Steering control device

Abstract

The present invention relates to a steering control device (2) configured to control a steering system (1) having a structure in which the power transmission path between a steering mechanism (4) and a steering operating mechanism (6) is separated, the steering operating mechanism (6) including a motor (32) configured to generate motor torque. The steering control device (2) includes a controller (50) configured to control the drive of the motor (32). The controller (50) detects an anomaly in the steering operating mechanism (6) when the value indicating a change in motor torque is a value indicating that the steering operating shaft is presumed to be in a state where it cannot move despite the application of motor torque.

Description

Technical Field

[0001] This invention relates to a steering control device. Background Technology

[0002] A steering system used in a vehicle includes a steering mechanism and a steering operating mechanism. The steering mechanism is operated by the driver. The steering operating mechanism uses motor torque as power to rotate the vehicle's steering wheels relative to the steering operating axis. Motor torque is the power output from a motor. Japanese Unexamined Patent Application Publication No. 2015-128943 (JP2015-128943A) discloses an example of a steering control device configured to control the drive of the steering system's motor. This steering control device is configured to detect mechanical abnormalities in the steering operating mechanism and issue an alert to the driver.

[0003] In JP 2015-128943A, in particular, an abnormality in the steering operating shaft is detected as a mechanical abnormality of the steering operating mechanism by utilizing the detection results from a torque sensor installed in the steering mechanism of the steering system. Summary of the Invention

[0004] Detection of mechanical malfunctions in the steering mechanism is particularly important in so-called steer-by-wire systems with a structure in which the power transmission path between the steering mechanism and the steering system is separate. This is because the driver is not informed of any mechanical malfunctions occurring in the steering mechanism via the steering system itself.

[0005] The present invention provides a steering control device in which mechanical abnormalities of the steering operating mechanism can be detected in a steering system with wire steering.

[0006] According to one aspect of the invention, a steering control device is configured to control a steering system having a structure in which the power transmission paths between the steering mechanism and the steering operating mechanism are separated. The steering mechanism is operated by the driver. The steering operating mechanism includes a motor configured to generate motor torque, which serves as the power for moving the steering operating axis to rotate the steering wheels of the vehicle. The steering control device includes a controller configured to control the drive of the motor to generate the motor torque. The controller is configured to detect an anomaly in the steering operating mechanism when a value indicating a change in motor torque is a value indicating a state in which the steering operating axis is presumed to be unable to move despite the application of motor torque.

[0007] Based on the above aspects, for example, the value used to indicate the change in motor torque and the value indicating a state where the gradient of the change increases sharply can be set as a value indicating a state where the steering operating shaft is presumed to be unable to move despite the application of motor torque. The gradient of the change in motor torque may increase sharply in the state where the steering operating shaft cannot move despite the application of motor torque. The state where the steering operating shaft cannot move despite the application of motor torque includes the possibility that an abnormality occurs in the steering mechanism and the steering operating shaft cannot move mechanically. That is, mechanical abnormalities of the steering mechanism can be detected in the above configuration. Therefore, mechanical abnormalities of the steering mechanism can be detected in a so-called steer-by-wire steering system.

[0008] In the above aspects, the controller can be configured to detect anomalies in the steering mechanism by comparing a value calculated as a value indicating a change in motor torque and corresponding to the gradient of that change with a gradient threshold, the gradient threshold being defined as indicating a state in which the steering shaft is presumed to be unable to move despite the application of motor torque.

[0009] The state where the steering shaft cannot move despite the application of motor torque includes situations where the steering shaft cannot move due to contact between the steering wheel and an obstacle such as a curb. This state is unlikely to occur when the vehicle speed is higher than low speeds.

[0010] In the above aspects, the controller can be configured to detect an anomaly in the steering mechanism when the vehicle speed is a value indicating that the speed is higher than a low speed including the vehicle coming to a stop.

[0011] According to the above configuration, erroneous judgments of abnormalities in the steering mechanism can be reduced due to the steering shaft being unable to move because of contact between the steering wheel and an obstacle such as a curb. Therefore, this configuration is effective in improving the accuracy of detecting abnormalities in the steering mechanism.

[0012] The contact state of the steering wheel with an obstacle such as a curb can be estimated based on the trajectory of the change in motor torque. In the above aspect, the value indicating that the steering operating shaft is presumed to be unable to move despite the application of motor torque can be set to a larger value than that determined by the change characteristics of the motor torque, which are estimated based on the elastic components of the steering wheel and the vehicle.

[0013] Based on the above configuration, false detections of anomalies can be reduced with high accuracy, and the accuracy of detecting anomalies in the steering operating mechanism can be improved. The state where the steering operating shaft cannot move despite the application of motor torque includes states that occur momentarily due to road conditions or the effect of instantaneous contact between the vehicle and obstacles such as curbs during driving.

[0014] In the above aspects, the controller can be configured to detect an anomaly in the steering mechanism when the value indicating the change in motor torque remains at a value indicating that the steering operating shaft is presumed to be in a state where it cannot move despite the application of motor torque.

[0015] Based on the above configuration, false detections of anomalies can be reduced with high accuracy, and this configuration is effective in improving the accuracy of anomaly detection in the steering operating mechanism. The state where the steering operating shaft cannot move despite the application of motor torque includes the state where the steering operating shaft cannot move due to limitations in the power output from the motor. This state can be determined based on the motor's control status.

[0016] In the above aspects, the controller can be configured to detect an abnormality in the steering mechanism when the control state of the motor is not in a restricted state, in which the power output from the motor is limited.

[0017] According to the above configuration, the false detection of anomalies can be reduced with high accuracy, and the configuration is effective in improving the accuracy of anomaly detection in steering operating mechanisms.

[0018] Based on the steering control device described above, mechanical abnormalities in the steering operating mechanism can be detected in a steering system with wire steering. Attached Figure Description

[0019] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, in which the same reference numerals denote the same elements, and in the drawings:

[0020] Figure 1 This is a schematic structural diagram of the steering system;

[0021] Figure 2 This is a flowchart illustrating the procedure for determining the occurrence of an abnormality in the steering control device; and

[0022] Figure 3 This is a schematic diagram used to describe the characteristics of motor torque variation. Detailed Implementation

[0023] The following describes an implementation of a steering control device applied to a steer-by-wire system with reference to the accompanying drawings. For example... Figure 1 As illustrated in the diagram, the steering system 1 of this embodiment is a steer-by-wire type steering system. The steering system 1 includes a steering control device 2 configured to control the operation of the steering system 1. The steering system 1 includes a steering mechanism 4 and a steering operating mechanism 6. The steering mechanism 4 is steered by the driver via a steering wheel 3. The steering operating mechanism 6 rotates the steering wheel 5 in response to the driver's steering operation of the steering mechanism 4. The steering system 1 of this embodiment has a structure in which the power transmission path between the steering mechanism 4 and the steering operating mechanism 6 is always mechanically separated.

[0024] The steering mechanism 4 includes a steering shaft 11 and a steering side actuator 12. The steering wheel 3 is connected to the steering shaft 11. The steering side actuator 12 applies a steering reaction force to the steering wheel 3 via the steering shaft 11 as a force against steering operation.

[0025] The steering-side actuator 12 includes a steering-side motor 14 and a reducer 15. The steering-side motor 14 serves as a drive source. The reducer 15 includes a worm gear and a wheel. The steering-side motor 14 is connected to the steering shaft 11 via the reducer 15.

[0026] The steering mechanism 6 includes a pinion shaft 21, a rack shaft 22, a rack housing 23, and a rack and pinion mechanism 24. The rack shaft 22 serves as a steering shaft connected to the pinion shaft 21. The rack housing 23 houses the rack shaft 22, enabling it to reciprocate in the axial direction. The rack and pinion mechanism 24 includes the pinion shaft 21 and the rack shaft 22. The rack housing 23 includes a first housing 25 and a second housing 26, each having a cylindrical shape. The rack shaft 22 and the pinion shaft 21 are arranged in the first housing 25 at a predetermined angle of intersection. The rack and pinion mechanism 24 is configured such that the pinion teeth 21a of the pinion shaft 21 mesh with the rack teeth 22a of the rack shaft 22. A tie rod 28 is connected to both ends of the rack shaft 22 via a rack end 27, which serves as a ball joint. The distal end of the tie rod 28 is connected to a steering knuckle (not shown) to which the steering wheel 5 is attached.

[0027] The pinion shaft 21 is configured to support the rack shaft 22 within the rack housing 23. That is, a support mechanism (not shown) provided in the steering operating mechanism 6 supports the rack shaft 22, allowing it to move along its axial direction, and this support mechanism presses the rack shaft 22 toward the pinion shaft 21. Therefore, the rack shaft 22 is supported within the rack housing 23. Furthermore, rotation of the rack shaft 22 is restricted. Another support mechanism can be provided to support the rack shaft 22 within the rack housing 23 without using the pinion shaft 21. In this case, the steering operating mechanism 6 can have a structure in which the pinion shaft 21 is omitted.

[0028] The steering mechanism 6 also includes a steering-side actuator 31 configured to apply power to the rack shaft 22 to move the rack shaft 22 axially and rotate the steering wheel 5. The steering-side actuator 31 includes a steering-side motor 32 serving as a drive source, a belt mechanism 33, and a ball screw mechanism 34. The steering-side actuator 31 is located at the connection between the first housing 25 and the second housing 26. The steering-side actuator 31 applies power to the rack shaft 22 such that the rotation of the steering-side motor 32 is transmitted to the ball screw mechanism 34 via the belt mechanism 33, and the ball screw mechanism 34 converts the rotation into reciprocating motion of the rack shaft 22 in the axial direction.

[0029] In the steering system 1 with the above structure, in response to the driver's steering operation, motor torque is applied as power from the actuator 31 on the steering side to the rack shaft 22 to change the steering angle of each steering wheel 5. At this time, a steering reaction force resisting the driver's steering operation is applied from the actuator 12 on the steering side to the steering wheel 3.

[0030] like Figure 1 As illustrated, the steering control unit 2 is connected to the steering-side motor 14 and the steered-side motor 32 to control the drive of motors 14 and 32. The steering control unit 2 controls the drive of motors 14 and 32 by controlling the supply of current, which serves as the control quantity for motors 14 and 32, based on detection results from various sensors. Examples of these sensors include a vehicle speed sensor 62, a torque sensor 63, a steering-side rotation angle sensor 64, a steered-side rotation angle sensor 65, a steering-side current sensor 66, and a steered-side current sensor 67.

[0031] Vehicle speed sensor 62 detects the vehicle speed value V, which is the vehicle's travel speed. Torque sensor 63 detects the steering torque Th applied to the steering shaft 11 by the driver's steering operation. Steering-side rotation angle sensor 64 detects the steering angle θs, which is the rotation angle of the rotating shaft of the steering-side motor 14. Steering-side rotation angle sensor 65 detects the steering angle θt, which is the rotation angle of the rotating shaft of the steering-side motor 32. Steering-side current sensor 66 acquires the voltage drop of the shunt resistor of the source of the switching element configured to be associated with the steering-side motor 14 in the inverter (not shown) as current, and the steering-side current sensor 66 detects this current as an actual current value Isq indicating the magnitude of the motor torque as the power output from the steering-side motor 14. The steering-side current sensor 67 acquires the voltage drop of the shunt resistor of the source of the switching element configured to be associated with the steering-side motor 32 connected to the inverter (not shown) as current, and the steering-side current sensor 67 detects this current as an actual current value Itq indicating the magnitude of the motor torque as the power output from the steering-side motor 32.

[0032] For example, an alarm device 61 located on the dashboard of the vehicle is connected to the steering control device 2. The alarm device 61 alerts the driver by illuminating or flashing the light. In this embodiment, the alarm device 61 alerts the driver to the occurrence of a mechanical malfunction in the steering mechanism 6.

[0033] Next, the configuration of steering control device 2 will be described. For example... Figure 1 As illustrated, the steering control device 2 includes a central processing unit (hereinafter referred to as "CPU") 50 and a memory 51. The CPU 50 executes programs stored in the memory 51 at predetermined calculation cycles to perform various types of control, including control of the drive of motors 14 and 32 to generate motor torque. In this embodiment, the CPU 50 is an example of a controller.

[0034] Specifically, the CPU 50 calculates a target reaction torque as a target value for the steering reaction force in response to the driver's steering operation, thereby generating the steering reaction force. For example, the CPU 50 calculates the target reaction torque based on the steering torque Th and the vehicle speed value V. The CPU 50 controls the drive of the steering-side motor 14 by supplying drive power to the steering-side motor 14 to generate a motor torque associated with the target reaction torque based on the steering angle θs of the steering-side motor 14 and the actual current value Isq. In this way, a steering reaction force is generated in the steering mechanism 4.

[0035] The CPU 50 counts the revolutions of the steering-side motor 32 starting from the midpoint θt0 based on the steering angle θt of the steering-side motor 32, and calculates the cumulative angle as the sum of the steering angles θt, starting from the midpoint θt0, which is the origin. The midpoint θt0 is the steering angle θt when the vehicle is traveling straight, and the midpoint θt0 corresponds to the midpoint of the pinion angle. The CPU 50 calculates the pinion angle θp, which is the steering angle of each steering wheel 5, by multiplying the cumulative angle by a conversion factor K based on the reduction ratio of the belt mechanism 33, the lead of the ball screw mechanism 34, and the speed ratio of the rack and pinion mechanism 24. The pinion angle θp indicates the rotation angle of the pinion shaft 21. For example, the pinion angle θp is positive to the left of the midpoint θp0 and negative to the right of the midpoint θp0.

[0036] The CPU 50 calculates a target pinion angle θp* as a target value for the pinion angle θp, such that the pinion angle θp reaches an angle responsive to the driver's steering operation. For example, the CPU 50 calculates the target pinion angle θp* based on the steering angle θs, such that the pinion angle θp has the same value as the steering angle θs. The CPU 50 calculates the target steering torque as a target value for power by performing feedback control to make the pinion angle θp follow the target pinion angle θp*. The CPU 50 controls the drive of the steering-side motor 32 by supplying drive power to the steering-side motor 32 to generate a motor torque associated with the target steering torque based on the steering angle θt of the steering-side motor 32 and the actual current value Itq. In this way, power is generated in the steering mechanism 6.

[0037] Next, a description of the processing to be executed by the CPU 50 to detect mechanical abnormalities in the steering operating mechanism 6 is given. In the following description, the CPU 50 executes the processing for detecting mechanical abnormalities in the steering operating mechanism 6 by performing periodic processing based on a program stored in the memory 51 in each control cycle. In this embodiment, the abnormality detected as a mechanical abnormality of the steering operating mechanism 6 is the following state: in this state, despite the fact that an obstacle such as a curb is not in contact with the steering wheel 5, the rack shaft 22 cannot move even when motor torque is applied.

[0038] like Figure 2 As illustrated in the diagram, CPU 50 determines whether the vehicle speed value V is greater than a predetermined low speed value V0 (V > V0) (step S10). The low speed value V0 is preset to indicate that the vehicle is at a low speed, including when it is stopped. This process is performed to determine whether the vehicle is traveling at a low speed, including when it is stopped, for example, at a low speed of several kilometers per hour. This condition is set based on the reason that a state in which the vehicle is traveling at a speed higher than the low speed is unlikely to cause the rack shaft 22 to be unable to move due to contact between the steering wheel 5 and an obstacle such as a curb. When CPU 50 determines that the vehicle speed value V is equal to or less than the low speed value V0 (step S10: No), CPU 50 determines that the vehicle is traveling at a low speed, including when it is stopped, and CPU 50 returns to the process of step S10 to repeat the process.

[0039] When the CPU 50 determines that the vehicle speed value V is greater than the low speed value V0 (step S10: Yes), the CPU 50 determines that the vehicle is traveling at a speed higher than the low speed, including when stopped, and the CPU 50 compares the torque gradient R with the gradient threshold Rth1 (step S20). The torque gradient R is a value calculated as an indication of the change in the actual current value Itq and indicates the gradient of that change. This process is performed to determine whether the gradient of the change in the motor torque of the steering-side motor 32 increases sharply. The gradient of the change in the motor torque of the steering-side motor 32 may increase sharply when the motor torque is applied but the rack shaft 22 cannot move. The state where the motor torque is applied but the rack shaft 22 cannot move includes the possibility that an abnormality has occurred in the steering operating mechanism 6 and the rack shaft 22 cannot move mechanically. That is, the process in step S20 is a process for detecting mechanical abnormalities in the steering operating mechanism 6.

[0040] In this embodiment, the torque gradient R is obtained by dividing the torque change ΔItq by the control cycle. The torque change ΔItq is the difference between the current value of the actual current value Itq and the previous value of the actual current value Itq one control cycle ago. When the control cycle is preset, the torque change ΔItq is a value that indicates the change of the actual current value Itq between control cycles and corresponds to the torque gradient R of the actual current value Itq. Therefore, in step S20, the torque change ΔItq can be used instead of the torque gradient R.

[0041] In step S20, the CPU 50 determines whether the torque gradient R is equal to or greater than the gradient threshold Rth1 (R≥Rth1). The gradient threshold Rth1 is described.

[0042] like Figure 3 The variation characteristic of the absolute value of the actual current Itq, indicated by the dashed line, corresponding to the motor torque of the steering-side motor 32, is defined such that: when the steering wheel 5 is not in contact with an obstacle such as a curb and no mechanical abnormality occurs in the steering mechanism 6, the absolute value of the actual current Itq continuously increases with an approximately constant gradient Rth0 as the absolute value of the pinion angle θp increases. Figure 3 The variation characteristics of the absolute value of the actual current value Itq, indicated by the continuous line in the diagram, are defined such that when a mechanical abnormality occurs in the steering mechanism 6, the absolute value of the actual current value Itq increases with a gradient Rthb. In the case of gradient Rthb, the absolute value of the actual current value Itq increases sharply relative to the increase of the absolute value of the pinion angle θp after a certain angle θa. For example... Figure 3The variation characteristics of the absolute value of the actual current value Itq, indicated by the long and short dashed lines, are defined such that when the steering wheel 5 contacts an obstacle such as a curb at angle θa, the gradient increases exponentially with respect to the increase in the absolute value of the pinion angle θp after angle θa. For example, the variation characteristics of the absolute value of the actual current value Itq are defined such that the absolute value of the actual current value Itq increases with gradient Rth0, then with gradient Rtha, represented by a tangent along the midpoint of the exponential increase, and finally approximates a state of increasing with gradient Rthb. Based on the characteristics of the elastic components of the rubber of each steering wheel 5 and the characteristics of the elastic components of the suspension of the vehicle connected to each steering wheel 5, the variation characteristics from the state of increasing with gradient Rth0 to the state of increasing with gradient Rtha can be experimentally determined. Figure 3 In the diagram, the horizontal axis represents the absolute value of the pinion angle θp, together showing the angles to the left and right of the midpoint θp0. Figure 3 In the diagram, the vertical axis represents the absolute value of the actual current value Itq, together showing the actual current value Itq when the motor 32 on the steering side rotates in the positive and negative directions.

[0043] In this embodiment, the gradient threshold Rth1 is set to a value within a range that is greater than gradient Rth1 and less than gradient Rthb, and close to gradient Rthb. This range is experimentally determined to indicate that the steering wheel 5 is not in contact with an obstacle such as a curb and that a mechanical malfunction has occurred in the steering mechanism 6.

[0044] Refer again Figure 2 The process is described below. When the CPU 50 determines in step S20 that the torque gradient R is less than the gradient threshold Rth1 (step S20: No), the CPU 50 determines that no mechanical abnormality has occurred in the steering operating mechanism 6, and the CPU 50 returns to the processing of step S10 to repeat step S10 and subsequent processing.

[0045] When the CPU 50 determines that the torque gradient R is equal to or greater than the gradient threshold Rth1 (step S20: Yes), the CPU 50 determines that a mechanical abnormality may occur in the steering operating mechanism 6, and the CPU 50 determines whether the torque gradient R is equal to or greater than the gradient threshold Rth2 (step S30). This process is performed to immediately determine that a mechanical abnormality has occurred in the steering operating mechanism 6. In this embodiment, the gradient threshold Rth2 is set to a value that is greater than the gradient threshold Rth1 and equal to the gradient Rthb, where gradient Rthb indicates that a mechanical abnormality has occurred in the steering operating mechanism 6.

[0046] When the CPU 50 determines that the torque gradient R is equal to or greater than the gradient threshold Rth2 (step S30: Yes), the CPU 50 detects a mechanical abnormality in the steering operating mechanism 6 and performs processing related to abnormality determination to immediately determine the abnormality (step 40). In step S40, the CPU 50 controls the illumination status to make the warning device 61 illuminate or flash to alert the driver that a mechanical abnormality has been detected in the steering operating mechanism 6. To record the detection of the mechanical abnormality in the steering operating mechanism 6, the CPU 50 records the abnormality information indicating the detection in the memory 51. When a diagnostic tool is connected to the steering control device 2 from the outside, the abnormality information recorded in the memory 51 is output to the diagnostic tool (not shown). In this embodiment, the memory 51 has a diagnostic function. Then, the CPU 50 proceeds to the processing for activating a fault protection operation in the event of a mechanical abnormality. In this embodiment, the fault protection operation in the event of a mechanical abnormality involves performing processing to safely stop the vehicle while issuing an alert to the driver.

[0047] When the CPU 50 determines in step S30 that the torque gradient R is less than the gradient threshold Rth2 (step S30: No), the CPU 50 determines whether the duration TC is equal to or longer than the threshold time TCth (step S50). The duration TC is the time during which the torque gradient R remains equal to or greater than the gradient threshold Rth1. This process is performed to determine whether the torque gradient R is momentarily equal to or greater than the gradient threshold Rth1 due to the influence of road conditions or the effect of instantaneous contact between the vehicle and an obstacle such as a curb during driving, in order to exclude other factors in the mechanical abnormality of the steering operating mechanism 6 despite the possibility of an abnormality. In this embodiment, the threshold time TCth is set to a value within an experimentally determined range to indicate that the torque gradient R is equal to or greater than the gradient threshold Rth1 due to the occurrence of a mechanical abnormality of the steering operating mechanism 6, rather than due to the influence of road conditions or the effect of instantaneous contact between the vehicle and an obstacle such as a curb during driving.

[0048] When the CPU 50 determines in step S50 that the duration TC is shorter than the threshold time TCth (step S50: No), the CPU 50 determines that the torque gradient R is momentarily equal to or greater than the gradient threshold Rth1 due to the influence of road conditions or the effect of instantaneous contact between the vehicle and an obstacle such as a curb during driving. In this case, the CPU 50 returns to the processing of step S10 to repeat step S10 and subsequent processing.

[0049] When the CPU 50 determines that the duration TC is equal to or longer than the threshold time TCth (step S50: Yes), the CPU 50 determines whether the control state of the steering-side motor 32 is a restricted state (step S60). This process is performed to determine whether the torque gradient R is equal to or greater than the gradient threshold Rth1 due to the restricted state where the power output from the steering-side motor 32 is limited, so as to further eliminate other factors in mechanical abnormalities of the steering operating mechanism 6 despite the possibility of possible abnormalities. In this embodiment, the restricted state is considered to be a state set when it is necessary to limit the power output from the steering-side motor 32, including a state set due to overheating of the steering-side motor 32 or an inverter (not shown) associated with the steering-side motor 32. In this embodiment, the process of step S60 is particularly effective when a restricted state is set, because the period required until the power output from the steering-side motor 32 is actually limited in the restricted state is longer than the threshold time TCth, and the state of "torque gradient R ≥ gradient threshold Rth1" can be sufficiently detected after the threshold time TCth.

[0050] When the CPU 50 determines in step S60 that the control state of the steering side motor 32 is a restricted state (step S60: Yes), the CPU 50 determines that the torque gradient R is equal to or greater than the gradient threshold Rth1 due to the restricted state, and the CPU 50 returns to the processing of step S10 to repeat step S10 and subsequent processing.

[0051] When the CPU 50 determines that the control state of the steering-side motor 32 is not in a restricted state (step S60: No), the CPU 50 detects a mechanical abnormality in the steering operating mechanism 6 and proceeds to step S40 to perform processing related to abnormality determination. In this case, similar to the above, the CPU 50 controls the illumination status to make the alarm device 61 illuminate or flash, and the CPU 50 records the abnormality information in the memory 51. Then, the CPU 50 proceeds to the processing for activating fault protection operation in the event of a mechanical abnormality.

[0052] The operation of this embodiment is described below. According to this embodiment, in step S20 for determining the magnitude of the torque gradient R, the gradient threshold Rth1, which indicates a state where the torque gradient R increases sharply, can be set to a value indicating that the rack shaft 22 is presumed to be in a state where it cannot move despite the application of motor torque. In a state where the rack shaft 22 cannot move despite the application of motor torque, the torque gradient R may increase sharply. The state where the rack shaft 22 cannot move despite the application of motor torque includes the possibility that an abnormality occurs in the steering operating mechanism 6 and the rack shaft 22 cannot move mechanically. That is, in this embodiment, a mechanical abnormality in the steering operating mechanism 6 can be detected.

[0053] The effects of this embodiment are described below. (1) This embodiment includes a process, such as step S20, for determining whether the torque gradient R is equal to or greater than the gradient threshold Rth1. Therefore, mechanical abnormalities of the steering operating mechanism 6 can be detected. Therefore, mechanical abnormalities of the steering operating mechanism 6 can be detected in the wire-controlled steering system 1.

[0054] (2) The state in which the rack shaft 22 cannot move despite the application of motor torque includes the state in which the rack shaft 22 cannot move due to contact between the steering wheel 5 and an obstacle such as a curb. This state is unlikely to occur when the vehicle speed value V is greater than the low speed value V0, which includes the vehicle coming to a stop.

[0055] This implementation includes a process, as in step S10, for determining whether the vehicle is traveling at a low speed, including when stopped. Therefore, it reduces erroneous determinations of abnormalities in the steering operating mechanism 6 caused by the rack shaft 22 being unable to move due to contact between the steering wheel 5 and an obstacle such as a curb. Thus, this implementation is effective in improving the accuracy of detecting abnormalities in the steering operating mechanism 6.

[0056] (3) The contact state between the steering wheel 5 and an obstacle such as a curb can be estimated based on the trajectory of the torque gradient R. In this embodiment, the gradient threshold Rth1 used in step S20 is set to a value greater than the gradient Rtha, which depends on the characteristics of the elastic components of the rubber of each steering wheel 5 and the characteristics of the elastic components of the suspension of the vehicle connected to each steering wheel 5. Therefore, false detections of abnormalities in the steering operating mechanism 6 caused by the rack shaft 22 being unable to move due to contact between the steering wheel 5 and an obstacle such as a curb can be reduced with higher accuracy. Therefore, in this embodiment, the detection accuracy of abnormalities in the steering operating mechanism 6 can be improved.

[0057] (4) The state in which the rack shaft 22 cannot move despite the application of motor torque includes the state that occurs momentarily due to the influence of road conditions or the effect of momentary contact between the vehicle and obstacles such as curbs during driving.

[0058] This implementation includes a process, as in step S50, to determine whether the torque gradient R is momentarily equal to or greater than the gradient threshold Rth1 due to road conditions or momentary contact between the vehicle and an obstacle such as a curb during driving. Therefore, false detections of abnormalities in the steering operating mechanism 6 caused by the rack shaft 22 being momentarily unable to move due to road conditions or momentary contact between the vehicle and an obstacle such as a curb during driving can be reduced. Thus, this implementation is effective in improving the accuracy of detecting abnormalities in the steering operating mechanism 6.

[0059] (5) The state in which the rack shaft 22 cannot move despite the application of motor torque includes the state in which the rack shaft 22 cannot move due to the limitation of the power output from the steering side motor 32. This state can be understood based on the control state of the steering side motor 32.

[0060] This implementation includes a process, as in step S60, to determine whether the torque gradient R is equal to or greater than the gradient threshold Rth1 due to a limitation state where the power output from the steering-side motor 32 is restricted. Therefore, erroneous determinations of abnormalities in the steering operating mechanism 6 caused by the rack shaft 22 being unable to move due to the restriction of power output from the steering-side motor 32 can be reduced. Thus, this implementation is effective in improving the accuracy of detecting abnormalities in the steering operating mechanism 6.

[0061] The above-described embodiments can be modified as follows. Furthermore, the following other embodiments can be combined without causing any technical inconsistencies. For example, the processing of step S60 can be performed before step S20 or step S30, or the execution order can be changed. In configurations where the processing of step S10 and thereafter is not performed under the constraint of the steering-side motor 32, the processing of step S60 can be omitted.

[0062] For example, the processing of step S50 can be performed between steps S20 and S30, or the execution order can be changed. If there is no particular need to detect mechanical abnormalities in the steering mechanism 6 to consider whether the abnormality is due to road conditions or momentary contact between the vehicle and obstacles such as curbs during driving, the processing of step S50 can be omitted.

[0063] The order of steps S20 and S30 can be changed. In step S30, the gradient threshold Rth2 can be appropriately changed, as long as it has a value greater than the gradient threshold Rth1. If step S10 is sufficient to rule out whether the steering wheel 5 is in contact with an obstacle such as a curb, step S30 can be omitted.

[0064] In step S20, the torque gradient R can be replaced by the torque change ΔItq of the actual current value Itq during a predetermined sampling period. In this case, the torque change ΔItq is a value that indicates the change of the actual current value Itq during the predetermined sampling period and corresponds to the torque gradient R of the actual current value Itq.

[0065] For example, the process of step S10 can be performed after step S20 or step S30, or the execution order can be changed. If the process of step S30 is sufficient to rule out whether the steering wheel 5 is in contact with an obstacle such as a curb, the process of step S10 can be omitted. That is, only one of the processes of step S10 and step S30 is required to rule out whether the steering wheel 5 is in contact with an obstacle such as a curb.

[0066] The following configuration can be used as a process for detecting mechanical abnormalities in the steering operating mechanism 6. When the process moves forward past the determination "step S30: No" instead of moving forward past the determination "step S30: Yes", the process proceeds to step S40. That is, an abnormality is determined when the count value increases or decreases each time the process moves forward past the determination "step S30: No" and the count value reaches a predetermined threshold.

[0067] The torque gradient R of the steering-side motor 32 can be detected by, for example, using the target steering operating torque as a target value of the motor torque to be output, the detection result from the axial force sensor set on the rack shaft 22, or a value that can be converted into the power output from the steering-side motor 32.

[0068] The alarm to the driver via alarm device 61 can be appropriately modified, as long as the alarm is issued in a way that allows the driver to perceive some change in the situation. Examples of such methods include an audible alarm and increasing the weight of steering operations by increasing steering reaction force. In addition to the alarm to the driver, the vehicle's communication functions can be used to notify a shop that can perform vehicle maintenance, such as the nearest dealership.

[0069] In the above embodiments, CPU 50 may be implemented as one or more processors configured to execute computer programs, one or more application-specific hardware circuits such as an application-specific integrated circuit configured to perform at least a portion of various processes, or a circuit that includes processors and application-specific hardware circuits in combination. Memory 51 may be any available medium accessible to a general-purpose or special-purpose computer.

[0070] In the above embodiment, the steering system 1 has a non-connecting structure in which the steering mechanism 4 and the steering operating mechanism 6 are always mechanically separated. The present invention is not limited to this structure. The steering system 1 may have a structure in which the steering mechanism 4 and the steering operating mechanism 6 can be mechanically separated by a clutch.

Claims

1. A steering control device (2) configured to control a steering system (1) having a structure in which a power transmission path is separated between a steering mechanism (4) and a steering operating mechanism (6), the steering mechanism (4) being steered by a driver, the steering operating mechanism (6) including a motor (32) configured to generate motor torque, the motor torque being used as a power for moving a steering operating axis to rotate a steering wheel (5) of a vehicle, the steering control device (2) being characterized in that it includes a controller (50) configured to control the drive of the motor (32) to generate the motor torque, wherein, The controller (50) is configured to detect an anomaly in the steering mechanism (6) when the value indicating the change in motor torque is a value indicating that the steering operating shaft is presumed to be in a state where it cannot move despite the application of motor torque. The controller (50) is configured to detect anomalies in the steering mechanism (6) by comparing a value calculated as an indication of the change in motor torque and corresponding to the gradient of the change with a gradient threshold, the gradient threshold being defined as indicating that the steering shaft is presumed to be in a state where it cannot move despite the application of motor torque. The value indicating that the steering shaft is presumed to be in a state where it cannot move despite the application of the motor torque is set to a value larger than that determined by the variation characteristics of the motor torque, which are estimated based on the elastic components of the steering wheel (5) and the elastic components of the vehicle.

2. The steering control device (2) according to claim 1, characterized in that, The controller (50) is configured to detect an anomaly in the steering mechanism (6) when the speed of the vehicle is a value indicating a low speed, including when the vehicle has come to a stop.

3. The steering control device (2) according to claim 1 or 2, characterized in that, The controller (50) is configured to detect an anomaly in the steering mechanism (6) when the value indicating the change in the motor torque remains at the value indicating that the steering operating shaft is presumed to be in a state where it cannot move despite the application of the motor torque for a preset threshold time.

4. The steering control device (2) according to claim 1 or 2, characterized in that, The controller (50) is configured to detect an anomaly in the steering mechanism (6) when the control state of the motor (32) is not a restricted state, in which the power output from the motor (32) is limited.

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