied to the
other embodiments described below.
Note that the permanent magnet is described as being ring-shaped in
this embodiment, similar functions can be provided even with a
disk-shaped permanent magnet.
A second embodiment of the present invention will be described with
reference to FIGS. 6 to 9. FIG. 6 shows an external appearance of a
non-contact rotational position sensor 200 according to this second
embodiment, and FIG. 7 shows an internal structure of the sensor.
As shown FIGS. 6 and 7, the sensor of this second embodiment is of
basically the same structure as that of the above first embodiment
except that an magnetic plate 30 is formed of one piece of magnetic
plate. In order to branch and shunt the magnetic flux generated
from the ring-shaped permanent magnet 10 to the protruded magnetic
substance portions 16, 17 and the protruded magnetic substance
portions 18, 19, it is just required tat the horizontal gaps are
formed in at least one of the upper and lower magnetic plates. In
this embodiment, the horizontal gaps are formed between the lower
magnetic plates 13 and 14. FIG. 8 shows a magnetization
distribution of the ring-shaped permanent magnet 10, and FIG. 9
shows a distribution of magnetic flux density vectors.
In this embodiment, a magnetic path is formed above the ring-shaped
permanent magnet 10, and therefore the amounts of magnetic flux
shunted to the protruded magnetic substance portions 16, 17 and the
protruded magnetic substance portions 18, 19 are somewhat reduced.
This embodiment however has advantages that, because of employing
one piece of upper magnetic plate 30, the number of parts is
reduced and the rotational position sensor can be manufactured with
more ease. Further, when the rotational position sensor is attached
at its lower surface to a target apparatus, an upper surface of the
sensor is faced to the outside. In such a case, this embodiment
provides another advantage of reducing an effect upon a sensor
output caused when any magnetic substance enters the sensor from
the outside.
FIG. 10 shows a third embodiment of the present invention. A
non-contact rotational position sensor 300 of this third embodiment
is modified from the structure of the above first embodiment in
that holes 31, 32 are formed respectively in the magnetic plates
11, 12. Magnetic resistance distributions in magnetic paths formed
in the magnetic plates 11, 12 can be adjusted depending on shapes
and sizes of the holes 31, 32. This arrangement is effective in
improving linearity in the relationship between the magnetic flux
density detected by the Hall device and the rotational angle of the
ring-shaped permanent magnet as compared with that in the
rotational position sensor of the above first embodiment. It is
also possible to further improve the linearity by forming similar
holes in the magnetic plates 13, 14 as well. While one hole is
formed in each magnetic plate in this embodiment, the present
invention is not limited to such an arrangement, and two or more
holes may be formed in each magnetic plate. This point is similarly
applied to the other embodiments described below.
FIG. 11 shows a fourth embodiment of the present invention. A
non-contact rotational position sensor 400 of this fourth
embodiment is modified from the structure of the above second
embodiment in that holes 31, 32 are formed in the magnetic plate
30. This arrangement is effective in improving linearity in the
relationship between the magnetic flux density detected by the Hall
device and the rotational angle of the ring-shaped permanent magnet
as compared with that in the rotational position sensor of the
above second embodiment.
FIG. 12 shows a fifth embodiment of the present invention. A
non-contact rotational position sensor 500 of this fifth embodiment
is modified from the structure of the above first embodiment in
that the ring-shaped permanent magnet 10 magnetized into a
double-pole magnet, shown in FIG. 2, is replaced by a single-pole
permanent magnet 10a in the form split into a semi-ring. The
permanent magnet 10a is magnetized upward or downward parallel to
the axial direction of the rotating shaft. In this case, the
magnetic flux entering the magnetic plate 11 is substantially
proportional to the area of a vertically projected surface of the
permanent magnet 10a upon the magnetic plate 11, and the vertically
projected surface area of the permanent magnet 10a is proportional
to the rotational angle thereof. The magnetic flux density detected
by the Hall device 21 is therefore proportional to the rotational
angle of the permanent magnet 10a. As a result, by sensing the
magnetic flux density detected by the Hall device 21, it is
possible to detect the rotational angle of the permanent magnet
10a, i.e., the rotational angle of the shaft 15.
FIG. 13 shows a sixth embodiment of the present invention. A
non-contact rotational position sensor 600 of this sixth embodiment
is modified from the structure of the above second embodiment in
that the ring-shaped permanent magnet 10 magnetized into a
double-pole magnet, shown in FIG. 7, is replaced by a single-pole
permanent magnet 10a in the form split into a semi-ring. The
magnetic flux generated from the permanent magnet 10a enters the
magnetic plate 30 and is then shunted to the protruded magnetic
substance portions 17, 19. After passing the Hall devices 21, 22
and the protruded magnetic substance portions 16, 18, the magnetic
fluxes enter the magnetic plates 13, 14 and then return to the
permanent magnet 10a, whereby magnetic path loops are formed. A
distribution ratio between the magnetic fluxes shunted to the
protruded magnetic substance portions 17, 19 is substantially
determined by a ratio of the area of a vertically projected surface
of the permanent magnet 10a upon the magnetic plate 13 to the area
of a vertically projected surface of the permanent magnet 10a upon
the magnetic plate 14. The magnetic flux density detected by the
Hall device 21 is therefore proportional to the rotational angle of
the permanent magnet 10a. As a result, by sensing the magnetic flux
density detected by the Hall device 21, it is possible to detect
the rotational angle of the permanent magnet 10a which is a
circular arc in shape, i.e., the rotational angle of the shaft
15.
FIG. 14 shows a seventh embodiment of the present invention. In a
non-contact rotational position sensor 700 of this seventh
embodiment, a rotor comprises a ring-shaped permanent magnet 10, a
magnetic yoke 35, and a shaft 15 for supporting the ring-shaped
permanent magnet 10. A stator comprises magnetic plates 31
surrounding the ring-shaped permanent magnet 10 from the outer
side, and Hall devices 21, 22 inserted in gaps between the magnetic
plates 31. The ring-shaped permanent magnet 10 is magnetized in the
radial direction, and looking round an outer circumferential
surface of the ring-shaped permanent magnet 10, it is magnetized
into a double-pole magnet. More specifically, the ring-shaped
permanent magnet 10 is magnetized outward in the radial direction
in one circumferential region of 180.degree., and magnetized inward
in the radial direction in the other circumferential region.
Magnetic plates sub-members 31a of the magnetic plates 31, which
form magnetic poles closest to the rotor, serve to collect the
magnetic flux generated from the ring-shaped permanent magnet 10,
and magnetic field distribution in the magnetic plate sub-members
31a do not directly affect signal outputs of the Hall devices 21,
22. Therefore, shapes of surfaces 31b of the magnetic plate
sub-members 31a directly facing the ring-shaped permanent magnet 10
are not required to be even in the rotating direction of the
ring-shaped permanent magnet 10. The magnetic flux collected by the
magnetic plate sub-member 31a of one magnetic plate 31 passes an
associated magnetic plate submember 31c and then the Hall device
21. Thereafter, the magnetic flux passes a magnetic plate
sub-member 31c and the magnetic plate sub-member 31a of the other
magnetic plate 31, and is then returned to the ring-shaped
permanent magnet 10. While the magnetic plate sub-member 31a and
the magnetic plate sub-member 31c are arranged on the same plane in
this embodiment, the present invention is not limited to such an
arrangement. Looking FIG. 14 from the observer side, the magnetic
plate sub-member 31c may be arranged on the front or rear side of
the ring-shaped permanent magnet 10 so as to provide a
three-dimensional structure.
FIG. 16 shows an eighth embodiment of the present invention. A
non-contact rotational position sensor 800 of this eighth
embodiment differs from that of the above first embodiment in that
two pairs of magnetic plates 50, 51 having protruded portions 50a,
51a, shown in FIG. 15, are employed instead of the magnetic plates
11, 12, 13 and 14 and the protruded magnetic substance portions 16,
17, 18 and 19, the protruded portions 50a, 51a being bent
substantially vertical to planes of the magnetic plates 50, 51. A
ring-shaped permanent magnet 10 is sandwiched between the
vertically spaced magnetic plates 50, 51 from above and below as
shown in FIG. 16. On that occasion, Hall devices 21, 22 are held
between the protruded portions 50a, 51a of the magnetic plates 50,
51. Magnetic paths substantially equivalent to those in the above
first embodiment were thereby formed to provide the function of a
non-contact rotational position sensor. According to this eighth
embodiment, since punching of the magnetic plates 50, 51 and
bending of the protruded portions 50a, 51a are just required, the
productivity can be increased as compared with the above first
embodiment in which the protruded magnetic substance portions 16,
17, 18 and 19 are provided on the magnetic plates 11, 12, 13 and
14.
A description will now be made of a ninth embodiment in which the
first embodiment of the present invention is applied to an actual
apparatus. Referring to FIG. 17, a rotating-axis penetrating hole
42, through which a rotating axis is to be extended to the outside,
is formed in a housing cover 41 of a target apparatus for which a
rotational angle is to be detected. The magnetic plates 13, 14,
including the protruded magnetic substance portions 16, 18 provided
thereon, and the Hall devices 21, 22 are mounted onto an outer
surface of the housing cover 41. An integral assembly of the
ring-shaped permanent magnet 10 and the shaft 15 is coupled to the
rotating axis of the target apparatus. Another integral unit of the
magnetic plates 11, 12 and a housing cover 40 of a rotational
position sensor 900 is then attached to the outer side of the above
integral unit. As a method of integrating the magnetic plates 11,
12 and the housing cover 40 of the rotational position sensor 900
into a one-piece unit, the so-called insert molding is superior in
productivity. With this method, the housing cover 40 is made of a
resin, for example, and the resin is molded into the housing cover
40 with the magnetic plates 11, 12 embedded therein.
In the above-described embodiments, the magnetic plates 11, 12, 13,
14 and 30 are illustrated as being rectangular plates. However, the
magnetic plates for use in the present invention are not limited to
a rectangular shape, but may have any of other suitable shapes such
as a disk, semi-disk, sector, and a trapezoid.
There are various non-contact rotational position sensors using
permanent magnets, including the sensor of the present invention.
When those non-contact rotational position sensors are assembled in
target apparatus, there is a possibility that any magnetic
substance may exist in the vicinity of the assembled non-contact
rotational position sensors. In such a case, an output signal of a
magnetic sensitive device, such as a Hall device, is adversely
affected by the presence of a magnetic substance. In a tenth
embodiment, therefore, a shield cover 45 provided with a magnetic
substance is attached to a housing cover 40 of a non-contact
rotational position sensor 1000, as shown in FIG. 18. This
arrangement is advantageous in reducing an effect of any external
magnetic substance upon an output signal of a magnetic sensitive
device, such as a Hall device.
One embodiment of a throttle valve assembly, to which the
non-contact rotational position sensor of the present invention is
attached, will be described below with reference to FIGS. 19 and
20.
A rotating shaft (rotating axis) 203 (corresponding to the shaft
15) is rotatably supported by a body 201. Numeral 200 denotes a
throttle valve for controlling an opening area of an air passage
formed in the body 201. The throttle valve 200 is fixed to the
rotating shaft 203 by screws. Numeral 202 denotes a resin cover
fixed to the body 201 by screws (210a-210c).
A through hole 204 is formed in the resin cover 202. A fore end of
the rotating shaft 203 is extended to the outside of the resin
cover 202 after passing the through hole 204.
A rectangular recess is formed in the resin cover 202 around the
through hole 204. Magnetic plates 13, 14 having a hole 51 formed at
the center thereof are stuck by bonding to an outer wall surface of
the resin cover 202 which defines the rectangular recess. The
magnetic plates 13, 14 are horizontally divided from each other,
and air gaps similar to those (a1, a2, b1 and b2) shown in FIG. 1
are formed between the magnetic plates 13 and 14.
In a state of the resin cover 202 being attached to the body 201,
the fore end of the rotating shaft 203 is extended to the outside
beyond the magnetic plates 13, 14.
An annular or semi-annular magnet 10 is fixed to a resin-made
attachment piece 110 having an attachment hole formed at the
center, and the fore end of the rotating shaft 203 is fixed by
press fitting to the central hole of the attachment piece 110.
With such an arrangement, the magnet 10 having an outer diameter
greater than the diameter of the hole 51 formed at the center of
the two magnetic plates 13, 14 can be attached to the fore end of
the rotating shaft 203 on the outer side of the magnetic plates 13,
14.
Numeral 40 denotes a resin-made auxiliary cover for covering an
area corresponding to the rectangular recess of the resin cover
202.
Inside the auxiliary cover 40, magnetic plates 11, 12 are bonded by
an adhesive to positions to face the magnetic plates 13, 14,
respectively. In a state where the auxiliary cover 40 is attached
to the resin cover 202, a pair of gaps G2 are formed between the
protruded magnetic substance portions 16, 18 provided on the
magnetic plates 13, 14 and between the protruded magnetic substance
portions 17, 19 provided on the magnetic plates 11, 12.
Hall devices 21, 22 as magnetic sensitive devices are disposed in
the gaps G2.
Thus, the same non-contact rotational position sensor as shown in
FIG. 1 to FIGS. 5A and 5B can be constructed at the fore end of the
rotating shaft of the throttle valve.
In this embodiment, a motor 207 is mounted to the body 201, and a
torque of the motor 207 is transmitted to the throttle valve
rotating shaft 203 through an intermediate gear 205 and a final
stage gear 206 fixed to the rotating shaft 203.
Numeral 208 denotes a stationary shaft for supporting the
intermediate gear 205. In this embodiment, the intermediate gear
205 is made of a resin material and the final stage gear 206 is
made of a sintered alloy. This material selection is advantageous
in that electromagnetic noises generated by the motor 207 are
absorbed by the final stage gear 20 made of a magnetic substance
and hence can be avoided from adversely affecting a magnetic
circuit of the sensor.
That effect can also be obtained by using a magnetic material to
form the intermediate gear 205 and/or the stationary shaft 208 for
supporting the intermediate gear 205.
Incidentally, when the final stage gear 206 is made of a magnetic
material, it must be taken into consideration that the final stage
gear 206 acts as part of the magnetic path of the leakage magnetic
flux passing the rotating shaft.
Also, even when the final stage gear 206 is made of a resin
material, a gear central portion is required to be made of a metal
to provide a securing force sufficient to fix the final stage gear
206 onto the rotating shaft with certainty. When such a metal
portion is made of a magnetic material, it likewise acts as part of
the magnetic path of the leakage magnetic flux passing the rotating
shaft of the magnet 10. Accordingly, a magnetic action of the metal
portion must also be taken into consideration.
The diameter of the hole 51 formed at the center of the two
magnetic plates 13, 14 or the gap between the magnetic material
member on the final stage gear side and the magnetic plates 13, 14
must be set in consideration of the above-described points.
In this embodiment, the air gaps G2 between the magnet 10 and the
magnetic plates 13, 14 are set to be smaller than any of the air
gap between the magnetic plates 13, 14 and the rotating shaft 203
and the air gap between the magnetic plates and the magnetic
material member on the side of the final stage gear 206 so that the
leakage magnetic flux passing the rotating shaft 203 is
minimized.
According to the present invention, the following advantages are
achieved. Satisfactory performance of a non-contact rotational
position sensor can be obtained while high flexibility in design is
ensured, even when confronting surfaces of magnetic paths on the
stator side and the rotor side are not shaped such that their
lengths are even in a direction perpendicular to the rotor rotating
direction. Also, since the magnetic flux can be effectively
concentrated to positions where magnetic sensitive devices are
attached, a non-contact rotational position sensor having high
accuracy and high sensitivity can be obtained. Further, when a used
permanent magnet is magnetized in the axial direction of a rotating
axis, a sufficient level of detection sensitivity can be provided
even with no magnetic material other than the permanent magnet
being disposed on the rotor side. The inertial moment of the rotor
is therefore reduced. As a result, the load of an actuator for
rotating the rotor can be reduced, and hence a response of the
rotor can be improved.
* * * * *