Title: Device for measuring the angle and/or the angular velocity of a rotatable body and/or the torque acting upon said body
Abstract: A device for measuring an angle and/or the torque acting on a rotatable body is proposed according to the invention, whereby the rotational angle is detected by means of magnetic or optical sensors. In particular, in a preferred exemplary embodiment, two devices (7, 8) are proposed, each of which comprises two optically readable code tracks. The two code tracks (1a, 1b or 2a, 2b) on one device (7 or 8) are similar in design and are offset in relation to each other, so that associated sensors (4) output a digital signal. The rotational angle is calculated based on the lag between the two digital signals. In a further embodiment it is provided that a torsion element (5) having a known torsional stiffness is situated between the two devices (7, 8). Torque transferred by the rotatable body (3) can also be calculated therefore from the angular difference of the two devices 7, 8. The device is used preferably in the steering axle of a motor vehicle.
Patent Number: 6,935,193 Issued on 08/30/2005 to Heisenberg, et al.
| Inventors:
|
Heisenberg; David (Gerlingen, DE);
Klotzbuecher; Thomas (Rudersberg, DE);
Haas; Gunter (Leonberg, DE);
Dorfmueller; Lutz (Gerlingen, DE);
Siegle; Henrik (Leonberg, DE);
Wenzler; Axel (Stuttgart, DE);
Marx; Klaus (Stuttgart, DE);
Jost; Franz (Stuttgart, DE);
Noltemeyer; Ralf (Wernau, DE);
Freitag; Martin (Munich, DE)
|
| Assignee:
|
Robert Bosch GmbH (Stuttgart, DE)
|
| Appl. No.:
|
148666 |
| Filed:
|
December 5, 2000 |
| PCT Filed:
|
December 5, 2000
|
| PCT NO:
|
PCT/DE00/04335
|
| 371 Date:
|
October 3, 2002
|
| 102(e) Date:
|
October 3, 2002
|
| PCT PUB.NO.:
|
WO01/42753 |
| PCT PUB. Date:
|
June 14, 2001 |
Foreign Application Priority Data
| Dec 06, 1999[DE] | 199 58 598 |
| Aug 22, 2000[DE] | 100 41 095 |
| Current U.S. Class: |
73/862.324 |
| Intern'l Class: |
G01L 003/02 |
| Field of Search: |
73/862324,862.624
|
References Cited [Referenced By]
U.S. Patent Documents
| 2978902 | Apr., 1961 | Felder.
| |
| 3871215 | Mar., 1975 | Pratt.
| |
| 4590806 | May., 1986 | Lutton et al.
| |
| 4624336 | Nov., 1986 | Eddy.
| |
| 5438882 | Aug., 1995 | Karim-Panahi et al.
| |
| 5734108 | Mar., 1998 | Walker et al.
| |
| 6296977 | Oct., 2001 | Kaise et al.
| |
| Foreign Patent Documents |
| 195 06 938 | Aug., 1996 | DE.
| |
| 0 313 999 | May., 1989 | EP.
| |
| 0 638 789 | Feb., 1995 | EP.
| |
Primary Examiner: Lefkowitz; Edward
Assistant Examiner: Martir; Lilybett
Attorney, Agent or Firm: Striker; Michael J.
Claims
1. A steering-wheel angular sensor for measuring an angle of a rotatable body,
the device comprising at least first and second devices operative for outputting
different signals to an evaluation circuit in response to a rotation of the rotatable
body, each of said devices including two optically readable code tracks and one
optical sensor assigned to each of said code tracks, said sensor being formed to
detect only signals from an assigned one of said code tracks and sending information
as electrical signals to the evaluation circuit, each of said code tracks having
numerous optically detectable markings, provided so that a number of said markings
on one side of said code tracks is equal to n, and a number of said markings on
the other of said code tracks equals n+b
1, so that the angle is measurable
by a modified vernier method in accordance with the formula:
##EQU7##
wherein α and β are measured values of the sensor,
n is a number of pole pairs, and
k is a whole number.
2. The steering-wheel angular sensor as defined in claim 1, wherein said markings
comprise fields that differ by at least one parameter selected from the group consisting
of light intensity, color, and size.
3. The steering-wheel angular sensor as defined in claim 2, wherein said markings
have light-dark fields that alternate with light-dark transitions.
4. The steering-wheel angular sensor as defined in claim 1; and further comprising
a light source which illuminate said markings.
5. The steering-wheel angular sensor as defined in claim 1, wherein at least
one said devises has two said code tracks with markings have a same design.
6. The steering-wheel angular sensor as defined in claim 1, wherein said markings
are designed so that the modified vernier method is useable anew on results of
measurements of said code tracks.
7. The steering-wheel angular sensor as defined in claim 1, wherein the device
further measures a torque of the rotating body, said device further comprising
a torsion element having a known torsional stiffness, wherein said torsion element
is switchable between said two devices.
8. The steering-wheel angular sensor as defined in claim 7, wherein said two
devices are formed so that the torque is measurable based on an offset angle between
said two devices.
9. The steering-wheel angular sensor as defined in claim 1; and further comprising
at least one further code tract.
10. The steering-wheel angular sensor as defined in claim 1; and further comprising
an enclosing metal cladding formed so as to protect said devices extensively against contamination.
11. The steering-wheel angular sensor as defined in claim 1; and further comprising
means for arranging the device relative to a steering axle of a motor vehicle so
as to measure said parameter of the steering axle as the rotatable body.
Description
BACKGROUND OF THE INVENTION
The invention concerns in general a device for measuring the angle and/or angular
velocity of a rotatable body, and, in particular, a device for measuring the angle
and/or angular velocity of a rotatable body and/or of the torque acting on it.
A very exact determination of a rotational angle is necessary for many systems,
e.g., in the automotive industry. A specific application of such a device is a
steering-wheel angle sensor, whereby enormous safety requirements exist.
A device is made known in DE-A-195 06 938 belonging to the applicant, which said
device is used to measure the angle and/or the angular velocity of the rotatable
body, in particular a body that can be rotated by more than 360°, according
to the preamble of claim
1. In the case of the known device, the first and
second devices are each formed out of a toothed wheel with associated angle sensor,
whereby the two toothed wheels-when the numbers of teeth are different-are in mesh
with one toothed wheel that is mounted on the steering-wheel shaft. Using a modified
vernier method, the angle of the steering axle can therefore be determined from
the current angular and/or phase difference between the two toothed wheels. This
device therefore offers the advantage that multiple rotations can be detected,
but it is disadvantageous in that the detection takes place by means of the interconnection
of toothed wheels and therefore not in a contactless manner. Moreover, the installation
space required for such a device is relatively large, making it difficult to integrate
it, particularly on the steering axle, where the multi-function switches are also
accommodated. Finally, a laborious evaluation using an arc tangent method is required
to measure the individual rotational angles.
Furthermore, diverse angle sensors are known that are based on contactless
detection. They are generally not suited to measuring angles with great accuracy.
These devices and methods also require expensive evaluation circuits and algorithms
or, alternatively, they have insufficient accuracy or an insufficient measuring
range if the device is suited only for use with small angles, for example.
There is a need, therefore, for an improved device for measuring the angle
and/or the angular velocity of a rotatable body and of the torque acting on it.
It is an object of the present invention to further develop a generic device-as
was made known in DE-A-195 06 939, for example-having at least first and second
devices that output different signals to an evaluation circuit in response to a
rotation of the body in such a fashion that it takes up very little space and makes
a simple evaluation and determination of the angle possible, whereby the detection
is to take place in contactless fashion overall.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a device for measuring the
angle and/or angular velocity of a rotatable body and/or of the torque acting on
it, which is a further improvement of the existing devices.
In particular, the invention proposes that, in the case of the generic device,
a field-producing and/or field-changing arrangement or an arrangement that responds
to the field is associated with the rotatable body and the stationary part of the
device as a component of every device. In this fashion, every one of the devices
that responds differently to a rotation of the body provides an output signal that
can be detected in contactless fashion. Once the angle is measured directly at
the rotatable body, the error influence-resulting from the tolerances of toothed
wheels used so far-can be avoided. Low-noise operation that is free from wear is advantageous.
Advantageously, the arrangement responding to the field can contain
a field-producing and/or field-changing arrangement, by way of which the mutually-influencing
or mutually-influenced fields can be evaluated in order to obtain the rotational
angle to be measured.
In order to obtain an insensitivity to fluctuations in the space between the
components
of the devices, it is preferred that at least one field flux concentrating element
is provided, in particular to form closed field lines. In this fashion, tolerances
and time-induced changes in fields can also be handled more easily, which makes
the width of the pole-face arc non-critical when magnets are used.
Advantageously, at least one of the field-producing and/or field-changing
arrangements provides a periodically changing field, in particular an electrical
and/or magnetic field. When a periodically changing field is involved, the detection
accuracy can be increased by means of an appropriate design of the sensors, whereby
minimal angular increments in particular can be determined with greater accuracy
by means of a periodically changing magnetic field. In general, the accuracy increases
with the number of pole pairs.
In the case of a preferred exemplary embodiment, at least one of the field-producing
and/or field-changing arrangements is designed extending around the periphery in
relation to the rotatable body, in particular located on said rotatable body or
integrated in it. This preferred exemplary embodiment makes a device possible that
requires only a minimal amount of space, so that it can be used easily as a steering
angular sensor.
At least one of the field-producing and/or field-changing arrangements can form
a radial field, e.g., a magnetic field, electrical field, or an electromagnetic
field. In this case, the sensors could be provided radially in relation to the
rotating body.
As an alternative, it is also possible that at least one of the field-producing
and/or field-changing arrangements forms an axial field, whereby a corresponding
positioning of the detection sensors is to be carried out.
Advantageously, at least two field-producing and/or field-changing
arrangements are provided that form different fields, in particular defining a
different number of field poles, whereby, in particular, this said number of field
poles can differ by one. By providing two field-producing and/or field-changing
arrangements, a complete decoupling can take place, in particular when two separate
detection arrangements are formed at appropriate locations.
In a preferred exemplary embodiment, at least one of the field-producing and/or
field-changing arrangements is designed as a multi-pole wheel or a multi-pole ring.
A multi-pole wheel or ring is an arrangement of poles that comprises, in alternating
fashion, inverse poles, or they also contain, in alternating fashion, field-producing
and non-field-producing or field-influencing and non-field-influencing portions.
The field-changing arrangement can advantageously have the shape of a punched,
slotted, or perforated disk, or a punched, slotted, or perforated ring, independently
of whether radial or axial fields are used.
So that each of the devices provides an output signal that is as easy to evaluate
as possible and is as linear as possible, at least one of the arrangements responding
to the field can contain two field sensors that deliver sinusoidal or asinusoidal
output signals, separated, in particular, by a quarter period of the periodic field
formed by the corresponding field-producing and/or field-changing arrangement.
As described above, the field can be an electrical field, a magnetic field, or
any electromagnetic field.
Advantageously, the sensors in this case are connected in a bridge
circuit, in particular a Wheatstone bridge circuit, and they output their signals
to said circuits. When the bridge circuit is used, subtraction can be performed.
When elements having a linear characteristic as well are used, the respective,
outputted angular value can be determined directly without using a complex arc
tangent procedure.
In the case of a particularly preferred exemplary embodiment, each sensor of a
device is connected in a partial-bridge circuit, in particular a half-bridge of
the bridge circuit.
Finally, it is preferred that the device according to the invention is used
as a steering-wheel angular sensor, and at least two field-producing and/or field-changing
arrangements are assigned to the steering shaft as field-pole code tracks, in particular
magnetic code tracks.
An alternative exemplary embodiment-that is essential to the invention in terms
of measuring an angle and/or torque-is provided that detects a rotational body
opposite to the fixed sensors using first and second optical devices. It is considered
to be particularly advantageous that the optical devices are attached to the rotatable
body-the steering axle of a motor vehicle in this case. The two devices substantially
comprise two optically readable code tracks, whereby each code track is associated
with an optical sensor. The advantage of optical sampling is the fact that the
beams of light are easier to detect and they cannot be influenced by electromagnetic
interference fields. Additionally, the optically-readable signal can be converted
to an electrical signal very easily using a photo-sensor. It is also advantageous
that a digital output signal is obtained by means of the optical sampling, based
on which digital output signal the angle or angular changes can be determined with
a high degree of accuracy and a high degree of insensitivity to contamination.
Advantageous further developments and improvements of the device described
in the main claim are made possible by means of the measures listed in the dependent
claims. In particular, the code signal is detected in digital and analog form by
means of a plurality of optically-readable markings, so that the rotational angle
can be determined using simple phase comparison between associated code tracks.
It is also favorable that the fields of the markings can be differentiated in
terms of their light intensity, color, and/or size. In the case of adjacent light-dark
fields in particular, unambiguous light-dark transitions occur that can be detected
based on the steep voltage jump of the electrical signal. An unambiguous delineation
therefore results, which is largely immune to interference.
The contrast between the light-dark fields and at the light-dark transitions
can be improved even further by illuminating the markings using a light source.
In the case of tracks on one device that have an identical design, this results
in two different signal sequences; this makes it particularly easy to determine
the angle, e.g., using a classical or modified vernier method. For this purpose,
the number of markings of adjacent tracks on one device are advantageously selected
to be different, in order to obtain a phase displacement that is changeable around
the circumference of the axis of rotation.
When an appropriate number of markings on a track is selected and when the markings
are designed appropriately, the vernier method and, in particular, the modified
vernier method, can be used to measure the angle. The measuring accuracy is advantageously
increased by correcting the results of the measurements from the code tracks anew
using the modified vernier method.
In cases where torque is to be determined as well, a torsion element having a
known torsional stiffness is used between the two devices. If the rotational angle
of the first as well as the second device is then measured, then the torque can
be advantageously determined from the difference of the two angles and the known
torsional stiffness. In this fashion, two variables can be measured simultaneously
using the device according to the invention.
The markings of the two devices are preferably selected so that the classical
or modified vernier method can be applied anew to the respective measured results.
This increases the measuring accuracy and/or the measuring range of the device
without requiring additional devices.
In order to protect the optical devices from potential risk of contamination
in
the motor vehicle, an enclosing metal-cladding for the device appears to be particularly advantageous.
An advantageous application of the device is seen in the case of a steering axle
of a motor vehicle, in order to measure the rotational angle and/or the torque.
These variables can be used for further vehicle functions that are required, for
example, to determine the dynamic vehicle stability, and to support the steering
effort and/or navigation.
In summary it can be stated that, with the means of achieving the object, according
to the invention, a simple detection of angles and/or angular velocities of a rotatable
body is given that also includes measurement of torque, whereby the evaluation
circuit can be designed simple in nature, and the space required to implement the
device is very small.
Further advantages and features of the present invention result from the
following-purely exemplary-description of a few preferred exemplary embodiments,
whereby the description makes reference to the attached drawings. dr
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a steering-wheel angular sensor according to a first preferred
exemplary embodiment of the invention in a systematic view (FIG. 1A), in
a tangential side view (FIG. 1B), in radial side views at different angular
positions (FIGS. 1C and 1D), and showing angular dimensions (FIG. 1E).
FIG. 2 shows a variant of the exemplary embodiment shown in FIG. 1 in corresponding
representation, in a systematic view (FIG. 2A), in a tangential side view
(FIG. 2B), and in radial side view at different angular positions (FIG.
2C and 2
d), whereby field-changing devices are implemented in this case,
as opposed to the field-producing devices used in FIG. 1.
FIG. 3 shows a further steering-wheel angular sensor device as the third preferred
exemplary embodiment of the device according to the invention, in which a radial
field is used instead of the axial field used in FIGS. 1 and 2.
FIG. 4 shows a variant of the embodiment shown in FIG. 3, whereby, as in FIG.
2, field-changing devices are used instead of field-producing devices.
FIG. 5 shows a further variant of the embodiment shown in FIG. 3 in different
angular positions (FIG. 5A, FIG. 5B), whereby a field-producing arrangement
functions as the field-changing arrangement.
FIG. 6 is a schematic view of the position detection in the case of the exemplary
embodiment shown in FIG. 5 using field flux concentrating elements. FIGS. 6
a
and 6
b show view of a field evaluation devices as a further component
of the arrangement corresponding to the field.
FIG. 7 shows an exemplary embodiment of a combination steering-angle/steering-torque
sensor (schematically).
FIG. 8 shows a further exemplary embodiment of a combination steering-angle/steering-torque
sensor (schematically).
FIG. 9 shows various designs of sensors according to FIG. 7 or 8, whereby
a plurality of sensors per magnetic track can also be present for the purpose of averaging.
FIG. 10 shows the evaluation of the signals from a combination steering-angle/steering-torque sensor.
FIG. 11 shows an optical device having two stacked optical devices, each of
which has two code tracks and four sensors.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following description, reference is largely made exclusively to magnetic
fields and, in the case of the exemplary embodiment shown in FIG. 4, reference
is made to an electrical field; one skilled in the art should recognize, however,
that random combinations, i.e., any electromagnetic fields, can be used. For example,
light diodes could be used as field poles instead of magnets, the emitted field
of which can be detected using appropriate opto-electronic sensors.
The exemplary embodiment shown in FIG. 1 includes a disk mounted on the steering
axle
10, on which disk code tracks
20,
22 are provided. Each
of the code tracks
20,
22 comprises a plurality of alternatingly
arranged permanent magnets, as indicated by the arrows pointing in different directions.
The two code tracks
20,
22 are distributed differently, whereby it
is particularly advantageous for the smallest possible difference to exist, e.g.,
a difference of only one pole pair. In the exemplary embodiment shown, one of the
tracks
20,
22 contains a spacing of n pole pairs, while the other
has a spacing of n+1 pole pairs. When the rotatable body
10 rotates-the
steering axle in this case-the code tracks
20,
22 are therefore rotated
by a corresponding angle in the exemplary embodiment shown. Sensor arrangements
12 and
14 are provided on a fixed part of the device over each of
the code tracks
20,
22. Using the sensor arrangement
12,
14,
the relative position of the magnetic code track
20 or
22 lying under
it can be detected.
The detected sensor elements can be measuring elements that produce conventional
sinusoidal/cosinusoidal signals, such as AMR-, GMR-Hall sensors. The evaluation
algorithm can be carried out according to the arc tangent method.
In the case of the exemplary embodiment shown, each of the sensor arrangements
12,
14 comprises two sensors
12a, 12b or
14a, 14b. The sensors
12a and
12b
or
14a and
14b provided in pairs in each case are
advantageously separated by a quarter or eighth period of the periodically changing
magnetic field formed by the code tracks
20,
22. Such a separation
makes it possible to connect the sensors as half-bridge of a Wheatstone bridge
circuit in each case, so that a simple evaluation circuit can be realized, because
subtraction is performed on the one hand and, on the other, a nearly linear angle
signal that can be evaluated directly is provided when elements are used having
substantially linear characteristics.
The angular positions detected therewith can be referenced against each other,
so that, when the generally known vernier method or, better, when a modified vernier
method, or a combination of the two is used, the real angle of the rotatable body
10 can be determined. The expanded vernier method is described in the publication
DE-A-195 06 938, so this procedure need not be described in further detail.
Although the field-producing portions of a respective device move on the
exemplary embodiment shown, one skilled in the art will recognize that a corresponding
reversal is also feasible, in which the sensor arrangements move with the rotatable
body, while the code tracks are provided fixed in position around the rotatable body.
The particularly advantageous distance between two sensors
12a, 12b
or
14a, 14b is shown in detail in the tangential
sectional view in FIG.
1B.
Finally, one can see, in the sectional views in FIGS. 1C and D, how the
respective code tracks are present in different positions with regard for the sensor
arrangements at different angles of the rotating body.
In the case of the exemplary embodiment shown in FIG. 2, a field-changing device
is used instead of the magnetic tracks, which said field-changing device also defines
code tracks
24,
26. The mode of action and the general construction
is similar to FIG. 1, so the description will not be repeated here. It is to be
mentioned, however, that, in the exemplary embodiment shown, a stationary permanent
magnet
28 is positioned underneath the disk, which said disk moves with
the rotatable body
10 and contains code tracks
24,
26. In
the exemplary embodiment shown, the code tracks are formed by means of simple recesses,
but one skilled in the art should recognize that the most diverse possibilities
can be used here. It would be feasible, for example, to provide regions having
a different magnetic permeability instead of the simple recesses. When fields other
than magnetic fields are used, a corresponding design would be feasible with consideration
for different dielectric properties, optical properties, or combination dielectric
and magnetic permeability properties.
A further exemplary embodiment of the device according to the invention is shown
in FIG. 3, in which the code tracks
20,
22 are not arranged on a
disk, but rather are integrated directly in the steering axle
10. The code
tracks therefore provide a radially periodically changing field that can be detected
using appropriately situated sensor arrangements
12,
14. The evaluation
is carried out as it is with the preceding exemplary embodiments using the vernier
method, so that the existing phase difference between the detection signals can
be used to determine the overall rotational angle of the steering axle. Every sensor
arrangement
12,
14 also comprises two sensors that are separated
by a quarter period λ/4 of the changing field, in order to make a simple
evaluation possible.
Shown in FIG. 4 is a further preferred exemplary embodiment of the device according
to the invention that basically combines the principles of the exemplary embodiments
presented in FIGS. 2 and 3. In the case of this exemplary embodiment, the rotating
body
10 is designed as a hollow tube, in the middle of which a simple current-carrying
wire or an optical waveguide-as the field-producing device-can be arranged. The
rotating body
10 contains two rings having recesses that form code tracks
24,
26 as described hereinabove. As is the case with the other exemplary
embodiments described previously, each of the code tracks should comprise a different
spacing, in particular a spacing that differs by one, i.e., one of the code tracks
should comprise a number of "n" openings, while the other should comprise a number
of "n+1" openings. The sensors are arranged in accordance with the exemplary embodiment
in FIG. 3, in order to detect the changing field in each case above a respective
track
24,
26 when the rotating body
10 rotates. The entire
rotational angle is determined from the difference-in particular, the phase difference
of two signals-in the usual manner by means of an evaluation circuit and the vernier method.
FIGS. 5
a and
5b show a schematic view of one of the first
and second devices that output different signals to a not shown evaluation circuit
in response to the rotation of the body
10. In the case of the exemplary
embodiment shown here, annular magnet multi-pole wheels
20,
22 and
24,
26 are used in similar fashion as with the exemplary embodiment
shown in FIG. 3, whereby the inner multi-pole ring is interconnected with the rotating
body
10, as in the preceding exemplary embodiments. The outer magnet pole
ring
24,
26 is designed rotatable in nature in relation to the rotatable
body
10 and the inner magnet pole ring
20,
22, so that a periodically
changing, reciprocal influence of the respective fields that are formed results.
In the case of the position shown in FIG. 5
a, respective magnet poles oppose
each other in such a fashion that the fields essentially cancel each other out.
In the angular position shown in FIG. 5
b, the poles are arranged in such
a fashion that the respective field strengths add up.
FIGS. 6
a and
6b show views of a field evaluation device
as a further component of the arrangement responding to the field, which said field
evaluation device includes two Hall sensors
12,
14 in front. The
fields produced by the multi-pole rings shown in FIG. 5 are directed to the Hall
sensors
12,
14 by field conducting elements
32,
34,
36. As one skilled in the art will recognize in the views shown in FIGS.
6
a, 6b, an upper flux concentrating piece
32 is provided
that guides field lines in the transition area between the two multi-pole rings
20,
22 and
24,
26 toward one of the Hall sensors. As
shown in FIG. 5
a, closed field lines are therefore formed in the upper portion
when the pole positions are anti-parallel, whereby a tee
36 is provided
as a further flux concentrating piece behind the upper Hall sensor
12,
14.
After the rotatable body is rotated toward a position in which the poles of the
multi-pole rings are parallel-as shown in FIG. 5
b-the field lines are closed
by the lower flux concentrating piece
34 and the tee
36, whereby
a further Hall sensor is situated between the tee
36 and the lower flux
concentrating piece
34. By providing two Hall sensors in the manner shown,
and by using a principle of differences, insensitivity to temperature fluctuations
and ageing can be obtained, because the output signal can be standardized against
the total flux. One skilled in the art should recognize, however, that this subtraction
is purely optional. As is the case with the preceding exemplary embodiments as
well, a portal to any fields other than magnetic fields can be provided.
In summary, it can be stated that the device according to the invention makes
it possible to determine the angle of the rotatable body exactly and simply, and
no contact, e.g., by toothed wheels or the like, is necessary. In other words,
a simple and exact angle measurement or angular velocity measurement takes place
in a contactless manner using simple, known components which-as mentioned hereinabove-should
advantageously contain elements having a linear characteristic. The different adaptations
to different field-producing and/or field-influencing devices should be common
knowledge to one skilled in the art and therefore need not be described here in
any greater detail. Once moveable parts can be eliminated entirely, the device
according to the invention is particularly suited for use as a steering-wheel angular
sensor, in particular since a high degree of measuring accuracy is given while
requiring only minimal installation space.
Although the present invention was described hereinabove completely and
in detail with reference to purely illustrative exemplary embodiments preferred
at this time, one skilled in the art should recognize that the most diverse modifications
are possible within the scope of protection defined by the claims. In particular,
one skilled in the art should recognize that individual features of an exemplary
embodiment can be combined in any fashion with other features of other exemplary
embodiments. In this context it would also be feasible, for example, to provide
one of the code tracks according to an arrangement of FIG. 4 or
5, while
the other code track is provided in accordance with a design according to FIG.
1 or
2.
Various exemplary embodiments of combination steering-angle/steering-torque
sensors, including the associated evaluation procedure, are shown in FIGS. 7 through
11. The multi-pole wheels are read in each case by sensor elements that deliver
sinusoidal/cosinusoidal signals. The evaluation of the output signals from the
sensor elements takes place according to the modified vernier method, about which
the following is to be noted:
Transfer of the modified vernier principle to the circumstances described
(FIG. 1
e):
- Determination of φ:
##EQU1##
- Equate and transform:
##EQU2##
- Therefore:
##EQU3##
##EQU4##
Errors that make their way into the evaluation can be reduced using special
correction procedures in which principles of the classical and/or the modified
vernier principle are taken into account.
In addition to the angle, the acting torque, e.g., the steering torque, can also
be determined using the sensors according to FIGS. 7 and 8.
The acting torque during the steering procedure causes the torsion bar integrated
in the steering column to twist. The upper end rotates in relation to the lower
end by a maximum of +/-5°, for example. In order to measure the torque, this
relative rotational angle-the "torsional angle"-must be measured. There are two
ways to do this: the absolute steering angle of the upper and lower ends of the
torsion bar are each determined using the method described under point
1).
The difference between the two angles equals the torsional angle. Or, it can be
measured directly via the relative displacement of two identically-coded pole wheels,
one of which is situated at the top of the torsion bar, and the other of which
is situated at the bottom of the torsion bar. A minimum of three pole wheels are
needed for this. These possible methods are presented in summary form in FIG.
9.
Various Exemplary Embodiments
Pole wheel combinations: Each pole wheel can thereby be regarded as a magnetic
code track as well.
Steering angle determination using
- two pole wheels, the pole pair number of which is relatively prime,
e.g., with n and n+1 pole pairs; they can also be situated as two code tracks on
one pole wheel;
- three pole wheels with n-1, n and n+1 pole pairs. This combination increases
the accuracy, while simultaneously creating redundancy. It is expandable to include
more pole wheels with corresponding pole pair numbers;
- Addition of a "three-poled" pole wheel for differentiation of area when
sensor elements are used that have ranges of unambiguousness of less than 360°;
- Expand the measuring range by a pole wheel number>2.
Determine the steering torque
- by calculating the absolute difference
- by measuring the relative angle of identically-coded pole wheels
For the exemplary embodiment shown in FIG. 8, a detailed description will now
be provided as to how the absolute angle and the torque can be measured simultaneously
using the same measuring principle and a minimal number of sensors and assemblies.
The two variables are determined in contactless fashion, and self-diagnosis is
possible. Access by different systems, such as via a CAN bus (Controller Area Network)
is possible.
The proposal is based, for example, on the simultaneous measurement of the steering
angle and the steering torque. A magnetic measuring method is presented as the
measuring principle. The proposal is not limited to this magnetic method, however.
Any principle-optical, eddy current, inductive, . . . -that is based on analog
sinusoidal-cosinusoidal signals can be used.
As illustrated in FIG. 7, a torsion bar is built into the steering system in
order
to measure the rotational angle and torque. Two multi-pole rings with M and M+X
magnetic poles are situated on the one end of the torsion bar. A third multi-pole
ring having N magnetic poles is situated at the other end. A sensor (AMR, Hall,
GMR, magnetoresistor) is located over each ring. Each sensor delivers a sinusoidal
signal and a cosinusoidal signal that is a function of the mechanical angle.
Measuring the Steering Angle
The multi-pole rings and sensors located on one end are used to measure the steering
angle. If X=2, the absolute angle can be determined using the modified vernier
method. This method is to be used here, and the absolute angle is calculated with
the signals S
1 (U sin(
1), U cos(
1)), and S
2 (U sin(
2),
U cos(
2)).
Measuring the Torque
The torque is measured via the angular difference. The torque is proportional
to the angular difference in the elastic measuring range of the torsion element.
The angular difference is determined via the two signals S
1 (U sin(
1),
U cos (
1)) and S
3 (U sin(
3), U cos(
3)) at the torsion ends.
The sensor delivers two signals:
Sensor
3 also delivers two signals:
Whereby U represents the electrical signals at the respective mechanical
angle w. A represents amplitudes, and O represents the offset values of the sensors.
By means of the mechanical rotation, the amplitudes and offsets of the four signals
can be determined from maxima and minima. An alternative method for offset determination
and offset compensation was demonstrated in DE-P 199 28482. The corrected signals
U# are purged of offset.
##EQU5##
The angular difference w
1-w
3 is the result that is sought.
Using analog electronic operations (multiplication, subtraction, comparation),
or by processing at the digital level, the difference can be determined as follows:
##EQU6##
The following applies for small angles: sin(w
1-w
3)=w
1-w
3
with 0.1% relative error in the angular interval (-4.4° to +4.4°)
in degrees or (-0.077 to -0.077) in rad.
The angular difference, therefore, is:
This evaluation method is very sensitive to the smallest angular differences.
Using the procedure described above, the torque can be determined directly from
the angular difference. Another starting point would be to adjust the difference
to zero using a closed loop. The controlled variable would be equal to the angular difference.
Remarks:
1) Another combination of signals is possible as well; they should also
lead to a sine of the angular difference.
2) The angular difference could also be obtained by means of the difference
between two absolute angle sensors. This would require 4 sensors and 4 multi-pole
rings, and the method would place requirements on the absolute angular measurements
that are too high. In this case, the difference of two large angle values is obtained.
Self-Diagnosis
Absolute angle: For the absolute angle, the known method of the modified
vernier principle is used. Tracking the whole-number k (allowed/not allowed) jumps
makes it possible to detect errors and implement a line-of-retreat strategy.
Torque: If the angular difference exceeds the maximum permissible range,
e.g., +/-4°, an error message is output. If overload occurs, for example,
the system stops intervening.
The new difference to be calculated (U# cos(1)*U# cos(3)+U#
sin(1)* U# sin(3))/(A1*A3) must not deviate from 1
by more than 0.5% (cos^2 (4°)=0.995.
Another alternative would be to check the expression (U# sin(3)*U#sin(3)+U#
cos(3)*U# cos(3))/(A3*A3)* for a deviation from 1 of
0.5%. At the same time, the whole number k must not perform any unpermitted jumps.
The device in particular for contactless and optical measurement of an angle
and/or torque according to FIG. 12 will be described in greater detail hereinbelow.
As illustrated in FIG. 12, the two devices
7 and
8 are situated on
one rotatable body
3. The rotatable body
3 is preferrably designed
as a steering axle in a motor vehicle and comprises a torsion element
5
with which the torque acting on the steering axle
3 can be measured. The
two devices
7,
8 are situated on both ends of the torsion element
5, so that, when the torque acts on the torsion element
5, a different
rotational angle than the angular difference Θ-Ψ can be measured.
The two devices
7,
8 each comprise two code tracks
1a,
1b or
2a, 2b. The code tracks are
designed equal in nature with regard for the width of their adjacent fields, but
they have a different number of markings
9 around their circumference. For
example, the code track
1a has 45 markings
9, the code track
1b has 50 markings
9, code track
2a has 44 markings
9, and code track
2b has 48 markings
9 distributed
around their circumferences. In an alternative exemplary embodiment of the invention,
it is provided to provide a multiple of these markings
9 around the circumference.
Two adjacent markings or fields
9 in each case differ in terms of their
light intensity, color and/or size. They are preferably designed as light-dark
fields, so that sharp and high-contrast light-dark transitions result. To increase
the contrast, light fixtures
6 are provided that are associated with the
devices
7,
8 in such a fashion that they shed the light reflected
by the markings
9 into associated sensors
4. As further illustrated
in FIG. 12, a sensor
4 is assigned to each code track
1a, 1b,
2a, 2b, which said sensor essentially receives
only the light reflected from the associated code track. The sensor
4 converts
the light signal received into uniform electrical signals, which can be picked
off as a digital signal S
1a, S
1b, S
2a and
S
2b at the output of the sensors
4, and are directed to a
not shown evaluation circuit.
An aspect that is considered essential to the invention is the fact that the
markings
9 of the code tracks
1a, 1b or
2a,
2b are designed uniform in nature. In each case, both code tracks
1a, 1b or
2a, 2b of the
devices
7 or
8 are coordinated with each other exactly and comprise
a relative phase offset. This phase offset is also reflected in the electrical
signal S
1a, S
1b, S
2a, S
2b,
as illustrated in FIG. 12 using the dashed lines. The offset, therefore, becomes
increasingly greater from one pulse to the next pulse as the rotational angle increases,
so that this difference is evaluated using a standard or, in particular, the known,
modified vernier method, which was also made known in DE 195 06 938 A1.
It should be noted that the smallest unit of a marking
9 is determined
in particular by means of the light-dark transition. The greater the contrast of
these transitions, the lower the sensitivity to disturbance, and the likelihood
that measuring errors will occur. To lower the susceptibility to interference,
an enclosing metal-cladding
10 is preferably provided, which encloses the
rotatable body
3 with the greatest sealing effect possible.
As described previously, 44 to 50 markings
9 were selected for each of
the four code tracks
1a, 1b, 2a and
2b
in order to obtain a high level of measuring accuracy and angle resolution
for the rotational angle using the modified vernier method, if possible. When the
markings
9 are selected in this manner, the measured values from the tracks
1a, 1b repeat five times per circumference and, in
the case of the tracks
2a, 2b, they repeat four times
per circumference. If these measured values undergo the modified vernier method
anew, a measured value results that is unambiguous around the entire circumference
(2 π). A high resolution for the angle is therefore obtained, which results
from the high dividend. At the same time, a range of unambiguousness of one full
rotation is obtained. The modified vernier method makes it possible for an angular
difference to be present between the first code tracks
1a, 1b
and the second code tracks
2a, 2b without diminishing
the accuracy. This angular difference can also result from the rotation of the
torsion bar
5, for example. If the angular difference Θ-Ψ is
measured in accordance with the two devices
7,
8, then the torque
transferred by the steering axle
3 can be determined in addition to the
torque when the torsional stiffness of the torsion element
5 is known.
In an alternative embodiment of the invention, one or more further optical code
tracks of a third device are feasible, of the type described hereinabove in conjunction
with the magnetic devices.
*
