JP2007304000A - Rotation angle detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotation angle detecting device which can ensure detection accuracy when detecting a rotation angle, and furthermore, even if, for example, sine waves and cosine waves for detecting the angle are used by equipment other than the rotation angle detecting device, which can ensure processing accuracy when the common use equipment carries out the processing using the sine waves and the cosine waves. <P>SOLUTION: A first magnetoresistive element 5 for detecting rotations of a first driven gear 3 outputs a first sine-wave signal Vs1 in the form of a sine wave as an output for an angular displacement and a first cosine-wave signal Vc1 in the form of a cosine wave as an output for the angular displacement, to a CPU 9. The CPU 9 compensates the signals Vs1, Vc1 by using a Fourier transform operation and a reverse Fourier transform operation, calculates an arctangent angle Arctanθa from compensated signals Vs1, Vc1 and recognizes it as a gear angle θa of the first driven gear 3. Then, the CPU 9 calculates a gear angle θx of a main driving gear 2, i.e., a steering angle of a steering wheel, by using the gear angle θa. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rotation angle detection device that detects an angle of a rotating object when it rotates.

Conventionally, a rotation angle detection device that detects the rotation angle of a movable object that rotates is widely used. In this type of rotational angle detection device, a magnetic or optical angle sensor is used to detect a sinusoidal signal sinθ whose output is a sine waveform 81 with respect to the angular displacement as shown in FIG. The cosine wave signal cosθ having an output having a cosine waveform 82 is obtained, and the arctangent Arctanθ (= tan ⁻¹ (sinθ / cosθ)) is calculated from the sine wave signal sinθ and the cosine wave signal cosθ. As shown in FIG. 7B, the arc tangent Arctan θ has a characteristic that the waveform 83 of the calculated angle with respect to the actual angle has linearity. Therefore, if the angle calculation is performed using this, the calculation process is simple. Processing will be enough. Therefore, the rotation angle detection device obtains the arctangent Arctan θ from the sine wave signal sin θ and the cosine wave signal cos θ, and calculates it as the rotation angle θ of the movable object.

  By the way, when the sine wave signal sinθ and the cosine wave signal cosθ are ideal values, as shown in FIG. 7C, the rotation angle is calculated from the arctangent Arctanθ at that time, as can be seen from the Lissajous waveform 84 having a perfect circle. It is possible to derive the correct angle when calculating. However, under the present circumstances, the sine wave signal sinθ and the cosine wave signal cosθ may be output with an error due to an error in the assembly position of the angle sensor or variations in circuit characteristics. In this case, as shown in FIG. 8A, the detected waveform of the arctangent Arctan θ with respect to the displacement amount of the movable object becomes a waveform 85 in which the linearity is impaired, and the difference from the ideal waveform 85a is affected as an error in the calculated angle. It will come out. Further, when this is seen as a Lissajous waveform, a Lissajous waveform 86 which is not a perfect circle is taken as shown in FIG. Therefore, when an error is included in the sine wave signal sinθ and the cosine wave signal cosθ, there is a problem that an accurate rotation angle cannot be calculated.

Therefore, for example, Patent Literature 1 discloses a technique for correcting the calculated angle obtained from the arctangent Arctan θ. The technology of Patent Document 1 obtains a sine wave signal and a cosine wave signal from an angle sensor at the time of shipment or start of operation of a rotation angle detection device, obtains an arctangent, and forms a radius that forms a Lissajous waveform of the arctangent. An angle is calculated, and a radius variation value indicating variation in the radius of the Lissajous waveform is obtained from the radius and the angle. Then, the radius variation value is subjected to Fourier transform and inverse Fourier transform to obtain a differential value, and the rotation angle is corrected using the differential value. When this type of rotation angle detection device is mounted on a vehicle, it is used as a steering angle sensor (SAS) for detecting the steering angle of a steering wheel, for example.
JP 2005-24398 A

  By the way, in recent vehicles, there is a vehicle type equipped with a vehicle stability control system (VSC: Vehicle Stability Control) as a system that makes it difficult to exceed the limit of the frictional force of the wheel against the road surface when turning. The vehicle stability control system adjusts the brake and engine output behavior when the vehicle enters the corner of the roadway at overspeed or the vehicle slips when the vehicle posture is disturbed due to sudden steering operation, etc. It is a system controlled by.

  The vehicle stability control system acquires rectangular waves (pulse encoder output) 87 and 88 whose number of pulses changes according to the steering rotation speed as shown in FIG. 9 from the angle sensor, and the rectangular wave 87 (the rectangular wave 88 also). The steering angle of the steering wheel is calculated by counting the number of possible pulses. The rectangular waves 87 and 88 are obtained by applying a predetermined threshold level to the time displacement waveforms 89 and 90 corresponding to changes in output with respect to the time displacement of the sine wave signal sinθ and the cosine wave signal cosθ, and a portion exceeding the threshold level is set to the H level. This corresponds to a signal in which the portion not exceeding is L level. The vehicle stability control system detects the steering angle and steering direction of the steering wheel by monitoring the pulses of the rectangular waves 87 and 88, and implements vehicle stability control.

  Here, since the steering angle sensor calculates the steering angle, when the vehicle stability control system calculates the steering angle (steering direction), it does not cause an increase in the number of parts and parts cost. A new angle sensor is not provided in the vehicle stability control system, and the steering angle sensor and the vehicle stability control system are connected by wiring, and the sine wave signal sinθ and cosine obtained by the angle sensor of the steering angle sensor are connected. It is also conceivable to use the wave signal cosθ in the vehicle stability control system.

  By the way, the steering angle obtained by the steering angle sensor is obtained by performing Fourier transform and inverse Fourier transform on arctangent Arctanθ obtained from the sine wave signal sinθ and cosine wave signal cosθ when angle correction is performed using the technique of Patent Document 1. Correction is made. However, since the steering angle is calculated by the vehicle stability control system using the sine wave signal sinθ and the cosine wave signal cosθ itself, the sine wave signal sinθ and the cosine wave signal cosθ are not corrected. Therefore, when the vehicle stability control system calculates the steering angle based on the sine wave signal sinθ and the cosine wave signal cosθ output from the steering angle sensor, even if the technique of Patent Document 1 is used, these sine wave signal sinθ and cosine Under the condition that the distortion component (error) is included in the wave signal cosθ, there arises a problem that an accurate steering angle cannot be calculated by the vehicle stability control system.

  The object of the present invention is to ensure the detection accuracy when detecting the rotation angle. Furthermore, for example, the sine wave signal and the cosine wave signal used for the angle detection are transmitted to other devices other than the rotation angle detection device. To provide a rotation angle detection device that can ensure the processing accuracy even when it is used when the shared device performs processing using these sine wave signal and cosine wave signal. is there.

  In order to solve the above problems, in the present invention, when detecting the angle of a rotating object, the detection signal is a sine wave signal that takes a sine wave output with respect to the angular displacement of the rotating object, and the angular displacement. An angle detection unit that outputs a cosine wave signal that takes an output of a cosine wave, an angle calculation unit that calculates an arctangent of the sine wave signal and the cosine wave signal, and calculates a rotation angle of the rotating object by the arctangent When the change of the sine wave signal and the cosine wave signal with respect to the angular displacement of the rotating object is seen, the inverse of the rotation angle detection device is provided so that the angular displacement waveform approaches an ideal waveform without distortion. The gist of the present invention is to provide correction means for correcting the sine wave signal and the cosine wave signal before the tangent is obtained.

  According to this configuration, the sine wave signal and the cosine wave signal detected by the angle detection unit are corrected to the ideal values by the correction unit, and as a result, the angular displacement waveform of the sine wave signal and the cosine wave signal is an ideal waveform without distortion. It will be in the state which took. Then, the angle calculation means calculates the arc tangent using the corrected sine wave signal and cosine wave signal, and calculates the arc tangent as the rotation angle of the rotating object. Therefore, since the rotation angle of the rotating object is calculated from the arc tangent obtained from the sine wave signal and cosine wave signal corrected to the ideal values, the angle error can be suppressed small and the effect of ensuring the accuracy of angle detection is high.

  In the present invention, the sine wave signal and the cosine wave signal are first corrected before the arc tangent is obtained, and the arc tangent is obtained using the corrected sine wave signal and cosine wave signal. . Therefore, for example, for the purpose of suppressing the number of parts of the angle detection system, when a configuration in which the sine wave signal and cosine wave signal of the angle detection means are shared with other devices other than the rotation angle detection device is used, On the other hand, it is possible to provide ideal sine wave signals and cosine wave signals that do not include distortion, and it is possible to perform accurate processing in the device.

  In the present invention, the correction means includes a correction value table storing correction values obtained by performing inverse Fourier transform on distortion components of the angular displacement waveform extracted by Fourier transforming the angular displacement waveform, and When the sine wave signal and the cosine wave signal are acquired, the correction value corresponding to the signal value at that time is read by referring to the correction value table, and the distortion of the sine wave signal and the cosine wave signal is read using the correction value. The gist of the present invention is to provide a computing means for computing the ideal values of the sine wave signal and the cosine wave signal by removing components.

  According to this configuration, when a correction value used when correcting the sine wave signal and the cosine wave signal is derived, a procedure for reading out by referring to the correction value table is taken. Therefore, the derivation of the correction value may be a simple process of referring to the correction value table, which contributes to shortening the processing time when correcting the sine wave signal and the cosine wave signal.

  In the present invention, the corrected sine wave signal and the cosine wave signal are output to another external device, and the external device includes output means for executing processing that requires the sine wave signal and the cosine wave signal. This is the gist.

  According to this configuration, if another device is connected to the output means serving as the signal input / output port of the rotation angle detection device, the sine wave signal and cosine wave signal close to the ideal waveform obtained by the rotation angle detection device can be connected. It is possible to output to the device. Therefore, when processing using a sine wave signal and a cosine wave signal is performed in the connected device, the processing is performed with a sine wave signal and a cosine wave signal close to an ideal waveform. Is possible.

The gist of the present invention is that it comprises update means for updating the correction value written in the correction value table when conditions for rewriting the correction value are met.
According to this configuration, since the correction value in the correction value table is updated by the updating means in a certain cycle, it becomes possible to correct the sine wave signal and the cosine wave signal using the optimum correction value each time, and the rotation. This is effective in improving the accuracy of angle detection.

  According to the present invention, when detecting the rotation angle, the detection accuracy can be ensured. Moreover, for example, the sine wave signal and the cosine wave signal used for the angle detection can be transmitted to other devices other than the rotation angle detection device. Even when it is used, when the shared device performs processing using these sine wave signal and cosine wave signal, the processing accuracy can be ensured.

Hereinafter, an embodiment of a rotation angle detection apparatus embodying the present invention will be described with reference to FIGS.
As shown in FIG. 1, the vehicle is equipped with a steering angle sensor (SAS) 1 that detects the steering angle of the steering wheel. The steering angle sensor 1 is provided with a main driving gear 2 fixed to a steering shaft that connects a steering wheel (rotating object) and a steering wheel. The main drive gear 2 is provided on the same axis as the steering shaft, and rotates in synchronization with the steering shaft when the steering wheel is steered. Two driven gears 3, 4 that can rotate with the main driving gear 2 are meshed with and engaged with the main driving gear 2. The steering angle sensor 1 corresponds to a rotation angle detection device.

  Each of the gears 2 to 4 is formed to have a different number of teeth. Here, for example, if the number of teeth of the main driving gear 2 is L and the number of teeth of the first driven gear 3 is M (<L), when the main driving gear 2 makes one rotation, the first driven gear 3 is M Rotate / L. For example, if the number of teeth of the second driven gear 4 is N (<L), the second driven gear 4 rotates N / L when the main driving gear 2 makes one rotation. That is, when the main drive gear 2 rotates, the driven gears 3 and 4 are in different rotational positions.

  Each driven gear 3, 4 is provided with magnetoresistive elements (MRE) 5, 6 capable of detecting the rotation angle of each driven gear 3, 4. The first magnetoresistive element 5 for the first driven gear 3 detects the magnetic field of the magnet 7 attached to the first driven gear 3 and changes the direction of the magnetic field of the magnet 7 that changes as the first driven gear 3 rotates. Take the corresponding output. The first magnetoresistive element 5 has a first sine wave signal Vs1 whose output has a sine waveform (sin waveform) with respect to the steering angle displacement of the steering wheel, that is, the rotation angle displacement of the first driven gear 3, and the rotation angle thereof. Two signals, i.e., a first cosine wave signal Vc1 having a cosine waveform (cos waveform) with respect to the displacement, are output as voltage values.

  The second magnetoresistive element 6 for the second driven gear 4 detects the magnetic field of the magnet 8 attached to the second driven gear 4 and changes the direction of the magnetic field of the magnet 8 that changes as the second driven gear 4 rotates. Take the corresponding output. The second magnetoresistive element 6 has a second sine wave signal Vs2 whose output has a sine waveform (sin waveform) with respect to the steering angle displacement of the steering wheel, that is, the rotation angle displacement of the second driven gear 4, and the rotation angle thereof. Two signals are output as a second cosine wave signal Vc2 whose output is a cosine waveform (cos waveform) with respect to the displacement. The magnetoresistive elements 5 and 6 and the magnets 7 and 8 constitute angle detection means.

  The steering angle sensor 1 is provided with a CPU (Central Processing Unit) 9 for calculating the steering angle of the steering wheel. The CPU 9 stores the first magnetoresistive element 5 and the second magnetoresistive element 6 described above, a ROM 10 storing various programs executed when the steering angle sensor 1 is operated, and various data used when calculating the steering angle. An EEPROM (Electrically Erasable Programmable ROM) 11 is connected. The CPU 9 constitutes angle calculation means, correction means (calculation means), and update means.

  The CPU 9 is provided with a waveform correction function for correcting the angular displacement waveforms 12 to 15, which are output change waveforms with respect to the angular displacement of the various signals Vs 1, Vc 1, Vs 2, and Vc 2, to waveforms that are close to ideal values. By the way, this kind of signal waveform of the first magnetoresistive element 5 and the second magnetoresistive element 6 shows, for example, the waveform 12 of the output change with respect to the angular displacement of the first sine wave signal Vs1 in FIG. The waveform 13 of the output change with respect to the angular displacement of the cosine wave signal Vc1 is shown in FIG. 2 and FIG. 3 because of the variation in the assembly of the magnetoresistive elements 5 and 6 and the respective circuit characteristics. , 13 may pulsate and be output in a state including distortion (error) (the waveform indicated by the broken line in FIGS. 2 and 3).

  The waveform correction function performed by the CPU 9 is a function that cancels this distortion and brings the angular displacement waveforms 12 to 15 closer to the ideal waveform, and this correction is based on the following concept. This will be described in detail below. When a signal change with respect to the angular displacement of each signal Vs1, Vc1, Vs2, Vc2 (that is, each angular displacement waveform 12-15) is a function F (x), this function F (x) Can be expressed by the following equation (1).

ここで、式(1)における各フーリエ係数は、ａ₀が定数項、ａ₁，ｂ₁が基本波成分、ｎ≧２のａ_n，ｂ_nが高調波成分であって、これらは三角関数の直交性を用いることにより、各々の係数値を求めることが可能である。

Here, each Fourier coefficient in the equation (1) is expressed as follows: a ₀ is a constant term, a ₁ and b ₁ are fundamental wave components, n ≧ 2 and a _n and b _n are harmonic components, and these are trigonometric functions. By using the orthogonality, it is possible to obtain each coefficient value.

Next, consider the case where the expression (1) is developed. Here, an example in which the angular displacement waveform 13 shown in FIG. Here, the function of the angular displacement waveform 13 is f (x), and the angular displacement waveform 13 takes a distortion waveform as shown in FIG. 3, whereby the Fourier coefficients a ₀ , a _n , b _n are shown in FIG. Suppose that the coefficient value is taken. In this case, Fourier coefficients are used until n reaches 5, but if the angular displacement waveform 13 is corrected more accurately than this, a Fourier coefficient where n is 5 or more is obtained, and this is calculated. It may take the form used. Under the above conditions, equation (1) can be expanded into the following equation (2).

ここで、式(2)からも分かるように、関数ｆ(ｘ)において式(2)の右辺から「0.01×sinx+0.01×cos3x+0.01×sin3x+0.01×cos5x+0.01×sin5x」の項を減算すれば、右辺に残る項はcosxのみとなることから、この減算を行えば関数ｆ(ｘ)の理想関数を求めることが可能である。即ち、歪みのない角度変位波形１３の理想関数をｆ₀(ｘ)とし、「0.01×sinx+0.01×cos3x+0.01×sin3x+0.01×cos5x+0.01×sin5x」の項を補正関数ｚ(ｘ)すると、次式(3)が成立する。

Here, as can be seen from equation (2), the term “0.01 × sinx + 0.01 × cos3x + 0.01 × sin3x + 0.01 × cos5x + 0.01 × sin5x” from the right side of equation (2) in function f (x) If subtraction is performed, the term remaining on the right side is only cosx. Therefore, the ideal function of the function f (x) can be obtained by performing this subtraction. That is, the ideal function of the angular displacement waveform 13 without distortion is f ₀ (x), and the term “0.01 × sinx + 0.01 × cos3x + 0.01 × sin3x + 0.01 × cos5x + 0.01 × sin5x” is the correction function z (x). Then, the following equation (3) is established.

これを図３に示すように信号波形から見た場合、角度変位波形１３の関数ｆ(ｘ)の波形から、「0.01×sinx」の波形、「0.01×cos3x」の波形、「0.01×sin3x」の波形、「0.01×cos5x」の波形及び「0.01×sin5x」の波形の計５波形を差し引いた波形が、理想関数ｆ₀(ｘ)の信号波形に相当することが分かる。

When this is viewed from the signal waveform as shown in FIG. 3, from the waveform of the function f (x) of the angular displacement waveform 13, a waveform of “0.01 × sinx”, a waveform of “0.01 × cos3x”, and “0.01 × sin3x” It can be seen that a waveform obtained by subtracting a total of five waveforms, the waveform of “0.01 × cos5x” and the waveform of “0.01 × sin5x”, corresponds to the signal waveform of the ideal function f ₀ (x).

Therefore, as can be seen from the equations (2) and (3), cosx corresponding to the ideal waveform of the angular displacement waveform 13 is a value obtained by subtracting the correction function z (x) from the function f (x). . Here, since the correction function z (x) is a value obtained by performing a Fourier transform on the function f (x), the correction function z (x) is subjected to an inverse Fourier transform and converted to a corrected function z ₀ (x). If the post-transform correction function z ₀ (x) after inverse Fourier transform is subtracted from the function f (x) that is a waveform including distortion, cosx that is an ideal waveform without distortion can be obtained. This also applies to the first sine wave signal Vs1, the second sine wave signal Vs2, and the second cosine wave signal Vc2, and the contents are the same except for the Fourier coefficients. Therefore, the details of the procedure for calculating the ideal values for these signals Vs1, Vs2, and Vc2 are omitted.

Therefore, in the waveform correction function of this example, a lookup table 16 is provided in the EEPROM 11 of the steering angle sensor 1 as shown in FIG. 1, and the actual value of the post-conversion correction function z ₀ (x) is stored in this lookup table 16. The correction value K is stored, and various signals Vs1, Vc1, Vs2, and Vc2 are corrected using the correction value K when calculating the steering angle. Note that the lookup table 16 constitutes correction means (correction value table).

  FIG. 5 shows the look-up table 16 of the first cosine wave signal Vc1. This correction value K is written at the angle detection pitch of the first driven gear 3, and in this example, at an interval of 1 deg and “0.01 × sinx”. ”,“ 0.01 × cos3x ”,“ 0.01 × sin3x ”,“ 0.01 × cos5x ”, and“ 0.01 × sin5x ”, the numerical values are divided and written. The correction value K is not limited to being written for each of these terms, and a value obtained by adding these may be written. 5 shows the look-up table 16 for the first cosine wave signal Vc1, but similar look-up tables 16 are stored in the EEPROM 11 for the other signals Vs1, Vs2, and Vc2.

  The look-up table 16 takes a procedure in which the correction value K is written by the operator when the steering angle sensor 1 is manufactured or shipped, for example. That is, for example, when the steering angle sensor 1 is manufactured or shipped, the main driving gear 2 is temporarily rotated to rotate the first driven gear 3 and the second driven gear 4 once, thereby obtaining the respective waveforms 12 to 12. 15 is subjected to Fourier transform to obtain a reference correction value Ka (that is, a correction function z (x)) that is a source of the correction value K, and the correction value K obtained by performing inverse Fourier transform on the reference correction value Ka is an angle. It is written in the EEPROM 11 at the detection pitch.

  As another example of writing the correction value K, when the steering angle sensor 1 is used, it has been sampled so far on condition that the first driven gear 3 and the second driven gear 4 have made one rotation. By performing Fourier transform and inverse Fourier transform on the respective waveforms 12 to 15, the correction value K obtained at this time may be overwritten on the lookup table 16 as the latest correction value. Furthermore, this is not limited to being overwritten every time both gears 3 and 4 make one revolution, and if both gears 3 and 4 have made one revolution, if a certain time has passed since the previous overwriting, it is a condition. The correction value K may be overwritten by performing Fourier transform and inverse Fourier transform. The correction value K may be written at different timings for the first driven gear 3 and the second driven gear 4.

  When calculating the steering angle, the CPU 9 acquires the first sine wave signal Vs1 and the first cosine wave signal Vc1 from the first magnetoresistive element 5, and corrects these signals Vs1 and Vc1 using the lookup table 16. For example, in the case of the first cosine wave signal Vc1, the CPU 9 reads the correction value K corresponding to the signal value of the first cosine wave signal Vc1 (function f (x)) at that time by referring to the lookup table 16. The first correction cosine wave signal Vc1R is calculated as the ideal value of the first cosine wave signal Vc1 by subtracting the correction value K from the first cosine wave signal Vc1 at that time. The angular displacement waveform of the first corrected cosine wave signal Vc1R is a signal waveform having an ideal cos waveform 17 as shown in FIG. The CPU 9 also calculates the first corrected sine wave signal Vs1R, which is the ideal value of the first sine wave signal Vs1, for the first sine wave signal Vs1 in the same procedure as the first cosine wave signal Vc1. The angular displacement waveform of the first corrected sine wave signal Vs1R is a signal waveform having an ideal sin waveform 18 as shown in FIG.

The CPU 9 that has calculated the first corrected sine wave signal Vs1R and the first corrected cosine wave signal Vc1R uses the first corrected sine wave signal Vs1R and the first corrected cosine wave signal Vc1R to calculate the arctangent Arctanθa (= tan ⁻¹ (sinθa / cos θa)) is calculated. Since the arctangent Arctan θa corresponds to the first driven gear angle θa, the CPU 9 calculates the arctangent Arctan θa as the first driven gear angle θa.

The CPU 9 obtains the second corrected sine wave signal Vs2R by correcting the second sine wave signal Vs2 in the same procedure as the case of the first sine wave signal Vs1 and the first cosine wave signal Vc1, and similarly the second cosine wave. A second corrected cosine wave signal Vc2R is obtained by correcting the signal Vc2. The CPU 9 that has calculated the second corrected sine wave signal Vs2R and the second corrected cosine wave signal Vc2R is the arc tangent Arctan θb (= tan ⁻¹ (sinθb / cos θb) of the second corrected sine wave signal Vs2R and the second corrected cosine wave signal Vc2R. ) Is calculated. Since the arctangent Arctan θb corresponds to the second driven gear angle θb, the CPU 9 calculates the arctangent Arctan θb as the second driven gear angle θb.

  When the CPU 9 calculates the first driven gear angle θa and the second driven gear angle θb, the CPU 9 calculates the main driving gear angle θx of the main driving gear 2, that is, the steering angle of the steering wheel by looking at the combination of these gear angles θa and θb. To do. The CPU 9 calculates the steering angle as an absolute angle, and detects the rotation of the steering wheel in a range of 4 rotations by detecting the angle in a detection range of 0 degrees to 1440 degrees, for example. The CPU 9 outputs the calculated angle data of the steering angle to various in-vehicle ECUs (meter ECU, engine ECU, etc.) via the in-vehicle LAN.

  As shown in FIG. 1, the steering angle sensor 1 is connected to a vehicle stability control system (VSC) 19 that makes it difficult to exceed the limit of the frictional force of the wheel against the road surface during turning. The vehicle stability control system 19 determines whether the vehicle slips when the vehicle enters the corner of the roadway at an overspeed or the vehicle body posture is disturbed due to a sudden steering operation or the like. The system is controlled by adjustment and is connected to the CPU 9 via an interface 20 in the steering angle sensor 1.

  Further, the CPU 9 of the steering angle sensor 1 uses the first sine wave signal Vs1 and the first cosine wave signal Vc1 of the magnetoresistive elements 5 and 6 as shown in FIG. 22 is acquired. When the CPU 9 receives the first sine wave signal Vs1 and the first cosine wave signal Vc1, the CPU 9 synchronizes with the calculation of the steering angle to set the time displacement waveforms 21 and 22 of the signals Vs1 and Vc1 to a preset threshold. The signal is converted into a sine side rectangular wave 23 and a cosine side rectangular wave 24 that are H level when the level Vh is exceeded and L level when the level Vh is lower. This threshold level Vh can be appropriately changed by rewriting the program contents of the CPU 9. The CPU 9 outputs the sine side rectangular wave 23 and the cosine side rectangular wave 24 to the vehicle stability control system 19.

  When the rectangular waves 23 and 24 are input, the vehicle stability control system 19 detects the steering angle of the steering wheel by counting the number of pulses of the sine-side rectangular wave 23 (cosine-side rectangular wave 24 is acceptable). At the same time, the steering direction of the steering wheel is detected by checking which edge of the sine side rectangular wave 23 and the cosine side rectangular wave 24 is detected first. The CPU 9 recognizes the operation state of the steering wheel by looking at the steering angle and the steering direction thus obtained, and performs vehicle stability control according to the steering operation state. The vehicle stability control system 19 corresponds to an external device, and the interface 20 corresponds to an output unit.

  In this example, the first sine wave signal Vs1 and the first cosine wave signal Vc1 (the second sine wave signal Vs2 and the second cosine wave signal Vc2) are corrected using Fourier transform and inverse Fourier transform, and the correction is performed. The steering angle of the steering wheel is detected by obtaining an arctangent from the first corrected sine wave signal Vs1R and the first corrected cosine wave signal Vc1R (second corrected sine wave signal Vs2R and second corrected cosine wave signal Vc2R). . Therefore, even if the various signals Vs1, Vc1, Vs2, and Vc2 output from the magnetoresistive elements 5 and 6 include distortion components (errors) due to an assembly error of the magnetoresistive elements 5 and 6, this correction causes the correction. The distortion component is canceled out, which is effective in ensuring the accuracy of detecting the steering angle of the steering wheel.

  In this example, the first sine wave signal Vs1 and the first cosine wave signal Vc1 (second sine wave signal Vs2 and second cosine wave signal Vc2) themselves are corrected. Therefore, for the purpose of reducing the number of parts of the angle detection system, the first sine wave signal Vs1 and the first cosine wave signal Vc1 (second sine wave signal Vs2 and second sine wave signal) obtained by the magnetoresistive elements 5 and 6 of the steering angle sensor 1 are used. Even if the cosine wave signal Vc2) is used not only in the steering angle sensor 1 but also in the vehicle stability control system 19, it is possible to make it difficult for the vehicle stability control system 19 to generate a control error. For this reason, it becomes possible to aim at coexistence with reduction of detection system parts, and ensuring of control accuracy of vehicle stability control.

According to the configuration of the present embodiment, the following effects can be obtained.
(1) Since the first sine wave signal Vs1 and the first cosine wave signal Vc1 (second sine wave signal Vs2 and second cosine wave signal Vc2) are corrected by using Fourier transform and inverse Fourier transform, these signals Vs1 , Vc1, Vs2, and Vc2, even if distortion components are included, these distortion components are canceled by correction. Therefore, the steering angle of the steering wheel is obtained by calculating the arc tangent from the first corrected sine wave signal Vs1R and the first corrected cosine wave signal Vc1R (the second corrected sine wave signal Vs2R and the second corrected cosine wave signal Vc2R) in which the error is canceled. Therefore, the detection accuracy of the steering angle can be ensured. Further, even if the arc tangent is obtained from the sine wave and cosine wave at the time of detecting the steering angle, the first sine wave signal Vs1 and the first cosine wave signal Vc1 (the second sine wave signal s2 and the second cosine) before the arc tangent is obtained. The wave signal Vc2) is corrected. Therefore, for the purpose of reducing the components of the angle detection system, the first sine wave signal Vs1 and the first cosine wave signal Vc1 acquired by the steering angle sensor 1 are output to the vehicle stability control system 19 and the first sine wave signal Vs1. Even if the first cosine wave signal Vc1 is shared by the steering angle sensor 1 and the vehicle stability control system 19, the first sine wave signal Vs1 and the first cosine wave signal Vc1 that do not include an error are the vehicle stability. Since it is provided to the control system 19, the control accuracy of the vehicle stability control system 19 can be ensured.

  (2) When correcting the various signals Vs1, Vc1, Vs2, and Vc2 output from the magnetoresistive elements 5 and 6, the correction value K is determined by referring to the lookup table 16 stored in the EEPROM 11 in the steering angle sensor 1. This is done by subtracting the correction value K from the original signal value read and detected. Accordingly, the correction of the various signals Vs1, Vc1, Vs2, and Vc2 can be performed by a simple process of referring to the lookup table 16. Therefore, when correcting the various signals Vs1, Vc1, Vs2, and Vc2, the correction process is performed. Effects such as shortening the time can be obtained.

  (3) The correction value K in the lookup table 16 is updated when a correction value update condition is satisfied, for example, when the steering wheel rotates once. Therefore, the first sine wave signal Vs1 and the first cosine wave signal Vc1 (the second sine wave signal Vs2 and the second cosine wave signal Vc2) can be corrected using the optimum correction value K each time. This further contributes to improving the detection accuracy of the steering angle.

  (4) The two magnetoresistive elements 5 and 6 are used, and the steering angle of the steering wheel is detected from the combination of two arctangents obtained from the outputs of the magnetoresistive elements 5 and 6. Therefore, for example, the angle of the steering angle can be detected with higher resolution than when only one magnetoresistive element is used.

In addition, this embodiment is not limited to the structure so far, You may change into the following aspects.
The number of magnetoresistive elements provided as the angle detection means is not limited to a plurality (two in the embodiment), and for example, only one may be provided. In this case, for example, only one driven gear that rotates with the main driving gear 2 is provided, and one magnetoresistive element that detects the rotation of the driven gear is provided.

  When a magnetic detection system is used as the angle detection means, this is not limited to the magnetoresistive elements 5 and 6 that detect the magnetic field direction of the magnet, but may be a Hall element that detects the magnetic field strength of the magnet, for example. Further, this type of angle detection means is not necessarily limited to a magnetic detection system, and for example, an optical sensor may be used.

  The correction method for the various signals Vs1, Vc1, Vs2, and Vc2 output from the magnetoresistive elements 5 and 6 is not necessarily limited to the method using Fourier and inverse Fourier transform, and is included in the various signals Vs1, Vc1, Vs2, and Vc2. This is not particularly limited as long as the distortion component can be eliminated.

  The output target from which the steering angle sensor 1 outputs the rectangular waves 23 and 24 is not necessarily limited to the vehicle stability control system 19, but the first sine wave signal Vs 1 and the first cosine wave signal detected by the magnetoresistive element 5. The device is not particularly limited as long as the device operates using Vc1 (the second sine wave signal Vs2 and the second cosine wave signal Vc2 of the magnetoresistive element 6 may be used).

  The process of converting the first sine wave signal Vs1 and the first cosine wave signal Vc1 into the rectangular waves 23 and 24 is not necessarily performed by the CPU 9. For example, the first sine wave signal Vs1 and the first cosine wave signal Vc1 are output from the steering angle sensor 1 to the vehicle stability control system 19, and the vehicle stability control system 19 outputs the first sine wave signal Vs1 and the first cosine wave. Processing for converting the signal Vc1 into the rectangular waves 23 and 24 may be performed.

  The rotation angle detection device is not limited to the steering angle sensor 1 that detects the steering angle of the steering wheel, and the application target is not particularly limited as long as it detects the rotation angle of the rotating object.

  Next, technical ideas that can be grasped from the above-described embodiment and other examples will be described below together with their effects.

  (1) In any one of claims 1 to 4, the angle detection means is provided for each driven gear that rotates with the main driving gear, and detects each rotation of the driven gear having a different number of teeth. The sine wave signal and the cosine wave signal corresponding to the rotation are output in units of the driven gear, and the angle calculation means outputs the sine wave signal and the cosine wave having different waveforms output from the angle detection means, respectively. The signal is used to determine the arc tangent for each driven gear, and the rotation angle of the rotating object is calculated from a plurality of combinations of arc tangents obtained.

The block diagram which shows schematic structure of the steering angle sensor in one Embodiment. The wave form diagram showing the change with respect to the angular displacement of the sine wave signal which a magnetoresistive element outputs. The wave form diagram showing the change with respect to the angular displacement of the cosine wave signal which a magnetoresistive element outputs. The table | surface which shows an example of a Fourier coefficient. The table figure which shows an example of the look-up table used at the time of signal correction. (A) is a waveform diagram of a rectangular wave derived by converting a sine wave signal, and (b) is a waveform diagram of a rectangular wave derived by converting a cosine wave signal. (A) is a waveform diagram showing the change with respect to the angular displacement of the sine wave signal and cosine wave signal output from the conventional angle sensor, and (b) is the change with respect to the arc tangent angular displacement obtained from the sine wave signal and cosine wave signal. Waveform diagram shown, (c) is a waveform diagram of a Lissajous waveform obtained from a sine wave signal and a cosine wave signal. (A) is a waveform diagram showing a change with respect to the angular displacement of the arctangent when the sine wave signal and the cosine wave signal contain distortion components, and (b) shows the distortion component in the sine wave signal and cosine wave signals. The waveform diagram of the Lissajous waveform when (A) is a waveform diagram of a rectangular wave derived by converting a sine wave signal, and (b) is a waveform diagram of a rectangular wave derived by converting a cosine wave signal.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering angle sensor as a rotation angle detection apparatus, 5, 6 ... Magnetoresistive element which comprises angle detection means, 7, 8 ... Magnet which comprises angle detection means, 9 ... Angle calculation means, correction | amendment means (calculation means) And a CPU constituting the updating means, 16 ... a look-up table constituting a correcting means (correction value table), 12 to 15 ... an angular displacement waveform, 19 ... a vehicle stability control system as an external device, 20 ... as an output means Interface, Vs1, Vs2 ... sine wave signal, Vc1, Vc2 ... cosine wave signal, Arctanθa, Arctanθb ... arctangent, K ... correction value.

Claims (4)

When detecting the angle of the rotating object, the detection signal is output as a sine wave signal that outputs a sine wave with respect to the angular displacement of the rotating object and a cosine wave signal that outputs a cosine wave with respect to the angular displacement. An angle detection means;
In a rotation angle detecting device comprising: an arc tangent of the sine wave signal and the cosine wave signal; and an angle calculating means for calculating a rotation angle of the rotating object by the arc tangent.
When the change of the sine wave signal and the cosine wave signal with respect to the angular displacement of the rotating object is viewed, the sine wave signal before obtaining the arc tangent so that the angular displacement waveform approaches an ideal waveform without distortion, and A rotation angle detection device comprising correction means for correcting the cosine wave signal. The correction means includes
A correction value table storing correction values obtained by inverse Fourier transforming distortion components of the angular displacement waveform extracted by Fourier transforming the angular displacement waveform;
When the sine wave signal and the cosine wave signal are acquired, the correction value corresponding to the signal value at that time is read with reference to the correction value table, and the sine wave signal and the cosine wave signal are read using the correction value. The rotation angle detection device according to claim 1, further comprising calculation means for calculating the ideal values of the sine wave signal and the cosine wave signal by removing distortion components.   The sine wave signal and the cosine wave signal that have been corrected are output to another external device, and the external device includes output means for executing processing that requires the sine wave signal and the cosine wave signal. The rotation angle detection device according to claim 1 or 2.   The rotation angle detection device according to claim 2, further comprising an updating unit that updates the correction value written in the correction value table when conditions for rewriting the correction value are met.

Images