U.S. patent application number 11/349141 was filed with the patent office on 2006-06-15 for position sensor, designed in particular for detecting a steering column torsion.
This patent application is currently assigned to MOVING MAGNET TECHNOLOGIES (S.A.). Invention is credited to Didier Angleviel, Didier Frachon, Pierre Gandel, Claude Oudet, Daniel Prudham.
Application Number | 20060123903 11/349141 |
Document ID | / |
Family ID | 8860691 |
Filed Date | 2006-06-15 |
United States Patent
Application |
20060123903 |
Kind Code |
A1 |
Gandel; Pierre ; et
al. |
June 15, 2006 |
Position sensor, designed in particular for detecting a steering
column torsion
Abstract
A position sensor, designed in particular for detecting a
steering column torsion, including a first magnetic structure
including a plurality of magnets and a second magnetic structure
including two ferromagnetic rings having a plurality of teeth and
defining an air gap. At least a magneto-sensitive element is placed
in the air gap. The first and second magnetic structures are
respectively integral with two parts in relative rotation. The two
ferromagnetic rings are nested and have each a substantially
tubular part forming axially oriented teeth connected by a
flux-closing zone, the detecting air gap being delimited by the
flux-closing zones.
Inventors: |
Gandel; Pierre; (Montfaucon,
FR) ; Frachon; Didier; (Besancon, FR) ;
Angleviel; Didier; (Besancon, FR) ; Oudet;
Claude; (Besancon, FR) ; Prudham; Daniel;
(Thise, FR) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
MOVING MAGNET TECHNOLOGIES
(S.A.)
Besancon
FR
|
Family ID: |
8860691 |
Appl. No.: |
11/349141 |
Filed: |
February 8, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10258585 |
Feb 13, 2003 |
7028545 |
|
|
PCT/FR02/00718 |
Feb 27, 2002 |
|
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11349141 |
Feb 8, 2006 |
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Current U.S.
Class: |
73/328 |
Current CPC
Class: |
G01L 3/104 20130101 |
Class at
Publication: |
073/328 |
International
Class: |
G01F 23/02 20060101
G01F023/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 2001 |
FR |
01/02905 |
Claims
1. A position sensor, comprising: a first magnetic structure
containing a plurality of magnets; a second magnetic structure
containing two ferromagnetic rings provided with a plurality of
teeth and defining an air gap; at least one magnetosensitive
element placed in the air gap; the first and second magnetic
structures being integral respectively with two parts in relative
rotation, wherein the two ferromagnetic rings are intermeshed and
each is provided with a substantially tubular part forming axially
oriented teeth, connected by a flux-closure zone, the air gap being
bounded by the flux-closure zones.
2. A position sensor according to claim 1, wherein the position
sensor is configured for detecting torsion of a steering
column.
3. A position sensor according to claim 1, wherein the first
magnetic structure is composed of a ferromagnetic tubular yoke
provided with a plurality of tangential notches in which are seated
thin magnets magnetized substantially radially in identical
directions.
4. A position sensor according to claim 3, wherein the thin magnets
are in a form of radially magnetized tiles.
5. A position sensor according to claim 3, wherein the thin magnets
are in a form of parallelepiped magnets magnetized in a direction
perpendicular to a plane of a main face.
6. A position sensor according to claim 1, wherein a height of the
teeth corresponds substantially to a height of the plurality of
magnets.
7. A position sensor according to claim 1, wherein at least one of
the first and second magnetic structures is movable relative to the
at least one magnetosensitive element.
8. A position sensor according to claim 1, wherein the at least one
magnetorestrictive element comprises N magnetosensitive elements, N
corresponding to a number of phases of a brushless DC motor whose
movement is controlled by the position sensor.
9. A position sensor according to claim 1, wherein the two
ferromagnetic rings are provided with flux-closure zones having a
shape of transverse disks.
10. A position sensor according to claim 1, wherein the two
ferromagnetic rings are provided with flux-closure zones having a
shape of half-toruses.
11. A position sensor according to claim 1, wherein the two
ferromagnetic rings are provided with flux-closure zones of tubular
shape.
12. A position sensor according to claim 1, wherein the two
ferromagnetic rings are provided with flux-closure zones cut to
form a plurality of teeth.
13. A position sensor according to claim 1, wherein the two
ferromagnetic rings are provided with flux-closure zones extending
over 360.degree. C.
14. A position sensor according to claim 1, wherein the two
ferromagnetic rings are provided with flux-closure zones extending
over an annular sector corresponding substantially to a dimension
of the magnetosensitive element.
15. A position sensor according to claim 1, wherein the two
ferromagnetic rings are composed of two movable toothed pieces and
two fixed elements.
16. A torsion sensor comprising: two rotating parts connected by an
elastic test member; a position sensor comprising two parts
integral respectively with the two rotating parts, the position
sensor being composed of a first magnetic structure containing a
plurality of radially magnetized magnets and a second magnetic
structure containing two ferromagnetic rings provided with a
plurality of teeth and defining an air gap, at least one
magnetosensitive element placed in the air gap, the first and
second magnetic structures being integral respectively with two
parts in relative rotation, wherein the two ferromagnetic rings are
intermeshed and each is provided with a substantially tubular part
forming axially oriented teeth, connected by a transverse
flux-closure zone, the air gap being bounded by the flux-closure
zones.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the art of position
sensors, and more particularly to position sensors intended to
measure the torsion of a steering column, although such an
application is not exclusive.
[0003] 2. Description of the Related Art
[0004] In the prior art there is known U.S. Pat. No. 4,984,474,
which describes a prior art sensor provided with a stator part
comprising a ferromagnetic piece forming radial teeth at two
levels, disposed facing multi-pole magnets that are radially
magnetized in alternating directions.
[0005] An additional ferromagnetic piece is disposed facing the
stator part, and forms an air gap in which there is placed a Hall
probe.
[0006] This prior art solution is not satisfactory, because it
leads to a loss of magnetic signal between the stator part and the
part containing the Hall probe. Furthermore, the magnetic field
generated by the magnets leads to losses due to the sensor
structure.
[0007] Also known in the prior art is a sensor described in U.S.
Pat. No. 4,784,002, which describes another position sensor
comprising a part provided with a plurality of axially oriented
magnets cooperating with radial teeth of a stator part.
[0008] This structure also leads to magnetic leaks and to reduced
efficiency, manifested by a poor "signal-to-noise" ratio.
BRIEF SUMMARY OF THE INVENTION
[0009] The object of the present invention is to overcome these
disadvantages by providing an improved position sensor with better
signal-to-noise ratio.
[0010] Another object of the invention is to reduce the radial
space requirement.
[0011] To this end, the invention relates in its most general
concept to a position sensor, intended in particular for detection
of the torsion of a steering column, comprising a first magnetic
structure containing a plurality of radially magnetized magnets and
a second magnetic structure containing two ferromagnetic rings
provided with a plurality of teeth and defining an air gap, in
which there is placed at least one magnetosensitive element, the
two magnetic structures being integral respectively with two parts
in relative rotation, characterized in that the two ferromagnetic
rings are intermeshed and each is provided with a substantially
tubular part forming axially oriented teeth, connected by a
transverse flux-closure zone, the detecting air gap being bounded
by the said flux-closure zones.
[0012] The first magnetic structure is advantageously composed of a
ferromagnetic tubular yoke provided with a plurality of tangential
notches, in which there are seated thin magnets magnetized
substantially radially in identical directions.
[0013] According to a preferred embodiment, the height of the teeth
corresponds substantially to the height of the magnets. According
to an alternative embodiment, the first and second magnetic
structures are movable relative to the magnetosensitive
element.
[0014] According to a special embodiment, the position sensor is
provided with N magnetosensitive elements, N corresponding to the
number of phases of a brushless DC motor whose movement is
controlled by the said sensor.
[0015] According to a first embodiment, the rings are provided with
flux-closure zones having the shape of disks.
[0016] According to a second embodiment, the rings are provided
with flux-closure zones having the shape of half-toruses.
[0017] According to a third embodiment, the rings are provided with
flux-closure zones cut to form a plurality of teeth.
[0018] According to another embodiment, the rings are provided with
flux-closure zones extending over 360.degree. C.
[0019] According to another alternative embodiment, the rings are
provided with flux-closure zones extending over an annular sector
corresponding substantially to the dimension of the
magnetosensitive element.
[0020] The invention also relates to a torsion sensor comprising
two rotating parts connected by an elastic test member, and a
position sensor comprising two parts integral respectively with the
said rotating parts, the position sensor being composed of a first
magnetic structure containing a plurality of radially magnetized
magnets and a second magnetic structure containing two
ferromagnetic rings provided with a plurality of teeth and defining
an air gap, in which there is placed at least one magnetosensitive
element, the two magnetic structures being integral respectively
with two parts in relative rotation, characterized in that the two
ferromagnetic rings are intermeshed and each is provided with a
substantially tubular part forming axially oriented teeth,
connected by a transverse flux-closure zone, the detecting air gap
being bounded by the said flux-closure zones.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0021] The present invention will be better understood by reading
the description hereinafter with reference to the attached drawings
pertaining to a non-limitative embodiment, wherein:
[0022] FIG. 1 illustrates a schematic view of a steering
column;
[0023] FIG. 2 illustrates an exploded view of a first practical
example of a sensor;
[0024] FIG. 3 illustrates a view of the second structure of the
said sensor;
[0025] FIG. 4 illustrates an enlarged view, in partial section, of
the sensor;
[0026] FIG. 5 illustrates an exploded view of a second
embodiment;
[0027] FIG. 6 illustrates the response curve of the sensor
according to FIG. 5;
[0028] FIG. 7 illustrates another alternative embodiment (fixed
probe and fixed stator);
[0029] FIG. 8 illustrates a cross-sectional view;
[0030] FIG. 9 illustrates an alternative embodiment of the
invention in which the detecting air gap is disposed between two
fixed elements.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The object of the invention is to overcome these problems of
low sensitivities and it relates to contactless position sensors
intended for the measurement of angles similar to or smaller than
10.degree. C., in applications such as steering-column torque
sensors, for example (the signal then will be processed to provide
steering assistance). The angular position sensor described
hereinafter is intended for the measurement of a very small angular
difference (a few degrees) between two shafts connected by a
torsion bar. Such an application for torque measurement is
described in FIG. 1. In the range of linear deformation of this
torsion bar, this angular difference (.alpha.1-.alpha.2) will be
proportional to the torque applied between the two shafts (1, 3)
connected by an elastically deformable test member (2). The
measurement of this angular difference by the sensor will allow an
electrical signal proportional to the applied torque to be
delivered at the output of the magnetosensitive element. In the
case of the steering-column torque sensor, the sensor (4) must also
permit measurement of the angular difference between two shafts
turning relative to the fixed frame of reference represented by the
passenger compartment of the vehicle. This means that .alpha..sub.1
and .alpha..sub.2 are angles that can be larger than 360.degree.
(the steering column can execute several turns). The angular
measurement must therefore take place between the two shafts (1, 3)
when the torsion bar (2) is deformed, each of the two shafts being
freely rotatable through several turns. A typical torsional working
angle in this application is from .+-.2.degree. to at most
.+-.4.degree.. It is therefore evident that the problem consists of
providing on the one hand a highly sensitive position sensor and on
the other hand a system with which the magnetosensitive element can
be fixed relative to the passenger compartment as the frame of
reference.
[0032] FIG. 2 illustrates an exploded view of a first practical
example of a sensor according to the invention.
[0033] It is composed of a first magnetic structure (5) and of
second magnetic structure formed by two intermeshing rings (6, 7).
The two magnetic structures have tubular general shape and are
coaxial.
[0034] The first magnetic structure (5) is formed by a yoke (8) of
tubular shape provided with cavities for seating a plurality of
thin magnets (9) magnetized in radial direction, or in a direction
parallel to the radial direction and passing through the center of
the magnet.
[0035] These magnets are embedded in a cavity having a thickness of
between 0.2 and 0.9 times that of the magnet.
[0036] The magnets are separated by angular sectors (10) of the
yoke.
[0037] The second structure is formed by two ferromagnetic rings
(6, 7) provided with teeth (11, 12) that extend axially and that
are separated by open intervals allowing intermeshing with the
teeth of the opposite ring.
[0038] The teeth are prolonged by respective flux-closure zones
(13, 14) extending generally in a transverse plane, perpendicular
to the main orientation of the teeth.
[0039] These two flux-closure zones bound an annular air gap (16)
in which there is positioned a magnetosensitive element (15).
[0040] FIG. 3 illustrates a view of the second structure in
assembled condition, without the first structure, which is now
lodged in the central cavity, and FIG. 4 shows a view in detail and
in section of the said sensor.
[0041] The first structure is provided with N magnets (9), and each
of the rings of the second structure has N teeth. The
magnetosensitive element (15), a programmable Hall-effect probe,
for example, is fixed relative to the fixed frame of reference
corresponding to the passenger compartment. It is placed in the air
gap (16) between the two ferromagnetic collectors (13, 14), each of
which has collected the flux of N teeth, and in such a way as to
allow the two collars to turn through several turns.
[0042] Each of the structures can rotate relative to the frame of
reference of the passenger compartment, and exhibits a differential
movement of a few degrees relative to the other as a function of
the applied torque, which will be manifested by a flux variation of
a few hundred Gauss in the rotating air-gap (16). The analog signal
emitted by the Hall probe (15) will therefore deliver an electrical
image of the torque applied between the two shafts supporting the
stator (6, 7) on the one hand and the rotor (5) on the other.
[0043] In the case of steering-column torque sensors, the torque
information is generally processed so as to drive an electric motor
of the brushless DC type (BLDC). The action of this electric motor
will be to provide electrical steering assistance, by delivering a
torque proportional to that detected by the torque sensor, while
following a position proportional to that of the steering column.
Such motors generally have three windings known as "phases", offset
by an electrical angle of 120.degree.. Rotation of these
three-phase motors is assured by a controller, which will generate
three sinusoidal signals of amplitude proportional to the torque
delivered by the torque sensor, while following a position
proportional to that of the steering column. In general, these two
torque and position signals are obtained from two different
sensors.
[0044] According to the invention described in FIG. 5, the magnetic
collectors (13, 14) can be toothed and can have D teeth (19, 20)
over 360.degree.. A magnetosensitive element (15) placed in the air
gap (16) of FIG. 5 will therefore sense an alternating magnetic
field, whose period is proportional to D and to the position of the
"stator" part (5) which is rotating relative to the fixed frame of
reference of the passenger compartment (but is a stator relative to
the rotor (6, 7)), and is also proportional to the torque exerted
between (5) and (6, 7).
[0045] If three magnetosensitive elements (21, 22, 23) spaced apart
by a pole offset equivalent to an electrical period of 120.degree.
are placed in the air gap (16), there is obtained at the output of
these three magnetosensitive elements the three sinusoidal curves
described in FIG. 6, the amplitude of which is proportional to the
torque exerted on the steering column, and which at the same time
yield information on the position of the steering column.
[0046] If the number D of teeth is chosen judiciously as a function
of the reduction ratio R that is often associated with the BLDC
motor, these two combined signals can be used directly to drive the
BLDC motor via a transistorized power module.
[0047] FIG. 7 illustrates another alternative embodiment, in which
the rings are provided with two flux-closure zones reduced to
reduced angular sectors (30, 31), whose dimensions correspond
substantially to the dimensions of the Hall probe (15).
[0048] The principle described hereinabove is not limited to
applications as a steering-column torque sensor but can also be
applied to measurements of very small angles, such as applications
as a brake-pedal or accelerator-pedal sensor. In fact, it is
possible to imagine the two ferromagnetic collectors (13, 14) as
not extending over 360.degree. but as being limited to a few dozen
degrees, as indicated in FIG. 7.
[0049] FIG. 8 illustrates a cross-sectional view of the sensor.
[0050] The alternative structure illustrated in FIG. 9 was
developed with the objective of creating the detecting air gap (16)
between two fixed elements (34, 35).
[0051] In the same way as in the structures illustrated in the
preceding figures, a variation of induction is created in the teeth
(11, 12) by an angular phase shift between the first magnetic
structure, or in other words the rotor (5), and two intermeshed
magnetic structures, which in this case are toothed pieces (32,
33). The magnetic circuit is then prolonged by fixed elements (34,
35) separated from the magnetic structures (32, 33) by a mechanical
gap (41). Thus, in this alternative, the rings (6, 7) are therefore
composed of two movable toothed pieces (32, 33) and two fixed
elements (34, 35).
[0052] The two fixed elements (34, 35) are composed of two
flux-integration zones (36, 37) that completely (angle of
360.degree.) or partly surround the toothed pieces (32, 33), and of
two magnetic-flux concentrators (38, 39), which create a detecting
air gap (16) in which there are inserted the magnetosensitive
element or elements (15, 40).
* * * * *