Rotation angle detector and method for detecting rotation angle

Abstract

To provide a rotation angle detector and a method for detecting a rotation angle which can detect the rotation angle of a rotating member with high accuracy while reducing cost.SOLUTION: A rotation angle detector 2 for detecting the rotation angle of an upper shaft 111 from a reference position comprises: a first gear 21 and a second gear 22 that rotate accompanying the rotation of the upper shaft 111 at different speeds; a first angle sensor 3 for detecting the rotation angle of the first gear 21; a second angle sensor 4 for detecting the rotation angle of the second gear 22; and an MCU 5 for calculating the rotation angle of the upper shaft 111 from a reference position on the basis of detection results of the first angle sensor 3 and the second angle sensor 4. The MCU 5 calculates an integer value of the rotation speed of the upper shaft 111 from the reference position on the basis of detection results of the first angle sensor 3 and the second angle sensor 4, and calculates the rotation angle of the upper shaft 111 from the reference position on the basis of the integer value and the detection result of the second angle sensor 4.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a rotation angle detection device and a rotation angle detection method. [Background technology]

[0002] Conventionally, a rotation angle detection device has been used to detect the steering angle of a steering wheel in a vehicle, for example. Information on the steering angle detected by the rotation angle detection device is used to control an electric power steering device or a steer-by-wire steering device, as well as a vehicle behavior control device that performs skid suppression control of the vehicle.

[0003] The rotation angle detection device described in Patent Document 1 includes a rotor having an engagement portion that engages with a steering shaft, a first detection body and a second detection body that rotate at different speeds as the rotor rotates, a first detection means that detects the rotation of the first detection body, and a second detection means that detects the rotation of the second detection body. The first detection means includes a magnet attached to the first detection body and an AMR element (anisotropic magnetoresistive element) arranged opposite the magnet. The second detection means includes a magnet attached to the second detection body and an AMR element arranged opposite the magnet.

[0004] The rotation angle detection device described in Patent Document 2, like the rotation angle detection device described in Patent Document 1, includes a first detection body and a second detection body that rotate at different speeds as the rotor rotates, a first detection means for detecting the rotation of the first detection body, and a second detection means for detecting the rotation of the second detection body. The first detection means has a magnet and an AMR element attached to the first detection body, but the second detection means uses an inexpensive Hall element instead of an AMR element as a magnetic field detection element arranged opposite the magnet attached to the second detection body. A phase difference signal R is calculated by subtracting the angle (θ2) of the detection signal of the second detection body from the angle (θ1) of the detection signal of the first detection body, and the approximate angle of the rotor is detected from the phase difference signal R. The precise rotation angle is then detected using this approximate angle and the detection signal of the first detection body. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-256138 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-96518 Summary of the Invention [Problem to be solved by the invention]

[0006] The rotation angle detection device described in Patent Document 2 uses a Hall element instead of an AMR element, thereby achieving lower costs than the rotation angle detection device described in Patent Document 1. However, in the rotation angle detection method described in Patent Document 2, there are multiple times when the phase difference (θ1-θ2) between the first detection body and the second detection body has the same value while the steering angle changes from the negative maximum value to the positive maximum value, so it is not possible to accurately determine the absolute angle of the steering angle over the entire range from the negative maximum value to the positive maximum value.

[0007] An object of the present invention is to provide a rotation angle detection device and a rotation angle detection method that are capable of detecting the rotation angle of a rotating member with high accuracy while achieving low cost. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the present invention provides a rotation angle detection device that detects the rotation angle of a rotating member from a reference position, comprising: a first gear and a second gear that rotate at different speeds as the rotating member rotates; a first angle sensor that detects the rotation angle of the first gear; a second angle sensor that detects the rotation angle of the second gear; and a calculation unit that calculates the rotation angle of the rotating member from the reference position based on the detection results of the first angle sensor and the second angle sensor, wherein the calculation unit calculates an integer value of the number of rotations of the rotating member from the reference position based on the detection results of the first angle sensor and the detection results of the second angle sensor, and calculates the rotation angle of the rotating member from the reference position based on the integer value and either the detection result of the first angle sensor or the detection result of the second angle sensor.

[0009] In addition, in order to achieve the above-mentioned object, the present invention provides a method for detecting a rotation angle of a rotating member from a reference position, which calculates an integer value of the number of rotations of the rotating member from the reference position based on detection results of rotation angles of a first gear and a second gear that rotate at different speeds as the rotating member rotates, and calculates the rotation angle of the rotating member from the reference position based on the integer value and either the detection result of the rotation angle of the first gear or the detection result of the rotation angle of the second gear. [Effects of the Invention]

[0010] According to the rotation angle detection device and the rotation angle detection method of the present invention, it is possible to detect the rotation angle of a rotating member with high accuracy while reducing costs. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of a vehicle equipped with an electric power steering device including a rotation angle detection device according to a first embodiment of the present invention. [Figure 2] 1(a) and 1(b) are diagrams showing the configuration of a rotation angle detection device according to the present embodiment. [Figure 3] 6(a) to 6(d) are explanatory diagrams showing the configuration and operation of a first angle sensor, with the first gear and second gear not shown. [Figure 4] 10 is an explanatory diagram showing an example of a circuit configuration for an MCU to detect the electrostatic capacitance between a first fixed electrode and a rotating electrode. FIG. [Figure 5] 10(a) and 10(b) are graphs showing the change in capacitance between the rotating electrode and the first and second fixed electrodes when the rotating electrode rotates 360°. [Figure 6] 10 is a graph showing the detected angle of the first angle sensor, in which the detection result of the first angle sensor is expressed as an angle equal to or greater than 0° and less than 360°, with the dashed line indicating the detected angle of the second angle sensor, and the solid line indicating the detected angle of the second angle sensor. [Figure 7] 10 is a graph showing a phase difference obtained by subtracting the angle detected by the second angle sensor 4 from the angle detected by the first angle sensor. [Figure 8] 10 is a graph showing a normalized phase difference obtained by normalizing the phase difference between the angle detected by the second angle sensor and the angle detected by the first angle sensor. [Figure 9] 10 is a graph in which a fixed-multiplication phase difference obtained by multiplying a normalized phase difference by a predetermined coefficient corresponding to a first transmission ratio and a second transmission ratio is shown by a dashed line, and an integer value of the number of rotations of the steering shaft obtained from the fixed-multiplication phase difference is shown by a solid line. [Figure 10] 10 is a graph showing an absolute rotation angle calculated from integer values ​​of the number of rotations of the upper shaft and the angle detected by the second angle sensor. [Figure 11] 10 is a flowchart showing an example of a procedure of a calculation process performed by an MCU to obtain an absolute rotation angle. [Figure 12]1A is a schematic diagram showing an overlapping state between the rotating electrode and the first and second fixed electrodes when the rotation angle of the rotating electrode is less than 90°, and FIG. 1B is a schematic diagram showing an overlapping state between the rotating electrode and the first and second fixed electrodes when the rotation angle of the rotating electrode is 90° or more. [Figure 13] 10A and 10B are plan views showing modified examples of the first fixed electrode and the second fixed electrode. [Figure 14] 10(a) and 10(b) are diagrams showing the configuration of a rotation angle detection device according to a second embodiment. [Figure 15] 1A is a diagram showing a rotary electrode attached to the surface of the second gear facing the substrate, and FIG. 1B is a diagram showing first and second fixed electrodes provided on the substrate. [Figure 16] 10(a) and 10(b) are diagrams showing the configuration of a rotation angle detection device according to a third embodiment. [Figure 17] 10(a) and 10(b) are diagrams showing the configuration of a rotation angle detection device according to a fourth embodiment. [Figure 18] 1A is a diagram showing the configuration of an induction plate attached to the surface of the first gear facing the substrate, and an induction plate attached to the surface of the second gear facing the substrate, and FIG. 1B is a plan view showing an electromagnetic coil and an electromagnetic coil provided on the substrate. DETAILED DESCRIPTION OF THE INVENTION

[0012] [First embodiment] FIG. 1 is a schematic diagram of a vehicle equipped with an electric power steering device 1 equipped with a rotation angle detection device 2 according to a first embodiment of the present invention.

[0013] As shown in FIG. 1, the electric power steering device 1 includes a steering wheel 10, a steering shaft 11 connected to the steering wheel 10, a rotation angle detection device 2 that detects the steering angle, which is the rotation angle of the steering shaft 11, a torque sensor 12 that detects the steering torque applied to the steering wheel 10, a rack shaft 13, left and right tie rods 14 that are swingably connected to both ends of the rack shaft 13, an electric motor 15 for power assist, a reduction mechanism 16 that reduces the rotation of an output rotating shaft 151 of the electric motor 15 and transmits the reduced rotation to the steering shaft 11, and a steering control device 17 that controls the electric motor 15.

[0014] The steering shaft 11 has a torsion bar 110 that twists due to steering torque, an upper shaft 111 that is closer to the steering wheel 10 than the torsion bar 110, and a lower shaft 112 that is closer to the rack shaft 13 than the torsion bar 110. The steering wheel 10 is attached to the upper end of the upper shaft 111 on the side opposite the torsion bar 110. The lower shaft 112 has pinion teeth 113 that mesh with rack teeth 131 provided on the rack shaft 13 provided on the lower end on the side opposite the torsion bar 110. The torque sensor 12 detects the steering torque based on the torsion angle of the torsion bar 110. When the steering shaft 11 rotates, the rack shaft 13 moves back and forth in the vehicle width direction, thereby turning the left and right steerable front wheels 18, 19.

[0015] The reduction gear mechanism 16 has a worm pinion 161 fixed to the output rotary shaft 151 of the electric motor 15 and a worm wheel 162 fixed to the lower shaft 112, with the worm pinion 161 meshing with the worm wheel 162. The output torque of the electric motor 15 is amplified by the reduction gear mechanism 16 and transmitted to the lower shaft 112 as an assist torque that assists the driver in steering the steering wheel 10. The electric motor 15 is provided with an absolute encoder 152 for detecting the rotation angle of the output rotary shaft 151.

[0016] The steering control device 17 controls the electric motor 15 based on the steering angle information obtained from the rotation angle detection device 2, the steering torque information obtained from the torque sensor 12, and the rotation angle information of the output rotation shaft 151 obtained from the encoder 152 of the electric motor 15, so that an assist torque corresponding to the steering angle and steering torque is applied to the steering shaft 11.

[0017] The rotation angle detection device 2 sets the rotation position of the steering shaft 11 when the steering wheel 10 is in the neutral position as a reference position, and detects the rotation angle of the steering shaft 11 from the reference position. More specifically, it detects the rotation angle of an upper shaft 111 directly connected to the steering wheel 10. The upper shaft 111 is a rotating member whose rotation angle is detected by the rotation angle detection device 2, and rotates 360° or more to one side and the other side from the reference position.

[0018] 2(a) and 2(b) are diagrams showing the configuration of a rotation angle detection device 2 according to this embodiment. Fig. 2(a) shows the rotation angle detection device 2 as seen along the rotation axis O of the upper shaft 111. Fig. 2(b) shows the rotation angle detection device 2 as seen from a direction perpendicular to the rotation axis O of the upper shaft 111.

[0019] The rotation angle detection device 2 mainly comprises a substrate 20, a first gear 21 and a second gear 22 that rotate at different speeds in accordance with the rotation of the upper shaft 111, a first angle sensor 3 that detects the rotation angle of the first gear 21 relative to the substrate 20, a second angle sensor 4 that detects the rotation angle of the second gear 22 relative to the substrate 20, an MCU (Micro Controller Unit) 5 as a calculation unit that calculates the rotation angle of the upper shaft 111 based on the detection results of the first angle sensor 3 and the second angle sensor 4, and a case 23 that houses these components.

[0020] The substrate 20 is fixed to the case 23 and is disposed so as not to rotate relative to the vehicle body. The first gear 21 rotates integrally with the upper shaft 111. The second gear 22 is meshed with the first gear 21 and rotates at a faster speed than the first gear 21. The MCU 5 is mounted on the substrate 20 and transmits the detection result of the rotation angle to the steering control device 17. Note that in FIG. 2(a), wiring patterns such as signal lines and power lines formed on the substrate 20 are not shown.

[0021] The first gear 21, the second gear 22, and the case 23 are made of insulating resin and are nonmagnetic and nonconductive. A through hole 210 is formed in the center of the first gear 21, and the upper shaft 111 is inserted through the through hole 210. The first gear 21 is fixed to the upper shaft 111 by, for example, adhesive. The second gear 22 integrally includes a flat-plate-shaped gear portion 221 and a shaft-shaped support shaft 222, and the support shaft 222 is rotatably supported by the case 23. The second gear 22 has a smaller diameter than the first gear 21 and rotates following the rotation of the first gear 21. The number of teeth of the second gear 22 is smaller than the number of teeth of the first gear 21, and the number of teeth of the first gear 21 is a non-integer multiple of the number of teeth of the second gear 22. In this embodiment, the first gear 21 has 50 teeth, and the second gear 22 has 22 teeth.

[0022] The second angle sensor 4 has a permanent magnet 41 fixed to the surface of the second gear 22 facing the substrate 20 at the center thereof, and a magnetic field detection element 42 mounted on the substrate 20. The permanent magnet 41 and the magnetic field detection element 42 face each other across a small air gap. The permanent magnet 41 is a two-pole magnet having one north pole 411 and one south pole 412, and the north pole 411 and the south pole 412 are aligned in the radial direction of the second gear 22. The magnetic field detection element 42 is preferably one with higher sensitivity than a Hall element, and for example, a giant magnetoresistive effect (GMR) sensor, an anisotropic magnetoresistive (AMR) sensor, or a tunneling magnetoresistive (TMR) sensor can be used.

[0023] A signal indicating the detection result of magnetic field detection element 42 is sent to MCU 5. MCU 5 can detect the angle of magnetic field detection element 42 with respect to substrate 20, i.e., the rotation angle of second gear 22, based on the signal from magnetic field detection element 42. That is, in this embodiment, second angle sensor 4 is a magnetic angle sensor that detects the rotation angle of second gear 22 by using magnetic field detection element 42 to detect the magnetic field of permanent magnet 41 that rotates together with second gear 22. Second angle sensor 4 has a higher resolution for detecting the rotation angle of second gear 22 than the resolution of first angle sensor 3 for detecting the rotation angle of first gear 21, is more accurate than first angle sensor 3, and has a smaller angle detection error than first angle sensor 3.

[0024] 3(a) to 3(d) are explanatory diagrams showing the configuration and operation of the first angle sensor 3, omitting the illustration of the first gear 21 and the second gear 22. The first angle sensor 3 has a rotating electrode 31 that rotates integrally with the upper shaft 111 and the first gear 21, and a first fixed electrode 321 and a second fixed electrode 322 that are arranged opposite the rotating electrode 31. The rotating electrode 31 is made of a non-magnetic conductor, such as aluminum or an aluminum alloy. One surface of the substrate 20 is arranged opposite the rotating electrode 31. A through-hole 200 is formed in the substrate 20, through which the upper shaft 111 is inserted.

[0025] The rotating electrode 31 is generally flat and has a through-hole 310 formed in the center. The upper shaft 111 is inserted through the through-hole 310. The rotating electrode 31 is fixed to the upper shaft 111 by, for example, welding. The rotating electrode 31 may also be fixed to the first gear 21 by, for example, adhesive. The rotating electrode 31 may also be integrally insert-molded with the first gear 21, or the rotating electrode 31 may be made of a conductive resin and two-color-molded integrally with the non-conductive resin that makes up the first gear 21.

[0026] The rotating electrode 31 integrally includes an annular portion 311 that surrounds the upper shaft 111 and two protruding portions 312 that protrude radially outward from the annular portion 311. The two protruding portions 312 are provided at positions that are point-symmetrical with respect to the rotation axis O of the upper shaft 111. Each of the protruding portions 312 is fan-shaped with a central angle of 90° about the rotation axis O of the upper shaft 111, and the portion between the two protruding portions 312 forms a fan-shaped cutout portion 313.

[0027] The first fixed electrode 321 and the second fixed electrode 322 are formed as a wiring pattern on the surface of the substrate 20 facing the rotating electrode 31. The first fixed electrode 321 and the second fixed electrode 322 are formed in an arc shape extending in the circumferential direction around the rotation axis O of the upper shaft 111, and their widths in the radial direction perpendicular to the rotation axis O of the upper shaft 111 vary depending on the circumferential position. Furthermore, the first fixed electrode 321 and the second fixed electrode 322 are formed so that the arc angle around the rotation axis O of the upper shaft 111 is in the range of 90°.

[0028] The first fixed electrode 321 is composed of an inner portion 321a and an outer portion 321b that sandwich the second fixed electrode 322 in the radial direction, and the inner portion 321a and the outer portion 321b are electrically connected at one end of the first fixed electrode 321. The inner portion 321a and the outer portion 321b have gradually narrower radial widths from one end to the other end of the first fixed electrode 321. The second fixed electrode 322 has gradually wider radial widths from one end to the other end of the first fixed electrode 321.

[0029] When the upper shaft 111 rotates together with the rotating electrode 31, the facing area of ​​the first fixed electrode 321 and the second fixed electrode 322 facing the protruding portion 312 of the rotating electrode 31 changes depending on the rotational position of the upper shaft 111. In Figures 3(a) to 3(c), the first fixed electrode 321 and the second fixed electrode 322 at the portions facing the protruding portion 312 of the rotating electrode 31 are indicated by dashed lines. The protruding portion 312 of the rotating electrode 31 faces the first fixed electrode 321 and the second fixed electrode 322 across a small air gap, and forms a capacitance between them.

[0030] That is, in this embodiment, the first angle sensor 3 is a capacitance-type angle sensor that detects the rotation angle of the first gear 21 based on the capacitance between the rotating electrode 31 and the first fixed electrode 321 and second fixed electrode 322. The protruding portion 312 functions as a capacitance generating portion of the rotating electrode 31.

[0031] 3(a) to 3(d) show states in which the rotating electrode 31 rotates together with the upper shaft 111 in the direction of arrow A (clockwise) by 45°. In the state shown in FIG. 3(a), half of the circumferential lengths of the first fixed electrode 321 and the second fixed electrode 322 do not face the protruding portion 312 of the rotating electrode 31, but are located in the portion corresponding to the notch 313 of the rotating electrode 31. As shown in FIG. 3(b), when the rotating electrode 31 is rotated 45° from the state shown in FIG. 3(a), the entire first fixed electrode 321 and the second fixed electrode 322 face the protruding portion 312 of the rotating electrode 31. When the rotating electrode 31 is rotated another 45°, as shown in FIG. 3(c), the portions of the rotating electrode 31 that did not face the protruding portion 312 of the rotating electrode 31 in the state shown in FIG. 3(a) face the protruding portion 312 of the rotating electrode 31. FIG. 3(d) shows a state in which the rotating electrode 31 is rotated another 45° from the state shown in FIG. 3(c). In this state, the entire first fixed electrode 321 and the entire second fixed electrode 322 do not face the protruding portion 312 of the rotating electrode 31 , but are located in the portion corresponding to the notched portion 313 of the rotating electrode 31 .

[0032] As described above, in the first angle sensor 3, the opposing area between the rotating electrode 31 and the first fixed electrode 321 and the second fixed electrode 322 changes depending on the rotational position of the upper shaft 111. The MCU 5 can detect a change in the capacitance between the rotating electrode 31 and the first fixed electrode 321 and a change in the capacitance between the rotating electrode 31 and the second fixed electrode 322 due to this change in opposing area. In addition, in this embodiment, because the rotating electrode 31 has two protruding portions 312, the capacitance between the rotating electrode 31 and each of the first fixed electrode 321 and the second fixed electrode 322 of the first angle sensor 3 changes by two periods during one rotation of the upper shaft 111. In other words, the electrical angle of the first gear 21 detected by the first angle sensor 3 changes by two periods during one rotation of the upper shaft 111. The electrical angle of the second gear 22 detected by the second angle sensor 4 is equal to the mechanical angle of the second gear 22.

[0033] 4 is an explanatory diagram showing an example of a circuit configuration for the MCU 5 to detect the capacitance between the first fixed electrode 321 and the rotating electrode 31. The example circuit configuration shown in FIG. 4 is modeled after the circuit configuration of a touch sensor that detects contact with a human finger. A circuit similar to that shown in FIG. 4 is also configured for the second fixed electrode 322.

[0034] The MCU 5 outputs a pulse signal from an output terminal 51, and a resistor 61 and a capacitor 62 are connected in series between the output terminal 51 and ground. A first fixed electrode 321 is connected to a node 63 between the resistor 61 and the capacitor 62. The potential at the node 63 is input to a gate element 64, and an output signal from the gate element 64 is input to an input terminal 52 of the MCU 5. The rotating electrode 31 is electrically grounded via the upper shaft 111. In this circuit configuration, if the facing area of ​​the protruding portion 312 of the rotating electrode 31 and the first fixed electrode 321 increases, the electrostatic capacitance between the rotating electrode 31 and the first fixed electrode 321 increases, and the response time from the rising edge of the pulse signal output by the MCU 5 to the rising edge of the output signal from the gate element 64 increases.

[0035] The MCU 5 detects the capacitance between the rotating electrode 31 and the first fixed electrode 321 based on this difference in response time. In other words, the magnitude of the capacitance between the rotating electrode 31 and the first fixed electrode 321 changes as the upper shaft 111 rotates, and the MCU 5 calculates the rotation angle of the upper shaft 111 from the magnitude of this capacitance as the detection result of the first angle sensor 3. Note that, although the resistor 61, the capacitor 62, and the gate element 64 are mounted on the substrate 20 as an example, some or all of these circuit components may be built into the MCU 5. Furthermore, the capacitor 62 may be omitted, and additional circuit components such as a resistor and a capacitor may be provided in addition to the circuit components illustrated in FIG. 4.

[0036] 5(a) and 5(b) are graphs showing changes in capacitance between the rotating electrode 31 and the first and second fixed electrodes 321 and 322 when the rotating electrode 31 rotates 360° in the direction of arrow A shown in FIGS. 3(a) to 3(d) from the reference position where the rotation angle of the rotating electrode 31 shown in FIG. 3(a) is 0°. As shown in FIGS. 5(a) and 5(b), in this embodiment, the capacitance between the rotating electrode 31 and the first and second fixed electrodes 321 and 322 changes by two periods while the upper shaft 111 rotates once. Therefore, in the following description, the speed transmission ratio from the upper shaft 111 to the rotating electrode 31 is assumed to be 0.50, and the speed transmission ratio from the upper shaft 111 to the second gear 22 is assumed to be 0.44 (=22 / 50). A calculation method by which the MCU 5 calculates the absolute value of the rotation angle of the upper shaft 111 will be described.

[0037] Here, the absolute value of the rotation angle refers to the rotation angle of the upper shaft 111 from the negative maximum value to the positive maximum value, where the rotation angle of the upper shaft 111 when the steering wheel 10 is in the neutral position is 0°, the rotation angle of the upper shaft 111 when the steering wheel 10 is rotated to the left until it hits the end is the negative maximum value (for example, -630°), and the rotation angle of the upper shaft 111 when the steering wheel 10 is rotated to the right until it hits the end is the positive maximum value (for example, 630°). Hereinafter, the absolute value of the rotation angle of the upper shaft 111 will be referred to as the absolute rotation angle. In addition, in this embodiment, a case will be described in which the negative maximum value of the absolute rotation angle is -630° and the positive maximum value is 630°, and the steering wheel 10 and the upper shaft 111 rotate a maximum of 3.5 times.

[0038] When the steering wheel 10 is rotated from a position where it abuts left to a position where it abuts right, the detection result of the first angle sensor 3 changes periodically, with one cycle being the range of half a rotation of the first gear 21 and the rotary electrode 31, and the detection result of the second angle sensor 4 changes periodically, with one cycle being the range of one rotation of the second gear 22 and the permanent magnet 41. For this reason, the absolute angle of the steering wheel 10 cannot be detected based on the detection result of the first angle sensor 3 alone or the detection result of the second angle sensor 4 alone.

[0039] In this embodiment, as described above, the speed transmission ratio from the upper shaft 111 to the rotating electrode 31 is 0.50, and the speed transmission ratio from the upper shaft 111 to the second gear 22 is 0.44. Therefore, when the detection result of the first angle sensor 3 is expressed as an angle greater than or equal to 0° and less than 360°, as the steering wheel 10 rotates left or right from the neutral position, the angle of the first gear 21 and the rotating electrode 31 detected by the first angle sensor 3 and the angle of the second gear 22 and the permanent magnet 41 detected by the second angle sensor 4 gradually deviate and the difference becomes larger. In this embodiment, the MUC 5 calculates the absolute rotation angle using the difference between the angle detected by the first angle sensor 3 and the angle detected by the second angle sensor 4. Next, a method for calculating this absolute rotation angle will be described with reference to FIGS. 6 to 10.

[0040] 6 is a graph showing the angle detected by the first angle sensor 3 as a result of expressing the capacitance between the rotating electrode 31 and the first and second fixed electrodes 321 and 322, which is the detection result of the first angle sensor 3, as an angle between 0° and less than 360° through numerical conversion by the MCU 5, and the angle detected by the second angle sensor 4 (between 0° and less than 360°) as a solid line. The horizontal axis of the graph shown in FIG. 6 is the absolute rotation angle of the upper shaft 111, and the vertical axis is the detected angles of the first angle sensor 3 and the second angle sensor 4.

[0041] As shown in this graph, when the detected angles of the first angle sensor 3 and the second angle sensor 4 are set to 0° when the absolute rotation angle is 0°, the difference between the detected angle of the first angle sensor 3 and the detected angle of the second angle sensor 4 gradually increases as the absolute value of the absolute rotation angle increases.

[0042] 7 is a graph showing the phase difference resulting from subtracting the angle detected by the second angle sensor 4 from the angle detected by the first angle sensor 3. When the steering wheel 10 is rotated leftward or rightward from the neutral position, the speed transmission ratio from the upper shaft 111 to the second gear 22 is smaller than the speed transmission ratio from the upper shaft 111 to the rotating electrode 31. Therefore, the angle detected by the second angle sensor 4 crosses zero before the angle detected by the first angle sensor 3, and the angle detected by the first angle sensor 3 crosses zero thereafter. During the period from when the angle detected by the second angle sensor 4 crosses zero until the angle detected by the first angle sensor 3 crosses zero, the absolute value of the difference between the angles detected by the first angle sensor 3 and the second angle sensor 4 temporarily exceeds 180°. Here, crossing zero means that the detected angle suddenly changes significantly from near 0° to near 360°.

[0043] FIG. 8 is a graph of the phase difference after a calculation process is performed in which the phase difference is subtracted by 360° when the angle detected by the second angle sensor 4 crosses zero before the angle detected by the first angle sensor 3 and the phase difference is 180° or greater, and is added by 360° when the phase difference is −180° or less. Hereinafter, this calculation process will be referred to as a normalization process, and the phase difference after normalization will be referred to as a normalized phase difference δ. By performing the normalization process, the line on the graph showing the normalized phase difference δ becomes linear, as shown in FIG. 8. In the graph of FIG. 8, the line representing −180° on the vertical axis is indicated by a dashed line, and the line representing +180° is indicated by a dashed line.

[0044] In this embodiment, MUC5 can accurately calculate the absolute rotation angle within a range in which the normalized phase difference δ shown in the graph of FIG. 8 falls between −180° and +180°, that is, within a range in which the detected angle of first angle sensor 3 and the detected angle of second angle sensor 4 do not deviate by more than one period when steering wheel 10 is rotated from the end position to the left to the end position to the right.

[0045] If the error in the detected angles of the first angle sensor 3 and the second angle sensor 4 is large, the detected angles of the first angle sensor 3 and the second angle sensor 4 will deviate by more than one period within the range in which the rotation angle detection device 2 should detect the absolute rotation angle (±630° in this example), making it impossible to accurately calculate the absolute rotation angle. In other words, for the MUC 5 to accurately calculate the absolute rotation angle, even when taking into account the detection errors of the first angle sensor 3 and the second angle sensor 4, the line representing the normalized phase difference δ shown in the graph of FIG. 8 must not intersect with the line indicating a phase difference of −180° (dashed line) or +180° (dashed line). The necessary condition for this, i.e., the allowable range of detection errors of the first angle sensor 3 and the second angle sensor 4, can be expressed mathematically as shown in Equation (1) below. The process of deriving Equation (1) will be described later.

number

[0046] Here, to accurately determine the absolute rotation angle, it is desirable that the first angle sensor 3 and the second angle sensor 4 have high accuracy and small detection error. However, using highly accurate sensors increases the cost of the device. For this reason, in this embodiment, an integer value of the number of rotations of the upper shaft 111 from a reference position is calculated based on the detection results of the first angle sensor 3 and the second angle sensor 4, and the absolute rotation angle is calculated based on the calculated integer value and the detection result of the second angle sensor 4. In other words, by using the detection result of the first angle sensor 3 only to calculate the integer value of the number of rotations of the upper shaft 111, the MCU 5 calculates the absolute rotation angle so that the detection error of the first angle sensor 3 does not adversely affect the accuracy of the final absolute rotation angle.

[0047] In this embodiment, an integer value of the number of rotations of the upper shaft 111 is calculated based on the normalized phase difference δ. Next, a method for calculating the integer value of the number of rotations of the upper shaft 111 will be described with reference to FIG.

[0048] <Calculation method for absolute rotation angle> FIG. 9 shows the fixed-magnification phase difference φ obtained by multiplying the normalized phase difference δ by a predetermined coefficient (−j / (ji)) according to the first speed transmission ratio and the second speed transmission ratio. s is shown by a dashed line, and the fixed phase difference φs 10 is a graph showing, by a solid line, integer values ​​of the number of rotations of the upper shaft 111 obtained from s The calculation formula for the fixed magnification phase difference φ is as follows: s corresponds to the absolute angle of the detected angle φ of the second angle sensor 4.

number

[0049] When the integer value of the number of rotations of the upper shaft 111 is R, R is obtained by the following equations (3) and (4).

number

number

[0050] Here, the normalized phase difference δ is calculated from the detected angle ψ of the first angle sensor 3 and the detected angle φ of the second angle sensor 4, and therefore includes the detection error εψ of the first angle sensor 3. However, as long as the detection error εψ of the first angle sensor 3 and the detection error εφ of the second angle sensor 4 are within a range that does not affect the integer value R of the number of rotations of the upper shaft 111 calculated by the above equations (3) and (4), the integer value R can be calculated accurately. The allowable conditions for the detection error εψ of the first angle sensor 3 and the detection error εφ of the second angle sensor 4 will be described later.

[0051] 10 is a graph showing the absolute rotation angle θ calculated by the following equation (5) from the integer value R of the number of rotations of the upper shaft 111 and the angle φ detected by the second angle sensor 4. The horizontal axis of the graph shown in FIG. 10 indicates the actual rotation angle of the upper shaft 111, and the vertical axis of the graph indicates the absolute rotation angle θ calculated by the calculation of the MCU 5.

number

[0052] As shown in equation (5), the calculation formula for calculating the absolute rotation angle θ does not include the angle ψ detected by the first angle sensor 3. Therefore, if the integer value R of the number of rotations of the upper shaft 111 can be accurately calculated, the absolute rotation angle θ can be accurately calculated as shown in the graph of FIG. 10 without being affected by the detection error εψ of the first angle sensor 3.

[0053] 11 is a flowchart showing an example of the procedure of a calculation process performed by the MCU 5 to calculate the absolute rotation angle θ. In the process shown in this flowchart, the MCU 5 first acquires the detection result of the first angle sensor 3 based on the magnitude of the capacitance between the rotating electrode 31 and the first and second fixed electrodes 321, 322 (step S1), and calculates the detected angle ψ of the first angle sensor 3, which expresses the detection result acquired in step S1 as an angle equal to or greater than 0° and less than 360° (step S2). Next, the MCU 5 acquires the detection result of the second angle sensor 4 based on a signal from the magnetic field detection element 42 (step S3), and calculates the detected angle ψ of the second angle sensor 4 (step S4).

[0054] Next, the MCU 5 calculates a phase difference by subtracting the angle φ detected by the second angle sensor 4 from the angle ψ detected by the first angle sensor 3 (step S5). If the phase difference calculated in step S5 is 180° or more (step S6: Yes), the MCU 5 subtracts 360° from the phase difference and sets the result as the normalized phase difference δ (step S7). If the phase difference calculated in step S5 is -180° or less (step S8: Yes), the MCU 5 adds 360° to the phase difference and sets the result as the normalized phase difference δ (step S9). If the phase difference calculated in step S5 is greater than -180° and less than 180°, the MCU 5 sets the phase difference calculated in step S5 as the normalized phase difference δ (step S10). The processes in steps S6 to S10 are phase difference normalization processes.

[0055] Next, the MCU 5 calculates the fixed-magnification phase difference φ s(Step S11), and calculates an integer value R of the number of rotations of the upper shaft 111 by calculating equation (3) or (4) (Step S12). Then, the MCU 5 calculates the absolute rotation angle θ by calculating equation (5) (Step S13). Information on the calculated absolute rotation angle θ is transmitted to the steering control device 17 as the detection result of the steering angle.

[0056] Here, we will explain how to calculate the rotation angle of the rotating electrode 31 using the first angle sensor 3. Here, we will explain how to calculate the rotation angle of the rotating electrode 31 for one period from 0° to 180° out of the range from 0° to 360° shown in Figures 5(a) and 5(b), but it is also possible to calculate the rotation angle of the rotating electrode 31 from 180° to 360° in the same way.

[0057] In this calculation method, the rotation angle of the rotating electrode 31 is calculated by dividing the range into two cases: a range where the rotation angle of the rotating electrode 31 is from 0° to 90°, i.e., a range where the overlapping area of ​​the rotating electrode 31 and the first fixed electrode 321 is larger than the overlapping area of ​​the rotating electrode 31 and the second fixed electrode 322, and a range where the rotation angle of the rotating electrode 31 is from 90° to 180°, i.e., a range where the overlapping area of ​​the rotating electrode 31 and the second fixed electrode 322 is larger than the overlapping area of ​​the rotating electrode 31 and the first fixed electrode 321.

[0058] 12(a) is a schematic diagram showing the overlapping state of the rotating electrode 31 with the first fixed electrode 321 and the second fixed electrode 322 when the rotation angle of the rotating electrode 31 is less than 90°. FIG. 12(b) is a schematic diagram showing the overlapping state of the rotating electrode 31 with the first fixed electrode 321 and the second fixed electrode 322 when the rotation angle of the rotating electrode 31 is 90° or more. Whether the rotation angle of the rotating electrode 31 is less than 90° or greater than 90° can be determined by whether the value calculated by the following formula (6) is less than 0.5 or greater than 0.5, where A is the overlapping area of ​​the rotating electrode 31 and the first fixed electrode 321 and B is the overlapping area of ​​the rotating electrode 31 and the second fixed electrode 322.

number

[0059] Hereinafter, the overlapping area between the rotating electrode 31 and the first fixed electrode 321 will be referred to as a first opposing area A, and the overlapping area between the rotating electrode 31 and the second fixed electrode 322 will be referred to as a second opposing area B. The first opposing area A can be calculated from the capacitance between the rotating electrode 31 and the first fixed electrode 321. The second opposing area B can be calculated from the capacitance between the rotating electrode 31 and the second fixed electrode 322.

[0060] (When the rotation angle of the rotating electrode 31 is less than 90°) As shown in FIG. 12(a), when the maximum width of the first fixed electrode 321 and the second fixed electrode 322 is h and the rotation angle of the rotating electrode 31 is x, the first opposing area A is expressed by the following formula (7), and the second opposing area B is expressed by the following formula (8).

number

number

[0061] Furthermore, the maximum sum of the overlapping areas of the rotating electrode 31 and the first and second fixed electrodes 321 and 322, i.e., the sum of the maximum value of the first opposing area A and the maximum value of the second opposing area B, is 90h. Therefore, the value obtained by dividing the total opposing area obtained by adding the first opposing area A and the second opposing area B by 90h is expressed by the following equation (9) using equations (7) and (8).

number

[0062] As a result, x can be calculated by the following formula (10).

number

[0063] (When the rotation angle of the rotating electrode 31 is 90° or more) As shown in FIG. 12(b), when the maximum width of the first fixed electrode 321 and the second fixed electrode 322 is h and the rotation angle of the rotating electrode 31 is x, the first opposing area A is expressed by the following formula (11), and the second opposing area B is expressed by the following formula (12).

number

number

[0064] Furthermore, the maximum sum of the overlapping areas of the rotating electrode 31 and the first fixed electrode 321 and the second fixed electrode 322, i.e., the sum of the maximum value of the first opposing area A and the maximum value of the second opposing area B, is 90h. Therefore, the value obtained by dividing the total opposing area obtained by adding the first opposing area A and the second opposing area B by 90h is expressed by the following equation (13) using equations (11) and (12).

number

[0065] As a result, x can be calculated by the following formula (14).

number

[0066] The first fixed electrode 321 and the second fixed electrode 322 may be modified as shown in Fig. 13. Fig. 3 shows a case where the first fixed electrode 321 is composed of an inner portion 321a and an outer portion 321b that sandwich the second fixed electrode 322 in the radial direction, but in the example shown in Fig. 13, the entire first fixed electrode 321 is formed radially inward of the second fixed electrode 322. Even when the first fixed electrode 321 and the second fixed electrode 322 are formed in this manner, the rotation angle of the rotating electrode 31 can be determined in the same manner as described above.

[0067] <Condition 1 for the detection error εψ of the first angle sensor 3 and the detection error εφ of the second angle sensor 4> Next, we will explain the conditions for the detection error εψ of the first angle sensor 3 and the detection error εφ of the second angle sensor 4, which are required to accurately perform normalization processing on the phase difference, which is the difference between the detection angle ψ of the first angle sensor 3 and the detection angle φ of the second angle sensor 4, and to prevent the detection angles of the first angle sensor 3 and the second angle sensor 4 from differing by more than one period.

[0068] The amount of change Δ in the normalized phase difference δ when the second gear 22 makes one rotation in conjunction with the rotation of the upper shaft 111 is calculated by the following equation (21). Furthermore, the range of variation Δ' in the phase difference over the entire detection range of the absolute rotation angle θ by the rotation angle detection device 2 is calculated by the following equation (22) using the above-mentioned Rmax.

number

number

[0069] In order to accurately calculate the absolute rotation angle θ, the normalized phase difference δ must vary with the rotation of the upper shaft 111, and the range of variation must satisfy the following equation (23). Therefore, Δ' must be greater than 0 and less than 360, as shown in the following equation (24), or in other words, must satisfy the following equation (25).

number

number

number

[0070] However, since the fluctuation range of the normalized phase difference δ changes depending on the detection error εψ of the first angle sensor 3 and the detection error εφ of the second angle sensor 4, when the detection error εψ of the first angle sensor 3 and the detection error εφ of the second angle sensor 4 are taken into consideration, Equation (24) becomes Equation (26) below.

number

[0071] By modifying equation (26), the above equation (1) is obtained as the condition that the absolute values ​​of the detection error εψ of the first angle sensor 3 and the detection error εφ of the second angle sensor 4 must satisfy.

[0072] <Condition 2 for the detection error εψ of the first angle sensor 3 and the detection error εφ of the second angle sensor 4> Next, the conditions for the detection error εψ of the first angle sensor 3 and the detection error εφ of the second angle sensor 4 to accurately calculate the integer value R of the number of rotations of the upper shaft 111 using equations (3) and (4) will be described.

[0073] In order to accurately obtain the integer value R of the number of rotations of the upper shaft 111, the fixed magnification phase difference φ s The difference between the angle φ detected by the second angle sensor 4 and the angle φ detected by the second angle sensor 4 must not vary by more than 180° from the true value without error due to the influence of the detection errors εψ and εφ. s The value of -φ (true value) is affected by the detection errors εψ and εφ. s -φ', the following equation (31) must be satisfied.

number

[0074] Here, the following equations (32) and (33) hold from the above equation (2) and the relationship δ=ψ−φ, and the following equation (34) holds from equations (32) and (33).

number

number

number

[0075] Substituting equation (34) into equation (31), we obtain the following equation (35).

number

[0076] The detection error εψ of the first angle sensor 3 and the detection error εφ of the second angle sensor 4 can take either a positive or negative value, so the left side of equation (35) becomes as shown in the following equation (36) under the condition that it is largest, and by transforming equation (36), the following equation (37) is obtained. Equation (37) is a necessary condition for the detection error εψ of the first angle sensor 3 and the detection error εφ of the second angle sensor 4 to accurately calculate the integer value R of the number of rotations of the upper shaft 111, i.e., the allowable range of the detection errors.

number

number

[0077] (Functions and Effects of the First Embodiment) According to the first embodiment described above, the first angle sensor 3 is of the capacitance type, while the second angle sensor 4 is of the magnetic type. Therefore, even if the first angle sensor 3 and the second angle sensor 4 are close to each other, the magnetic field of the second angle sensor 4 does not affect the detection accuracy of the first angle sensor 3. This makes it possible to suppress an increase in the size of the device and to improve the accuracy of the detection result of the rotation angle of the upper shaft 111. Furthermore, by forming the first and second fixed electrodes 321, 322 as wiring patterns on the substrate 20, it is possible to reduce the cost of the first angle sensor 3. In other words, according to the present embodiment, it is possible to detect the rotation angle of the upper shaft 111 with high accuracy while achieving low costs.

[0078] [Modification of the first embodiment] The above first embodiment may be modified as follows.

[0079] In the first embodiment, the case where the absolute rotation angle θ is calculated from the integer value R of the number of rotations of the upper shaft 111 and the detected angle φ of the second angle sensor 4 has been described. However, this is not limiting, and the absolute rotation angle θ may be calculated from the integer value R of the number of rotations of the upper shaft 111 and the detected angle ψ of the first angle sensor 3. Even in this case, the detection error εφ of the second angle sensor 4 can be prevented from being included in the calculation result of the absolute rotation angle θ, thereby improving the detection accuracy of the rotation angle of the upper shaft 111 compared to when the detection error εψ of the first angle sensor 3 and the detection error εφ of the second angle sensor 4 are included in the calculation result of the absolute rotation angle θ. However, by calculating the absolute rotation angle θ from the detected angle φ of the second angle sensor 4, which have relatively high detection accuracy, and the integer value R of the number of rotations of the upper shaft 111, the detection accuracy of the rotation angle of the upper shaft 111 is improved compared to when the absolute rotation angle θ is calculated from the detected angle ψ of the first angle sensor 3 and the integer value R of the number of rotations of the upper shaft 111.

[0080] Furthermore, in the first embodiment, the case where the first angle sensor 3 is a capacitance-type angle sensor and the second angle sensor 4 is a magnetic-type angle sensor has been described, but conversely, the first angle sensor 3 may be a magnetic-type angle sensor and the second angle sensor 4 may be a capacitance-type angle sensor. In other words, if one of the first angle sensor 3 and the second angle sensor 4 is a capacitance-type angle sensor and the other is a magnetic-type angle sensor, the magnetic field of the magnetic-type angle sensor will not affect the detection accuracy of the capacitance-type angle sensor, and the detection accuracy of the rotation angle of the upper shaft 111 will be improved.

[0081] [Second embodiment] 14(a) and 14(b) are diagrams showing the configuration of a rotation angle detection device 2A according to a second embodiment. In the first embodiment, the second angle sensor 4 is magnetic, but in the second embodiment, the second angle sensor 4A is capacitive. The second angle sensor 4A has a rotating electrode 43 attached to the surface of the second gear 22 facing the substrate 20, and first and second fixed electrodes 441, 442 provided on the substrate 20 as a wiring pattern.

[0082] FIG. 15(a) is a structural diagram showing the rotating electrode 43 attached to the surface of the second gear 22 facing the substrate 20. FIG. 15(b) is a structural diagram showing first and second fixed electrodes 441, 442 provided on the substrate 20. The rotating electrode 43 is made of a semicircular sector-shaped conductor and is electrically grounded by a ground wire (not shown). The first fixed electrode 441 is made of an inner portion 441a and an outer portion 441b that sandwich the second fixed electrode 442 in the radial direction. The inner portion 441a and the outer portion 441b are electrically connected to one end of the first fixed electrode 441. The radial widths of the inner portion 441a and the outer portion 441b gradually narrow from one end to the other end of the first fixed electrode 441. The radial width of the second fixed electrode 442 gradually widens from one end to the other end.

[0083] 4, the MCU 5 can detect the capacitance between the rotating electrode 43 and the first fixed electrode 441 and the capacitance between the rotating electrode 43 and the second fixed electrode 442, and can obtain the rotation angle of the second gear 22 with respect to the substrate 20 from these capacitances. Then, the rotation angle of the upper shaft 111 can be detected from the rotation angle of the second gear 22 in the same manner as in the first embodiment.

[0084] [Third embodiment] 16(a) and 16(b) are diagrams showing the configuration of a rotation angle detection device 2B according to a third embodiment. In the first embodiment, the first angle sensor 3 is a capacitance type, but in the third embodiment, the first angle sensor 3A is a magnetic type. The first angle sensor 3A has a rotary magnet 33 attached to the surface of the first gear 21 facing the circuit board 20 and a magnetic field detection element 34 mounted on the circuit board 20. The rotary magnet 33 and the magnetic field detection element 34 face each other via a small air gap. The rotary magnet 33 is a four-pole magnet having two north poles and one south pole. The magnetic field detection element 34 is, for example, a giant magnetoresistive effect (GMR) sensor, an anisotropic magnetoresistive (AMR) sensor, or a tunneling magnetoresistive (TMR) sensor.

[0085] A signal indicating the detection result of the magnetic field detection element 34 is sent to the MCU 5. The MCU 5 can detect the angle of the rotary magnet 33 relative to the substrate 20, i.e., the rotation angle of the first gear 21, based on the signal from the magnetic field detection element 34. Then, the rotation angle of the upper shaft 111 can be detected from the rotation angle of the first gear 21, in the same manner as in the first embodiment.

[0086] [Fourth embodiment] 17(a) and 17(b) are diagrams showing the configuration of a rotation angle detection device 2C according to a fourth embodiment. In the fourth embodiment, a first angle sensor 3B and a second angle sensor 4B are induction-type sensors. The first angle sensor 3B has a guide plate 35 that rotates integrally with the first gear 21 and an electromagnetic coil 36 provided in a position facing the guide plate 35. The second angle sensor 4B has a guide plate 45 that rotates integrally with the second gear 22 and an electromagnetic coil 46 provided in a position facing the guide plate 45.

[0087] Fig. 18(a) is a structural diagram showing an induction plate 35 attached to the surface of the first gear 21 facing the substrate 20, and an induction plate 45 attached to the surface of the second gear 22 facing the substrate 20. Fig. 18(b) is a plan view showing the electromagnetic coils 36 and 46 provided on the substrate 20. The induction plates 35 and 45 are made of a conductive metal such as aluminum, and are electrically grounded. The electromagnetic coils 36 and 46 are formed as wiring patterns on the substrate 20.

[0088] The guide plate 35 of the first angle sensor 3B integrally includes a circular ring portion 351 that surrounds the upper shaft 111 and two protruding portions 352 that protrude radially outward from the circular ring portion 351, and the two protruding portions 352 are provided at positions that are point-symmetrical with respect to the rotation axis O of the upper shaft 111. Each of the protruding portions 352 has a sector shape with a central angle of 90° centered on the rotation axis O of the upper shaft 111.

[0089] The electromagnetic coil 36 of the first angle sensor 3B is formed so that the central angle thereof is within a range of 90° around the rotation axis O of the upper shaft 111. When the guide plate 35 rotates together with the upper shaft 111, the inductance of the electromagnetic coil 36 changes according to the opposing area between the protruding portion 352 of the guide plate 35 and the electromagnetic coil 36. The MCU 5 can determine the rotation angle of the first gear 21 relative to the circuit board 20 from this change in inductance.

[0090] The guide plate 45 of the second angle sensor 4B has a semicircular sector shape that surrounds the center of the second gear 22. The electromagnetic coil 46 of the second angle sensor 4B is formed within a range of 180° around the rotation center of the second gear 22. When the guide plate 45 rotates together with the upper shaft 111, the inductance of the electromagnetic coil 46 changes according to the opposing area between the guide plate 45 and the electromagnetic coil 46. The MCU 5 can determine the rotation angle of the second gear 22 relative to the circuit board 20 from this change in inductance.

[0091] In this fourth embodiment, the rotation angle of the upper shaft 111 can be detected in the same manner as in the first embodiment from the rotation angles of the first gear 21 and the second gear 22 detected by the first angle sensor 3B and the second angle sensor 4B.

[0092] [Fifth embodiment] In the fifth embodiment, the worm wheel 162 of the reduction gear mechanism 16 shown in FIG. 1 is used as a first gear for detecting the rotation angle of the upper shaft 111, and the encoder 152 of the electric motor 15 is used as a first angle sensor. The rotation angle of the worm wheel 162 can be obtained by multiplying the rotation angle detected by the encoder 152 by the reciprocal of the reduction ratio of the reduction gear mechanism 16. However, because the worm wheel 162 is attached to the lower shaft 112, the rotation angle obtained from the encoder 152 is a value that is shifted from the rotation angle of the upper shaft 111 by the torsion angle of the torsion bar 110. The second angle sensor may have the configuration of any one of the first to fourth embodiments.

[0093] In this fifth embodiment, the rotation angle of the upper shaft 111 is detected in the same manner as in the first embodiment, making it possible to detect the rotation angle of the upper shaft 111 with high accuracy while reducing costs.

[0094] (Summary of embodiments and modifications) Next, the technical ideas grasped from the above-described embodiments will be described by using the reference numerals and the like in the embodiments. However, the reference numerals in the following description do not limit the scope of the claims to the configurations specifically shown in the embodiments.

[0095] [1] A rotation angle detection device (2, 2A, 2B, 2C) for detecting a rotation angle of a rotating member (upper shaft 111) from a reference position, the device comprising: a first gear (21) and a second gear (22) that rotate at different speeds in accordance with the rotation of the rotating member (111); a first angle sensor (3, 3A, 3B) that detects the rotation angle of the first gear (21); a second angle sensor (4, 4A, 4B) that detects the rotation angle of the second gear (22); and a rotation angle detection device (2, 2A, 2B, 2C) for detecting the rotation angle of the rotating member (111) based on the detection results of the first angle sensor (3, 3A, 3B) and the second angle sensor (4). a calculation unit (MCU5) that calculates a rotation angle from the reference position, wherein the calculation unit (5) calculates an integer value of the number of rotations of the rotating member (111) from the reference position based on the detection result of the first angle sensor (3, 3A, 3B) and the detection result of the second angle sensor (4, 4A, 4B), and calculates the rotation angle of the rotating member (111) from the reference position based on the integer value and either the detection result of the first angle sensor (3, 3A, 3B) or the detection result of the second angle sensor (4, 4A, 4B).

[0096] [2] The rotation angle detection device (2, 2A, 2B, 2C) described in [1] above, wherein the calculation unit (5) calculates the rotation angle of the rotating member (111) from the reference position based on the detection result of the angle sensor having higher rotation angle detection accuracy out of the first angle sensor (3, 3A, 3B) and the second angle sensor (4, 4A, 4B) and the integer value.

[0097] [3] The rotation angle detection device (2) described in [1] above, wherein one of the first angle sensor (3) and the second angle sensor (4) is a capacitance-type angle sensor that detects the rotation angle by the capacitance between a rotating electrode and a fixed electrode, and the other is a magnetic-type angle sensor that detects the rotation angle by detecting the magnetic field of a rotating magnet.

[0098] [4] The rotation angle detection device (2) according to any one of [1] to [3] above, wherein the allowable ranges of εψ and εφ are expressed by the following two equations: a detection error of the first angle sensor (3) is εψ, a detection error of the second angle sensor (4) is εφ, a speed transmission ratio from the rotating member (111) to the electrical angle of the first gear (21) whose rotation angle is detected by the first angle sensor (3) is j, a speed transmission ratio from the rotating member (111) to the electrical angle of the second gear (22) whose rotation angle is detected by the second angle sensor (4) is i, and Rmax is an integer obtained by rounding up the decimal point of a quotient obtained by dividing the size of an angle range in which the calculation unit (5) should calculate the rotation angle of the rotating member (111) by (i × 360). TIFF2025132674000029.tif3191

[0099] [5] A method for detecting a rotation angle of a rotating member (111) from a reference position, the method comprising: calculating an integer value of the number of rotations of the rotating member (111) from the reference position based on a detection result of rotation angles of a first gear (21) and a second gear (22), which rotate at different speeds in accordance with the rotation of the rotating member (111); and calculating the rotation angle of the rotating member (111) from the reference position based on either the detection result of the rotation angle of the first gear (21) or the detection result of the rotation angle of the second gear (22) and the integer value.

[0100] [6] The method for detecting a rotation angle according to [5] above, wherein the rotation angle of the rotating member (111) from the reference position is calculated based on the integer value and one of the detection results of the rotation angle of the first gear (21) and the detection result of the rotation angle of the second gear (22), whichever has higher detection accuracy.

[0101] [7] The method for detecting a rotation angle according to the above item [5] or [6], further comprising: calculating a phase difference, which is a difference between the rotation angle of the first gear (21) and the rotation angle of the second gear (22); performing normalization processing to subtract 360° from the phase difference if the calculated phase difference is 180° or more; and adding 360° to the phase difference if the calculated phase difference is -180° or less, to obtain a normalized phase difference; and calculating an integer value of the number of rotations of the rotating member (111) based on the normalized phase difference.

[0102] [8] The method for detecting a rotation angle according to the above-mentioned [7], wherein the difference between the value obtained by multiplying the normalized phase difference by a coefficient according to the speed transmission ratio from the rotating member (111) to the first gear (21) and the second gear (22) and the rotation angle of the second gear (22) is calculated, and an integer value of the number of rotations of the rotating member (111) is calculated based on the difference.

[0103] Although the embodiments and modifications of the present invention have been described above, the above embodiments and modifications do not limit the scope of the invention as claimed. It should be noted that not all of the combinations of features described in the embodiments and modifications are necessarily essential to the means for solving the problems of the invention. [Explanation of symbols]

[0104] 111...Upper shaft (rotating member) 2, 2A, 2B, 2C...Rotation angle detection device 20... Board 21... First gear 22...Second gear 3, 3A, 3B...First angle sensor 4, 4A, 4B... Second angle sensor 5... MCU (calculation unit)

Claims

1. A rotation angle detection device that detects a rotation angle of a rotating member from a reference position, a first gear and a second gear that rotate at different speeds in accordance with the rotation of the rotating member; a first angle sensor that detects a rotation angle of the first gear; a second angle sensor that detects a rotation angle of the second gear; a calculation unit that calculates a rotation angle of the rotating member from the reference position based on a detection result of the first angle sensor and a detection result of the second angle sensor, the calculation unit calculates an integer value of the number of rotations of the rotating member from the reference position based on the detection result of the first angle sensor and the detection result of the second angle sensor, and calculates a rotation angle of the rotating member from the reference position based on either the detection result of the first angle sensor or the detection result of the second angle sensor and the integer value. Rotation angle detection device.

2. the calculation unit calculates the rotation angle of the rotating member from the reference position based on the integer value and a detection result of one of the first angle sensor and the second angle sensor, whichever has higher rotation angle detection accuracy. The rotation angle detection device according to claim 1 .

3. One of the first angle sensor and the second angle sensor is a capacitance-type angle sensor that detects a rotation angle by electrostatic capacitance between a rotating electrode and a fixed electrode, and the other is a magnetic-type angle sensor that detects a rotation angle by detecting a magnetic field of a rotating magnet. The rotation angle detection device according to claim 1 .

4. 4. The rotation angle detection device according to claim 1, wherein the allowable ranges of εψ and εφ are expressed by the following two equations: εψ is a detection error of the first angle sensor, εφ is a detection error of the second angle sensor, j is a speed transmission ratio from the rotating member to the electrical angle of the first gear, whose rotation angle is detected by the first angle sensor, i is a speed transmission ratio from the rotating member to the electrical angle of the second gear, whose rotation angle is detected by the second angle sensor, and Rmax is an integer obtained by dividing the size of an angle range in which the calculation unit is to calculate the rotation angle of the rotating member by (i × 360) and rounding up the quotient.

5. A method for detecting a rotation angle of a rotating member from a reference position, comprising: calculating an integer value of the number of rotations of the rotating member from the reference position based on a detection result of rotation angles of a first gear and a second gear which rotate at different speeds in accordance with the rotation of the rotating member, and calculating a rotation angle of the rotating member from the reference position based on the integer value and one of the detection result of the rotation angle of the first gear and the detection result of the rotation angle of the second gear; How to detect the rotation angle.

6. calculating a rotation angle of the rotating member from the reference position based on the integer value and one of the detection results of the rotation angle of the first gear and the detection result of the rotation angle of the second gear, whichever has higher detection accuracy; The method for detecting a rotation angle according to claim 5.

7. calculating a phase difference that is a difference between a rotation angle of the first gear and a rotation angle of the second gear; a normalization process is performed to subtract 360° from the phase difference when the calculated phase difference is 180° or more, and to add 360° to the phase difference when the calculated phase difference is −180° or less, thereby obtaining a normalized phase difference; calculating an integer value of the number of rotations of the rotating member based on the normalized phase difference; The method for detecting a rotation angle according to claim 5 or 6.

8. calculating a difference between a value obtained by multiplying the normalized phase difference by a coefficient according to a speed transmission ratio from the rotating member to the first gear and the second gear and a rotation angle of the second gear, and calculating an integer value of the number of rotations of the rotating member based on the difference; The method for detecting a rotation angle according to claim 7.

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