Tire angle correction device

Abstract

To provide a tire angle correction device that is able to correct a tire angle during traveling of an independently steered vehicle.SOLUTION: In an independently steered vehicle, steering torque output from a steering motor in accordance with a target tire angles θ*1-θ*4 is transmitted to each tire via a torque transmission device, and each tire is steered. A target tire angle calculation control unit 25 of a tire angle correction device 20 calculates a target tire angle θ*1-θ*4 of each tire, based on a moving-direction instruction value instructed from a moving-direction instruction device 15, and gives an instruction to the steering motor. During traveling of the vehicle, the target tire angle calculation control unit 25 acquires respective detection tire angles θs1-θs4 of the tires detected by tire angle sensors 651-654 and 671-674 and performs feedback control on the target tire angles θ*1-θ*4. Further, the target tire angle calculation control unit 25 corrects the target tire angles θ*1-θ*4 in accordance with tire loads Lt1-Lt4 applied to the respective tires detected by the tire load sensors 661-664 and 681-684.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] This invention relates to a tire angle correction device. [Background technology]

[0002] Conventional techniques for adjusting the tire angle of a vehicle are known.

[0003] For example, the steering device disclosed in Patent Document 1 includes a manual toe angle adjustment mechanism between the steering motor (electric motor unit) and the tire (wheel) so that the toe angle can be easily adjusted. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-34952 [Overview of the project] [Problems that the invention aims to solve]

[0005] The technology described in Patent Document 1 is merely a mechanical toe angle adjustment mechanism and does not correct for deviations in tire angle caused by the output of the steering motor while the vehicle is running after toe angle adjustment. Furthermore, the steering device described in Patent Document 1 is not equipped with a tire angle sensor, nor does it address malfunctions of the tire angle sensor in independently steering vehicles.

[0006] In independently steered vehicles, where each wheel can be steered independently, it is necessary to detect the actual tire angle during driving and use feedback control to optimally control the tire angle according to the driving conditions. Methods for detecting the actual tire angle include using a tire angle sensor such as an encoder, or estimating it from the detected value of the steering motor's angle sensor. In this specification, the term "detected tire angle" includes both the tire angle detected by the tire angle sensor and the tire angle estimated from the detected value of the motor angle sensor.

[0007] However, if the tire angle sensor is improperly installed, or if gear tooth skipping occurs in the torque transmission device between the steering motor and the tire due to external force or the like during traveling when using the angle sensor of the steering motor, the correct actual tire angle cannot be detected. Consequently, feedback control is performed based on an erroneous detected tire angle, which results in increased traveling loss and occurrence of unnecessary vehicle behavior such as yaw turning. As described above, when the tire angle detected by the tire angle sensor deviates from the actual tire angle, the prior art cannot correct the tire angle.

[0008] The present invention has been made in view of the foregoing points, and an object of the present invention is to provide a tire angle correction device capable of correcting a tire angle while an independently steerable vehicle is traveling. [[Means for Solving the Problems]]

[0009] The tire angle correction device according to the present invention is applied to an independently steerable vehicle (100) in which three or more tires (91-94) can be steered independently, steering torque output by steering motors (71-74) in accordance with target tire angles (θ * 1-θ * 4) is transmitted to each tire via torque transmission devices (81-84) to steer each tire, and is a device that calculates and corrects target tire angles.

[0010] This tire angle correction device includes a target tire angle calculation control unit (25). The target tire angle calculation control unit calculates the target tire angle of each tire based on a movement direction instruction value instructed by a movement direction instruction device (15), and instructs the steering motor of the calculated target tire angle.

[0011] While the vehicle is traveling, the target tire angle calculation control unit acquires detected tire angles (θs1-θs4) of the respective tires detected by tire angle sensors (651-654, 671-674), and performs feedback control on the target tire angles based on the detected tire angles.

[0012] Furthermore, the target tire angle calculation control unit 25 corrects the target tire angle according to the tire load (Lt1-Lt4) applied to each tire detected by the tire load sensors (661-664, 681-684). Preferably, the target tire angle calculation control unit corrects the target tire angle in a direction that reduces the absolute value of the tire load.

[0013] In this invention, the tire angle can be corrected while an independently steering vehicle is in motion. [Brief explanation of the drawing]

[0014] [Figure 1] A block diagram of an independently steering vehicle equipped with a tire angle correction device according to the first embodiment. [Figure 2] Block diagram of an independently steering vehicle equipped with a tire angle correction device according to the second embodiment. [Figure 3] A diagram illustrating the vehicle operation specific to vehicles with independent four-wheel steering. [Figure 4] A diagram showing tire angles during cornering based on the Ackermann theory. [Figure 5] A diagram showing the state where the tires are parallel to the direction of travel while driving in a straight line. [Figure 6] A diagram showing a state where the tires are tilted relative to the direction of travel while driving in a straight line. [Figure 7] This diagram shows the expected vehicle behavior when the right front wheel tire angle sensor malfunctions. [Figure 8] This diagram shows the simulation results of the tire load (tire torque) generated on each tire when the tire angle sensor on the right front wheel malfunctions. [Figure 9] Block diagrams of the tire angle correction device according to the first and second embodiments. [Figure 10] A block diagram illustrating angular feedback control. [Figure 11] A diagram illustrating the correction of the target tire angle. [Figure 12] This diagram shows that the abnormality detection threshold is set variably according to the target tire angle. [Figure 13] Flowchart of the process performed by the tire angle correction device. [Figure 14] A diagram illustrating the operation of an SBW vehicle. [Modes for carrying out the invention]

[0015] Embodiments of the tire angle correction device will be described based on the drawings. The following first and second embodiments will be collectively referred to as "this embodiment." The tire angle correction device of this embodiment is a device that calculates and corrects the target tire angle in an independently steered vehicle in which three or more tires can be steered independently, typically a four-wheel independently steered vehicle. It functions as a "vehicle driving control device" in that it constantly calculates the target tire angle and instructs the steering motor while the vehicle is running. However, in this embodiment, we will focus on the function of correcting the target tire angle in particular and refer to it as a "tire angle correction device."

[0016] (First and second embodiments) Referring to Figures 1 to 4, the independently steering vehicle 100 equipped with the tire angle correction device 20 of the first and second embodiments, and the configuration of the tire angle correction device 20 will be described. The first and second embodiments differ only in the configuration of the tire angle sensor and tire load sensor used in the vehicle 100; otherwise, they are common and will be described together.

[0017] Figure 1 shows an independently steering vehicle 100 equipped with the tire angle correction device 20 of the first embodiment, and Figure 2 shows an independently steering vehicle equipped with the tire angle correction device 20 of the second embodiment. In the independently steering vehicle 100, the four tires 91-94 can be steered independently. The left front wheel 91 is labeled "FL", the right front wheel 92 is labeled "FR", the left rear wheel 93 is labeled "RL", and the right rear wheel 94 is labeled "RR". The symbols for each element below, and the numbers "1"-"4" at the end of the angle and load symbols, correspond to the FL, FR, RL, and RR tires 91-94, respectively. The abnormality notification device 30 and vehicle speed detection device 40, shown in dashed boxes in Figures 1 and 2, are optional configurations that can be adopted as appropriate, and will be described later with reference to Figure 9.

[0018] Vehicle 100 is equipped with steering motors 71-74 corresponding to each tire 91-94, and torque transmission devices 81-84 consisting of belts, gears, etc. The steering torques T1-T4 output by the steering motors 71-74 are transmitted to each tire 91-94 via the torque transmission devices 81-84, causing each tire 91-94 to steer. The steering motors 71-74 are electromechanical integrated motors, in which a mechanical motor section including a stator and rotor around which windings are wound, and a motor drive unit that controls the drive current supplied to the windings are integrated. For example, the motor section is composed of a three-phase brushless motor.

[0019] The tire angle correction device 20 adjusts the target tire angle θ of each tire 91-94 based on the direction of movement indicated value from the direction of movement indicator device 15. * 1-θ * Calculate 4 and instruct the steering motors 71-74. The steering motors 71-74 will adjust the actual tire angle of each tire 91-94 (hereinafter referred to as "actual tire angle") to the target tire angle θ. * 1-θ * The drive current is controlled to approach 4, outputting steering torques T1-T4. The tire angle is represented with a neutral position parallel to the vehicle's longitudinal axle as 0, and counterclockwise rotation as positive, and clockwise rotation from the neutral position as negative.

[0020] The rotation angle of the steering motors 71-74 is detected by motor angle sensors 651-654, and the motor current flowing through the windings is detected by motor current sensors 661-664. Using this information, the steering motors 71-74 output steering torques T1-T4 through current feedback control. The operation of the steering motors 71-74 themselves is guaranteed by initial checks, etc., and it is assumed that the steering torques T1-T4 are output normally as instructed.

[0021] In the first embodiment shown in Figure 1, tire angle sensors 671-674, such as encoders, that directly detect the tire angle of each tire 91-94, and tire load sensors 681-684, such as load cells, that directly detect the tire load applied to each tire 91-94 are provided. The tire load includes longitudinal forces and tire torque. For example, since tire torque may be defined as positive or negative depending on the direction, the magnitude of the tire load is expressed as an absolute value.

[0022] The tire angle correction device 20 acquires the detected tire angles θs1-θs4 of each tire detected by the tire angle sensors 671-674, and the tire load Lt1-Lt4 of each tire detected by the tire load sensors 681-684. The detected tire angles θs1-θs4 are also fed back to the steering motors 71-74.

[0023] In the second embodiment shown in Figure 2, the tire angles θs1-θs4 and tire loads Lt1-Lt4 are estimated from the detected motor angles and motor currents, rather than being directly detected, and are acquired by the tire angle correction device 20. In other words, in the second embodiment, the tire angle sensor is composed of motor angle sensors 651-654 that detect the rotation angles of the steering motors 71-74. Based on the characteristics of the torque transmission devices 81-84, such as the gear ratio, the tire angles θs1-θs4 are estimated from the rotation angles of the steering motors 71-74.

[0024] In the second embodiment, the tire load sensor is comprised of motor current sensors 661-664 that detect the motor current flowing through the windings of the steering motors 71-74. Since motor current and motor torque are correlated, and motor torque and tire torque are correlated, the tire loads Lt1-Lt4 are estimated from the motor current of the steering motors 71-74 based on the characteristics of the torque transmission devices 81-84.

[0025] In the second embodiment, the detected values ​​of the motor angle sensors 651-654 and the motor current sensors 661-664 are used not only for feedback control of the steering motors 71-74 but also as information for the tire angle correction device 20. Compared to the first embodiment, dedicated tire angle sensors 671-674 and tire load sensors 681-684 are not required, thus reducing the number of parts in the vehicle 100.

[0026] Here, the conversion from motor angle to tire angle θs1-θs4, and the conversion from motor current to tire load Lt1-Lt4 may be performed by the motor angle sensors 651-654 and motor current sensors 661-664, or by the tire angle correction device 20. Furthermore, as an intermediate form between the first and second embodiments, only one of the tire angle sensors or tire load sensors may be composed of either a motor angle sensor or a motor current sensor.

[0027] Hereinafter, the term "detected tire angle" will include the tire angle directly detected by the tire angle sensors 671-674 of the first embodiment, and the tire angle estimated from the detected value of the motor angle sensor 651-654 of the second embodiment. Furthermore, the first and second embodiments will be treated collectively, and the symbols of the tire angle sensors, including the motor angle sensor, will be denoted as "651-651, 671-674," and the symbols of the tire load sensors, including the motor current sensor, will be denoted as "661-664, 681-684."

[0028] Next, before describing the configuration of the tire angle correction device 20, we will discuss the issues related to the detected tire angle of the tire angle sensor that may occur in the independently steering vehicle 100, and the target tire angle θ. * 1-θ * The significance of correcting point 4 will be explained with reference to Figures 3 to 8. Conventionally, in typical vehicles, the left and right pairs of tires are mechanically connected via links, and the tires steer in response to steering. In the future, it is expected that this will evolve into steer-by-wire vehicles, where the steering and the links between the left and right pairs of tires are mechanically separated, and four-wheel independent steering vehicles, where the left and right rear wheels, in addition to the left and right front wheels, can also be steered independently.

[0029] As shown in Figure 3, the four-wheel independent steering vehicle 100 can achieve vehicle motions such as small-radius turning, diagonal movement, and lateral movement. In the diagram of small-radius turning, symbol C indicates the turning center. Since these vehicle motions are enabled, the vehicle is advantageous for traveling on narrow roads, parallel parking and the like. In the following figures, the front side of the independent steering vehicle 100 is illustrated in a streamlined form. The characters "front / rear" and "center of gravity" of the vehicle are only shown in Figure 3 and are omitted in the following figures.

[0030] As shown in Figure 4, the four-wheel independent steering vehicle 100 can perform turning based on the Ackermann theory. The target tire angles θ of the respective tires 91 to 94 * 1-θ * 4 are set such that the width center line of the tire is tangent to a turning circle centered on the turning center C, in other words, the width center line of the tire is perpendicular to the straight line connecting the turning center C and the tire center.

[0031] Here, attention is focused on the tire angle during traveling and its control purpose. During straight traveling, in order to minimize traveling loss to maximize the power consumption efficiency of the electric vehicle, as shown in Figure 5, it is preferable to set the tire angles θ1 to θ4 of all tires 91 to 94 to zero. When the tire is parallel to the traveling direction, the direction of tire rolling resistance is parallel to the traveling direction and opposite to the traveling direction.

[0032] In contrast, in the toe-in state shown in Figure 6, the tires 91 and 92 are inclined with respect to the traveling direction, and the tire angles θ1 and θ2 are not zero (θ1<0, θ2>0). While toe-in stabilizes the straight-line performance of the vehicle 100, the direction of tire rolling resistance is inclined with respect to the traveling direction, and a sideslip force is generated in a direction orthogonal to the width center line of the tire. The resultant force of the tire rolling resistance and the sideslip force is parallel to the traveling direction and opposite to the traveling direction. This sideslip force (frictional force in the tire lateral direction) increases traveling loss.

[0033] In order to appropriately control the tire angles in accordance with the traveling state as described above, the actual tire angles are detected by the tire angle sensors 651 to 654 and 671 to 674, and the target tire angles θ * 1-θ *Feedback control is required for 4. This control assumes that the actual tire angles θ1-θ4 and the detected tire angles θs1-θs4 match. However, if the tire angle sensors 651-654 and 671-674 are improperly installed, or if the motor angle sensor 651-654 is used and external forces during driving cause gear skipping in the torque transmission device 81-84, the correct actual tire angles θ1-θ4 will not be detected. As a result, a discrepancy will occur between the actual tire angles θ1-θ4 and the detected tire angles θs1-θs4.

[0034] In the example shown in Figure 7, the actual tire angle θ2 and the detected tire angle θs2 are diverging due to abnormalities in the tire angle sensors 652 and 672 of the right front wheel 92. In feedback control, the target tire angle θ * Although the system intends to drive straight by setting the value of 2 to zero, in reality, the right front wheel (92) continues to point inward, causing yaw turning. In this way, feedback control is performed based on an incorrectly detected tire angle, resulting in increased driving losses and the occurrence of unnecessary vehicle behaviors such as yaw turning.

[0035] Here, an abnormality detection threshold Ltth is set as the upper limit of the range in which the absolute values ​​of the tire load |Lt1|-|Lt4| do not pose a practical problem. The absolute values ​​of the tire loads of the tires other than the right front wheel 92, |Lt1|, |Lt3|, and |Lt4|, are less than the abnormality detection threshold Ltth. On the other hand, the absolute value of the tire load of the right front wheel 92, |Lt2|, is greater than or equal to the abnormality detection threshold Ltth. In the figure, the block arrow representing the absolute value of the tire load of the right front wheel 92, |Lt2|, is drawn larger than the block arrows for the other tires 91, 93, and 94.

[0036] From this, it can be inferred that for tires 91, 93, and 94 other than the right front wheel 92, the actual tire angles θ1, θ3, and θ4 match the detected tire angles θs1, θs3, and θs4 within the acceptable range, and that the tire angle sensors 651, 653, 654, 671, 673, and 674 are functioning normally. On the other hand, for the right front wheel 92, the actual tire angle θ2 and the detected tire angle θs2 deviate beyond the acceptable range, and it can be inferred that the tire angle sensors 652 and 672 are malfunctioning.

[0037] Figure 8 shows the relationship between tire angle and tire load (tire torque) (simulation results) when there is a difference between the actual tire angle θ2 and the detected tire angle θs2 of the right front wheel 92 during constant speed straight driving. Target tire angles θ of the left front (FL) wheel 91, left rear (RL) wheel 93, and right rear (RR) wheel 94, other than the right front (FR) wheel 92. * 1, θ * 3, θ * 4. The actual tire angles θ1, θ3, θ4, and the detected tire angles θs1, θs3, θs4 are all 0 [deg]. If the actual tire angle θ2 of the right front wheel 92 is 0 [deg], then all tire loads Lt1-Lt4 will be 0 [Nm].

[0038] However, if an error occurs in the detected tire angle θs2 of the right front wheel 92, feedback control will work to return the right front wheel 92 to the straight-ahead direction, targeting the tire angle θ * The actual tire angle θ2 will be a value that deviates from 0. Accordingly, the tire loads Lt1-Lt4 change linearly. In Figure 8, the toe-out case is shown on the right and the toe-in case is shown on the left, relative to the baseline where the tire angle is zero. The absolute value of the tire load of the right front wheel 92, |Lt2|, is larger than the absolute values ​​of the tire loads of the other tires 91, 93, and 94, |Lt1|, |Lt3|, and |Lt4|.

[0039] For example, if the absolute value of the tire load |Lt2| of the right front wheel 92 is greater than or equal to the abnormality detection threshold Ltth, then it is determined that there is an abnormality in that the detected tire angle θs2 of the right front wheel 92's tire angle sensors 652 and 672 deviates from the actual tire angle θ2. Then, the target tire angle θ of the right front wheel 92 is set by an angle equivalent to the difference between the actual tire angle θ2 and the detected tire angle θs2. * By correcting for 2, the actual tire angle θ2 approaches 0 [deg]. As a result, the absolute value of the tire load on the right front wheel 92, |Lt2|, is reduced to approach 0.

[0040] Based on this concept, the tire angle correction device 20 of this embodiment detects tire loads Lt1-Lt4 during driving and determines abnormalities in tire angle sensors 651-654 and 671-674. Furthermore, for tires where an abnormality in the tire angle sensor has been determined, the device corrects the target tire angle to reduce the absolute value of the tire load, thereby bringing the actual tire angle closer to the original target value and preventing increased driving losses and the occurrence of unnecessary vehicle behavior.

[0041] Next, the configuration of the tire angle correction device 20 will be described with reference to Figures 9 to 12. As shown in Figure 9, the tire angle correction device 20 comprises a target tire angle calculation control unit 25, a tire angle sensor abnormality determination unit 26, and, as an optional configuration, a corrected tire angle storage unit 27. The tire angles θs1-θs4 detected by tire angle sensors 651-651 and 671-674 are input to the target tire angle calculation control unit 25. The tire loads Lt1-Lt4 detected by tire load sensors 661-664 and 681-684 are input to the target tire angle calculation control unit 25 and the tire angle sensor abnormality determination unit 26.

[0042] The target tire angle calculation control unit 25, as a basic function of the tire angle correction device 20, determines the target tire angle θ based on the movement direction indicator value indicated by the movement direction indicator device 15. * 1-θ * The system calculates 4 and instructs the steering motors 71-74. The target tire angle calculation control unit 25 also acquires the detected tire angles θs1-θs4 of each tire detected by the tire angle sensors 651-654 and 671-674, and sets the target tire angle θ * 1-θ * Feedback control is applied to 4.

[0043] Figure 10 shows the configuration of the angle feedback control. The sign and angle symbol of the element ending in "1" corresponding to the left front wheel 91 are shown as representative. The target tire angle calculation control unit 25 includes a correction calculator 255, a deviation calculator 256, an adder 257, a multiplier 258, etc. The deviation calculator 256 is the target tire angle θ * The tire angle deviation Δθ1 is calculated between 1 and the detected tire angle θs1 detected by tire angle sensors 651 and 671. The adder 257 calculates the target tire angle θ* 1 is added to the tire angle deviation Δθ1. The multiplier 258 multiplies the value calculated by the adder 257 by a gain and outputs it to the steering motor 71.

[0044] As described later, when an abnormality in the tire angle sensor is determined based on the tire load Lt1 detected by the tire load sensors 661 and 681, the corrected tire angle is input to the correction calculator 255. In the example in Figure 10, the corrected tire angle is subtracted in the correction calculator 255, but the addition or subtraction in the correction calculator 255 may be changed as appropriate depending on the definition of positive or negative for the corrected tire angle.

[0045] The tire angle sensor abnormality determination unit 26 determines that if the absolute value of the tire load |Lt1|-|Lt4| for any tire is greater than or equal to the abnormality determination threshold Ltth, then the tire angle detected by the corresponding tire angle sensor is abnormal, meaning it deviates from the actual tire angle. When the tire angle sensor abnormality determination unit 26 determines that there is an abnormality in the tire angle sensor, it transmits an abnormality flag and a correction instruction to the target tire angle calculation control unit 25.

[0046] The target tire angle calculation control unit 25 calculates the target tire angle θ according to the tire load Lt1-Lt4. * 1-θ * Correction 4. Specifically, when the tire angle sensor abnormality determination unit 26 determines that the tire angle sensor is abnormal, the target tire angle calculation control unit 25 receives an abnormality flag and a correction instruction, and for the corresponding tire, it reduces the absolute value of the tire load |Lt1|-|Lt4| by adjusting the target tire angle θ. * 1-θ * Correct 4. Target tire angle θ * 1-θ * The correction in step 4 continues until the absolute value of the tire load |Lt1|-|Lt4| falls below the abnormality detection threshold Ltth, and the abnormality flag disappears, i.e., until the abnormality is resolved.

[0047] In Figure 11, the white circles and squares indicate the actual tire angle and detected tire angle before correction, while the hatched circles and squares indicate the actual tire angle and detected tire angle after correction. Let α be the actual tire angle before correction, and β be the actual tire angle after correction (0 < β < α). Assuming straight-line driving, the actual tire angle before correction is tilted relative to the direction of travel, and the tire load exceeds the abnormality detection threshold Ltth. However, since the detected tire angle is the same as the target tire angle, 0 [deg], this state is maintained by feedback control.

[0048] When the tire angle sensor abnormality detection unit 26 detects an abnormality and issues a correction instruction, the target tire angle calculation control unit 25 corrects the target tire angle in the negative direction until the corrected actual tire angle falls below the abnormality detection threshold. The detected tire angle shifts in the negative direction while maintaining the difference with the actual tire angle. At this time, the amount of angle change (α-β) from the actual tire angle before correction to the actual tire angle after correction, i.e., when the abnormality detection is resolved, is defined as the "corrected tire angle," which is the amount of correction relative to the target tire angle. The corrected tire angle storage unit 27 stores the corrected tire angle.

[0049] In this embodiment, focusing on the correlation between the detected tire angle and the actual tire angle and the tire load during driving, the target tire angle calculation control unit 25 calculates the target tire angle θ according to the tire load Lt1-Lt4. * 1-θ * 4 is corrected. Specifically, the target tire angle calculation control unit 25 adjusts the target tire angle θ in a direction that reduces the absolute value of the tire load |Lt1|-|Lt4|. * 1-θ * Correction 4. This allows the tire angle correction device 20 of this embodiment to correct the tire angle while the independently steering vehicle 100 is in motion.

[0050] Furthermore, in this embodiment, the target tire angle correction is not performed at all times. Instead, the tire angle sensor abnormality determination unit 26 instructs the target tire angle calculation control unit 25 to correct the angle only when the absolute value of the tire load |Lt1|-|Lt4| is greater than or equal to a predetermined abnormality determination threshold Ltth. In other words, even if the detected tire angle and the actual tire angle do not perfectly match, no correction is performed if the angle difference is within an acceptable range. This reduces the computational load.

[0051] Furthermore, if the tire angle sensors 651-654 and 671-674 malfunction, the detected tire angle will remain inaccurate unless corrected using appropriate equipment and procedures, and correction control will be repeatedly performed. Therefore, the corrected tire angle at the time of the initial malfunction is stored in the corrected tire angle storage unit 27, and thereafter, the target tire angle calculation control unit 25 uses the corrected tire angle stored in the corrected tire angle storage unit 27 to determine the target tire angle θ. * 1-θ * Calculate 4. This will suppress the occurrence of correction control in subsequent cycles.

[0052] Furthermore, as shown in Figure 12, the abnormality detection threshold is set variably according to the target tire angle. The tire load caused by deviations in the detected tire angle differs between straight-line driving and turning states. Therefore, by setting the abnormality detection threshold variably according to the target tire angle, the occurrence of false detections can be reduced, and the sensitivity of abnormality detection can be increased.

[0053] The tire angle correction device 20 of this embodiment is preferably mounted on a vehicle 100 equipped with an abnormality notification device 30 that notifies the driver of any abnormalities. When the tire angle sensor abnormality determination unit 26 determines that there is an abnormality in the tire angle sensor, it notifies the abnormality notification device 30. The abnormality notification device 30 notifies the driver of the abnormality, which can encourage them to have maintenance performed at a dealer or other facility at an early stage.

[0054] The tire angle correction device 20 of this embodiment is preferably mounted on a vehicle equipped with a vehicle speed detection device 40 that detects vehicle speed. The vehicle speed is input to the target tire angle calculation control unit 25 and the tire angle sensor abnormality determination unit 26. Only when the vehicle speed is within a predetermined range, the tire angle sensor abnormality determination unit 25 makes an abnormality determination, and the target tire angle θ is determined by the target tire angle calculation control unit 26. * 1-θ * Correction 4 is performed. When turning at high speed, the absolute value of the target tire angle is smaller than when turning at low speed. Also, when turning at high speed, the tires are more likely to slip, and the impact on tire load due to the discrepancy between the actual tire angle and the detected tire angle becomes smaller. Therefore, by excluding the high-speed range and performing abnormality detection only at a predetermined vehicle speed or below, false detections can be reduced.

[0055] The flowchart in Figure 13 shows the processing performed by the tire angle correction device 20. In the flowchart explanation, the symbol "S" represents a step. Steps S3, S4, S7, and S10, indicated by the dashed lines, may not be performed depending on the configuration of the tire angle correction device 20 or the vehicle 100. This process is repeated each time a direction of movement indicator value is input while the vehicle 100 is in motion.

[0056] In S1, the target tire angle calculation control unit 25 calculates the target tire angle θ of each tire based on the movement direction indicator value. * 1-θ * Calculate 4. If the corrected tire angle has been stored in the corrected tire angle storage unit 27 in the previous routine, the target tire angle calculation control unit 25 uses the stored corrected tire angle to calculate the target tire angle θ. * 1-θ * Calculate 4. In S2, the drive current of the steering motors 71-74 is controlled so that the detected tire angle θs1-θs4 becomes the target tire angle θ * 1-θ * Feedback control is used to bring the value closer to 4.

[0057] In S3, the tire angle sensor abnormality determination unit 26 determines the target tire angle θ * 1-θ *The abnormality detection threshold is set variably according to 4. In a vehicle 100 equipped with a vehicle speed detection device 40, in S4 it is determined whether the vehicle speed is within a predetermined range, for example, below the vehicle speed threshold. If NO in S4, for example, if the vehicle is traveling at high speed, the routine ends. If YES in S4, the process moves to S5, and the tire angle sensor abnormality detection unit 26 obtains tire loads Lt1-Lt4 from tire load sensors 661-664 and 681-684.

[0058] In S6, the tire angle sensor abnormality determination unit 26 determines whether the absolute value of the tire load |Lt1|-|Lt4| for each tire 91-94 is greater than or equal to the abnormality determination threshold Ltth. If the result is NO for all tires 91-94 in S6, the routine ends. If the result is YES for any tire in S6, the corresponding tire angle sensors 651-654 and 671-674 are determined to be abnormal.

[0059] In a vehicle 100 equipped with an abnormality notification device 30, in S7, when the tire angle sensor abnormality determination unit 26 determines that there is an abnormality in the tire angle sensor, it notifies the abnormality notification device 30, which then alerts the driver to the abnormality. In S8, the tire angle sensor abnormality determination unit 26 outputs an abnormality flag and a correction instruction to the target tire angle calculation control unit 25.

[0060] In S9, the target tire angle calculation control unit 25 determines that for tires where the tire angle sensors 651-654 and 671-674 have detected abnormalities, it will reduce the target tire angle θ in a direction that reduces the absolute value of the tire load |Lt1|-|Lt4|. * 1-θ * Correction is performed on 4. This correction continues until the absolute value of the tire load |Lt1|-|Lt4| falls below the abnormality detection threshold Ltth. In addition, in a configuration in which the tire angle correction device 20 is equipped with a corrected tire angle storage unit 27, in S10 the corrected tire angle storage unit 27 stores the corrected tire angle.

[0061] Finally, referring to Figure 14, the operation of a steer-by-wire (SBW) system vehicle (hereinafter referred to as "SBW vehicle") 109, in which the left and right front wheels 91 and 92 are connected by a rack bar 95, will be explained in relation to the operation of a four-wheel independent steering vehicle 100. The rack bar 95 of the SBW vehicle 109 is mechanically separated from the steer (steering device) 19. When the steering motor 79 is driven by an electrical signal from the steer 19, the rack bar 95 moves left and right, and the left and right front wheels 91 and 92, located at both ends of the rack bar 95, steer in conjunction. An angle sensor 679 detects the stroke of the rack bar 95 and calculates the steering angles of the left and right front wheels 91 and 92.

[0062] [1] If the relationship between the actual tire angles of the left and right front wheels 91 and 92 is toe-in or toe-out, it is impossible to adjust the tire angle while driving, and the tires will continue to be subjected to load. In contrast, in the four-wheel independent steering vehicle 100, it is possible to adjust the individual tire angles, and the tire load can be minimized.

[0063] [2] If the left and right front wheels 91 and 92 are shifted from the neutral position to, for example, the left side during straight-line driving, and are in turning mode, this is not detected as an abnormality because the tire load is relatively small.

[0064] [3] In SBW vehicle 109, during cornering, the cornering does not occur according to the Ackermann theory due to the structural limitations of the link mechanism between the rack bar 95 and tires 91 and 92. Therefore, even under normal conditions, the tire load is relatively large, making it impossible to distinguish it from an abnormality caused by a deviation in the detected tire angle, and thus an abnormality cannot be detected.

[0065] (Other embodiments) (a) The tire angle correction device 20 may not include a corrected tire angle storage unit 27 if there is no need to reduce the computational load, and may repeatedly calculate the corrected tire angle each time it receives an abnormality flag and a correction instruction from the tire angle sensor abnormality determination unit.

[0066] (b) The tire angle correction device 20 does not need to include a tire angle sensor abnormality determination unit 26 that determines an abnormality by comparing the absolute value of the tire load |Lt1|-|Lt4| with an abnormality determination threshold Ltth. In that case, the target tire angle calculation control unit 25 will always target the tire angle θ even for small differences between the detected tire angle and the actual tire angle. * 1-θ * You may perform correction 4.

[0067] (c) In Figures 1 and 2, the tire angle correction device 20 is shown as a higher-level control device for the motor drive unit integrated with the steering motors 71-74. The configuration is not limited to this, and the tire angle correction device 20 and the motor drive units of each steering motor 71-74 may function as a single unit. For example, the four motor drive units may communicate with each other to cooperate in realizing the function of the tire angle correction device 20.

[0068] (d) The independently steerable vehicle equipped with the tire angle correction device 20 is not limited to four-wheeled vehicles, but can include three-wheeled vehicles, six-wheeled vehicles, etc., as long as it is a "vehicle in which three or more tires can be independently steered."

[0069] The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from its spirit.

[0070] The disclosure of "a tire angle correction device in which the abnormality determination threshold is variably set according to the target tire angle" may be combined with a disclosure of a tire angle correction device that specifies that it includes a corrected tire angle storage unit.

[0071] The disclosure of "a tire angle correction device mounted on a vehicle equipped with a vehicle speed detection device for detecting vehicle speed, wherein the tire angle sensor abnormality determination unit performs abnormality determination and the target tire angle calculation control unit performs correction of the target tire angle only when the vehicle speed is within a predetermined range," and the disclosure of "a tire angle correction device mounted on a vehicle equipped with an abnormality notification device for notifying the driver of an abnormality, wherein the tire angle sensor abnormality determination unit notifies the abnormality notification device when it determines that the tire angle sensor is abnormal," may be combined with each other.

[0072] Each control unit (target tire angle calculation control unit, tire angle sensor abnormality determination unit) and its method described in this disclosure may be implemented by a dedicated computer provided by configuring a processor and memory programmed to execute one or more functions embodied by a computer program. Alternatively, each control unit and its method described in this disclosure may be implemented by a dedicated computer provided by configuring a processor by one or more dedicated hardware logic circuits. Alternatively, each control unit and its method described in this disclosure may be implemented by one or more dedicated computers configured by a combination of a processor and memory programmed to execute one or more functions and a processor configured by one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by the computer on a computer-readable non-transitional tangible recording medium. [Explanation of symbols]

[0073] 15...Movement direction indicating device, 20. Tire angle correction device, 25. Target tire angle calculation control unit, 26... Tire angle sensor abnormality detection unit, 27... Corrected tire angle memory unit, 651-654...Motor angle sensor (tire angle sensor), 661-664... Motor current sensor (tire load sensor), 671-674... Tire angle sensor, 681-684... Tire load sensor, 71-74... Steering motor, 81-84... Torque transmission device, 91-94... tires, 100... (independent steering) vehicles.

Claims

1. Three or more tires (91-94) can be steered independently, and the target tire angle (θ) * 1 - θ * In an independently steering vehicle (100) in which steering torque output by steering motors (71-74) in accordance with 4) is transmitted to each tire via torque transmission devices (81-84) and each tire is steered, a tire angle correction device that calculates and corrects the target tire angle, The system includes a target tire angle calculation control unit (25) that calculates the target tire angle for each tire based on the direction of movement indicated by the direction of movement indicator (15) and instructs the steering motor accordingly. While the vehicle is in motion, the target tire angle calculation control unit, The detected tire angles (θs1-θs4) of each tire detected by the tire angle sensors (651-654, 671-674) are acquired, and feedback control is performed with respect to the target tire angle. A tire angle correction device that corrects the target tire angle according to the tire load (Lt1-Lt4) applied to each tire detected by tire load sensors (661-664, 681-684).

2. The system further includes a tire angle sensor abnormality determination unit (26) that determines that if the absolute value of the tire load for any tire is greater than or equal to an abnormality determination threshold, the tire angle detected by the corresponding tire angle sensor is abnormal because it deviates from the actual tire angle. When the tire angle sensor abnormality detection unit determines that the tire angle sensor is abnormal, The tire angle correction device according to claim 1, wherein the target tire angle calculation control unit corrects the target tire angle in a direction that reduces the absolute value of the tire load.

3. It has a corrected tire angle storage unit (27) that stores a corrected tire angle, which is a correction amount for the target tire angle, The tire angle correction device according to claim 2, wherein the target tire angle calculation control unit calculates the target tire angle using the corrected tire angle stored in the corrected tire angle storage unit.

4. The tire angle correction device according to claim 2, wherein the abnormality determination threshold is set variably according to the target tire angle.

5. The tire angle sensor is comprised of motor angle sensors (651-654) that detect the rotation angle of the steering motor. A tire angle correction device according to any one of claims 1 to 4, wherein the tire angle is estimated from the rotation angle of the steering motor based on the characteristics of the torque transmission device.

6. The tire load sensor is comprised of a motor current sensor (661-664) that detects the motor current flowing through the windings of the steering motor. A tire angle correction device according to any one of claims 1 to 4, wherein the tire load is estimated from the motor current based on the characteristics of the torque transmission device.

7. It is mounted on a vehicle equipped with a vehicle speed detection device (40) that detects vehicle speed, The tire angle correction device according to any one of claims 2 to 4, wherein the tire angle sensor abnormality determination unit performs abnormality determination and the target tire angle calculation control unit performs correction of the target tire angle only when the vehicle speed is within a predetermined range.

8. It is installed in a vehicle equipped with an abnormality notification device (30) that notifies the driver of an abnormality, The tire angle correction device according to any one of claims 2 to 4, wherein the tire angle sensor abnormality determination unit notifies the abnormality notification device when it determines that the tire angle sensor is abnormal.

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