JP5096399B2 - Rotation angle detector - Google Patents

Description

  The present invention relates to a rotation angle detection device that detects a rotation angle of a rotating body with an absolute value.

  In recent years, various systems for improving running stability, such as a vehicle stability control system and an electronically controlled suspension system, are being mounted on the vehicle as the functions of the vehicle become higher. These systems acquire the steering angle of steering as one piece of vehicle posture information, and control the vehicle posture to be in a stable state based on the posture information. For this reason, for example, a rotation angle detection device for detecting the steering angle of the steering is provided in the steering column of the vehicle. As this type of rotation angle detecting device, for example, as shown in Patent Document 1, first and second driven gears having different numbers of teeth are meshed with a main gear that rotates integrally with a steering shaft, and these driven gears are engaged. A configuration is known in which the rotation angle of the main driving gear and hence the steering shaft is obtained based on the rotation angle of the gear.

  In the configuration of Document 1, magnets are provided on the first and second driven gears so as to be integrally rotatable, and magnetic sensors (MR sensors) are provided corresponding to these magnets. When the direction of the magnetic flux generated from the magnet changes with the rotation of the first and second driven gears, the magnetic sensor outputs a sine signal and a cosine signal according to the change in the magnetic flux direction. The control device of the rotation angle detection device calculates the arc tangent value based on the sine signal and the cosine signal as the rotation angle of the first and second driven gears, and based on these rotation angles, the rotation angle of the main driving gear is an absolute value. calculate.

More specifically, in the apparatus of this document 1, the absolute rotation angle of the main driving gear is calculated based on the following idea.
First, the rotation angle θ of the main driving gear is expressed by the following expression (A) from the ratio of the number of teeth z of the main driving gear and the number of teeth m of the first driven gear. “Α ′” is an actual rotation angle of the first driven gear with respect to the rotation angle θ of the main driving gear.

θ = mα ′ / z (A)
The rotation angle α ′ of the first driven gear is expressed by the following equation (B). However, “α” is the rotation angle of the first driven gear during one period of the magnetic sensor output, “i” is the number of periods indicating what period the output from the magnetic sensor is, and “Ω”. Is the detection range (one cycle) of the magnetic sensor.

α ′ = α + iΩ (B)
The absolute rotation angle θr of the main driving gear is expressed by the following equation (C) by substituting the equation (B) into “α ′” of the equation (A).

θr = m (α + iΩ) / z (C)
The device of Patent Document 1 obtains the rotation angle of the main driving gear as an absolute value based on the equation (C). That is, if the period number i of the magnetic sensor output is known, the absolute rotation angle θr of the main driving gear can be calculated. Therefore, in Patent Document 1, the period number i is first calculated when calculating the absolute rotation angle θr. To do. The procedure for calculating the number of periods i is as follows.

  The apparatus first calculates the first temporary absolute rotation angle θab of the main driving gear expressed as a function of the difference between the rotation angles α and β of the first and second driven gears in one cycle of the magnetic sensor output by the following formula ( Calculate based on D).

θab = Δab · mn / z (n−m) (D)
However, the value calculated as follows is applied to the value of Δab.
Δab = α−β (α−β ≧ 0)
・ Δab = α−β + Ω (α−β <0)
Further, the second temporary absolute rotation angle θa of the main drive gear with respect to the rotation angle α of the first driven gear with the smaller number of teeth of the first and second driven gears, here, the first driven gear is represented by the following equation (E): Calculate based on

θa = mα / z (E)
Next, using the values of the first and second temporary absolute rotation angles θab and θa calculated by the equations (D) and (E), the number of periods of the magnetic sensor output corresponding to the first driven gear i is calculated based on the following equation (F).

i = (θab−θa) / (mΩ / z) (F)
Then, the absolute rotation angle θr of the main gear is calculated based on the equation (C) using the number of periods i calculated by the equation (F). In such a rotation angle detection device of the absolute angle detection method, the rotation mode of the main driving gear whose origin is the reference position (absolute angle 0 °) set in the rotation direction of the main driving gear is the rotation of the steering shaft that is the rotation detection target. As an aspect, that is, it is detected as rotation information of the steering wheel that is rotated a plurality of times in both forward and reverse directions with the neutral position (steering angle = 0 °) as a reference.

  Here, changes in the first and second rotation angles α and β and the absolute rotation angle θr with respect to the actual rotation angle θ of the main gear will be described with reference to the graph of FIG. In the graph, the horizontal axis represents the actual rotation angle θ (steering operation angle) of the main gear, the left vertical axis represents the absolute rotation angle θr, and the right vertical axis represents the rotation angle α of the first and second driven gears. , Β. In the graph, when the rotation angle θ is 0 °, the steering is in a neutral position (straight forward state), and the right operation direction of the steering is positive and the left operation direction is negative with respect to the neutral position. To do.

  As shown in the graph, theoretically, when the rotation angle θ of the main driving gear rotates by a predetermined angle ± θ1 determined by the number of teeth of the main driving gear and the number of teeth of the first and second driven gears. The phase difference between the first and second driven gears is eliminated. When the rotation angle of the main driving gear reaches these predetermined angles ± θ1, the cycle number i of the magnetic sensor corresponding to the first driven gear is the number of teeth of the main driving gear and the teeth of the first and second driven gears. The maximum cycle number imax that can be taken within the detection range of the absolute rotation angle θr determined by the number is changed to 0 cycle that is the minimum cycle number. That is, if there is no error in either of the first and second driven gears, the number of periods i is within the detection range of the absolute rotation angle θr (the range corresponding to the rotation angle θ = −θ1 to + θ1). Varies between 0 and imax. Then, by using this cycle number i, the absolute rotation angle θr of the main driving gear can be accurately obtained.

JP 2007-127609 A

  However, in the conventional rotation angle detecting device including the one in Patent Document 1 in which the two driven gears are engaged with the main driving gear, an error caused by a backlash between the main driving gear and the two driven gears or the like. Thus, the detection ranges of the first and second magnetic sensors, that is, the values of the rotation angles of the first and second driven gears in one cycle of the magnetic sensor output actually deviate from the theoretical values.

  For example, it is assumed that the first driven gear has an error of + δ and the second driven gear has no error. In this case, as shown in the graph of FIG. 15, before the rotation angle θ of the main driving gear reaches the predetermined angle + θ1, that is, when the rotation angle θ reaches + θ2 (<+ θ1), The rotation angle α overtakes the rotation angle β of the second driven gear. Therefore, in terms of calculation, at this time, the number i of periods of the magnetic sensor output corresponding to the first driven gear changes from the predetermined number imax to zero. The number of periods i is calculated based on the above formula (F). If there is an error in the first driven gear, this results in θab <θa, that is, θab−θa <0. For this reason, the period number i is a negative value and cannot be calculated correctly. Therefore, in this example, the absolute rotation angle θr calculated when the rotation angle θ (steering operation angle) of the main gear is within the range of + θ2 to + θ1 does not become a correct value, and is used for vehicle control. It is not possible.

  Further, it is assumed that there is no error in the first driven gear and there is an error of + δ in the second driven gear. In this case, as shown in the graph of FIG. 16, the value of the rotation angle α of the first driven gear is the rotation of the second driven gear until the rotation angle θ of the main driving gear reaches −θ2 (> −θ1). Cannot keep up with the value of angle β. Therefore, in calculation, the period number i of the magnetic sensor output corresponding to the first driven gear when the rotation angle θ is −θ1 is originally 0 (zero), but is maintained at the predetermined period number imax. Is done. That is, when the number of periods i is calculated based on the formula (F), the value of θab−θa in the formula is theoretically the maximum limit value θabLimit of the first temporary absolute rotation angle θab, that is, the first And when the difference between the rotation angles α and β of the second driven gear is maximized, it does not become larger than the value of the first temporary absolute rotation angle θab calculated based on the above formula (D). However, if there is an error in the second driven gear, the value of θab−θa becomes larger than the maximum limit value θabLimit due to this, and the period number i cannot be calculated correctly. Therefore, in this example, the absolute rotation angle θr calculated when the rotation angle θ of the main driving gear is in the range of −θ1 to −θ2 does not become a correct value, and thus cannot be used for vehicle control.

  As described above, in the apparatus of Patent Document 1, when the actual steering operation angle is out of a certain angle range (here, ± θ2), the correct absolute rotation angle θr is not calculated. The absolute rotation angle θr calculated at this time cannot be used for vehicle control. For this reason, in the conventional apparatus, there is a situation in which measures are taken such as limiting the angle range that can be detected. That is, in theory, only the absolute rotation angle θr calculated in a range (−θ2 to + θ2) smaller than the range (−θ1 to + θ1) of the rotation angle θ of the main driving gear capable of detecting the absolute rotation angle θr is available. Could not be used to control.

  The present invention has been made to solve the above problems, and its purpose is to suppress the influence of detection errors caused by backlash between the main driving gear and the driven gear, and to reduce the rotation angle of the main driving gear. An object of the present invention is to provide a rotation angle detection device capable of accurately detecting the entire range that can be theoretically detected.

  The invention according to claim 1 is the first and second sensors provided corresponding to the first and second driven gears having different numbers of teeth rotating in conjunction with the main driving gear rotating integrally with the rotation detection target. Calculating means for calculating the rotation angles α and β of the first and second driven gears in the detection range Ω of these sensors based on the output of the sensor and calculating the rotation angle of the main driving gear as an absolute value based on the calculation results. And the calculating means calculates the first and second temporary absolute rotation angles θab and θa of the main driving gear based on the following formulas (a) and (b), and the first calculation based on the following formula (c). In the rotation angle detection device that calculates the number of cycles i of the output from the sensor and finally calculates the absolute rotation angle θr of the main driving gear based on the following equation (d), the calculation means calculates the number of cycles i. The following relational expression (e) holds when obtaining If it is determined, the number of periods i is calculated based on the following formula (c). If it is determined that the following relational expression (f) is established, the first and second formulas in the following formula (c) are used. When the following maximum limit value θabLimit is added to the value of the difference between the temporary absolute rotation angles θab and θa, and when it is determined that the following relational expression (g) holds, the first expression in the following expression (c) Further, the gist of the present invention is to calculate the period number i by subtracting the following maximum limit value θabLimit from the difference value between the second temporary absolute rotation angles θab and θa.

θab = Δab · mn / z (nm) (a)
{Δab = α−β (α−β ≧ 0), Δab = α−β + Ω (α−β <0)}
θa = mα / z (b)
i = (θab−θa) / (mΩ / z) (c)
θr = m (α + iΩ) / z (d)
0 ≦ θab−θa ≦ θabLimit (e)
θab−θa <0 (f)
θab−θa> θabLimit (g)
However, m, n, and z are the number of teeth of the first and second driven gears and the main driving gear. ΘabLimit is a value (maximum limit) of the first temporary absolute rotation angle θab calculated based on the above formula (a) when the difference between the rotation angles α and β of the first and second driven gears becomes maximum. Value).

  As described above, if there is an error in the first driven gear, the first driven gear before the actual rotation angle θ of the main driving gear reaches the upper limit value of the angular range that can be theoretically detected. The value of the rotation angle α of the gear overtakes the value of the rotation angle β of the second driven gear. Due to this, the number of periods i changes from its maximum value to the minimum value of 0 period. That is, originally, the absolute rotation angle θr should be calculated using the maximum value of the number of cycles described above, but the absolute rotation angle θr is calculated using the 0 cycle that is the minimum value of the number of cycles. Therefore, the predetermined angle before the rotation angle θ of the main driving gear reaches the upper limit of the theoretically detectable angle range, that is, the value of the rotation angle α of the first driven gear is the rotation angle of the second driven gear. There is a concern that an accurate absolute rotation angle θr cannot be calculated from a predetermined angle overtaking the value of β until the upper limit is reached.

  In this regard, according to the present invention, when it is determined that the difference between the first and second temporary absolute rotation angles θab and θa is smaller than 0, the first and second temporary absolute The number of periods i is calculated using a value obtained by adding the maximum limit value θabLimit to the difference between the rotation angles θab and θa (“i = (θab−θa + θabLimit) z / mΩ”). Accordingly, the difference value between the first and second temporary absolute rotation angles θab and θa, and hence the value of the period number i, does not become a negative value, and the period number i is correctly calculated. That is, the period number i is maintained at the maximum value until the rotation angle of the main driving gear reaches the upper limit value of the angle range that can be theoretically detected. Therefore, even when the rotation angle of the main driving gear reaches the upper limit value from the predetermined angle before reaching the upper limit value of the angle range that can be theoretically detected, the actual rotation angle of the main driving gear can be accurately determined. The absolute rotation angle θr can be calculated.

  Further, if there is an error in the second driven gear, the rotation angle of the first driven gear until the rotation angle of the main drive gear exceeds a lower limit value of the theoretically detectable angular range and reaches a predetermined value. The value of α cannot catch up with the value of the rotation angle β of the second driven gear. Due to this, the period number i is maintained at the maximum value until the rotation angle θ of the main driving gear exceeds the lower limit value and reaches the predetermined value. That is, the absolute rotation angle θr should be calculated using the zero period that is the minimum value of the period number, but the absolute value of the rotation number θr is calculated using the maximum value of the period number. For this reason, from the lower limit of the angle range in which the rotation angle of the main gear can be detected theoretically, the above-mentioned predetermined angle that is larger than this, that is, the value of the rotation angle α of the first heavy gear is the second value. There is a concern that an accurate absolute rotation angle θr cannot be calculated until the value of the rotation angle β of the driven gear catches up.

  In this regard, in the present invention, when it is determined that the difference between the first and second temporary absolute rotation angles θab and θa is larger than the maximum limit value θabLimit, the first and second temporary absolute rotation angles θab and θa are determined. The number of periods i is calculated using a value obtained by subtracting the maximum limit value θabLimit from the difference between the absolute rotation angles θab and θa (“i = (θab−θa−θabLimit) z / mΩ”). As a result, the difference value between the first and second temporary absolute rotation angles θab and θa does not become larger than the maximum limit value θabLimit, and the cycle number i is correctly calculated. That is, when the rotation angle θ of the main driving gear is at the lower limit value of the angle range that can be theoretically detected, the cycle number i is set to 0 cycle. Therefore, the rotation angle θ of the main driving gear corresponds to the actual rotation angle of the main driving gear even between the lower limit of the angle range in which the detection is theoretically possible and the above-described predetermined angle that is larger than this. An accurate absolute rotation angle θr can be calculated.

  As described above, even in the angular range in the vicinity of the upper limit value and the lower limit value of the angular range that can be theoretically detected in the main driving gear, which has conventionally been difficult to accurately calculate the absolute rotation angle θr, the number of cycles described above is used. Through the correction process of i, the absolute rotation angle θr can be accurately calculated. That is, the absolute rotation angle θr of the main drive gear can be accurately calculated in all ranges that can be theoretically detected.

  According to the present invention, it is possible to suppress the influence of detection error caused by backlash between the main driving gear and the driven gear, and to accurately detect the rotation angle of the main driving gear in a theoretically detectable range. it can.

The block diagram which shows schematic structure of a rotation angle detection apparatus. The flowchart which similarly shows the calculation procedure of a rotation angle. (A), (b) is a graph which shows the relationship between the rotation angle of the 1st and 2nd driven gear in the detection range of a 1st and 2nd magnetic sensor, and the actual rotation angle of a main drive gear. (A) is a graph which shows the relationship between the rotation angle of the 1st and 2nd driven gear in the detection range of the 1st and 2nd magnetic sensor, and the actual rotation angle of a main driving gear, (b) is 1st. And a graph showing the relationship between the phase difference of the second driven gear and the actual rotation angle of the main gear, and (c) is a graph showing the relationship between the first temporary absolute rotation angle and the actual rotation angle of the main gear. . The graph which shows the relationship between a 2nd temporary absolute rotation angle and the actual rotation angle of a main drive gear. The graph which shows the relationship between the cycle number of a magnetic sensor output, and the actual rotation angle of a main gear. The graph which shows the relationship between the absolute rudder angle value of the main driving gear finally calculated, and the actual rotation angle of the main driving gear. The graph which shows the relationship between the absolute steering angle value in case there is no error in any of the 1st and 2nd driven gear, and the actual rotation angle of the main gear. The graph which shows the relationship between the absolute steering angle value when there is an error in the first driven gear (the second driven gear has no error) and the actual rotation angle of the main drive gear. The graph which shows the relationship between the absolute steering angle value when there is an error in the second driven gear (the first driven gear has no error) and the actual rotation angle of the main drive gear. The flowchart which shows the calculation procedure of the period number of a magnetic sensor output. When there is an error in the first driven gear (the second driven gear has no error), the relationship between the absolute steering angle value calculated based on the corrected cycle number i and the actual rotation angle of the main gear is Graph showing. When there is an error in the second driven gear (the first driven gear has no error), the relationship between the absolute steering angle value calculated based on the corrected period number i and the actual rotation angle of the main gear is Graph showing. 6 is a graph schematically showing a relationship between an absolute rudder angle value and an actual rotation angle of the main gear when there is no error in any of the first and second driven gears in the conventional rotation angle detection device. Similarly, a graph schematically showing a relationship between an absolute rudder angle value and an actual rotation angle of the main gear when there is an error in the first driven gear (the second driven gear has no error). Similarly, a graph schematically showing a relationship between an absolute steering angle value and an actual rotation angle of the main drive gear when there is an error in the second driven gear (the second driven gear has no error).

Hereinafter, an embodiment in which the present invention is embodied in a rotation angle detection device that detects a steering angle of a steering will be described.
As shown in FIG. 1, the rotation angle detection device 10 is a box-shaped housing that is fixed to a structure such as a steering column (not shown) disposed around a steering shaft 11 that connects a steering wheel and a steering wheel. 12 is provided. The housing 12 accommodates a main driving gear 13 that can be rotated integrally with the steering shaft 11 and is fitted and fixed coaxially. The first and second driven gears 14 that mesh with the main driving gear 13 are housed in the housing 12. 15 is rotatably supported.

  The first and second driven gears 14 and 15 are provided so as to have different numbers of teeth. Therefore, when the main driving gear 13 rotates in conjunction with the rotation of the steering shaft 11, the rotation angles α ′ and β ′ of the first and second driven gears 14 and 15 with respect to the rotation angle θ of the main driving gear 13 are different. Value. For example, when the number of teeth of the main driving gear 13 is z, the number of teeth of the first driven gear 14 is m, and the number of teeth of the second driven gear 15 is n (m <n <z), the main driving gear 13 rotates once. In this case, the first driven gear 14 rotates z / m, and the second driven gear 15 rotates z / n.

  As shown by a broken line in FIG. 1, first and second driven gears 14 and 15 are provided with first and second magnets (permanent magnets) 16 and 17 so as to be integrally rotatable. Further, in the vicinity of the first and second magnets 16 and 17 (precisely, directly below), first and second magnetic sensors 18 and 19 for detecting a magnetic field generated from these magnets are disposed. As the first and second magnetic sensors 18 and 19, so-called MR sensors in which, for example, four magnetoresistive elements (MRE) are connected in a bridge shape can be employed. The resistance value of the magnetoresistive element changes according to the applied magnetic field (more precisely, the direction of the magnetic flux). Then, the first and second magnetic sensors 18 and 19 detect the midpoint potential of the bridge-shaped circuit described above according to the change of the magnetic field applied to them (more precisely, the change of the direction of the magnetic flux). Output as a signal.

  The first magnetic sensor 18 detects a change in the direction of the magnetic flux emitted from the first magnet 16 as the first driven gear 14 rotates, and continuously according to the rotation angle α ′ of the first driven gear 14. The two analog signals that change with each other, that is, the first sine signal Vs 1 and the first cosine signal Vc 1 are output to the microcomputer 21 disposed in the housing 12. The first sine signal Vs1 and the first cosine signal Vc1 are obtained when the first driven gear 14 rotates by the detection range Ω of the first magnetic sensor 18, that is, the main gear 13 is (m / z) Ω. One cycle when rotating. The phase of the first cosine signal Vc1 is shifted by a quarter period with respect to the first sine signal Vs1.

  The second magnetic sensor 19 detects a change in the direction of the magnetic flux emitted from the second magnet 17 as the second driven gear 15 rotates, and continuously according to the rotation angle β ′ of the second driven gear 15. The two analog signals that change with time, that is, the second sine signal Vs2 and the second cosine signal Vc2 are output to the microcomputer 21. The second sine signal Vs2 and the second cosine signal Vc2 are obtained when the second driven gear 15 rotates by the detection range Ω of the second magnetic sensor 19, that is, the main gear 13 is (n / z) Ω. One cycle when rotating. The phase of the second cosine signal Vc2 is shifted by a quarter period with respect to the second sine signal Vs2.

  The microcomputer 21 includes a CPU (central processing unit) 22, a ROM (read only memory) 23, a RAM (write / read memory) 24, and the like. The ROM 23 stores various control programs for comprehensively controlling the entire rotation angle detection device 10. The RAM 24 is a data storage area, that is, a work area for the CPU 22 to execute various processes by developing the control program in the ROM 23. An example of the control program stored in the ROM 23 is a rotation angle calculation program. The rotation angle calculation program is a program for obtaining the rotation angle θ of the steering shaft 11 as an absolute value based on detection signals from the first and second magnetic sensors 18 and 19.

The outline of the calculation process of the absolute rotation angle θr of the steering shaft 11 by the microcomputer 21 is as follows.
Here, first, the rotation angle θ of the main driving gear 13 and the rotation angle α ′ of the first driven gear 14 with respect to the rotation angle θ are expressed by the following equation (1) according to the number of teeth z and m. The relationship shown is established.

θ = mα ′ / z (1)
Further, the rotation angle α ′ of the first driven gear 14 with respect to the rotation angle θ of the main driving gear 13 can also be expressed by the following equation (2).

α ′ = α + iΩ (2)
Here, α is the rotation angle of the first driven gear 14 in the detection range (one cycle) Ω of the first magnetic sensor 18. i is an integer value indicating how many times the detection range of the first magnetic sensor 18 is repeated, that is, what period of the first sine signal Vs1 and the first cosine signal Vc1. In the following description, the integer value is referred to as the number of cycles of the first driven gear 14.

Then, when Expression (2) is substituted into Expression (1), the following Expression (3) is obtained.
θ = m (α + iΩ) / z (3)
When the formula (3) is developed and arranged, the following formula (4) is obtained.

θ = θa + (m / z) Ωi (4)
However, θa is the rotation angle (absolute value) of the main driving gear 13 with respect to the rotation angle α of the first driven gear 14 in the detection range (one cycle) Ω of the first magnetic sensor 18. The rotation angle (θa) is expressed by the following equation.

θa = mα / z
Therefore, if the rotation angle (θa) and the number of periods i of the first driven gear 14 are known, the rotation angle θ can be calculated based on the above equation (4). The microcomputer 21 obtains the rotation angle (θa) and the period number i of the first driven gear 14 based on the rotation angle calculation program stored in the ROM 23, and applies these to the above equation (4). An absolute rotation angle θr of the main driving gear 13 is calculated.

<1. Calculation of absolute rudder angle value>
Next, as a method for detecting the rotation angle θ of the steering shaft 11, that is, the main driving gear 13 by the rotation angle detection device 10 configured as described above, the procedure for calculating the absolute rotation angle θr by the microcomputer 21 is shown in FIG. This will be described in detail according to the flowchart of FIG. The calculation process is executed according to a rotation angle calculation program stored in the ROM 23.

<1-1. Rotation angle calculation process of driven gear>
As shown in FIG. 2, when the microcomputer 21 calculates the absolute rotation angle θr of the main driving gear 13, first, detection signals from the first and second magnetic sensors 18 and 19 are sent through an A / D converter (not shown). Obtain (steps S101 and S102). The microcomputer 21 then detects the first and second driven gears 14 in the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19 based on the acquired detection signal after A / D conversion. , 15 are obtained (steps S103 and S104).

  That is, the rotation angle α is calculated by the microcomputer 21 as an arc tangent (α = (Ω / 360 °) tan−1 (Vs1 / Vc1)) based on the first sine signal Vs1 and the first cosine signal Vc1. Stored in the RAM 24. The rotation angle β is calculated by the microcomputer 21 as an arc tangent (β = (Ω / 360 °) tan−1 (Vs2 / Vc2)) based on the second sine signal Vs2 and the second cosine signal Vc2. Stored in the RAM 24. The rotation angles α and β are stored in the ROM 23 in advance in a table that defines the relationship between the detection signals from the first and second magnetic sensors 18 and 19 and the arctangent value corresponding to the signals. You may make it obtain | require by referring the table stored in ROM23.

  Incidentally, the rotation of the first and second driven gears 14 and 15 in the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19 with respect to the change in the actual rotation angle θ of the main driving gear 13. The angles α and β change as shown in the graphs of FIGS. In the graph, the horizontal axis represents the rotation angle θ of the main driving gear 13, and the vertical axis represents the first and second driven gears 14 in the detection range (one cycle) Ω of the first and second magnetic sensors 18, 19. 15 rotation angles α and β are shown.

  As shown in the graph, the first and second driven gears 14 and 15 in the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19 as the rotational angle θ of the main gear increases. The rotation angles α and β repeat rising and falling at a predetermined cycle according to the difference in the number of teeth m and n of the first and second driven gears 14 and 15. That is, the rotation angles α and β are changed every time the first and second driven gears 14 and 15 are rotated by the detection range Ω of the first and second magnetic sensors 18 and 19, in other words, the main driving gear 13 is rotated. Each time it rotates by mΩ / z or nΩ / z, the rising and falling are repeated.

  For example, here, the number of teeth z of the main driven gear 13 is 60, the number of teeth m of the first driven gear 14 is 25, the number of teeth n of the second driven gear 15 is 26, the first and second magnetic sensors 18, The 19 detection range Ω is 180 °. In this case, the rotation angle α of the first driven gear 14 is changed every time the main driving gear 13 is rotated by 75 °, and the rotation angle β of the second driven gear 15 is changed every time the main driving gear 13 is rotated by 78 °. Repeats rising and falling.

<1-2. Temporary rotation angle calculation process for main gear>
Next, the microcomputer 21 rotates the rotation angles of the first and second driven gears 14 and 15 within the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19 calculated in steps S103 and S104. α and β are read from the RAM 24, and the first temporary absolute rotation angle θab of the main driving gear 13 is obtained based on the rotation angles α and β (step S105). The microcomputer 21 stores the calculated first temporary absolute rotation angle θab in the RAM 24. The first temporary absolute rotation angle θab is equal to the rotation angle α of the first driven gear 14 in the detection range (one cycle) Ω of the first magnetic sensor 18 and the detection range (one cycle) of the second magnetic sensor 19. ) Is the rotation angle of the main driving gear 13 obtained based on the difference Δab (= α−β) from the rotation angle β of the second driven gear 15 at Ω. The first temporary absolute rotation angle θab is the same as the rotation angle β of the second driven gear 15 in the expressions (1) and (2) and the detection range (one cycle) Ω of the second magnetic sensor 19. Based on the following equations (5) and (6) calculated in the same manner, the following equation (7) is obtained.

θ = nβ ′ / z (5)
β ′ = β + jΩ (6)
Here, β is the rotation angle of the second driven gear 15 within the detection range (one cycle) Ω of the second magnetic sensor 19. j is an integer value indicating how many times the detection range of the second magnetic sensor 19 is repeated, that is, how many cycles of the second sine signal Vs2 and the second cosine signal Vc2.

θab = Δab · mn / z (nm) (7)
Where m is the number of teeth of the first driven gear 14, n is the number of teeth of the second driven gear 15, z is the number of teeth of the main driven gear 13, and Ω is detected by the first and second magnetic sensors 18 and 19. It is a range (period).

  The difference Δab represents the phase difference between the rotation angles α and β of the first and second driven gears 14 and 15 in the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19. For the phase difference, a value converted into a positive value per detection range Ω is used. That is, the value obtained as follows is applied to the equation (7) as the difference Δab.

・ When α−β ≧ 0 Difference Δab = α−β
・ When α−β <0 Difference Δab = (α−β) + Ω
Incidentally, the formula (7) is obtained as follows. That is, first, when α-β is expressed using the equations (1), (2), (5), and (6), the following equation is obtained.

α−β = (α′−iΩ) − (β′−jΩ)
= (Z / m) θ− (z / n) θ− (i−j) Ω
When θ = θab in the relational expression is solved for θab, the following expression is obtained.

θab = mn / z (n−m) · {(α−β) + (i−j) Ω}
However, when α−β ≧ 0, i = j
When α−β <0 i = j + 1
Here, when Δab = (α−β) + (i−j) Ω, the equation (7) is obtained.

  Since the number of teeth of the first and second driven gears 14 and 15 is different, as shown in the graph of FIG. 4A, the rotation angle θ of the main driving gear 13 is set on the horizontal axis and the first and second driven gears 14 and 15 have different numbers of teeth. When the rotation angles α and β of the two driven gears 14 and 15 are plotted on the vertical axis, the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19 with respect to the rotation angle θ of the main driving gear 13 is plotted. The rotation angles α and β of the first and second driven gears 14 and 15 have different values. Therefore, as shown in the graph of FIG. 4B, the rotation angle θ of the main driving gear 13 is set on the horizontal axis, and the difference Δab between the rotation angles α and β of the first and second driven gears 14 and 15 is set. Is plotted on the vertical axis, the first and second driven gears in the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19 with respect to the change in the rotation angle θ of the main gear 13. The value of the difference Δab between the rotation angles α and β of 14 and 15 changes linearly. That is, the difference between the rotation angle θ of the steering shaft 11 and the rotation angles α and β of the first and second driven gears 14 and 15 in the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19. Since Δab is in a proportional relationship, the difference Δab between the rotation angles α and β is a specific value with respect to the rotation angle θ of the main driving gear 13. Therefore, the rotation angle θ of the main driving gear 13 can be calculated as an absolute value based on the difference Δab between the rotation angles α and β.

  Therefore, as shown in the graph of FIG. 4C, the first temporary absolute rotation angle of the main driving gear 13 calculated based on the above equation (7) with the actual rotation angle θ of the main driving gear 13 as the horizontal axis. When θab is plotted on the vertical axis, the value of the first temporary absolute rotation angle θab also changes linearly with respect to the change in the rotation angle θ of the main driving gear 13.

  As described above, the rotation angle α of the first and second driven gears 14 and 15 in the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19 with respect to the rotation angle θ of the main driving gear 13. , Β repeats rising and falling at different predetermined periods according to the difference in the number of teeth m, n of the first and second driven gears 14, 15, respectively. These first and second magnetic sensors The phase difference between the rotation angles α and β of the first and second driven gears 14 and 15 in the detection range (one cycle) Ω of 18 and 19 disappears when the rotation angle θ of the main driving gear 13 reaches a predetermined value. . For this reason, the difference Δab calculated based on the rotation angles α, β of the first and second driven gears 14, 15 in the detection range (one cycle) Ω of the first and second magnetic sensors 18, 19 and the first As for the temporary absolute rotation angle θab of 1, the positions of the rotation angles α and β of the first and second driven gears 14 and 15 in the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19, respectively. The rise and fall are repeated for each rotation angle θ at which the phase difference disappears. That is, the calculation range (period) Ωx (= 0 ° to x °) of the first temporary absolute rotation angle θab is also determined by the ratio of the number of teeth of the first and second driven gears 14 and 15 and the main driving gear 13, and is calculated. The range (period) Ωx is expressed by the following equation (8).

Ωx = mnΩ / z (nm) (8)
In the same manner as described above, the number of teeth z of the main driving gear 13 is 60, the number of teeth m of the first driven gear 14 is 25, the number of teeth n of the second driven gear 15 is 26, and the first and second magnetic sensors 18. , 19 is set to 180 °, the calculation range (period) Ωx of the first temporary absolute rotation angle θab is 1950 °.

<1-3. α → θa conversion>
Next, the microcomputer 21 calculates the second temporary absolute rotation angle θa of the main driving gear 13 with respect to the rotation angle α of the first driven gear 14 within the detection range (one cycle) Ω of the first magnetic sensor 18 by the following formula ( 9) based on the calculation (step S106). The microcomputer 21 stores the calculated second temporary absolute rotation angle θa in the RAM 24.

θa = mα / z (9)
Incidentally, the second temporary absolute rotation angle θa changes as shown in the lower graph of FIG. 5 with respect to the change of the actual rotation angle θ of the main driving gear 13. In the graph, the horizontal axis represents the rotation angle θ of the main driving gear 13 and the vertical axis represents the second temporary absolute rotation angle θa. As shown in the graph, as the rotation angle θ of the main driving gear 13 increases, the second temporary absolute rotation angle θa rises at a predetermined cycle according to the number m of teeth of the first driven gear 14. Repeat with falling. That is, the calculation range (period) Ωy (= 0 ° to y °) of the second temporary absolute rotation angle θa is determined by the gear ratio of the first driven gear 14 and the main driving gear 13. The calculation range (period) Ωy of the absolute rotation angle θa is expressed by the following equation (10).

Ωy = mΩ / z (10)
As described above, the number of teeth z of the main driven gear 13 is 60, the number of teeth m of the first driven gear 14 is 25, the number of teeth n of the second driven gear 15 is 26, and the detection range of the first magnetic sensor 18 is the same. When Ω is 180 °, the calculation range (period) Ωy of the second temporary absolute rotation angle θa is 75 °.

<1-4. Period calculation processing>
Next, the microcomputer 21 reads the first and second temporary absolute rotation angles θab and θa calculated in steps S105 and S106 from the RAM 24, and based on the first and second temporary absolute rotation angles θab and θa. Then, the period number i of the first driven gear 14 is calculated (step S107). The microcomputer 21 stores the calculated cycle number i in the RAM 24. As described above, the period number i is an integer value indicating how many times the detection range of the first magnetic sensor 18 is repeated, and is obtained by the following equation (11). This equation (11) is obtained by solving for the number of periods i with θ = θab in the equation (4).

i = (θab−θa) / (mΩ / z) (11)
However, mΩ / z indicates a change amount (rotation amount) of the main driving gear 13 per one output cycle of the first magnetic sensor 18.

  As shown in the central graph of FIG. 6, when the actual rotational angle θ of the main driving gear 13 is plotted on the horizontal axis and the period number i calculated by the above equation (11) is plotted on the vertical axis, Every time the driven gear 14 rotates by the same angle as the detection range Ω of the first magnetic sensor 18, that is, every time the main gear 13 rotates by mΩ / z, the period number i increases. Since the calculation range (period) Ωx of the first temporary absolute rotation angle θab of the main driving gear 13 is 0 ° to x °, when the main driving gear 13 rotates exceeding the x °, the period number i is Returning to 0 (zero), counting of the number of periods i is started again.

<1-5. Absolute rotation angle calculation processing>
Finally, the microcomputer 21 reads out the second temporary absolute rotation angle θa calculated in the previous step S106 and the cycle number i calculated in step S107 from the RAM 24, and the second temporary absolute rotation angle θa and the cycle number i. Based on the above, the official absolute rotation angle θr of the main driving gear 13 is calculated (step S108).

  Specifically, by applying the previously calculated second provisional absolute rotation angle θa and period number i to the above equation (4), that is, “θ = θa + (m / z) Ωi”, the absolute rotation The angle θr is calculated.

  The relationship between the actual rotation angle θ of the main driving gear 13 and the absolute rotation angle θr of the main driving gear 13 calculated based on the equation (4) is shown in the central graph of FIG. In the graph, the horizontal axis represents the actual rotation angle θ of the main driving gear 13 and the vertical axis represents the absolute rotation angle θr. As shown in the graph, the absolute rotation angle θr of the main driving gear 13 changes linearly with a change in the actual rotation angle θ of the main driving gear 13. The slope of the straight line indicating the change in the value of the absolute rotation angle θr is determined by 1, which is a value of the ratio between the actual rotation angle θ of the main driving gear 13 and the absolute rotation angle θr calculated based on the above equation (4). . Thus, since the actual rotation angle θ of the main driving gear 13 and the absolute rotation angle θr are in a proportional relationship, the actual rotation angle θ of the main driving gear 13 and the absolute rotation angle θr have a one-to-one correspondence. . That is, the absolute rotation angle θr of the main driving gear 13, in other words, the absolute steering angle value of the steering can be immediately detected.

  The calculation range Ωr of the absolute rotation angle θr of the main gear 13 is the same as the calculation range Ωx of the first temporary absolute rotation angle θab calculated in the previous step S105, and is calculated based on the equation (8). The Therefore, as described above, the number of teeth m of the first driven gear 14 is 25, the number of teeth n of the second driven gear 15 is 26, the number of teeth z of the main driving gear 13 is 60, and the first magnetic sensor 18 is used. When the detection range Ω of 180 is 180 °, the calculation range Ωr of the absolute rotation angle θr is 1950 ° according to the equation (8). That is, in this case, the rotation angle θ of the main driving gear 13 can be immediately detected as an absolute value in the range of 0 ° to 1950 °. This corresponds to slightly more than 5 rotations (± 2.7 rotations) of the steering shaft. The microcomputer 21 uses the absolute rotation angle θr of the main driving gear 13 calculated as described above as the steering steering angle (absolute steering angle value) to improve the running stability of the vehicle stability control system, the electronically controlled suspension system, and the like. Output to various systems (more precisely, their control devices) for improvement.

<2. Correction of period number i>
Here, in the rotation angle detection device 10 of this example, the first and second driven gears 14 and 15 are engaged with the main driving gear 13 as described above. For this reason, the detection ranges (one cycle) of the first and second magnetic sensors 18 and 19 are actually caused by an error due to backlash between the main driving gear 13 and the first and second driven gears 14 and 15. ) The values of the rotation angles α and β of the first and second driven gears 14 and 15 at Ω deviate from the theoretical values. Therefore, the absolute rotation angle θr calculated based on the rotation angles α and β of the first and second driven gears 14 and 15 in the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19. There is also a concern that the above will be affected by the error. Accordingly, in this regard, first, a case where there is no error in both the first and second driven gears 14, 15 will be described, and then a case where there is an error in the first and second driven gears 14, 15 will be described. To do. In the following description, the number of teeth z of the main driving gear 13 is 60, the number of teeth m of the first driven gear 14 is 25, the number of teeth n of the second driven gear 15 is 26, and the first and second magnetic gears. The detection range Ω of the sensors 18 and 19 is 180 °.

<2-1. When there is no error>
First, the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19 when there is no error due to backlash between the main driving gear 13 and the first and second driven gears 14 and 15. The rotation angles α and β of the first and second driven gears 14 and 15 will be described with reference to the graph of FIG. In the graph, the horizontal axis represents the actual rotation angle θ (steering operation angle) of the main driving gear 13, the left vertical axis represents the absolute rotation angle θr of the main driving gear 13 calculated by the above equation (4), and the right vertical axis. The axes indicate the rotation angles α and β of the first and second driven gears 14 and 15 in the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19, respectively. In the graph, the midpoint of the calculation range Ωr of the absolute rotation angle θr is the origin (absolute rotation angle 0 °). Here, since the calculation range Ωr of the absolute rotation angle θr is 1950 °, in the graph, the upper limit value of the calculation range Ωr is + 975 ° and the lower limit value is −975 °. That is, in this example, the absolute rotation angle θr is calculated in the range of −975 ° to + 975 °. The origin at which the absolute rotation angle θr is 0 ° corresponds to the steering neutral position at which the actual rotation angle θ of the main driving gear 13 is 0 °. In addition, the rotation angle θ decreases when the steering wheel is rotated to the left, and increases when the steering wheel is rotated to the right.

  As shown enlarged in the lower right of FIG. 8, theoretically, when the actual rotation angle θ (steering operation angle) of the main driving gear 13 reaches + 975 °, in other words, enlarged in the lower left of FIG. 8. As shown, when the actual rotation angle θ of the main driving gear 13 reaches −975 °, the first and second in the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19. The phase difference between the rotation angles α and β of the driven gears 14 and 15 is eliminated. That is, theoretically, the cycle number i changes from 25 cycles to 0 cycle at the time when the rotation angle θ reaches + 975 °, in other words, when the rotation angle θ reaches −975 °. By using this cycle number i, the absolute rotation angle θr of the main driving gear 13 is accurately calculated.

<2-2. When there is an error in the first driven gear>
Next, the case where there is an error in the first driven gear 14 will be described. For example, it is assumed that there is an error of + 5 ° between the main driving gear 13 and the first driven gear 14 and there is no error between the main driving gear 13 and the second driven gear 15. At this time, the first and second absolute rotation angles θr of the main driving gear 13 and the detection ranges (one cycle) Ω of the first and second magnetic sensors 18 and 19 with respect to the rotation angle θ that is an actual steering operation angle. The rotation angles α and β of the second driven gears 14 and 15 change as shown in the graph of FIG. The graph of FIG. 9 corresponds to the previous graph of FIG.

  As shown enlarged below in FIG. 9, the rotation angle of the first driven gear 14 within the detection range (one cycle) Ω of the first magnetic sensor 18 at the time when the rotation angle θ reaches + 948 °. The value of α is larger than the value of the rotation angle β of the second driven gear 15 in the detection range (one cycle) Ω of the second magnetic sensor 19. That is, in the calculation, the period number i changes from 25 rotations to 0 rotations at the time when the rotation angle θ reaches + 948 °. This is because the period number i becomes a negative value. That is, as described above, the period number i of the first driven gear 14 is calculated based on the above formula (11), that is, “i = (θab−θa) / (mΩ / z)”. If there is an error in the driven gear 14, “θab <θa”, that is, “θab−θa <0” is caused. That is, in this case, the period number i of the first driven gear 14 is a negative value, and a correct value of the period number i cannot be obtained. Therefore, the absolute rotation angle θr of the main driving gear 13 calculated using this cycle number i is not a correct value. In this example, the absolute rotation angle θr calculated when the rotation angle θ, which is the actual steering operation angle, is in the range of 948 ° to 975 ° does not become a correct value, so this should be used for vehicle control. I can't.

<2-3. When there is an error in the second driven gear>
Next, a case where there is an error in the second driven gear 15 will be described. For example, it is assumed that there is no error between the main driving gear 13 and the first driven gear 14 and there is a + 5 ° error between the main driving gear 13 and the second driven gear 15. At this time, the first and second absolute rotation angles θr of the main driving gear 13 and the detection ranges (one cycle) Ω of the first and second magnetic sensors 18 and 19 with respect to the rotation angle θ that is an actual steering operation angle. The rotation angles α and β of the second driven gears 14 and 15 change as shown in the graph of FIG. The graph of FIG. 10 also corresponds to the previous graph of FIG.

  As shown enlarged below in FIG. 10, the rotation of the first driven gear 14 within the detection range (one cycle) Ω of the first magnetic sensor 18 at the time when the rotation angle θ reaches −948 °. The value of the angle α is smaller than the value of the rotation angle β of the second driven gear 15 in the detection range (one cycle) Ω of the second magnetic sensor 19. That is, in the calculation, the period number i changes from 0 period to 26 periods at the time when the rotation angle θ reaches −948 °.

  This is due to the following reason. First, as described above, the period number i of the first magnetic sensor 18 accompanying the rotation of the first driven gear 14 is the above equation (11), that is, “i = (θab−θa) / (mΩ / z)”. The value of “θab−θa” is theoretically never larger than the maximum limit value θabLimit of the first temporary absolute rotation angle θab. This maximum limit value θabLimit is the first and second magnetic values in the equation (7), which is an arithmetic expression of the first temporary absolute rotation angle θab, that is, “θab = Δab · mn / z (n−m)”. This is a calculated value when the difference Δab between the rotation angles α and β of the first and second driven gears 14 and 15 in the detection range (one cycle) Ω of the sensors 18 and 19 becomes maximum. Since the maximum value of the difference Δab is the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19, the maximum limit value θabLimit is expressed by the following equation (12).

θabLimit = Ωmn / {z (nm)} (12)
Incidentally, since “z = 60”, “m = 25”, “n = 26”, and “Ω = 180 °” are set here, by substituting these values into the equation (12), the maximum limit is set. The value θabLimit is calculated as 1950 °.

  However, if there is an error in the second driven gear 15, the value of “θab−θa” becomes a value larger than the maximum limit value θabLimit, and the correct value of the number of periods i cannot be obtained. . Therefore, the absolute rotation angle θr of the main driving gear 13 calculated using this cycle number i is not a correct value. In this example, the absolute rotation angle θr calculated when the rotation angle θ, which is the actual steering operation angle, is within the range of −975 ° to −948 ° is not a correct value, and is used for vehicle control. I can't do it.

  As described above, when there is an error due to backlash or the like between the main driving gear 13 and the first and second driven gears 14 and 15, the rotation angle θ of the main driving gear 13 is within a certain angular range (the above-described specific example). In the case of deviating from ± 948 °), the correct absolute rotation angle θr is not calculated. That is, in theory, the absolute rotation angle θr can be calculated within a range of ± 975 °, but an actual accurate value is calculated within a range of ± 948 °. Therefore, when the calculated value of the absolute rotation angle θr is used for vehicle control, the range of the absolute rotation angle θr that can be detected is smaller than the range that can be detected theoretically, that is, ± 948 °. There is a concern that it must be restricted within the range.

  Therefore, in this example, in order to eliminate such a concern, that is, in order to make it possible to use the absolute rotation angle θr output from the rotation angle detection device 10 for various control of the vehicle in the entire range that is theoretically possible. The configuration like this is adopted. That is, as described above, since the value of the cycle number i deviates from the theoretical value due to the error of the first and second driven gears 14 and 15, the absolute value of the error can be obtained by correcting the cycle number i. The influence on the rotation angle θr is reduced. Specifically, even if there is an error in the first driven gear 14, the period number i is corrected so that the period number i can be calculated as 25 periods until the rotation angle θ of the main driving gear 13 reaches + 975 °. To do. Even if there is an error in the second driven gear 15, the cycle number i is corrected so that the cycle number i can be calculated as 0 cycle from the time when the rotation angle θ of the main drive gear 13 reaches −975 °.

<2-4. i correction processing>
Next, the calculation process of the cycle number i will be described in detail according to the flowchart shown in FIG. This flowchart is executed according to the cycle number calculation program stored in the ROM 23 when the process proceeds to step S107 in the flowchart of FIG. 2 in the process of calculating the absolute rotation angle θr of the main gear 13.

  When calculating the period number i, the microcomputer 21 first reads the first and second temporary absolute rotation angles θab, θa stored in the RAM 24, and the difference between them is 0 ° or more and θabLimit. It is determined whether or not the value is within the range, that is, whether or not the relationship indicated by “0 ° ≦ θab−θa ≦ θabLimit” is satisfied (step S201).

  When the microcomputer 21 determines that the relationship represented by “0 ° ≦ θab−θa ≦ θabLimit” is established (YES in step S201), the microcomputer 21 proceeds to step S202. In step S202, the microcomputer 21 calculates the period number i based on the equation (11), that is, “i = (θab−θa) / (mΩ / z)”, and the value of the calculated period number i. Is returned to the main routine shown in the flowchart of FIG. 2 (return).

  When the microcomputer 21 determines in step S201 that the relationship represented by “0 ° ≦ θab−θa ≦ θabLimit” is not established (NO in step S201), the microcomputer 21 proceeds to step S203. In step S203, the microcomputer 21 determines whether or not the relationship of “θab−θa <0 °” is established.

  When the microcomputer 21 determines that the relationship represented by “θab−θa <0 °” is established (YES in step S203), the microcomputer 21 proceeds to step S204. In step S204, the microcomputer 21 calculates the number of periods i based on the following equation (13), and returns the value of the calculated number of periods i as a return value to the main routine shown in the flowchart of FIG. ).

i = (θab−θa + θabLimit) / (mΩ / z) ”(13)
When the microcomputer 21 determines in step S203 that the relationship represented by “θab−θa <0 °” is not satisfied (NO in step S203), the value of “θab−θa” is greater than θabLimit. Assuming that the value is large (step S205), the process proceeds to step S206. This is because, when the value of “θab−θa” is not 0 ° or more and not less than θabLimit, and is not less than 0 °, the value of “θab−θa” is necessarily greater than θabLimit. It is because it turns out that it is a big value.

  In step S206, the microcomputer 21 calculates the number of periods i based on the following equation (14), and returns the value of the calculated number of periods i as a return value to the main routine shown in the flowchart of FIG. 2 (return). .

i = (θab−θa−θabLimit) / (mΩ / z) ”(14)
By calculating the absolute rotation angle θr using the period number i calculated in this manner, the absolute value is accurate in the entire range that can be detected theoretically (the entire range of the calculation range Ωr of the absolute rotation angle θr). The rotation angle θr can be calculated. Here, since “z = 60”, “m = 25”, “n = 26”, and “Ω = 180 °”, the theoretically detectable range in this case is 0 ° to 1950 ° ( An accurate absolute rotation angle θr is calculated over the entire range of ± 975 °.

  More specifically, conventionally, when there is an error in the first driven gear 14, there is an angle range in which it is difficult to calculate an accurate absolute rotation angle θr with respect to the actual rotation angle θ of the main driving gear 13. As described above, is caused by “θab−θa <0” due to the error.

  In this point, in this example, when the microcomputer 21 determines that “θab−θa <0” when calculating the number of periods i, it is assumed that the first driven gear 14 has an error. The maximum limit value θabLimit is added to the value of “θab−θa”, and the number of periods i is calculated using the addition result (see step S204 in FIG. 11). Accordingly, the calculated cycle number i does not become a negative value, and the cycle number i can be calculated as 25 cycles until the actual rotation angle θ of the main driving gear 13 reaches + 975 °. Therefore, unlike the case where the number of periods i is calculated uniformly based on the above equation (11), accurate absolute rotation is possible even when the actual rotation angle θ of the main driving gear 13 is within the range of + 948 ° to + 975 °. The angle θr can be calculated.

  As shown in the graph of FIG. 12, the upper limit value of the range of the absolute rotation angle θr that can be actually detected is expanded from the conventional + 948 ° to the original + 975 °, that is, 27 ° to the plus side. For this reason, the value of the rotation angle α of the first driven gear 14 in the detection range (one cycle) Ω of the first magnetic sensor 18 is the boundary when the actual rotation angle θ of the main driving gear 13 reaches + 948 °. After the rotation angle β of the second driven gear 15 exceeds the detection range (one cycle) Ω of the second magnetic sensor 19, the absolute rotation is continued until the actual rotation angle θ reaches + 975 °. The angle θr can be calculated accurately. Therefore, conventionally, only the absolute rotation angle θr calculated when the actual rotation angle θ of the main gear 13 is in the range of −975 ° to 948 ° can be used, but the rotation angle θ is −975. It becomes possible to use all of the absolute rotation angles θr calculated when the angle is within the range of ° to + 975 °.

  Conventionally, even when there is an error in the second driven gear 15, there is an angle range in which it is difficult to calculate an accurate absolute rotation angle θr with respect to the actual rotation angle θ of the main driving gear 13. As described above, it is caused by “θab−θa> θabLimit” due to an error.

  In this regard, in this example, when the microcomputer 21 determines that “θab−θa> θabLimit” when calculating the number of periods i, it is assumed that the second driven gear 15 has an error. The maximum limit value θabLimit is subtracted from the value of “θab−θa”, and the period number i is calculated using the subtracted value (see step S206 in FIG. 11). Since the value of “θab−θa−θabLimit” does not exceed the value of the maximum limit value θabLimit, when the actual rotation angle θ of the main driving gear 13 becomes −975 °, the cycle number i is calculated as 0 cycle. It becomes possible. For this reason, unlike the case where the number of periods i is calculated uniformly based on the equation (11), even if the actual rotation angle θ of the main driving gear 13 is within the range of −975 ° to −948 °, the accurate The absolute rotation angle θr can be calculated.

  As shown in the graph of FIG. 13, the lower limit value of the range of the absolute rotation angle θr that can be actually detected is enlarged from the conventional −948 ° to the original −975 °, that is, by 27 ° on the minus side. For this reason, the value of the rotation angle α of the first driven gear 14 in the detection range (one cycle) Ω of the first magnetic sensor 18 is the second value until the actual rotation angle θ of the main driving gear 13 reaches −948 °. Even when the rotation angle β of the second driven gear 15 does not catch up with the detection range (one cycle) Ω of the magnetic sensor 19, the actual rotation angle θ is in the range of −975 ° to −948 °. The absolute rotation angle θr calculated at a certain time is correct. Therefore, conventionally, only the absolute rotation angle θr calculated when the actual rotation angle θ of the main driving gear 13 is in the range of −948 ° to 975 ° can be used, but the rotation angle θ is −975. It becomes possible to use all of the absolute rotation angles θr calculated when the angle is within the range of ° to + 975 °.

  Therefore, it is not necessary to limit the range of the absolute rotation angle θr that can be detected to, for example, the range of ± 948 ° described above, but the entire range that can be detected theoretically, that is, the actual rotation angle θ is ± 975 °. All of the absolute rotation angles θr calculated when in the range can be used for various controls of the vehicle. That is, as compared with the case where the range of the absolute rotation angle θr that can be detected is limited to a range of ± 948 °, only a total of 54 ° can be detected, 27 ° to the plus side and 27 ° to the minus side. The range expands.

<Effect of Embodiment>
Therefore, according to the present embodiment, the following effects can be obtained.
When it is determined that the difference value between the first and second temporary absolute rotation angles θab and θa is smaller than 0, a value obtained by adding the maximum limit value θabLimit to the difference value is used. The period number i is calculated. Thereby, the value of the difference, and hence the value of the period number i, does not become a negative value, and the period number i is correctly calculated. That is, when the rotation angle θ of the main driving gear 13 is the detection range (one cycle) Ω of the first magnetic sensor 18, the rotation angle α of the first driven gear 14 is the detection range of the second magnetic sensor 19 ( The number of periods i is also in the period from + 948 °, which exceeds the value of the rotation angle β of the second driven gear 15 in 1 cycle) Ω, to + 975 °, which is the upper limit value of the theoretically detectable angle range. Is maintained at its maximum value of 25 periods. Therefore, the actual rotation angle θ of the main driving gear 13 can be theoretically detected from + 948 °, where the value of the rotation angle α of the first driven gear 14 exceeds the value of the rotation angle β of the second driven gear 15. An accurate absolute rotation angle θr can be calculated even before reaching + 975 °, which is the upper limit value of the angular range.

  Further, when it is determined that the difference value between the first and second temporary absolute rotation angles θab and θa is larger than the maximum limit value θabLimit, a value obtained by subtracting the maximum limit value θabLimit from the difference value The number of periods i is calculated using. Thereby, the value of the difference does not become larger than the value of the maximum limit value θabLimit, and the period number i is correctly calculated. That is, the first driven gear 14 in the detection range (one cycle) Ω of the first magnetic sensor 18 from −975 °, which is the lower limit value of the angular range in which the rotational angle θ of the main driving gear 13 can theoretically be detected. The number of periods i is the minimum value even when the value of the rotation angle α catches up with the rotation angle β of the second driven gear 15 in the detection range (one period) Ω of the second magnetic sensor 19 to -948 °. It is set as 0 period which is. Accordingly, the value of the rotation angle α of the first driven gear 14 is set to the second driven gear 15 from −975 °, which is the lower limit value of the angle range in which the actual rotation angle θ of the main driving gear 13 can theoretically be detected. An accurate absolute rotation angle θr can be calculated even in the range up to −948 °, which catches up with the rotation angle β.

  As described above, the upper limit value of + 975 ° and the lower limit value of −975 °, which are theoretically detectable in the absolute rotation angle θr, which has conventionally been difficult to calculate the accurate absolute rotation angle θr. Even in the vicinity of the angular range, the absolute rotation angle θr can be accurately calculated through the correction processing of the period number i described above. That is, the absolute rotation angle θr of the main driving gear 13 can be accurately calculated in all ranges that can be theoretically detected.

  And, as in this example, by applying the rotation angle detection device 10 as a steering angle sensor with the steering shaft 11 as a rotation detection target, the rotation angle of the steering shaft 11, that is, the steering operation angle, can be set in a wider range. Can be detected.

<Other embodiments>
In addition, you may implement this Embodiment as follows.
-The processing order of step S105 and step S106 may be reversed or may be processed in parallel.

  The number of teeth z of the main driving gear 13 and the number of teeth m and n of the first and second driven gears 14 and 15 can be changed as appropriate. However, it is necessary to maintain the following relationship between the number of teeth. That is, the number of teeth z, m, n is set so that the relational expression “z> m, n” and “m> n” or “m <n” is satisfied. In this case, the driven gear with a small number of teeth corresponds to the first driven gear in the present invention.

In addition, in this example, the number of teeth m and n is set so that the difference in the number of teeth between the first and second driven gears 14 and 15 is 1, but the difference in the number of teeth is a natural number of 2 or more. Is also possible.
In this example, as the first and second magnetic sensors 18 and 19, those having a detection range Ω of 180 ° are employed, but sensors having other detection ranges may be employed. For example, one having a detection range of 360 ° is conceivable.

  In this example, the rotation angles α and β of the first and second driven gears 14 and 15 in the detection range (one cycle) Ω of the first and second magnetic sensors 18 and 19 are set as the first and second Although the calculation is performed based on the detection signals from the magnetic sensors 18 and 19, an optical sensor may be employed instead of such a magnetic sensor.

  In this example, the absolute steering angle sensor that detects the steering operation angle is embodied. However, it can be applied as a rotation detection device that detects the rotation mode of the entire rotation shaft corresponding to the steering shaft 11.

  In this example, the steering shaft 11 is coaxially fitted to the main driving gear 13 so as to be integrally rotatable. However, the steering shaft 11 may be interlocked by meshing with the teeth of the main driving gear 13. Good. Even in this case, the rotation angle of the main driving gear 13 can be calculated as the rotation angle of the steering shaft 11. The same applies to the case where a rotation axis other than the steering shaft 11 is employed as the rotation detection target.

  DESCRIPTION OF SYMBOLS 10 ... Rotation angle detection apparatus, 11 ... Steering shaft (rotation detection object), 13 ... Main drive gear, 14 ... 1st driven gear, 15 ... 2nd driven gear, 18 ... 1st magnetic sensor, 19 ... 2nd Magnetic sensor 21... Microcomputer (calculation means).

Claims (1)

Detection ranges of these sensors based on outputs from the first and second sensors provided corresponding to the first and second driven gears having different numbers of teeth rotating in conjunction with the main driving gear that rotates integrally with the rotation detection target. Calculating rotation angles α and β of the first and second driven gears in Ω, and calculating means for calculating the rotation angle of the main driving gear as an absolute value based on the calculation results. First and second temporary absolute rotation angles θab and θa of the main driving gear are calculated based on (a) and (b), and the number of cycles i of the output from the first sensor is calculated based on the following formula (c). In the rotation angle detection device that finally calculates the absolute rotation angle θr of the main driving gear based on the following formula (d):
When determining that the following relational expression (e) is satisfied when obtaining the period number i, the arithmetic means calculates the period number i based on the following expression (c), and the following relational expression (f) Is determined to hold, the following maximum limit value θabLimit is added to the difference between the first and second provisional absolute rotation angles θab, θa in the following formula (c), and the following relational expression: When it is determined that (g) holds, the following maximum limit value θabLimit is subtracted from the difference between the first and second provisional absolute rotation angles θab, θa in the following formula (c), and the period A rotation angle detection device for calculating the number i.
θab = Δab · mn / z (nm) (a)
{Δab = α−β (α−β ≧ 0), Δab = α−β + Ω (α−β <0)}
θa = mα / z (b)
i = (θab−θa) / (mΩ / z) (c)
θr = m (α + iΩ) / z (d)
0 ≦ θab−θa ≦ θabLimit (e)
θab−θa <0 (f)
θab−θa> θabLimit (g)
However, m, n, and z are the number of teeth of the first and second driven gears and the main driving gear. ΘabLimit is a value (maximum limit) of the first temporary absolute rotation angle θab calculated based on the above formula (a) when the difference between the rotation angles α and β of the first and second driven gears becomes maximum. Value).

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