WO2004051192A2

WO2004051192A2 - Rotation angle detection device

Info

Publication number: WO2004051192A2
Application number: PCT/JP2003/015367
Authority: WO
Inventors: Makoto Inoue
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2002-12-05
Filing date: 2003-12-02
Publication date: 2004-06-17
Also published as: JP2004184326A; WO2004051192A3

Abstract

The rotation angle detection device of the present invention contains i) a rotation detecting body; ii) a first rotator engaging with the rotation detecting body; iii) a second rotator engaging with the first rotator; iv) a first detector that detects the rotation angle of the first rotator; v) a second detector that detects the rotation angle of the second rotator; and vi) a self-evaluating section. Referencing to the output range of the first and the second signals detected by the first and the second detectors under the normal condition of the rotation detecting body, the self-evaluating section determines, through calculation of the output range of the signals, the normal condition and the abnormal condition ranges. When at least one of the values of the signals is in the abnormal condition range, the self-evaluating section judges that the rotation detecting body is in an abnormal operation.

Description

DESCRIPTION

ROTATION ANGLE DETECTION DEVICE

TECHNICAL FIELD

The present invention relates to a rotation angle detection device employed for a vehicle control system in an automobile and the like.

BACKGROUND ART In order to detect a rotation angle of a rotator, such as a steering wheel on an automobile that rotates beyond 360° (within a predetermined rotation range), the prior art has introduced a detection device in which two rotators engage with the main axle of the steering wheel. According to the device, an absolute rotation angle of the main axle is derived from each rotation angle of the phase- shifted rotators.

Specifically, a sensor employing a magnetic resistance element and the like detects the rotation angle of the two rotators as different electric signals. The absolute rotation angle of the main axle is obtained through calculation of the two signals. Here will be described how the detection device evaluates abnormal conditions occurred in a sensor or in an amplifying circuit that amplifies the electric signal. Fig. 6 is a view showing each waveform of two electric signals a and b. Fig. 7 shows a normal condition range of the output of the two signals. Each of signals a and b shows a value corresponding to the rotation angle of each rotator, and has a maximum value and a minimum value. The device evaluates the range between the maximum value and the minimum value of the output as the normal condition range - the range satisfying the condition of not- less-than minimum value and not-more-than maximum value of the output of signal a, and not-less-than minimum value and not-more-than maximum value of the output of signal b. Therefore, the device has evaluated occurrence of abnormal condition when the detected value of the electric signal is out of the aforementioned range.

As a technical reference relating to the prior-art, for example, published Japanese translations of PCT international publication for patent applications Hll-500828 is well known.

With the evaluation method above, however, the detection device can evaluate that detecting functions normally work despite of having abnormalities in the device. This is because that no consideration is given on correlation between the phase-shifted two electric signals. That is, the normal condition range has been conventionally determined by the signals as an independent factor with no correlation therebetween. As a result, insufficient accuracy in detecting abnormal conditions has been a problem in the conventional device.

DISCLOSURE OF THE INVENTION

The detection device of the present invention contains i) a rotation detecting body rotatable beyond 360°; ii) a first rotator engaging with the rotation detecting body; iii) a second rotator engaging with the first rotator; iv) a first detector that detects the rotation angle of the first rotator; v) a second detector that detects the rotation angle of the second rotator; and vi) a self- evaluating section. The self-evaluating section evaluates the condition of the rotation detecting body according to the first and second signals from the first detector and the first and second signals from the second detector. To be more specific, referring to each range of the first and the second signals fed from the first and the second detector under the normal condition of the rotation detecting body, the evaluating section calculates the minimum value and the maximum value of the output signal. In the evaluation, the area between the minimum value and the maximum value is determined as a normal condition range, whereas the area being out of the range is determined as an abnormal condition range. The detection device evaluates that the rotation detecting body is in abnormal operation when at least one of the first signals and the second signals fed from the first and the second detectors is in the abnormal condition range.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows the normal condition range and the abnormal condition range detected by a rotation angle detection device of a first exemplary embodiment of the present invention.

Fig. 2 shows waveforms of output signals in the rotation angle detection device of the first embodiment.

Figs. 3 A, 3B, and 3C are a front view, a plan view, and a side view, respectively, showing the structure of the detection device.

Fig. 4 shows the detecting principle of the detection device. Fig. 5 shows the normal condition range and the abnormal condition range detected by a rotation angle detection device of a second exemplary embodiment.

Fig. 6 shows waveforms of output signals in a conventional rotation angle detection device.

Fig. 7 shows the normal condition range and the abnormal condition range detected by a conventional rotation angle detection device. DETAILED DESCRIPTION OF CARRYING OUT OF THE INVENTION

The exemplary embodiments of the present invention are described hereinafter with reference to the accompanying drawings.

FIRST EXEMPLARY EMBODIMENT

Referring to Figs. 1 through 4, the structure of the first embodiment will be described hereinafter.

Fig. 1 shows the normal condition range and the abnormal condition range detected by a rotation angle detection device of the embodiment. Fig. 2 shows waveforms of a first signal and a second signal. Fig. 3A is a front view of the structure of the rotation angle detection device, similarly, Fig. 3B is a plan view, and Fig. 3C is a side view of the structure. Fig. 4 is a perspective view showing the detecting principle of the device.

Firstly, the structure of the rotation angle detection device will be described.

The rotation angle detecting device contains, as shown in Figs. 3A through 3C, i) rotation detecting body 1 of a steering wheel, ii) first rotator 2 having a gear on its periphery, and hi) first detector 3 for detecting the direction of the magnetic field produced by magnet 4. Magnet 4 is disposed in a mid section of first rotator 2, so that it rotates with first rotator 2. The device further contains iv) worm gear 5 attached to first rotator 2, v) second rotator 6 having a gear on its periphery, and vi) second detector 7 for detecting the direction of the magnetic field produced by magnet 8. Magnet 8 is disposed in a mid section of second rotator 6, so that it rotates with second rotator 6. Each of first detector 3 and second detector 7 is formed of a magnet and an anisotropic magnetic resistance (AMR) element. The AMR element detects each direction of the magnetic field produced by magnets 4 and 8 that are fixed in first rotator 3 and second rotator 6, respectively, as shown in Fig. 4. First detector 3 outputs a first signal and a second signal, as shown in Fig. 2. The first signal changes its shape with a period of 180° according to a sine curve, on the other hand, the second signal changes its shape with a period of 180° according to a cosine curve.

Like first detector 3, second detector 7 outputs a first signal having a sine curve and a second signal having a cosine curve, both the signals change the waveform with a period of 180°.

Worm gear 5 transmits the rotation of first rotator 2 to second rotator 6 with a constant reduction gear ratio with respect to first rotator 2. With the structure above, the rotation of rotation detecting body 1 is transmitted, via first rotator 2, to second rotator 6.

Next will be described how such a structured device detects the rotation angle. The ratio of rotation between rotation detecting body 1 and first rotator 2 is derived from each number of the teeth of the gear formed around the periphery of each rotating axle. Suppose that first rotator 2 and rotation detecting body 1 rotate with a ratio of a:l, i.e., first rotator 2 rotates a-times faster than rotation detecting body 1. Converting the rotation of first rotator 2 into rotation detecting body 1, first detector 3 detects the rotation angle of 180/a degrees. On the other hand, the ratio of rotation between rotation-detecting body 1 and second rotator 6 via worm gear 5 is defined by the number of the teeth of each gear formed around the periphery of detecting body 1 and rotator 6, and worm gear 5 with a reduction gear ratio. Now suppose that second rotator 6 rotates with a ratio of (1 b) - the rotation of second rotator 6 is reduced by the worm gear - with respect to rotation detecting body 1. Converting the rotation of rotator 6 into that of rotation detecting body 1, second detector 7 detects the rotation angle of 180 x b degrees. According to the two values calculated above, the device allows second detector 7 to determine a wide-range rotation angle, and allows first detector 3 to detect a rotation angle with high accuracy.

Here will be described in detail how the detector detects the rotation angle. First detector 3 and second detector 7 are, as shown in Fig. 4, disposed directly below magnet 4 in first rotator 2 and magnet 8 in second rotator 6, respectively. When first rotator 2 rotates, the direction of magnetic field passing through first detector 3 changes. Similarly, the rotation of second rotator 6 changes the direction of magnetic field passing through second detector 7. As a result, each of the two detectors outputs a first signal having a sine curve and a second signal having a cosine curve. Each detector outputs the signal with a period of 180°, therefore, the output of the first signal is detected as a sin 20 waveform, and the output of the second signal is detected as a cos 2Θ waveform. With the two signals, the rotation angle is obtained from the expression below: tan 20 = sin 2Θ / cos 20 (Exp. 1).

In the structure of the first embodiment, as shown in Fig. 1, the output has an offset of 2.5V from the origin. First detector 3 and second detector 7 are formed of an anisotropic magnetic resistance (AMR) element. In the wake of amphfying by each amplifying circuit (not shown) with identical amplification factor, each detector detects a first signal with a sine curve and a second signal with a cosine curve in the range of output characteristics shown in Fig. 2. The amplitude of each signal varies according to changes in ambient temperature. The calculation of the rotation angle employs tan (20) as shown in the Exp. 1 — the change in amplitude can be ignored in the calculation because of being canceled out each other, as shown in the expression 2 below: tan 2Θ = Asin 2Θ / Acos 20 = sin 20 / cos 20 (Exp. 2),

(where A represents amplitude). According to the embodiment, as shown in Fig. 1, each of first detector 3 and second detector 7 determine two-dimensional loci with respect to the maximum and the minimum values of sine-curve signal and the cosine-curve signal in the range of output characteristics — the range is obtained, as described above, by each amphfying circuit with the same amphfication factor. The loci give two circles, as shown in Fig. 2. As a result, the area between the two circles is determined as the normal output range.

The process above is explained by the following expressions: min. value 1 ≤ sin 2Θ ≤ max. value 1 (Exp. 3), min. value 2 ≤ cos 2Θ ≤ max. value 2 (Exp. 4).

The two output ranges above are to be squared to obtain the expressions 5 and 6 below:

(min. value l)² ≤ (sin 2Θ)² ≤ (max. value l)² (Exp. 5), where, | min. value 1 1 ≤ | sin 201 . (min. value 2)² ≤ (cos 2Θ)² ≤ (max. value 2)² (Exp. 6), where, | min. value 21 ≤ | cos 201 . Furthermore, adding the expressions above finds the expression 7 below: (min. value l)² + (min. value 2)² ≤ (sin 2Θ)² + (cos 2Θ)²

≤ (max. value l)² + (max. value 2)² (Exp. 7). The Exp. 7 shows that the locus of the point (sin 2Θ, cos 20) on the x-y plane gives a doughnut-shaped area surrounded by the inner circle with a diameter of the value obtained by the expression 8 and the outer circle with a diameter of the value determined by the expression 9 below;

V (min. value l)² + (min. value 2)² (Exp. 8), (max. value l)² + (max. value 2)² (Exp . 9).

That is, an output detected within the doughnut-shaped area can be determined to have a normal condition. According to the structure of the embodiment, as described earlier, the output signals have an offset of 2.5V. By the offsetting, the normal condition range has a doughnut-shaped area not less than the circle with a diameter calculated by the Exp. 8 and not more than the circle with a diameter calculated by the Exp. 9, having a center of x, y- coordinates (2.5, 2.5). Through the calculation, the device can thus immediately evaluate an abnormal condition when detecting a signal out of the range of the doughnut shape. In this way, the device can increase the reliability in evaluating an abnormal condition with higher accuracy than the prior-art device. Besides, each of the first and the second detectors is formed of a magnet and a magnetometric sensor, and each magnet is fixed to the first rotator and the second rotator. The structure provides a non-contact detection in determining the rotation angle of the first and the second rotators, whereby detection with high accuracy can be maintained even in a long period of use.

SECOND EXEMPLARY EMBODIMENT

Now will be described a structure of the second embodiment, with reference to Fig. 5.

Fig. 5 shows the principle of detection of the structure in accordance with the second embodiment. Like the first embodiment, in the wake of amphfication by each amplifying circuit (not shown) having an identical amphfication factor, first detector 3 and second detector 7 output a sine-wave signal as a first signal and a cosine-wave signal as a second signal in the range of output characteristics shown in Fig. 2. In the embodiment, as is the case in the first embodiment, the outputs of the signals have an offset of 2.5V Therefore, the locus of the signals detected gives a circle having a diameter calculated by the expression 10 under the environmental conditions similar to the case in the first embodiment:

R = ^ (cos 2Θ - 2.5)²+ (sin 2θ - 2.5)² (Exp. 10).

The diameter R derived from the Exp. 10 varies as environmental change, for example, ambient temperature, however, in a short time — few milliseconds, a perceptible change is not observed. Therefore, the following evaluation method will work well.

Suppose that an environmental change expected within a period — for example, a change in ambient temperature in few milliseconds - is not more than 5°C. Under the condition, specifying an evaluation value "d" and comparing it with a value ΔR that represents an actual change in diameter of the locus. If the ΔR is greater than the evaluation value d, the device determines that an abnormality occurs. In the evaluation, the square of the diameter R, i.e., ΔR² can be employed. In this case, the evaluation value d should be determined so as to correspond to the value ΔR². According to the present invention. The self-evaluating section calculates the sum of the first signal squared and the second signal squared, or the square root of the sum. If a variation of the calculated sum or the square root of the sum exceeds a specified value in a predetermined period, the device finds occurrence of abnormalities, thereby enhancing the reliability in evaluating an abnormal condition with higher accuracy.

With the evaluation above, the device can find an occurrence of abnormalities, even if the value of the locus diameter R after having a change measures in the normal condition area. This also contributes to an accurate detection of abnormal condition. According to the present invention, as described above, referencing to the output characteristics of the first and the second signals detected by the first and the second detectors under the normal condition of the rotation detecting body, the detecting device calculates the minimum value and the maximum value of the signal output. From the calculation, the area not-less-than the minimum value and not-more-than the maximum value is determined as a normal condition area, and the rest is defined as an abnormal condition area. When at least one of the outputs of the first and the second signals detected at the first and the second detectors is in the abnormal condition area, the device evaluates that the rotation detecting body has abnormalities. The calculation of the normal condition area with reference to the output characteristics of the first and the second signals allows the device to provide a reliable evaluation with high accuracy in detecting an abnormal condition.

INDUSTRIAL APPLICABILITY

The present invention relates to a rotation angle detection device employed for a vehicle control system in an automobile and the like. It is the object of the present invention to improve accuracy of detecting abnormal conditions.

Claims

1. A rotation angle detection device comprising: a) a rotation detecting body rotatable beyond 360°; b) a first rotator engaging with the rotation detecting body; c) a second rotator engaging with the first rotator; d) a first detector that detects a rotation angle of the first rotator; e) a second detector that detects a rotation angle of the second rotator; and f) a self-evaluating section that evaluates normal condition and abnormal condition of the rotation detecting body according to i) a first signal and a second signal detected by the first rotator, and ii) a first signal and a second signal detected by the second rotator, wherein, referencing to output characteristics of the first and the second signals detected by the first and the second detectors under the normal condition of the rotation detecting body, the self-evaluating section calculates a minimum value and a maximum value of signal outputs to determine a normal condition range being not-less-than the minimum value and being not-more-than the maximum value, and an abnormal condition range being other than the normal range, and the self-evaluating section judges that the rotation detecting body is in abnormal operation when at least one of the values of the first signals and the second signals fed from the first and the second detectors is in the abnormal condition range.

2. The rotation angle detection device of Claim 1, wherein each of the first and the second detectors is formed of a magnet and a magnetometric sensor, and each magnet is fixed to the first rotator and the second rotator.

3. A rotation angle detection device comprising: a) a rotation detecting body rotatable beyond 360°; b) a first rotator engaging with the rotation detecting body; c) a second rotator engaging with the first rotator; d) a first detector that detects a rotation angle of the first rotator; e) a second detector that detects a rotation angle of the second rotator; and f) a self-evaluating section that evaluates normal condition and abnormal condition of the rotation detecting body according to i) a first signal and a second signal detected by the first rotator, and ii) a first signal and a second signal detected by the second rotator, wherein, the self-evaluating section calculates a sum of the first signal squared and the second signal squared, or a square root of the sum, and if a variation of the calculated sum or the square root of the sum exceeds a specified value in a predetermined period, the self-evaluating section judges that the rotation detecting body is in an abnormal condition.

4. The rotation angle detection device of Claim 3, wherein each of the first and the second detectors is formed of a magnet and a magnetometric sensor, and each magnet is fixed to the first rotator and the second rotator.

5. The rotation angle detection device of Claim 1, wherein a gear is disposed along a periphery of the rotation detecting body.

6. The rotation angle detection device of Claim 3, wherein a gear is disposed along a periphery of the rotation detecting body.