Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
2001-10-01
2003-03-25
Noori, Max (Department: 2862)
Measuring and testing
Dynamometers
Responsive to torque
Reexamination Certificate
active
06536293
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotational angle detecting apparatus for detecting an rotational angle of a rotor, a torque sensor using the rotational angle detecting apparatus, and a steering apparatus for generating steering assistance force by driving an electric motor based on the result of the detection of the torque sensor.
2. Description of Related Art
Some steering apparatus for automobiles assist steering by driving electric motors thereof, so as to lighten drivers' load. A steering apparatus comprises an input shaft connected to a steering wheel, an output shaft connected to wheels for steering through a pinion and a rack, for example, and a torsion bar which connects the input shaft and the output shaft. A steering torque applied to the input shaft is detected as torsion generated on the torsion bar by a torque sensor. An electric motor for steering assistance, which interlocks with the output shaft, is driven and controlled based on the detected steering torque.
In an essential structure example of a rotational angle detecting apparatus and a torque sensor based on Patent Application Laid-Open No.2000-352502 proposed by the present applicant, a steering shaft is connected to a steering wheel
4
at an upper end thereof and to a torsion bar
5
at a lower end thereof as shown in FIG.
1
. An upper shaft
23
of the steering shaft has a plurality of (
FIG. 1
shows ten) protruding objects
7
,
7
. . . made of magnetic material, with a predetermined tilt angle and along a circumferential surface of an intermediate portion
6
thereof. When the upper shaft
23
rotates, the protruding object
7
moves in an axial direction of the upper shaft
23
. For detecting an adjacent part of the protruding object
7
moving in an axial direction of the upper shaft
23
, a MR sensor
1
(a magneto-resistance effect element) is fixed to an immovable portion of the automobile body, having an appropriate space with and being parallel to the intermediate portion
6
.
A lower shaft
18
of the steering shaft is connected to the torsion bar
5
at an upper end thereof and to a pinion
10
at a lower end thereof. The lower shaft
18
, similarly with the upper shaft
23
, has a plurality of (
FIG. 1
shows ten) protruding objects
9
,
9
. . . made of magnetic material, with a predetermined tilt angle and along a circumferential surface of an intermediate portion
8
thereof. When the lower shaft
18
rotates, the protruding object
9
moves in an axial direction of the lower shaft
18
. For detecting an adjacent part of the protruding object
9
moving in an axial direction of the lower shaft
18
, a MR sensor
2
(a magneto-resistance effect element) is fixed to an immovable portion of the automobile body, having an appropriate space with and being parallel to the intermediate portion
8
.
The MR sensor
1
has sensors
1
A and
1
B, which have 180° different electrical angles, at the interior thereof. Detected signals V
1
A and V
1
B indicating the part of the protruding object
7
, which are detected by the sensors
1
A and
1
B, are respectively given to a signal processing unit
11
. The signal processing unit
11
detects a rotational angle of the upper shaft
23
based on the detected signals V
1
A and V
1
B. A rotational angle detecting apparatus of the upper shaft
23
is thus constructed from the sensors
1
A,
1
B and the signal processing unit
11
.
The MR sensor
2
has sensors
2
A and
2
B, which have 180° different electrical angles, at the interior thereof. Detected signals V
2
A and V
2
B indicating the part of the protruding object
9
, which are detected by the sensors
2
A and
2
B, are respectively given to a signal processing unit
11
. The signal processing unit
11
detects a rotational angle of the lower shaft
18
based on the detected signals V
2
A and V
2
B. A rotational angle detecting apparatus of the lower shaft
18
is thus constructed from the sensors
2
A,
2
B and the signal processing unit
11
.
The MR sensors
1
and
2
are provided in a condition where the detected signals V
1
A and V
2
A (output of sensor) are at the same phase and the detected signals V
1
B and V
2
B (output of sensor) are at the same phase as shown in
FIG. 3
when no steering torque is applied to the steering wheel
4
and the torsion bar
5
is not twisted.
A torsion angle of the torsion bar
5
is several degrees at the utmost. The signal processing unit
11
calculates a steering torque based on difference between the rotational angle of the upper shaft
23
obtained from a detected signal V
1
A or V
1
B and the rotational angle of the lower shaft
18
obtained from a detected signal V
2
A or V
2
B, and outputs a torque signal.
In a torque sensor constructed as described above, every 36° the upper shaft
23
and the lower shaft
18
rotate, each part of the protruding object
7
and the protruding object
9
where is most adjacent to each detecting surface of the sensors
1
A,
1
B and the sensors
2
A,
2
B makes a return trip in axial direction of the upper shaft
23
and the lower shaft
18
. The position in axial direction of the upper shaft
23
and the lower shaft
18
of each part of the protruding object
7
and the protruding object
9
where is most adjacent to each detecting surface of the sensors
1
A,
1
B and the sensors
2
A,
2
B corresponds to the rotational angle of the upper shaft
23
and the lower shaft
18
.
In practice, the above-mentioned program for calculating each rotational angle of the upper shaft
23
and the lower shaft
18
is omitted. When a steering torque is applied to the steering wheel
4
and the torsion bar
5
is twisted, voltage difference &Dgr;V corresponding to the torsion angle arises between each detected signal of sensors
1
A and
2
A, and each detected signal of sensors
1
B and
2
B. The torsion angle is obtained by calculating the voltage difference &Dgr;V at the signal processing unit
11
. The signal processing unit
11
outputs the torque signal expressing the steering torque.
However the above-mentioned rotational angle detecting apparatus and the torque sensor do not have means for detecting malfunction of the sensors
1
A,
1
B,
2
A, and
2
B when malfunction occurs. Consequently when the rotational angle detecting apparatus and the torque sensor fail, a torque is calculated based on erroneous detected signals, and an erroneous torque signal is outputted.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made with the aim of solving the above problem.
It is an object of the invention to provide a rotational angle detecting apparatus which can detect malfunction.
Another object of the invention is to provide a torque sensor comprising the rotational angle detecting apparatus.
A further object of the present invention is to provide a steering apparatus comprising the torque sensor.
In a rotational angle detecting apparatus according to the first invention, one or a plurality of targets are arranged on a rotor, to output signals which repeat periodical increase and decrease in accordance with rotation of the rotor. First detecting means detects an adjacent part of the target. Second detecting means detects a part, which is a predetermined angle distant in a circumferential direction of the rotor from the part detected by the first detecting means. The rotational angle of the rotor is detected based on a detected signal which is outputted from the first detecting means or the second detecting means. A memory stores pairs of detected signal values which the first detecting means and the second detecting means should output synchronously. Judging means judges whether a pair of detected signal values, which is approximately the same as a pair of detected signal values outputted from the first detecting means and the second detecting means synchronously, is included in the pairs of detected signal values stored in the memory. When the judging means judges in the negative, a malfunction indicating signal is outputted.
Consequently the above-mentioned
Birch & Stewart Kolasch & Birch, LLP
Noori Max
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