Steering angle detection device

Abstract

To provide a steering angle detection device capable of increasing precision of a detection result of a steering angle while suppressing upsizing of the device.SOLUTION: A steering angle detection device 2 for detecting a steering angle that is a rotational angle of a steering shaft 11 connected to a steering wheel 10 comprises: a first gear 21 and a second gear 22 that rotate at mutually different speeds; a first angle sensor 3 for detecting a rotational angle of the first gear 21; a second angle sensor 4 for detecting a rotational angle of the second gear 22; and an MCU 5 for calculating an absolute angle of the steering angle on the basis of detection results of the first angle sensor 3 and the second angle sensor 4. The first angle sensor 3 has a rotating electrode 31 that integrally rotates with the first gear 21, and a fixed electrode 32 disposed opposite to the rotating electrode 31, and the capacitance between the rotating electrode 31 and the fixed electrode 32 is changed because of rotation of the steering shaft 11. The MCU 5 calculates the absolute angle of the steering angle with the magnitude of the capacitance as a detection result of the first angle sensor 3.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a steering angle detection device for detecting a steering angle. [Background technology]

[0002] Various configurations of steering angle detection devices have been proposed for detecting the steering angle of a steering wheel as a steering member. Information on the steering angle detected by the steering angle detection devices 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 steering angle detection device described in Patent Document 1 includes a main rotor connected to a steering shaft, a sub-rotor meshed with the main rotor, a first sensor unit for detecting the angular position of the main rotor, and a second sensor unit for detecting the angular position of the sub-rotor. The first sensor unit includes an induction rotor attached to the main rotor and a stator inductively coupled to the induction rotor. The second sensor unit includes a magnetic body attached to the sub-rotor and a magnetic field sensor such as a Hall element, an AMR element, or a GMR sensor.

[0004] The steering angle detection device described in Patent Document 2 includes a rotating body having an engagement portion that engages with the steering shaft, a first detector and a second detector that rotate at different speeds in conjunction with the rotation of the rotating body, a first detector that detects the rotation of the first detector, and a second detector that detects the rotation of the second detector. The first detector has a magnet attached to the first detector and an AMR element disposed opposite the magnet. The second detector has a magnet attached to the second detector and a Hall element disposed opposite the magnet. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent Application Publication No. 2180296 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-96518 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, a steering angle detection device having two rotating members (the main rotor and sub-rotor in Patent Document 1, the first detection body and the second detection body in Patent Document 2) that rotate with the rotation of the steering shaft and a magnetic field sensor (the stator and magnetic field sensor in Patent Document 1, the AMR element and the Hall element in Patent Document 2) that magnetically detects the rotation of these rotating members may have a problem in which the magnetic field for detecting the rotation of one of the two rotating members interferes with the magnetic field for detecting the rotation of the other rotating member, resulting in an error in the steering angle detection result. Furthermore, if the distance between the rotation axes of the two rotating members is increased to avoid magnetic field interference, the size of the device will increase. Therefore, an object of the present invention is to provide a steering angle detection device that can improve the accuracy of the steering angle detection result while suppressing an increase in the size of the device. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention provides a steering angle detection device that detects a steering angle, which is the rotation angle of a steering shaft connected to a steering wheel, comprising: a first gear and a second gear that rotate at different speeds in accordance with the rotation of the steering shaft; 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 absolute angle of the steering angle based on the detection results of the first angle sensor and the second angle sensor, wherein the first angle sensor has a rotating electrode that rotates integrally with the first gear and a fixed electrode arranged opposite the rotating electrode, and the capacitance between the rotating electrode and the fixed electrode changes as the steering shaft rotates, and the calculation unit calculates the absolute angle of the steering angle from the magnitude of the capacitance as the detection result of the first angle sensor. [Effects of the Invention]

[0008] According to the steering angle detection device of the present invention, it is possible to improve the accuracy of the steering angle detection result while suppressing an increase in size. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of a vehicle equipped with a steer-by-wire steering system including a steering angle detection device according to an embodiment of the present invention. [Figure 2] 1(a) and 1(b) are diagrams showing the configuration of a steering angle detection device. [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] FIG. 10 is an explanatory diagram showing an example of a circuit configuration for detecting whether a fixed electrode overlaps a rotating electrode. [Figure 5] Graph (a) shows the change in the state of each fixed electrode when the rotating electrode rotates 360° from the reference position. Graph (b) shows the on / off states of the 16 fixed electrodes shown in (a) as the detection results of the first angle sensor. [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 from the angle detected by the first angle sensor. [Figure 8] 10 is a graph showing a normalized phase difference obtained by performing a normalization process to reduce the phase difference when the detected angle of the second angle sensor crosses zero earlier than the detected angle of the first angle sensor and the absolute value of the phase difference becomes 180° or more. [Figure 9] 10 is a graph in which a fixed-multiplication phase difference obtained by multiplying a normalized phase difference by a predetermined coefficient according to a first speed transmission ratio and a second speed 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 steering angle calculated from an integer value of the number of rotations of the steering shaft and an angle detected by a second angle sensor. [Figure 11] 6 is a flowchart showing an example of a procedure of a calculation process performed by an MCU to obtain an absolute steering angle. [Figure 12] 1A is a plan view showing a rotary electrode of the first angle sensor together with a steering shaft of the first angle sensor according to Modification 1. FIG. 1B is a plan view showing a substrate on which a plurality of fixed electrodes of the first angle sensor according to Modification 1 are formed as a wiring pattern. [Figure 13] 10A is a graph showing the change in the state of the four fixed electrodes when the rotating electrode according to Modification 1 rotates 360° from the reference position, and FIG. 10B is a graph showing the on / off states of the four fixed electrodes as the detection results of the first angle sensor. [Figure 14] 1(a) is a plan view showing the rotary electrode of the first angle sensor together with the steering shaft according to Modification 2. FIG. 1(b) is a plan view showing a substrate on which a plurality of fixed electrodes of the first angle sensor are formed as a wiring pattern. [Figure 15]14(a) and 14(b) are graphs showing the change in capacitance between the first fixed electrode and the rotating electrode, and the change in capacitance between the second fixed electrode and the rotating electrode when the rotating electrode shown in FIG. 14(b) rotates 360° from the reference position. [Figure 16] 1A is a schematic diagram showing an overlapping state between the rotating electrode 81 and the first and second fixed electrodes when the rotation angle of the rotating electrode 81 is less than 90°, and FIG. 1B is a schematic diagram showing an overlapping state between the rotating electrode 81 and the first and second fixed electrodes when the rotation angle of the rotating electrode 81 is 90° or more. [Figure 17] 14(b) is a plan view showing a modified example in which the shapes of the first fixed electrode and the second fixed electrode shown in FIG. 14(b) are modified. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Embodiment Mode] FIG. 1 is a schematic diagram of a vehicle equipped with a steer-by-wire steering device 1 equipped with a steering angle detection device 2 according to an embodiment of the present invention.

[0011] As shown in FIG. 1, the steering device 1 includes a steering wheel 10, a steering shaft 11 that rotates integrally with the steering wheel 10, a steering angle detection device 2 that detects the steering angle, which is the rotation angle of the steering shaft 11, a reaction force application device 12 that applies a steering reaction force 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, a reduction mechanism 15 that has a pinion gear 151 that meshes with rack teeth 131 of the rack shaft 13, an electric motor 16 that applies an axial moving force to the rack shaft 13 via the reduction mechanism 15, and a steering control device 17 that controls the electric motor 16 and the reaction force application device 12 based on the steering angle detected by the steering angle detection device 2.

[0012] The reduction gear mechanism 15 has a worm wheel 152 to which a pinion gear 151 is fixed, and a worm gear 153 fixed to a motor shaft 161 of the electric motor 16. When the pinion gear 151 rotates due to the rotation of the electric motor 16, the rack shaft 13 moves back and forth in the vehicle width direction, and the left and right steerable front wheels 18, 19 are steered.

[0013] 2(a) and 2(b) are diagrams showing the configuration of the steering angle detection device 2 according to this embodiment. Fig. 2(a) shows the steering angle detection device 2 as seen along the rotation axis O of the steering shaft 11. Fig. 2(b) shows the steering angle detection device 2 as seen from a direction perpendicular to the rotation axis O of the steering shaft 11.

[0014] The steering angle detection device 2 includes, as its main components, a substrate 20, a first gear 21 and a second gear 22 that rotate at different speeds in accordance with the rotation of the steering shaft 11, 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 absolute angle of the steering angle 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.

[0015] The substrate 20 is fixed to a case 23 and is disposed so as not to rotate relative to the vehicle body. The first gear 21 rotates integrally with the steering shaft 11. 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 steering angle to the steering control device 17. Note that in FIG. 2(a), the wiring patterns such as signal lines and power lines formed on the substrate 20 are not shown.

[0016] 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 steering shaft 11 is inserted through the through hole 210. The first gear 21 is fixed to the steering shaft 11 by, for example, adhesive. The second gear 22 integrally includes a flat gear portion 221 and a shaft-like 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 number of teeth of the first gear 21 is 50, and the number of teeth of the second gear 22 is 22.

[0017] 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.

[0018] A signal indicating the detection result of magnetic field detection element 42 is sent to MCU 5. MCU 5 can detect the angle of permanent magnet 41 relative to substrate 20, i.e., the rotation angle of second gear 22, based on the signal from magnetic field detection element 42. Second angle sensor 4 has a higher resolution for detecting the rotation angle of second gear 22 than the resolution for detecting the rotation angle of first gear 21 by first angle sensor 3, is more accurate than first angle sensor 3, and has a smaller angle detection error than first angle sensor 3.

[0019] 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 rotary electrode 31 that rotates integrally with the steering shaft 11 and the first gear 21, and a plurality of fixed electrodes 32 arranged opposite the rotary electrode 31. The rotary 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 rotary electrode 31. A through-hole 200 is formed in the substrate 20, through which the steering shaft 11 is inserted.

[0020] The fixed electrodes 32 are formed as a wiring pattern on the surface of the substrate 20 facing the rotating electrode 31. In this embodiment, 16 fixed electrodes 32 are formed on the substrate 20, and the 16 fixed electrodes 32 are formed at equal intervals in a 90° sector-shaped range centered on the rotation axis O of the steering shaft 11, and are lined up in the rotation direction of the rotating electrode 31. Each of the 16 fixed electrodes 32 is connected to the MCU 5.

[0021] The rotating electrode 31 is generally flat and has a through-hole 310 formed in the center. The steering shaft 11 is inserted through the through-hole 310. The rotating electrode 31 is fixed to the steering shaft 11 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 insert-molded integrally 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.

[0022] The rotary electrode 31 integrally includes an annular portion 311 that surrounds the steering shaft 11 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 steering shaft 11. Each of the protruding portions 312 is fan-shaped with a central angle of 90° about the rotation axis O, and the portion between the two protruding portions 312 forms a fan-shaped cutout portion 313.

[0023] When the steering shaft 11 rotates together with the rotating electrode 31, the number of fixed electrodes 32 that face the rotating electrode 31 in the normal direction of the substrate 20 changes depending on the rotational position of the steering shaft 11. Hereinafter, the state in which the rotating electrode 31 and the fixed electrode 32 face each other in the normal direction of the substrate 20 will be referred to as "overlapping." When the rotating electrode 31 and the fixed electrode 32 overlap, the protruding portion 312 of the rotating electrode 31 faces the fixed electrode 32 with a small air gap between them, and a capacitance is formed between them. In other words, the protruding portion 312 functions as a capacitance-forming portion of the rotating electrode 31.

[0024] 3(a) to 3(d) show states in which the rotating electrode 31 rotates together with the steering shaft 11 in 45° increments in the direction of arrow A (clockwise direction). In FIG. 3(a), none of the 16 fixed electrodes 32 overlap the protruding portions 312 of the rotating electrode 31, and they are located in the portions corresponding to the cutout portions 313 of the rotating electrode 31. As shown in FIG. 3(b), when the rotating electrode 31 rotates 45° from the state shown in FIG. 3(a), half of the 16 fixed electrodes 32 (eight fixed electrodes 32) overlap the protruding portions 312 of the rotating electrode 31. When the rotating electrode 31 rotates another 45°, as shown in FIG. 3(c), all of the 16 fixed electrodes 32 overlap the protruding portions 312 of the rotating electrode 31. FIG. 3(d) shows a state in which the rotating electrode 31 has rotated another 45° from the state shown in FIG. 3(c). In this state, the eight fixed electrodes 32 that were not overlapped with the protruding portions 312 of the rotating electrode 31 in the state shown in FIG. 3(b) now overlap with the protruding portions 312 of the rotating electrode 31.

[0025] As described above, the first angle sensor 3 has a number of fixed electrodes 32 facing the rotary electrode 31 that changes depending on the rotational position of the steering shaft 11. The MCU 5 can detect whether each of the 16 fixed electrodes 32 overlaps with the protruding portion 312 of the rotary electrode 31. In addition, in this embodiment, the rotary electrode 31 has two protruding portions 312, so that the capacitance between the rotary electrode 31 of the first angle sensor 3 and each of the multiple fixed electrodes 32 changes by two periods during one rotation of the steering shaft 11. 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 steering shaft 11. 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.

[0026] 4 is an explanatory diagram showing an example of a circuit configuration in which the MCU 5 detects whether one of the 16 fixed electrodes 32 overlaps with the protruding portion 312 of the rotating electrode 31. This example of a circuit configuration is modeled after the circuit configuration of a touch sensor that detects contact with a human finger. Similar circuits are configured for the other 15 fixed electrodes 32.

[0027] 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 fixed electrode 32 is connected to a node 63 between the resistor 61 and the capacitor 62. The potential of the node 63 is input to a gate element 64, and an output signal of the gate element 64 is input to an input terminal 52 of the MCU 5. The rotating electrode 31 is electrically grounded via the steering shaft 11. In this circuit configuration, when the fixed electrode 32 overlaps with the protruding portion 312 of the rotating electrode 31, the capacitance between the fixed electrode 32 and the rotating electrode 31 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 of the gate element 64 becomes longer than when the fixed electrode 32 and the rotating electrode 31 do not overlap.

[0028] Based on this difference in response time, the MCU 5 detects whether the fixed electrode 32 overlaps the protruding portion 312 of the rotating electrode 31. In other words, the magnitude of the capacitance between the rotating electrode 31 and the fixed electrode 32 changes as the steering shaft 11 rotates, and the MCU 5 calculates the absolute steering angle 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.

[0029] FIG. 5(a) is a graph showing the change in the state of each fixed electrode 32 when the rotating electrode 31 rotates 360° from the reference position, where the rotation angle is 0°, in the direction of arrow A shown in FIGS. 3(a) to 3(d). In the graph of FIG. 5(a), the first of the 16 fixed electrodes 32 to overlap with the protruding portion 312 when the rotating electrode 31 rotates in the direction of arrow A from the state shown in FIG. 3(a) is designated as the first fixed electrode 32, and the last fixed electrode 32 to overlap with the protruding portion 312 is designated as the 16th fixed electrode 32. In addition, in the graph of FIG. 5(a), when more than half of the surface area of ​​each fixed electrode 32 overlaps with the protruding portion 312 of the rotating electrode 31, it is designated as a rising edge (ON), and when more than half of the surface area of ​​each fixed electrode 32 no longer overlaps with the protruding portion 312, it is designated as a falling edge (OFF). As shown in this graph, there are 32 combinations of ON / OFF states for the 16 fixed electrodes 32.

[0030] 5(b) is a graph in which the 32 on / off states of the 16 fixed electrodes 32 shown in FIG. 5(a) are expressed as integers from 0 to 31 as detection results of the first angle sensor 3 through calculation processing by the MCU 5. As shown in the graph in FIG. 5(b), in this embodiment, the capacitance between the rotating electrode 31 of the first angle sensor 3 and the 16 fixed electrodes 32 changes by two periods while the steering shaft 11 makes one rotation. For this reason, in the following description, the speed transmission ratio from the steering shaft 11 to the rotating electrode 31 is assumed to be 0.50, and the speed transmission ratio from the steering shaft 11 to the second gear 22 is assumed to be 0.44 (=22 / 50), and a calculation method by which the MCU 5 calculates the absolute steering angle will be described.

[0031] Here, the absolute angle refers to the steering angle from the negative maximum value to the positive maximum value, where 0° is the steering angle when the steering wheel 10 is in the neutral position, the negative maximum value (e.g., -630°) is the steering angle when the steering wheel 10 is rotated all the way to the left, and the positive maximum value (e.g., 630°) is the steering angle when the steering wheel 10 is rotated all the way to the right. Hereinafter, the absolute angle of the steering angle will be referred to as the absolute steering angle. In addition, in this embodiment, a case will be described in which the negative maximum value of the absolute steering angle is -630° and the positive maximum value is 630°, and the steering wheel 10 makes a maximum of 3.5 turns.

[0032] 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.

[0033] In this embodiment, as described above, the speed transmission ratio from the steering shaft 11 to the rotating electrode 31 is 0.50, and the speed transmission ratio from the steering shaft 11 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 steering 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 steering angle will be described with reference to FIGS. 6 to 10.

[0034] 6 is a graph showing the detected angle of the first angle sensor 3 by a dashed line and the detected angle of the second angle sensor 4 (0° or more and less than 360°) by a solid line when the detection result of the first angle sensor 3 is expressed as an angle of 0° or more and less than 360° by multiplying the integers from 0 to 31 shown in FIG. 5(b) by a predetermined coefficient k (=11.25=360 / 32). The horizontal axis of the graph shown in FIG. 6 is the absolute steering angle of the steering wheel 10, and the vertical axis is the detected angles of the first angle sensor 3 and the second angle sensor 4.

[0035] 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 steering 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 steering angle increases.

[0036] 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 left or right from the neutral position, the speed transmission ratio from the steering shaft 11 to the second gear 22 is smaller than the speed transmission ratio from the steering shaft 11 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 after that. 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°.

[0037] FIG. 8 is a graph of the phase difference after calculation in which the phase difference is subtracted by 360° when the detected angle of the second angle sensor 4 crosses zero before the detected angle of the first angle sensor 3 and the phase difference is 180° or more, and the phase difference is added by 360° when the phase difference is −180° or less.

[0038] Hereinafter, this calculation process will be referred to as normalization processing, and the phase difference after normalization processing will be referred to as normalized phase difference δ. By performing normalization processing, the line of 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.

[0039] In this embodiment, the MUC 5 can accurately calculate the absolute steering 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 the first angle sensor 3 and the detected angle of the second angle sensor 4 do not deviate by more than one cycle when the steering wheel 10 is rotated from the end position on the left to the end position on the right.

[0040] 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 steering angle detection device 2 should detect the absolute steering angle (±630° in this example), making it impossible to accurately calculate the absolute steering angle. In other words, for the MUC 5 to accurately calculate the absolute steering angle, even when taking into account the detection errors of the first angle sensor 3 and the second angle sensor 4, it is necessary that the line of the normalized phase difference δ shown in the graph of FIG. 8 does not intersect with the line indicating a phase difference of −180° (dashed line) or the line indicating a phase difference of +180° (dashed line). The necessary condition for this, i.e., the allowable range of the 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

[0041] Here, in order to accurately determine the absolute steering 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 steering shaft 11 from the neutral position is calculated based on the detection results of the first angle sensor 3 and the second angle sensor 4, and the absolute steering 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 steering shaft 11, the MCU 5 calculates the absolute steering angle so that the detection error of the first angle sensor 3 does not adversely affect the accuracy of the final absolute steering angle.

[0042] In this embodiment, an integer value of the number of rotations of the steering shaft 11 is calculated from the normalized phase difference δ. Next, a method for calculating the integer value of the number of rotations of the steering shaft 11 will be described with reference to FIG.

[0043] <Calculation method for absolute steering 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 φ s 1 is a graph showing, by a solid line, integer values ​​of the number of rotations of the steering shaft 11 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

[0044] When the integer value of the number of rotations of the steering shaft 11 is R, R is obtained by the following equations (3) and (4).

number

number

[0045] 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 steering shaft 11 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.

[0046] 10 is a graph showing the absolute steering angle θ calculated by the following equation (5) from the integer value R of the number of rotations of the steering shaft 11 and the angle φ detected by the second angle sensor 4. The horizontal axis of the graph shown in FIG. 10 indicates the actual steering angle of the steering shaft 11, and the vertical axis of the graph indicates the absolute steering angle θ, which is the rotation angle of the steering shaft 11 calculated by the MCU 5.

number

[0047] As shown in equation (5), the calculation formula for calculating the absolute steering 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 steering shaft 11 can be accurately calculated, the absolute steering 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.

[0048] 11 is a flowchart showing an example of the procedure of a calculation process performed by the MCU 5 to calculate the absolute steering 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 fixed electrode 32 (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).

[0049] 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.

[0050] 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 steering shaft 11 by calculating equation (3) or (4) (Step S12). Then, the MCU 5 calculates the absolute steering angle θ by calculating equation (5) (Step S13). Information on the calculated absolute steering angle θ is transmitted to the steering control device 17 as the detection result of the steering angle.

[0051] <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.

[0052] The amount of change Δ in the normalized phase difference δ when the second gear 22 makes one rotation in accordance with the rotation of the steering shaft 11 is calculated by the following equation (11). The range of variation Δ' in the phase difference over the entire detection range of the absolute steering angle θ by the steering angle detection device 2 is calculated by the following equation (12) using the above-mentioned Rmax.

number

number

[0053] In order to accurately calculate the absolute steering angle θ, the normalized phase difference δ varies with the rotation of the steering shaft 11, and the range of variation must satisfy the following equation (13). Therefore, as shown in the following equation (14), Δ' must be greater than 0 and less than 360, in other words, it must satisfy the following equation (15).

number

number

number

[0054] 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 (14) becomes Equation (16) below.

number

[0055] By modifying equation (16), 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.

[0056] <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 steering shaft 11 using equations (3) and (4) will be described.

[0057] In order to accurately obtain the integer value R of the number of rotations of the steering shaft 11, the fixed multiplication 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 (21) must be satisfied.

number

[0058] Here, the following equations (22) and (23) hold from the above equation (2) and the relationship δ=ψ−φ, and the following equation (24) holds from equations (22) and (23).

number

number

number

[0059] Substituting equation (24) into equation (21) gives equation (25) below.

number

[0060] 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 (25) becomes as shown in the following equation (26) under the condition that it is largest, and by transforming equation (26), the following equation (27) is obtained. Equation (27) 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 steering shaft 11, i.e., the allowable range of the detection errors.

number

number

[0061] (Actions and Effects of the Embodiments) According to the embodiment described above, the first angle sensor 3 is a capacitance type that utilizes the capacitance between the rotating electrode 31 and the fixed electrode 32, while the second angle sensor 4 is a 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 prevent the device from becoming large and to improve the accuracy of the steering angle detection results. Furthermore, by forming the fixed electrode 32 of the first angle sensor 3 as a wiring pattern on the substrate 20, the cost of the first angle sensor 3 can be reduced.

[0062] [Modification 1 of the first angle sensor] Next, with reference to FIGS. 12 and 13 , a first angle sensor 7 according to Modification 1, which is a modification of the first angle sensor 3 of the above embodiment, will be described. FIG. 12( a) is a plan view showing a rotating electrode 71 of the first angle sensor 7 together with the steering shaft 11. FIG. 12( b) is a plan view showing a substrate 20 on which multiple fixed electrodes 72 of the first angle sensor 7 are formed as a wiring pattern. The rotating electrode 71 is disk-shaped with a through-hole 710 formed in the center, and rotates integrally with the first gear 21 and the steering shaft 11, similar to the above embodiment. Although not shown in FIG. 12( b), the substrate 20 also has mounted thereon the MCU 5 and the magnetic field detection element 42 of the second angle sensor 4, which are connected to the multiple fixed electrodes 72, similar to the above embodiment.

[0063] The rotating electrode 71 is made of a non-magnetic conductor, such as aluminum or an aluminum alloy. The rotating electrode 71 may be integrally insert-molded with the first gear 21, or may be made of a conductive resin and two-color-molded with the non-conductive resin that constitutes the first gear 21. The rotating electrode 71 is electrically grounded via the steering shaft 11.

[0064] A plurality of arc-shaped slits 711 to 714 extending along the rotation direction are formed in the rotating electrode 71. In the example shown in Fig. 12(a), a first row of a plurality of slits 711, a second row of a plurality of slits 712, a third row of a plurality of slits 713, and a fourth row of a plurality of slits 714 are formed in the rotating electrode 71. The plurality of slits 711 to 714 are, for example, spaces, but the slits 711 to 714 may be filled with a non-conductive material such as resin.

[0065] When the arc angle of each of the first row of slits 711 is α, the arc angle of each of the second row of slits 712 is half of α, the arc angle of each of the third row of slits 713 is one-fourth of α, and the arc angle of each of the fourth row of slits 714 is one-eighth of α. In the example shown in Figure 12(a), α is 90°. Here, the arc angle is the angle formed by a line segment connecting one end of each of the slits 711-714 to the rotation axis O of the steering shaft 11 and a line segment connecting the other end of each of the slits 711-714 to the rotation axis O of the steering shaft 11.

[0066] The first row of slits 711 is formed inside the second to fourth row of slits 712-714 and is aligned in the circumferential direction centered on the rotational axis O of the steering shaft 11. The second row of slits 712 is formed outside the first row of slits 711 and is aligned in the circumferential direction centered on the rotational axis O of the steering shaft 11. The third row of slits 713 is formed outside the second row of slits 712 and is aligned in the circumferential direction centered on the rotational axis O of the steering shaft 11. The fourth row of slits 714 is formed outside the third row of slits 713 and is aligned in the circumferential direction centered on the rotational axis O of the steering shaft 11.

[0067] Four fixed electrodes 72 are formed on the substrate 20, corresponding to the first row of slits 711, the second row of slits 712, the third row of slits 713, and the fourth row of slits 714. Each fixed electrode 72 has an arc shape centered on the rotation axis O of the steering shaft 11 and is aligned in the radial direction. The arc angle β of the fixed electrode 72 is 1 / 8 of α, the same as the arc angle of each of the fourth row of slits 714.

[0068] The fixed electrodes 72 corresponding to the multiple slits 711 in the first row have a small capacitance between them and the rotating electrode 71 when they face any of the multiple slits 711, and a large capacitance between them and the rotating electrode 71 when they do not face any of the slits 711. Similarly, the fixed electrodes 72 corresponding to the multiple slits 712 in the second row, the multiple slits 713 in the third row, and the multiple slits 714 in the fourth row have a small capacitance between them and the rotating electrode 71 when they face the slits 712, 713, and 714, and a large capacitance between them and the rotating electrode 71 when they do not face any of the slits 712, 713, and 714.

[0069] 13(a) is a graph showing the change in the state of each fixed electrode 72 when the rotating electrode 71 is rotated 360° in the direction of arrow A in FIG. 12(a) from a reference position, where none of the multiple fixed electrodes 72 faces the first through fourth rows of slits 711, 712, 713, and 714. In the graph of FIG. 13, of the four fixed electrodes 72, the fixed electrode 72 corresponding to the multiple slits 711 in the first row is numbered first, and the fixed electrodes 72 corresponding to the multiple slits 712, 713, and 714 in the second through fourth rows are numbered second through fourth, respectively. When each fixed electrode 72 overlaps with a slit 711, 712, 713, or 714, it is considered to be off, and when it does not overlap with a slit 711, 712, 713, or 714, it is considered to be on. As shown in this graph, there are 32 combinations of on / off states for the four fixed electrodes 72, similar to the above embodiment.

[0070] 13(b) is a graph in which the 32 on / off states of the four fixed electrodes 72 are expressed as integers from 0 to 31 as the detection results of the first angle sensor 7 through arithmetic processing by the MCU 5. The MCU 5 regards the on / off states of the four fixed electrodes 72 as binary numerical values, and can express the detection results of the first angle sensor 7 as integers from 0 to 31. As in the above embodiment, the capacitance between the rotating electrode 71 and the four fixed electrodes 72 of the first angle sensor 7 changes by two periods while the steering shaft 11 and the rotating electrode 71 make one rotation. As a result, even when the first angle sensor 7 according to Modification 1 is used, the absolute steering angle θ can be calculated as in the above embodiment.

[0071] [Modification 2 of the first angle sensor] Next, with reference to FIGS. 14 and 15, a first angle sensor 8 according to Modification 2, which is a modification of the first angle sensor 3 of the above embodiment, will be described. FIG. 14(a) is a plan view showing a rotating electrode 81 of the first angle sensor 8 together with the steering shaft 11. FIG. 14(b) is a plan view showing a substrate 20 on which a plurality of fixed electrodes 82 of the first angle sensor 8 are formed as a wiring pattern. The rotating electrode 81 is disk-shaped with a through-hole 810 formed in the center, and rotates integrally with the first gear 21 and the steering shaft 11, as in the above embodiment. In FIG. 14(b), the outline of the rotating electrode 81 is shown by a two-dot chain line.

[0072] The rotating electrode 81 has the same configuration as the rotating electrode 31 of the above embodiment, and integrally includes an annular portion 811 that surrounds the steering shaft 11 and two protruding portions 812 that protrude radially outward from the annular portion 811, with a notch 813 formed between the two protruding portions 812. The rotating electrode 81 is electrically grounded via the steering shaft 11. Although not shown in FIG. 14(b), the MCU 5 and the magnetic field detection element 42 of the second angle sensor 4 that are connected to the multiple fixed electrodes 82 are mounted on the substrate 20, as in the above embodiment.

[0073] In this example, two fixed electrodes 82 are formed on substrate 20. Each fixed electrode 82 is formed in an arc shape extending in the circumferential direction around the rotation axis of steering shaft 11, and the width of fixed electrode 82 in the radial direction perpendicular to rotation axis O of steering shaft 11 varies depending on the circumferential position. Furthermore, the two fixed electrodes 82 are formed within a range of an arc angle of 90° about rotation axis O of steering shaft 11. Hereinafter, one of the two fixed electrodes 82 will be referred to as a first fixed electrode 821, and the other will be referred to as a second fixed electrode 822.

[0074] The radial width of the first fixed electrode 821 gradually narrows from one end to the other end. The radial width of the second fixed electrode 822 gradually widens from one end to the other end of the first fixed electrode 821. The total width of the radial width of the first fixed electrode 821 and the radial width of the second fixed electrode 822 is constant over the entire range of an arc angle of 90°. When the angular position of one end of the first fixed electrode 821 is 0° and the angular position of the other end of the first fixed electrode 821 is 90°, the radial width of the first fixed electrode 821 and the radial width of the second fixed electrode 822 at an angular position of 45° are the same.

[0075] 15(a) and 15(b) are graphs showing the change in capacitance between the first fixed electrode 821 and the rotating electrode 81, and the change in capacitance between the second fixed electrode 822 and the rotating electrode 81 when the rotating electrode 81 rotates 360° in the direction of arrow A in FIG. 14(b) from the reference position (0°) of the position (rotation angle) of the rotating electrode 81 shown in FIG. 14(b). As in the above embodiment, the capacitance between the rotating electrode 81 and the first fixed electrode 821 and between the rotating electrode 81 and the second fixed electrode 822 changes by two periods per rotation of the steering shaft 11 and the rotating electrode 81. The MCU 5 can detect the rotation angle of the rotating electrode 81 from the capacitance between the first fixed electrode 821 and the second fixed electrode 822 and the rotating electrode 81, and can calculate the absolute steering angle θ as in the above embodiment.

[0076] Next, we will explain how to calculate the rotation angle of the rotating electrode 81 using the first angle sensor 8. Here, we will explain how to calculate the rotation angle of the rotating electrode 81 for one period from 0° to 180° out of the range from 0° to 360° shown in Figures 15(a) and 15(b), but the rotation angle of the rotating electrode 81 from 180° to 360° can also be calculated in a similar manner.

[0077] In this calculation method, the rotation angle of the rotating electrode 81 is calculated by dividing the range into two cases: a range where the rotation angle of the rotating electrode 81 is from 0° to 90°, i.e., a range where the overlapping area of ​​the rotating electrode 81 and the first fixed electrode 821 is larger than the overlapping area of ​​the rotating electrode 81 and the second fixed electrode 822, and a range where the rotation angle of the rotating electrode 81 is from 90° to 180°, i.e., a range where the overlapping area of ​​the rotating electrode 81 and the second fixed electrode 822 is larger than the overlapping area of ​​the rotating electrode 81 and the first fixed electrode 821.

[0078] 16(a) is a schematic diagram showing the overlapping state of the rotating electrode 81 with the first fixed electrode 821 and the second fixed electrode 822 when the rotation angle of the rotating electrode 81 is less than 90°. FIG. 16(b) is a schematic diagram showing the overlapping state of the rotating electrode 81 with the first fixed electrode 821 and the second fixed electrode 822 when the rotation angle of the rotating electrode 81 is 90° or more. Whether the rotation angle of the rotating electrode 81 is less than 90° or greater than 90° can be determined by whether the value calculated by the following formula (31) is less than 0.5 or greater than 0.5, where A is the overlapping area of ​​the rotating electrode 81 and the first fixed electrode 821 and B is the overlapping area of ​​the rotating electrode 81 and the second fixed electrode 822.

number

[0079] Hereinafter, the overlapping area between the rotating electrode 81 and the first fixed electrode 821 will be referred to as a first opposing area A, and the overlapping area between the rotating electrode 81 and the second fixed electrode 822 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 81 and the first fixed electrode 821. The second opposing area B can be calculated from the capacitance between the rotating electrode 81 and the second fixed electrode 822.

[0080] (When the rotation angle of the rotating electrode 81 is less than 90°) As shown in FIG. 16(a), when the maximum width of the first fixed electrode 821 and the second fixed electrode 822 is h and the rotation angle of the rotating electrode 81 is x, the first opposing area A is expressed by the following formula (32), and the second opposing area B is expressed by the following formula (33).

number

number

[0081] Furthermore, the maximum sum of the overlapping areas of the rotating electrode 81 and the first fixed electrode 821 and the second fixed electrode 822, that is, the sum of the maximum value of the first opposing area A and the maximum value of the second opposing area B, is 90h, and 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 (34) using equations (32) and (33).

number

[0082] As a result, x can be calculated by the following formula (35).

number

[0083] (When the rotation angle of the rotating electrode 81 is 90° or more) As shown in FIG. 16(b), when the maximum width of the first fixed electrode 821 and the second fixed electrode 822 is h and the rotation angle of the rotating electrode 81 is x, the first opposing area A is expressed by the following formula (36), and the second opposing area B is expressed by the following formula (37).

number

number

[0084] Furthermore, the maximum sum of the overlapping areas of the rotating electrode 81 and the first fixed electrode 821 and the second fixed electrode 822, 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, and 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 (38) using equations (36) and (37).

number

[0085] As a result, x can be calculated by the following equation (39).

number

[0086] The shapes of the first fixed electrode 821 and the second fixed electrode 822 shown in FIG. 14(b) may be modified as shown in FIG. 17. In the example shown in FIG. 17, the first fixed electrode 821 is composed of an inner portion 821a and an outer portion 821b that sandwich the second fixed electrode 822 in the radial direction, and the inner portion 821a and the outer portion 821b are electrically connected at one end of the first fixed electrode 821. The inner portion 821a and the outer portion 821b have gradually narrower radial widths from one end to the other end of the first fixed electrode 821. The second fixed electrode 822 has gradually wider radial widths from one end to the other end of the first fixed electrode 821. Even if the shapes of the first fixed electrode 821 and the second fixed electrode 822 are modified in this way, the rotation angle of the rotating electrode 81 can be calculated in the same manner as described above.

[0087] (Summary of embodiments and modifications) Next, the technical ideas grasped from the above-described embodiment and modified examples will be described by using the reference numerals and symbols in the embodiment and modified examples. However, the reference numerals in the following description do not limit the scope of the claims to the configurations specifically shown in the embodiment.

[0088] [1] A steering angle detection device (2) for detecting a steering angle, which is a rotation angle of a steering shaft (11) connected to a steering wheel (10), includes a first gear (21) and a second gear (22) that rotate at different speeds in accordance with the rotation of the steering shaft (11), a first angle sensor (3, 7, 8) that detects the rotation angle of the first gear (21), a second angle sensor (4) that detects the rotation angle of the second gear (22), and a calculation unit ( and a MCU (MCU5), wherein the first angle sensor (3, 7, 8) has a rotating electrode (31, 71, 81) that rotates integrally with the first gear (21) and a fixed electrode (32, 72, 82) that is arranged opposite to the rotating electrode (31, 71, 81), and the capacitance between the rotating electrode (31, 71, 81) and the fixed electrode (32, 72, 82) changes with rotation of the steering shaft (11), and the calculation unit (5) calculates the absolute angle of the steering angle from the magnitude of the capacitance as a detection result of the first angle sensor (3, 7, 8).

[0089] [2] The steering angle detector (2) according to the above [1], wherein the fixed electrode (32, 72, 82) is formed on a substrate (2) disposed opposite the rotary electrode (31, 71, 81).

[0090] [3] The steering angle detection device (2) according to the above [1] or [2], wherein the first angle sensor (3) has a plurality of the fixed electrodes (32) arranged along the rotation direction of the rotary electrode (31), and the number of the fixed electrodes (32) facing the rotary electrode (31) changes depending on the rotation position of the steering shaft (11).

[0091] [4] The steering angle detection device (2) according to the above [1] or [2], wherein the first angle sensor (7) has a plurality of arc-shaped slits (711, 712, 713, 714) formed in the rotating electrode (71) and extending along the rotation direction, and a plurality of the fixed electrodes (72) are provided corresponding to each of the plurality of arc-shaped slits (711, 712, 713, 714).

[0092] [5] The steering angle detection device (2) according to the above [1] or [2], wherein the first angle sensor (8) has the fixed electrode (82) formed in an arc shape extending in a circumferential direction around the rotation axis of the steering shaft (11), and the width of the fixed electrode (82) in a radial direction perpendicular to the rotation axis (O) of the steering shaft (11) varies depending on the position in the circumferential direction.

[0093] [6] The steering angle detection device (2) according to [1] above, wherein the capacitance between the rotary electrode (31, 71, 81) and the plurality of fixed electrodes (32, 72, 82) of the first angle sensor (3, 7, 8) changes over a plurality of periods during one rotation of the steering shaft (11).

[0094] [7] The steering angle detection device (2) described in [1] above, wherein the calculation unit (5) calculates an integer value (R) of the number of rotations of the steering shaft (11) from a neutral position based on detection results of the first angle sensor (3, 7, 8) and the second angle sensor (4), and calculates an absolute angle of the steering angle based on the integer value (R) and the detection result of the second angle sensor (4).

[0095] 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]

[0096] 1...Steering device 10...Steering wheel 11...Steering shaft 2...Steering angle detection device 20... Board 21... First gear 22...Second gear 3...First angle sensor 4... Second angle sensor 5... MCU (calculation unit) 31, 71, 81...Rotating electrodes 32, 72, 82...Fixed electrodes 711, 712, 713, 714...Slits O...Rotation axis

Claims

1. A steering angle detection device for detecting a steering angle, which is a rotation angle of a steering shaft connected to a steering wheel, a first gear and a second gear that rotate at different speeds in accordance with rotation of the steering shaft; 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 an absolute angle of the steering angle based on detection results of the first angle sensor and the second angle sensor, the first angle sensor has a rotary electrode that rotates integrally with the first gear and a fixed electrode that is disposed opposite to the rotary electrode, and an electrostatic capacitance between the rotary electrode and the fixed electrode changes with rotation of the steering shaft; the calculation unit calculates the absolute angle of the steering angle using the magnitude of the capacitance as the detection result of the first angle sensor. Steering angle detection device.

2. the fixed electrode is formed on a substrate disposed opposite the rotating electrode; The steering angle detection device according to claim 1 .

3. the first angle sensor has a plurality of the fixed electrodes arranged along a rotation direction of the rotary electrode, and the number of the fixed electrodes facing the rotary electrode changes depending on the rotation position of the steering shaft; The steering angle detection device according to claim 1 or 2.

4. The first angle sensor has a plurality of arc-shaped slits formed in the rotary electrode and extending along the rotation direction, and a plurality of the fixed electrodes are provided corresponding to the plurality of arc-shaped slits, respectively. The steering angle detection device according to claim 1 or 2.

5. the first angle sensor has a fixed electrode formed in an arc shape extending in a circumferential direction around a rotation axis of the steering shaft, and a width of the fixed electrode in a radial direction perpendicular to the rotation axis of the steering shaft varies depending on a position in the circumferential direction; The steering angle detection device according to claim 1 or 2.

6. the capacitance between the rotary electrode and the plurality of fixed electrodes of the first angle sensor changes by a plurality of periods during one rotation of the steering shaft; The steering angle detection device according to claim 1 .

7. the calculation unit calculates an integer value of the number of rotations of the steering shaft from a neutral position based on detection results of the first angle sensor and the second angle sensor, and calculates an absolute angle of the steering angle based on the integer value and the detection result of the second angle sensor. The steering angle detection device according to claim 1 .

Images