Steering control system

Abstract

The present invention provides a steering control device that can effectively determine if an abnormality has occurred in the steering unit. [Solution] The steering control device controls the steering system. The steering control device performs a steering current acquisition process to acquire a steering-side actual current value Ib, which is the current generated in the steering motor; a steering axis related value acquisition process to acquire a pinion angle θp, which is a value that can be converted into the amount of movement of the rack axis; and an abnormality determination process to determine an abnormality in the steering unit based on the steering-side actual current value Ib and the pinion angle θp. The abnormality determination process includes a steering current axial force calculation process that calculates the steering current axial force Fi based on the steering-side actual current value Ib; a reference axial force calculation process that calculates a reference axial force Fb, which is calculated based on the pinion angle θp and is a reference axial force for the amount of movement of the rack axis; a comparison process that compares the steering current axial force Fi and the reference axial force Fb; and a determination process that determines whether an abnormality has occurred in the steering unit based on the result of the comparison process.

Description

Technical Field

[0001] The present invention relates to a steering control device.

Background Art

[0002] For example, Patent Document 1 discloses a steering control device for controlling a steering device that executes control to steer a steered wheel in conjunction with the rotation of a steering wheel. The steering control device uses a detection value detected from steering means including a steering unit to perform an abnormality determination as to whether an abnormality has occurred in the steering unit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In ensuring the reliability of a steering device, a technique related to the abnormality determination of a steering unit is important. Therefore, development from various viewpoints is required for a method capable of determining an abnormality of the steering unit. This is not limited to the steering unit constituting a steer-by-wire type steering device, and is the same for, for example, the steering unit constituting an electric power steering device.

Means for Solving the Problems

[0005] A steering control device capable of solving the above problems is a steering control device that controls a steering system mounted on a vehicle, which includes a steering unit having a steering motor, a steering shaft connected to the steering wheels of the vehicle, and a power transmission mechanism that transmits the torque of the steering motor to the steering shaft. The steering control device is configured to perform a steering current acquisition process to acquire a steering current value, which is a current generated in the steering motor, from the steering system; a steering shaft related value acquisition process to acquire a steering shaft related value, which is a value that can be converted into a movement amount of the steering shaft, from the steering system; and an abnormality determination process to determine that an abnormality has occurred in the steering unit based on the steering current value and the steering shaft related value. The abnormality determination process includes: a steering current axial force calculation process that calculates the steering current axial force based on the steering current value; a reference axial force calculation process that calculates a reference axial force, which is calculated based on the steering axis-related values ​​and is a reference axial force for the amount of movement of the steering axis; a comparison process that compares the steering current axial force with the reference axial force; and a determination process that determines, based on the result of the comparison process, that an abnormality has occurred in the steering unit.

[0006] According to the steering control device described above, it is possible to suitably determine if an abnormality has occurred in the steering unit by comparing the steering current axial force acting on the rack shaft based on the steering current value generated by the steering motor with the reference axial force acting on the rack shaft via the power transmission mechanism and the road surface in relation to the amount of movement of the rack shaft, in which case the relationship is not appropriate.

[0007] In the steering control device described above, for example, the reference axial force may be an axial force defined by a function that takes the steering axis-related values ​​as input and outputs the axial force acting on the steering axis. In the steering control device described above, the function may be defined by an axial force map that defines the relationship between the steering axis-related values ​​and vehicle speed and the axial force acting on the steering axis.

[0008] According to the steering control device described above, even if vehicle speed is also taken into consideration in order to improve the accuracy of the abnormality detection process, the increase in the computational load required to derive the reference axial force can be suppressed.

[0009] In the steering control device described above, the abnormality detection process may be performed when the vehicle is moving at an extremely low speed, including when it is stopped. According to the steering control device described above, the conditions under which abnormality detection processing is performed can be optimized.

[0010] In the steering control device described above, the abnormality determination process is configured to derive a plurality of determination results regarding the abnormality of the steering unit, and the plurality of determination results may include a process that divides them according to the severity of the abnormality of the steering unit.

[0011] According to the steering control device described above, while determining that the output loss is excessive, it is possible to distinguish and determine the severity of the abnormality in the steering unit, such as a pre-steering lock state and a steering lock state.

[0012] In the steering control device described above, the abnormality determination process may include a process for calculating a system output compensation component, which is a component that appears in the vehicle according to the characteristics of the vehicle but is not included in the reference axial force, and the system output compensation component may be taken into account during the comparison process.

[0013] According to the steering control device described above, abnormality detection processing can be performed effectively even when considering the entire vehicle on which the steering system is installed. In the steering control device described above, the comparison process may include a process of comparing the magnitude of the difference obtained by subtracting the reference axial force and the system output compensation component from the steering current axial force with a first threshold.

[0014] According to the steering control device described above, it is possible to quantitatively determine if the relationship between the steering current axial force and the reference axial force is inappropriate. In the above-described steering control device, the steering system may include a reaction force unit in which the power transmission path between the unit and the steering unit is separated. The reaction force unit may include a reaction force motor, a steering shaft connected to the steering wheel of the vehicle, and a reaction force transmission mechanism that transmits a reaction force torque, which is the torque of the reaction force motor and is a reaction force against the operation of the driver, to the steering wheel via the steering shaft.

[0015] According to the above-described steering control device, even for a steering unit mounted on a steer-by-wire type vehicle, an abnormality determination process can be suitably performed. In the above-described steering control device, the steering control device may include a reaction force calculation process for calculating the reaction force torque based on the steering current axial force.

[0016] According to the above-described steering control device, even when adopting a configuration for determining that an abnormality has occurred in a steering unit mounted on a steer-by-wire type vehicle, the scale of design changes can be kept small.

Advantages of the Invention

[0017] According to the present invention, it is possible to suitably determine that an abnormality has occurred in the steering unit.

Brief Description of the Drawings

[0018] [Figure 1] It is a diagram showing the overall configuration of a steering system according to the first embodiment. [Figure 2] It is a block diagram showing the functions of the steering control device of FIG. 1. [Figure 3] It is a block diagram showing the functions of the axial force calculation unit of FIG. 2. [Figure 4] It is a block diagram showing the functions of the abnormality determination unit of FIG. 2. [Figure 5] (a) and (b) are graphs showing the general relationship between the axial force and the steering angle at the vehicle speed.

Embodiments for Carrying Out the Invention

[0019] <First Embodiment> Hereinafter, the first embodiment of the present invention will be described. <Overall Configuration> As shown in FIG. 1, the steering control device 1 controls the steering system 2. The steering system 2 is, for example, a steer-by-wire type steering device for a vehicle. The steering system 2 includes a reaction force unit 4 and a steering unit 6. The reaction force unit 4 is steered by a driver via the steering wheel 3. The steering unit 6 steers the left and right steering wheels 5 of the vehicle in response to the steering input by the driver to the reaction force unit 4. The steering system 2 has, for example, a structure in which the power transmission path between the reaction force unit 4 and the steering unit 6 is mechanically separated at all times. The power transmission path between the reaction force actuator 12 described later and the steering actuator 31 described later is mechanically separated at all times.

[0020] The reaction force unit 4 includes a steering shaft 11 and a reaction force actuator 12. The steering shaft 11 is connected to the steering wheel 3 so as to be rotatable integrally with the steering wheel 3. The reaction force actuator 12 includes a reaction force motor 13 and a reaction force transmission mechanism 14. The reaction force motor 13 is connected to the steering shaft 11 via the reaction force transmission mechanism 14. The reaction force motor 13 outputs a reaction force torque, which is a torque that resists the steering of the driver's steering wheel 3. The reaction force transmission mechanism 14 transmits the reaction force torque output by the reaction force motor 13 to the steering shaft 11. The reaction force transmission mechanism 14 is, for example, a worm and wheel mechanism. The reaction force motor 13 is, for example, a three-phase brushless motor.

[0021] The steering unit 6 comprises a pinion shaft 21, a rack shaft 22, a rack housing 23, a rack and pinion mechanism 24, and a steering actuator 31. The rack shaft 22 is a steering shaft connected to the pinion shaft 21. The rack shaft 22 and the pinion shaft 21 are arranged within the rack housing 23 at a predetermined intersection angle. The rack housing 23 reciprocates the rack shaft 22. The rack and pinion mechanism 24 is configured by the meshing of pinion teeth 21a formed on the pinion shaft 21 and rack teeth 22a formed on the rack shaft 22. As a result, the pinion shaft 21 rotates in accordance with the reciprocating motion of the rack shaft 22. Tie rods 26 are connected to both ends of the rack shaft 22 via ball joints 25. The ends of the tie rods 26 are connected to knuckles to which the vehicle's steering wheels 5 are assembled. In other words, the rack shaft 22 is connected to the vehicle's steering wheels 5.

[0022] The steering actuator 31 comprises a steering motor 32 and a power transmission mechanism 33. The steering motor 32 is connected to the rack shaft 22 via the power transmission mechanism 33. The steering motor 32 outputs a steering torque, which is the torque that steers the steering wheels 5 relative to the rack shaft 22, via the power transmission mechanism 33. The power transmission mechanism 33 transmits the steering torque output by the steering motor 32 to the rack shaft 22. The steering motor 32 is, for example, a three-phase brushless motor.

[0023] More specifically, the power transmission mechanism 33 comprises a belt mechanism 34 and a ball screw mechanism 35. The belt mechanism 34 includes a pair of pulleys 41 and 42 and a belt 43 wrapped between the pair of pulleys 41 and 42. The pair of pulleys 41 and 42 are made of resin, and the belt 43 is made of rubber. The ball screw mechanism 35 includes a threaded portion 22b formed on the rack shaft 22 and a ball screw nut 46 that screws onto the threaded portion 22b via a plurality of balls 45. The pulley 41 is connected to the rotating shaft 32a of the steering motor 32. The pulley 42 is fixed to the outer circumference of the ball screw nut 46. As a result, the steering actuator 31 transmits the rotation of the rotating shaft 32a of the steering motor 32 to the ball screw mechanism 35 via the belt mechanism 34, and the ball screw mechanism 35 converts this into reciprocating motion of the rack shaft 22, thereby applying steering torque to the rack shaft 22.

[0024] In the steering system 2 configured in this way, steering torque is output from the steering actuator 31 to the rack shaft 22 in response to the driver's steering input, causing the rack shaft 22 to reciprocate and changing the steering angle θi of the steering wheels 5. At this time, the reaction force actuator 12 outputs a reaction force torque, which is a torque that opposes the driver's steering input. As a result, in the steering system 2, the steering torque Th required for the driver's steering input is changed by the reaction force output from the reaction force actuator 12. In other words, it is possible to provide feedback to the driver who is steering the steering wheel 3.

[0025] <Electrical Configuration> Each component of the steering control device 1 is equipped with a CPU and memory. Each component of the steering control device 1 performs various processes by having the CPU execute a program stored in memory at predetermined calculation cycles. The CPU and memory constitute a microcomputer, which is a processing circuit. The memory includes computer-readable media such as RAM (Random Access Memory) and ROM (Read Only Memory). However, it is only an example that various processes are implemented by software. The processing circuits of each component of the steering control device 1 may be configured to implement at least some of the processes by hardware circuits such as logic circuits. In this way, various processes are executed in the steering control device 1.

[0026] The steering control device 1 is connected to the reaction motor 13 and the steering motor 32, and performs operations to control the reaction motor 13 and the steering motor 32, respectively. The steering control device 1 also performs an abnormality detection process to determine if there is an abnormality in the steering unit 6, such as when the relationship between the steering current axial force Fi and the reference axial force Fb is inappropriate. The steering current axial force Fi is the axial force that actually acts on the rack shaft 22 via the power transmission mechanism 33 and the road surface. The reference axial force Fb is a reference axial force that acts on the rack shaft 22 via the power transmission mechanism 33 and the road surface with respect to the amount of movement of the rack shaft 22. An abnormality in the steering unit 6 includes, for example, an abnormality in which the steering motor 32 generates steering torque, but the steering torque is not properly transmitted to the reciprocating motion of the rack shaft 22 via the power transmission mechanism 33. In this embodiment, such an abnormality is called an excessive output loss abnormality, from the viewpoint that the steering torque of the steering motor 32 cannot be smoothly transmitted to the rack shaft 22, that is, that excessive loss occurs in the steering torque. Furthermore, the steering control device 1 is connected to an on-board warning device 51 consisting of warning lights, speakers, etc., and executes a process to output an abnormality determination flag Flag to the warning device 51, indicating the result of the abnormality determination process.

[0027] The steering control device 1 receives detection results from various sensors. These sensors include, for example, a vehicle speed sensor 52, a torque sensor 53, a reaction force side rotation angle sensor 54, a steering side rotation angle sensor 55, a reaction force side current sensor 57, and a steering side current sensor 58.

[0028] The vehicle speed sensor 52 detects the vehicle speed V, which is the vehicle's travel speed. The torque sensor 53 detects the steering torque Th applied to the steering shaft 11. The reaction force side rotation angle sensor 54 detects the reaction force side rotation angle θa, which is the rotation angle of the rotation axis 13a of the reaction force motor 13, as a relative angle within a range of 360°. The steering side rotation angle sensor 55 detects the steering side rotation angle θb, which is the rotation angle of the rotation axis 32a of the steering motor 32, as a relative angle.

[0029] The reaction force side current sensor 57 detects the actual reaction force side current value Ia, which is the actual current value supplied to the reaction force motor 13. The reaction force side current value Ia indicates the magnitude of the reaction force torque output by the reaction force motor 13. For example, the reaction force side current value Ia is positive when generating torque to rotate the steering wheel 3 to the right, and negative when generating torque to rotate the steering wheel 3 to the left. The steering side current sensor 58 detects the actual steering side current value Ib, which is the actual current value supplied to the steering motor 32. The steering side current value Ib indicates the magnitude of the steering torque output by the steering motor 32. For example, the steering side current value Ib is positive when generating torque to steer the steering wheel 5 to the right, and negative when generating torque to steer the steering wheel 5 to the left.

[0030] In this embodiment, the steering-side actual current value Ib is an example of a steering current value, which is the current generated in the steering motor 32. The steering-side rotation angle θb is an example of a steering axis-related value, which is a value that can be converted into the amount of movement of the steering axis. Inputting the detection results of various sensors into the steering control device 1 is an example of the process by which the steering control device 1 acquires the detection values ​​of various sensors from the steering system 2. In particular, the process by which the steering control device 1 acquires the detected steering-side actual current value Ib is an example of a steering current acquisition process. Furthermore, the process by which the steering control device 1 acquires the detected steering-side rotation angle θb is an example of a steering axis-related value acquisition process.

[0031] <Functions of the reaction force control unit> As shown in Figure 2, the steering control device 1 includes a reaction force control unit 70 and a steering control unit 80.

[0032] The reaction force control unit 70 receives the steering torque Th, vehicle speed V, reaction force side rotation angle θa, steering current axial force Fi, and target pinion angle θp* as input. Based on the steering torque Th, vehicle speed V, reaction force side rotation angle θa, steering current axial force Fi, and target pinion angle θp*, the reaction force control unit 70 controls the power supply to the reaction force motor 13. The target pinion angle θp* is a target control amount for the pinion angle θp, which is the rotation angle of the pinion shaft 21. The steering current axial force Fi, target pinion angle θp*, and pinion angle θp are calculated by the steering control unit 80.

[0033] The reaction force control unit 70 includes a steering angle calculation unit 71, a reaction force control amount calculation unit 72, and an energization control unit 73. The steering angle calculation unit 71 receives the reaction force side rotation angle θa as input. The steering angle calculation unit 71 converts the reaction force side rotation angle θa into an integrated angle that includes a range exceeding 360° by, for example, counting the number of rotations of the reaction force motor 13 from the steering neutral position, which is the position of the steering wheel 3 when the vehicle is moving straight. The steering angle calculation unit 71 calculates the steering angle θs, which is the rotation angle of the steering shaft 11, by multiplying the converted integrated angle by the conversion coefficient of the reaction force transmission mechanism 14. The steering angle θs is positive if the angle is, for example, to the right of the steering neutral position, and negative if the angle is to the left. The steering angle θs thus obtained is output to the steering angle ratio change control unit 82 of the steering control unit 80.

[0034] The reaction force control amount calculation unit 72 receives the steering torque Th, vehicle speed V, steering current axial force Fi, and target pinion angle θp* as input. Based on the steering torque Th, vehicle speed V, steering current axial force Fi, and target pinion angle θp*, the reaction force control amount calculation unit 72 calculates the reaction force command value Ts* as the target reaction force control amount for the reaction force torque. In this embodiment, the processing performed by the reaction force control amount calculation unit 72 is an example of reaction force calculation processing.

[0035] More specifically, the reaction force control amount calculation unit 72 includes an axial force calculation unit 75 and a target reaction force calculation unit 76. The axial force calculation unit 75 receives the vehicle speed V, the steering current axial force Fi, and the target pinion angle θp* as input. Based on the vehicle speed V, the steering current axial force Fi, and the target pinion angle θp*, the axial force calculation unit 75 calculates the axial force component F corresponding to the axial force acting on the rack shaft 22 that operates to steer the steering wheel 5. The axial force component F distributes the angular axial force Fr and the steering current axial force Fi, described later, in their respective distribution ratios so that the axial force acting on the rack shaft 22 through the steering wheel 5 is appropriately reflected.

[0036] For example, as shown in Figure 3, the axial force calculation unit 75 includes an angle axial force calculation unit 101, a steering current axial force filter 102, and a distribution ratio calculation unit 103. The angular axial force calculation unit 101 receives the vehicle speed V and the target pinion angle θp* as input. Based on the vehicle speed V and the target pinion angle θp*, the angular axial force calculation unit 101 calculates the angular axial force Fr. The angular axial force Fr is an ideal value of the axial force arbitrarily set by simulation or the like. The angular axial force Fr is calculated in the dimension of torque (N·m). Furthermore, the angular axial force Fr is calculated as an axial force that does not reflect road surface information such as minute bumps that do not affect the lateral behavior of the vehicle or steps that do affect the lateral behavior of the vehicle. For example, the angular axial force Fr is calculated so that the absolute value of the angular axial force Fr increases as the absolute value of the target pinion angle θp* increases. Also, the angular axial force Fr is calculated so that the absolute value of the angular axial force Fr increases as the vehicle speed V increases. The angular axial force Fr thus obtained is output to the multiplier 104. The angle axial force calculation unit 101 may also accept the pinion angle θp or the steering angle θs as input instead of the target pinion angle θp*.

[0037] The steering current axial force filter 102 receives the steering current axial force Fi as input. The steering current axial force filter 102 calculates the filtered steering current axial force Fi_f by applying a predetermined filtering process to the steering current axial force Fi. The predetermined filtering process is a process that extracts the frequency components from the steering current axial force Fi that are to be transmitted to the driver via the reaction force motor 13, and is, for example, a low-pass filter that blocks high-frequency components and extracts only low-frequency components. The filtered steering current axial force Fi_f thus obtained is output to the multiplier 105.

[0038] Here, the steering current axial force Fi is an estimated value of the axial force actually acting on the rack shaft 22 that operates to steer the steering wheels 5, that is, the axial force actually transmitted to the rack shaft 22. The steering current axial force Fi is calculated in the dimension of torque (N·m). Furthermore, the steering current axial force Fi is calculated as an axial force that reflects road surface information. For example, the steering current axial force Fi is calculated assuming that the torque applied to the rack shaft 22 by the steering motor 32 is balanced by the torque corresponding to the force applied to the rack shaft 22 through the steering wheels 5. In this case, the steering current axial force Fi is calculated such that the absolute value of the steering current axial force Fi increases as the absolute value of the steering side actual current value Ib increases.

[0039] The distribution ratio calculation unit 103 receives the vehicle speed V as input. Based on the vehicle speed V, the distribution ratio calculation unit 103 calculates the distribution ratio Di. The distribution ratio Di is the distribution ratio of the filtered steering current axial force Fi_f when obtaining the axial force component F by distributing the angular axial force Fr and the filtered steering current axial force Fi_f. In other words, the distribution ratio Di indicates the reflection state of the filtered steering current axial force Fi_f to the axial force component F, and consequently, the reflection state of the steering current axial force Fi to the reaction force component Tb*. Furthermore, the distribution ratio Di indicates the reflection state of the steering current axial force Fi to the reaction force command value Ts*. More specifically, the distribution ratio calculation unit 103 has a distribution ratio map that defines the relationship between the vehicle speed V and the distribution ratio Di, and takes the vehicle speed V as input to perform a map calculation on the distribution ratio Di.

[0040] The distribution ratio Di obtained in this way is output to the multiplier 105 and the subtractor 106. The multiplier 105 multiplies the filtered steering current axial force Fi_f obtained by the steering current axial force filter 102 by the distribution ratio Di to calculate the final steering current axial force Fim. The final steering current axial force Fim obtained in this way is output to the adder 108. The subtractor 106 subtracts the distribution ratio Di from "1" stored in the storage unit 107 to calculate the distribution ratio Dr. The distribution ratio Dr is the distribution ratio of the angular axial force Fr when the angular axial force Fr and the steering current axial force Fim are distributed to obtain the axial force component F. In other words, the value of the distribution ratio Dr is calculated so that the sum with the distribution ratio Di is "1 (100%)". The distribution ratio includes the concept of a zero value where only either the angular axial force Fr or the steering current axial force Fim is distributed to the axial force component F. Note that the memory unit 107 refers to a predetermined storage area of ​​a memory (not shown).

[0041] The distribution ratio Dr obtained in this way is output to the multiplier 104. The multiplier 104 multiplies the angular axial force Fr obtained by the angular axial force calculation unit 101 by the distribution ratio Dr and outputs the final angular axial force Frm to the adder 108. The adder 108 calculates the axial force component F using the final angular axial force Frm and the final steering current axial force Fim. The axial force component F obtained in this way is output to the subtractor 77.

[0042] Returning to the explanation of Figure 2, the target reaction force calculation unit 76 receives the steering torque Th and vehicle speed V as input. Based on the steering torque Th and vehicle speed V, the target reaction force calculation unit 76 calculates the reaction force component Tb*. The reaction force component Tb* represents the motor torque required to rotate the steering wheel 3 in the direction of the driver's steering, i.e., the assist force to assist the driver's steering. The reaction force component Tb* thus obtained is then output to the energization control unit 73 as a reaction force command value Ts* obtained through the subtractor 77 by subtracting the axial force component F obtained by the axial force calculation unit 75.

[0043] The power supply control unit 73 receives the reaction force command value Ts*, the reaction force side rotation angle θa, and the reaction force side actual current value Ia as input. Based on the reaction force command value Ts*, the power supply control unit 73 calculates the reaction force current command value for the reaction force motor 13. The reaction force current command value is the target value of the torque to be generated by the reaction force motor 13. The power supply control unit 73 then finds the difference between the reaction force current command value and the current value on the dq coordinate obtained by converting the reaction force side actual current value Ia based on the reaction force side rotation angle θa, and controls the power supply to the reaction force motor 13 to eliminate this difference. As a result, the reaction force motor 13 outputs a reaction force torque corresponding to the reaction force command value Ts*. In other words, it is possible to provide the driver with an appropriate tactile sensation corresponding to the road surface reaction force.

[0044] <Functions of the steering control unit> The steering control unit 80 receives the vehicle speed V, the steering angle θb, and the steering angle θs as input. Based on the vehicle speed V, the steering angle θb, and the steering angle θs, the steering control unit 80 controls the power supply to the steering motor 32.

[0045] The steering control unit 80 includes a pinion angle calculation unit 81, a steering angle ratio change control unit 82, a pinion angle feedback control unit 83 (pinion angle F / B control unit 83 in the figure), a power supply control unit 84, and an abnormality detection unit 85.

[0046] The pinion angle calculation unit 81 receives the steering-side rotation angle θb as input. The pinion angle calculation unit 81 converts the steering-side rotation angle θb into an integrated angle that includes a range exceeding 360° by, for example, counting the number of rotations of the steering motor 32 from the rack neutral position, which is the position of the rack axis 22 when the vehicle is moving straight. Here, the rotation axis 32a of the steering motor 32 is connected to the rack axis 22 in a manner that allows it to be linked via the power transmission mechanism 33. In other words, the pinion axis 21 is connected to the rack axis 22 in a manner that allows it to be linked via the rack and pinion mechanism 24. Therefore, there is a correlation between the amount of movement of the rack axis 22 and the pinion angle θp, and there is also a correlation between the steering-side rotation angle θb and the pinion angle θp. Therefore, the pinion angle θp can be obtained from the steering-side rotation angle θb by utilizing this correlation. Specifically, the pinion angle calculation unit 81 calculates the pinion angle θp by multiplying the converted integrated angle by a transmission coefficient. The transmission coefficient is the reduction ratio of the belt mechanism 34 of the power transmission mechanism 33, the lead of the ball screw mechanism 35, and the rotational speed ratio of the rack and pinion mechanism 24. The pinion angle θp is positive when it is, for example, to the right of the rack neutral position, and negative when it is to the left. The pinion angle θp thus obtained is output to the pinion angle feedback control unit 83 and the abnormality detection unit 85.

[0047] The steering angle ratio change control unit 82 receives the vehicle speed V and the steering angle θs as input. The steering angle ratio change control unit 82 calculates the converted angle θvg by adding an adjustment amount Δθa to the steering angle θs. The steering angle ratio change control unit 82 varies the adjustment amount Δθa, which is the ratio of the converted angle θvg to the steering angle θs, according to the vehicle speed V. For example, the adjustment amount Δθa is varied so that the change in the converted angle θvg in response to the change in the steering angle θs is larger when the vehicle speed V is low than when it is high. The converted angle θvg thus obtained is output as the target pinion angle θp* to the pinion angle feedback control unit 83 and the axial force calculation unit 75 of the reaction force control unit 70.

[0048] The pinion angle feedback control unit 83 receives the target pinion angle θp* and the pinion angle θp as input. The pinion angle feedback control unit 83 calculates a steering torque command value T* as a target control amount that will be the target of the steering torque through feedback control of the pinion angle θp in order to make the pinion angle θp follow the target pinion angle θp*. The steering torque command value T* thus obtained is output to the energization control unit 84.

[0049] The power supply control unit 84 receives the steering torque command value T*, the steering rotation angle θb, and the steering actual current value Ib as input. Based on the steering torque command value T*, the power supply control unit 84 calculates the steering current command value for the steering motor 32. The steering current command value is the target value of the torque to be generated by the steering motor 32. The power supply control unit 84 then calculates the difference between the steering current command value and the current value on the dq coordinate obtained by converting the steering actual current value Ib detected through the steering current sensor 58 based on the steering rotation angle θb, and controls the power supply to the steering motor 32 to eliminate this difference. As a result, the steering motor 32 outputs a steering torque corresponding to the steering torque command value T*, and the rotation axis 32a of the steering motor 32 rotates by an angle corresponding to the steering torque command value T*.

[0050] The abnormality detection unit 85 receives the vehicle speed V, pinion angle θp, and steering-side actual current value Ib as input. Based on the vehicle speed V, pinion angle θp, and steering-side actual current value Ib, the abnormality detection unit 85 performs an abnormality detection process to determine whether an abnormality has occurred in the steering unit 6. It also generates an abnormality detection flag Flag indicating the result of the abnormality detection process. The abnormality detection flag Flag thus obtained is output to the warning device 51.

[0051] <About abnormality detection processing> As shown in Figure 4, the abnormality determination unit 85 includes a steering current axial force calculation unit 801, a reference axial force calculation unit 802, a system output compensation component calculation unit 803, an addition / subtraction unit 804, an absolute value processing unit 805, a comparison unit 806, and a threshold calculation unit 807.

[0052] The steering current axial force calculation unit 801 receives the steering-side actual current value Ib as input. The steering current axial force calculation unit 801 calculates the steering current axial force Fi by multiplying the steering-side actual current value Ib by a predetermined gain Kt. The predetermined gain Kt is such that the absolute value of the steering current axial force Fi increases as the absolute value of the steering-side actual current value Ib increases. The steering current axial force Fi thus obtained is output to the addition / subtraction unit 804 and the axial force calculation unit 75 of the reaction force control unit 70. In this embodiment, the processing performed by the steering current axial force calculation unit 801 is an example of steering current axial force calculation processing.

[0053] The reference axial force calculation unit 802 receives the vehicle speed V and the pinion angle θp as input. The reference axial force calculation unit 802 calculates the reference axial force Fb based on the vehicle speed V and the pinion angle θp. The reference axial force calculation unit 802 has an axial force map that defines the relationship between the pinion angle θp and the reference axial force Fb. Multiple axial force maps are provided, for example, according to the vehicle speed V. The reference axial force calculation unit 802 takes the pinion angle θp as input, selects an axial force map according to the vehicle speed V, and performs a map calculation to calculate the reference axial force Fb. An axial force map is an example of a function that specifies that a predetermined output value is output for a predetermined input value. The reference axial force Fb thus obtained is output to the addition / subtraction unit 804. In this embodiment, the processing performed by the reference axial force calculation unit 802 is an example of the reference axial force calculation process.

[0054] More specifically, the reference axial force Fb is the reference axial force acting on the rack shaft 22 via the power transmission mechanism 33 and the road surface for a given amount of movement of the rack shaft 22. The reference axial force Fb is calculated in torque dimensions (N·m).

[0055] Next, the shape of the axial force map will be described. The axial force map is defined by a normative model that relates the steering angle θi of the steering wheel 5 to the axial force acting on the rack shaft 22 for the steering system 2. The relationship defined by the normative model is a design relationship and is an ideal relationship. For example, as shown in Figures 5(a) and (b), it is generally known that the relationship between the steering angle of the steering wheel of a vehicle and the axial force acting on the rack shaft changes depending on the vehicle speed V. Figure 5(a) shows the case where the vehicle speed V is at a very low speed, including when the vehicle is stopped. Figure 5(b) shows the case where the vehicle speed V is at low speed, medium speed, and high speed. The relationship between the steering angle of the steering wheel and the axial force acting on the rack shaft shows that at very low speeds, the gradient, which is the rate of change of axial force with respect to the change in steering angle, is smaller compared to the low, medium, and high speeds. On the other hand, the relationship between the steering angle of the steering wheels and the axial force acting on the rack axis indicates a large hysteresis range caused by the friction between the steering wheels and the road surface in response to changes in the steering angle of the steering wheels. This relationship can be used as a standard for the steering angle of the steering wheels of a vehicle and the axial force acting on the rack axis.

[0056] In contrast, in this embodiment, there is a correlation between the amount of movement of the rack shaft 22 and the pinion angle θp. In this case, by referring to the pinion angle θp, it is possible to calculate the axial force that serves as the reference for the axial force acting on the rack shaft 22 via the power transmission mechanism 33 and the road surface, relative to the amount of movement of the rack shaft 22. The axial force thus obtained can be used as an indicator in the abnormality detection process.

[0057] The axial force map of this embodiment is set with the pinion angle θp on the horizontal axis and the reference axial force Fb on the vertical axis, taking into consideration the relationship between the steering angle of the general steering wheel and the axial force acting on the rack shaft. In this embodiment, there are two types of axial force maps: an axial force map for extremely low speeds designed considering the relationship at extremely low speeds as illustrated in Figure 5(a), and an axial force map for low, medium, and high speeds designed considering the relationship at low, medium, and high speeds as illustrated in Figure 5(b).

[0058] The system output compensation component calculation unit 803 calculates the system output compensation component Fs. The system output compensation component Fs is a component that appears in the vehicle according to the characteristics of the vehicle when the vehicle equipped with the steering system 2 is steered, but is not defined by the normative model of the steering system 2. The system output compensation component Fs is a component that corresponds to the loss of steering torque that occurs according to the characteristics of the vehicle equipped with the steering system 2.

[0059] Here, the components defined by the normative model are static components that appear steadily due to the specifications of the steering system 2. The static components due to the specifications of the steering system 2 include, for example, components that appear as a constant influence on the axial force of the rack shaft 22 due to the specification that the steering angle ratio is made variable in the steering angle ratio change control unit 82. In contrast, the system output compensation component Fs includes static components that appear steadily due to the vehicle specifications and dynamic components that appear transiently depending on the behavior of the vehicle. The static components due to the vehicle specifications include components that are not defined by the normative model of the steering system 2, and for example, components that appear as a constant influence on the axial force of the rack shaft 22 due to the specifications of the suspension and alignment of the vehicle on which the steering system 2 is installed. The dynamic components include components that are not defined by the normative model of the steering system 2, and for example, components that appear as a transient influence on the axial force of the rack shaft 22 in response to changes in the normative model. In other words, the system output compensation component Fs is a component that takes into account the so-called viscous component, inertial component, or spring component that affects the axial force of the rack shaft 22 for the steering system 2 and the vehicle on which the steering system 2 is installed. The system output compensation component Fs thus obtained is output to the addition / subtraction unit 804.

[0060] The addition / subtraction unit 804 receives the steering current axial force Fi, the reference axial force Fb, and the system output compensation component Fs as inputs. The addition / subtraction unit 804 calculates the system internal steering torque cross amount Fl, which is the difference obtained by subtracting the reference axial force Fb and the system output compensation component Fs from the steering current axial force Fi. The system internal steering torque cross amount Fl thus obtained is output to the absolute value processing unit 805.

[0061] The absolute value processing unit 805 receives the system internal steering torque cross amount Fl as input. The absolute value processing unit 805 obtains the absolute value of the system internal steering torque cross amount Fl and calculates the system internal steering torque cross amount absolute value Flabs. The system internal steering torque cross amount absolute value Flabs thus obtained is output to the comparison unit 806.

[0062] The comparison unit 806 receives the absolute value of the system steering torque cross amount, Flabs, and the steering torque cross determination threshold, Fth, as input. Based on the absolute value of the system steering torque cross amount, Flabs, and the steering torque cross determination threshold, the comparison unit 806 performs a threshold comparison process to compare the magnitudes of the absolute value of the system steering torque cross amount, Flabs, and the steering torque cross determination threshold, Fth. The comparison unit 806 also performs a flag generation process to generate abnormality determination flags, Flag(Flag1, Flag2), based on the results of the threshold comparison process. The abnormality determination flags thus obtained are output to the warning device 51.

[0063] More specifically, the abnormality determination flag Flag includes abnormality determination flag Flag1 and abnormality determination flag Flag2. In the flag generation process, the comparison unit 806 includes a process of not generating an abnormality determination flag Flag if the threshold comparison process derives a result in which the absolute value of the system internal steering torque cross amount Flabs is less than the first threshold Fth1. On the other hand, the comparison unit 806 includes a process of generating abnormality determination flag Flag1 if the threshold comparison process derives a result in which the absolute value of the system internal steering torque cross amount Flabs is greater than or equal to the first threshold Fth1 and less than the second threshold Fth2. On the other hand, the comparison unit 806 includes a process of generating abnormality determination flag Flag2 if the threshold comparison process derives a result in which the absolute value of the system internal steering torque cross amount Flabs is greater than or equal to the second threshold Fth2.

[0064] The threshold calculation unit 807 outputs a steering torque cross determination threshold Fth to the comparison unit 806. The steering torque cross determination threshold Fth is set from the viewpoint of indicating a state in which the relationship between the axial force actually acting on the rack shaft 22 via the power transmission mechanism 33 and the road surface and the reference axial force acting on the rack shaft 22 via the power transmission mechanism 33 and the road surface with respect to the amount of movement of the rack shaft 22 is inappropriate. The threshold calculation unit 807 reads the steering torque cross determination threshold Fth from a predetermined storage area of ​​a memory (not shown) and outputs it.

[0065] In this embodiment, an inappropriate relationship refers to a state in which the relationship between the steering current axial force Fi and the reference axial force Fb is inappropriate. This inappropriate relationship refers to a state in which the relationship between the steering current axial force Fi and the reference axial force Fb is inappropriate even when considering the system output compensation component Fs. An inappropriate relationship between the steering current axial force Fi and the reference axial force Fb can occur in the case of excessive output loss abnormality, where the steering torque is generated by the steering motor 32, but the steering torque is not properly transmitted to the reciprocating motion of the rack shaft 22 via the power transmission mechanism 33. Excessive output loss abnormality includes cases caused by the occurrence of a steering lock precursor state, such as jamming of the balls 45 in the ball screw mechanism 35 or partial damage to the ball screw nut 46. Furthermore, excessive output loss abnormality includes cases where the steering lock precursor state continues, for example, when the ball screw mechanism 35 of the power transmission mechanism 33 becomes stuck and stops operating. The steering lock state is a condition in which the output loss is particularly large compared to the steering lock precursor state, even among the abnormalities of excessive output loss. The steering torque loss judgment threshold Fth is set as a range value experimentally determined through simulations, etc., based on the perspective of determining the abnormalities of excessive output loss, including the steering lock state and the steering lock precursor state described above.

[0066] More specifically, the steering torque loss determination threshold Fth includes a first threshold Fth1 and a second threshold Fth2 which is a value greater than the first threshold Fth1. The first threshold Fth1 is a threshold for determining a pre-steering lock state. The second threshold Fth2 is a threshold for determining a steering lock state. The first threshold Fth1 is a value set considering a fixed value Fth0, which is a margin, to a predetermined value To that has been experimentally determined to be able to determine a pre-steering lock state. In other words, the first threshold Fth1 is a value obtained by adding the predetermined value To and the fixed value Fth0. The fixed value Fth0 is a value within a range that has been experimentally determined to be able to suppress misjudgments.

[0067] In this embodiment, the steering current axial force Fi is the axial force that actually acts on the rack shaft 22 when the vehicle equipped with the steering system 2 is steered, whereas the reference axial force Fb is an axial force defined by a reference model in the design. Therefore, the intermediate subtraction value FA, which is obtained by subtracting the reference axial force Fb from the steering current axial force Fi, is expected to fall within a predetermined range, provided that the output loss of steering torque is not excessive. This predetermined range is expected to include the loss of steering torque that occurs according to the characteristics of the vehicle equipped with the steering system 2, i.e., the system output compensation component Fs. Thus, the system internal steering torque loss amount Fl, i.e., the absolute value of the system internal steering torque loss amount Flabs, obtained by subtracting the system output compensation component Fs from the intermediate subtraction value FA, falls within a range of a predetermined value To that has been experimentally determined to allow for the determination of a pre-steering lock state, with zero as the reference.

[0068] In contrast, the absolute value of the steering current axial force Fi is assumed to be excessive when the output loss of steering torque is large, even though the steering motor 32 is generating steering torque, because the steering torque is not being properly transmitted to the reciprocating motion of the rack shaft 22 via the power transmission mechanism 33. Therefore, the absolute value of the steering current axial force Fi is excessive compared to the absolute value of the reference axial force Fb. Consequently, the intermediate subtracted value FA, which is obtained by subtracting the reference axial force Fb from the steering current axial force Fi, is assumed to reach a value that deviates significantly from the predetermined range when the output loss of steering torque is large. This deviation is assumed to reach a large value even when considering the steering torque loss that occurs depending on the characteristics of the vehicle on which the steering system 2 is installed, i.e., the system output compensation component Fs. As a result, the system internal steering torque loss amount Fl, or the absolute value of the system internal steering torque loss amount Flabs, obtained by subtracting the system output compensation component Fs from the intermediate subtraction value FA, reaches a range that deviates significantly from the range of a predetermined value To that has been experimentally determined to be able to determine a precursory state of steering lock, with zero as the reference.

[0069] Considering the above, in this embodiment, the first threshold Fth1 is a value obtained by adding a predetermined value To and a fixed value Fth0. Therefore, if the threshold comparison process derives a result in which the absolute value of the steering torque loss amount Flabs within the system is greater than or equal to the first threshold Fth1, it is possible to determine that the output loss is excessive, that is, that it is either a pre-steering lock state or a steering lock state. Furthermore, if the threshold comparison process derives a result in which the absolute value of the steering torque loss amount Flabs within the system is greater than or equal to the first threshold Fth1 and less than the second threshold Fth2, it is possible to determine that it is a pre-steering lock state even if the output loss is excessive. Also, if the threshold comparison process derives a result in which the absolute value of the steering torque loss amount Flabs within the system is greater than or equal to the second threshold Fth2, it is possible to determine that it is a steering lock state even if the output loss is excessive. In other words, according to this embodiment, when determining that the output loss of steering torque is excessive, it is possible to distinguish and determine the severity of the abnormality, such as a pre-steering lock state and a steering lock state.

[0070] In this embodiment, the series of processes performed by the addition / subtraction unit 804, the absolute value processing unit 805, the comparison unit 806, and the threshold calculation unit 807 is an example of a comparison process that compares the steering current axial force Fi with the reference axial force Fb.

[0071] <Warning Processing> As shown in Figure 1, the warning device 51 receives an abnormality determination flag, Flag. When the warning device 51 receives an abnormality determination flag, Flag, it controls the operation of warning lights, speakers, etc., in accordance with the type of abnormality determination flag, Flag1, Flag2. For example, the warning device 51 controls the warning lights to illuminate in a color corresponding to the type of abnormality determination flag, Flag1, Flag2. In this case, the warning device 51 controls the warning lights to illuminate yellow when abnormality determination flag Flag1 is received, and to illuminate red when abnormality determination flag Flag2 is received.

[0072] <Effects and Effects of the First Embodiment> The steering control unit 80 determines an abnormality due to excessive output loss by comparing the steering current axial force Fi with the reference axial force Fb. The steering control unit 80 also has an abnormality determination unit 85 that performs an abnormality determination process to determine whether the output loss of the steering torque is excessive.

[0073] More specifically, the abnormality determination unit 85 includes a steering current axial force calculation unit 801, a reference axial force calculation unit 802, an addition / subtraction unit 804, a comparison unit 806, and a threshold calculation unit 807. The steering current axial force calculation unit 801 calculates the steering current axial force Fi based on the steering side actual current value Ib. The reference axial force calculation unit 802 calculates the reference axial force Fb by applying an axial force map defined by a function that outputs the axial force acting on the rack shaft 22 based on the pinion angle θp, which is a steering axis related value. The steering current axial force Fi is the axial force that actually acts on the rack shaft 22 via the power transmission mechanism 33 and the road surface. The reference axial force Fb is a reference axial force that acts on the rack shaft 22 via the power transmission mechanism 33 and the road surface with respect to the amount of movement of the rack shaft 22, and can be used as a reference for the amount of movement of the rack shaft 22. The addition / subtraction unit 804 subtracts the reference axial force Fb and the system output compensation component Fs calculated by the system output compensation component calculation unit 803 from the steering current axial force Fi to calculate the system internal steering torque cross amount Fl. The system internal steering torque cross amount Fl is converted to the absolute value of the system internal steering torque cross amount Flabs by the absolute value processing unit 805 and then input to the comparison unit 806. The comparison unit 806 compares the absolute value of the system internal steering torque cross amount Flabs with the steering torque cross determination threshold Fth (Fth1, Fth2) output from the threshold calculation unit 807. Through this comparison, the relationship between the steering current axial force Fi and the reference axial force Fb as an index is compared.

[0074] The comparison results indicate that if the absolute value of the steering torque loss within the system, Flabs, is greater than or equal to the steering torque loss determination threshold Fth, then even considering the system output compensation component Fs, the relationship between the steering current axial force Fi and the reference axial force Fb is considered inappropriate. This condition can occur in cases of excessive output loss, where the steering motor 32 generates steering torque, but the steering torque is not correctly transmitted to the reciprocating motion of the rack shaft 22 via the power transmission mechanism 33. Excessive output loss is an example of a malfunction in the steering unit 6. The steering control device 1 of this embodiment determines such excessive output loss malfunctions from the perspective of the axial force acting on the rack shaft 22 through an abnormality determination process. That is, it determines that the relationship between the steering current axial force Fi that actually acts on the rack shaft 22 via the power transmission mechanism 33 and the road surface, and the reference axial force Fb that acts on the rack shaft 22 via the power transmission mechanism 33 and the road surface in relation to the amount of movement of the rack shaft 22 is inappropriate. Therefore, the steering control device 1 of this embodiment can suitably determine that an abnormality has occurred in the steering unit 6, such as an excessive output loss.

[0075] <Effects of the First Embodiment> According to the embodiment described above, the following further effects can be obtained. (1-1) The reference axial force calculation unit 802 in the abnormality determination unit 85 includes a process of calculating the reference axial force Fb using an axial force map that defines the relationship between the pinion angle θp and the vehicle speed V and the axial force acting on the rack shaft 22. This makes it possible to suppress the increase in the computational load required to derive the reference axial force Fb, even if the vehicle speed V is also taken into consideration in order to improve the accuracy of the abnormality determination process.

[0076] (1-2) The comparison unit 806 in the abnormality determination unit 85 can distinguish and determine the severity of the abnormality of the steering unit 6, such as a pre-steering lock state and a steering lock state, while determining that the output loss is excessive. Therefore, in the vehicle, measures can be taken according to the result of the comparison unit 806, such as illuminating a warning light with the warning device 51, as a measure corresponding to the severity of the abnormality of the steering unit 6. Therefore, when an abnormality occurs in the steering unit 6, the severity of the abnormality of the steering unit 6 can be appropriately understood by the vehicle driver or maintenance personnel. In particular, in the pre-steering lock state, the abnormality of the steering unit 6 can be understood by the vehicle driver or maintenance personnel prior to reaching the steering lock state, and the need for maintenance inspection can be made clear.

[0077] (1-3) The abnormality determination unit 85 includes a system output compensation component calculation unit 803. The system output compensation component calculation unit 803 includes a process for calculating a system output compensation component Fs, which is a component that appears in the vehicle according to the characteristics of the vehicle on which the steering system 2 is installed, and is a component that is not defined by the normative model. Therefore, the comparison unit 806 can consider components that are not included in the normative axial force Fb because they are not defined in the normative model. Thus, the normative axial force Fb, which is a standard that considers the entire system of the vehicle on which the steering system 2 is installed, can be used as an index during the abnormality determination process, and the abnormality determination process can be performed suitably even when considering the entire vehicle on which the steering system 2 is installed.

[0078] (1-4) The comparison unit 806 in the abnormality determination unit 85 includes a process of comparing the magnitude of the absolute value of the steering torque cross amount Flabs within the system and the steering torque cross determination threshold Fth. Therefore, when determining that an abnormality has occurred in the steering unit 6, it is possible to quantitatively determine that the relationship between the steering current axial force Fi and the reference axial force Fb is inappropriate. This is effective in ensuring the reproducibility of the results of the abnormality determination process.

[0079] (1-5) In this embodiment, the steering system 2 is a steer-by-wire type steering device, and the steering current axial force Fi is used for both the calculation of reaction torque and the abnormality detection process. Therefore, even when adopting a configuration that determines whether an abnormality has occurred in the steering unit 6, the scale of design changes can be kept to a minimum.

[0080] <Second Embodiment> The second embodiment will now be described with reference to the drawings. This embodiment differs from the first embodiment in the configuration of the abnormality detection unit 85. For this reason, components similar to those in the first embodiment are denoted by the same reference numerals and their descriptions are omitted.

[0081] As shown by the dashed line in Figure 4, the abnormality determination unit 85 of this embodiment has an extremely low speed determination unit 810. The vehicle speed V is input to the extremely low speed determination unit 810. The extremely low speed determination unit 810 includes a process to determine whether the input vehicle speed V is an extremely low speed, including when the vehicle is stopped. If the abnormality determination unit 85 determines that the vehicle speed V is an extremely low speed, it includes a process to generate an abnormality determination flag Flag. In this case, the reference axial force calculation unit 802 will calculate the reference axial force Fb using the axial force map for extremely low speeds. On the other hand, if the abnormality determination unit 85 determines that the vehicle speed V is not an extremely low speed, that is, that the vehicle speed V is low, medium, or high speed, it includes a process not to generate an abnormality determination flag Flag. In other words, the reference axial force calculation unit 802 of this embodiment only needs to have an axial force map corresponding to the extremely low speed, and can eliminate the axial force maps corresponding to the low, medium, and high speeds.

[0082] <Effects of the second embodiment> According to the second embodiment described above, the same functions and effects as those of the first embodiment can be obtained, and in addition, the following effects can be obtained.

[0083] (2-1) The abnormality detection unit 85 includes an extremely low-speed detection unit 810. Therefore, the abnormality detection unit 85 can generate an abnormality detection flag Flag at extremely low speeds, including when the vehicle is stopped, which is a vehicle speed V at which changes in the reference axial force Fb are more likely to appear. Therefore, the conditions under which the abnormality detection flag Flag is generated can be optimized.

[0084] <Other Embodiments> Each of the above embodiments may be modified as follows. Furthermore, the following other embodiments can be combined with each other to the extent that they do not conflict with the technical standards.

[0085] In the first embodiment, the steering system 2 was configured as a steer-by-wire steering device, but it may also be configured as an electric power steering device. In an electric power steering device, the steering wheel 3 and the steering wheels 5 shown in Figure 1 are mechanically connected. That is, the steering shaft 11, pinion shaft 21, and rack shaft 22 function as power transmission paths between the steering wheel 3 and the steering wheels 5. As the steering wheel 3 is turned, the rack shaft 22 reciprocates, changing the steering angle θi of the steering wheels 5. The electric power steering device has an assist motor and an assist control device. The assist motor is located in the same position as the reaction motor 13 or steering motor 32 shown in Figure 1. The assist motor generates an assist force to assist in the operation of the steering wheel 3. The assist force is a torque in the same direction as the steering direction of the steering wheel 3, and is a steering torque for turning the steering wheels 5. The assist control device corresponds to the steering control device 1. The assist control device controls the drive of the assist motor, which is the object of control. In this case, the assist control device only needs to have a configuration corresponding to the abnormality determination unit 85 of the steering control unit 80 shown in Figure 2, that is, a configuration corresponding to the steering current axial force calculation unit 801. Such a configuration corresponding to the steering current axial force calculation unit 801 can calculate the steering current axial force Fi based on the current value generated in the assist motor. In other words, the configuration corresponding to the abnormality determination unit 85 performs abnormality determination processing by comparing the steering current axial force Fi calculated based on the current generated in the assist motor with the reference axial force Fb. In electric power steering systems, the sum of the steering current axial force Fi calculated based on the current generated in the assist motor and the steering torque Th, which is the manual torque by the driver, corresponds to the axial force actually acting on the rack shaft 22 that operates to steer the steering wheels 5. Therefore, the configuration corresponding to the abnormality determination unit 85 can also perform abnormality determination processing by comparing the sum of the torque Tsum with the reference axial force Fb. Other embodiments described here can also be applied to the second embodiment.

[0086] In the first embodiment, the steering current axial force filter 102 was applied to the steering current axial force Fi in the axial force calculation unit 75, but the steering current axial force filter 102 may be omitted. The other embodiments described herein can also be applied to the second embodiment.

[0087] In the first embodiment, the system output compensation component Fs calculated by the system output compensation component calculation unit 803 is subtracted by the addition / subtraction unit 804, but this is not limited to this. For example, by setting the steering torque cross determination threshold Fth calculated by the threshold calculation unit 807 to a threshold that takes the system output compensation component Fs into consideration, the subtraction of the system output compensation component Fs by the addition / subtraction unit 804 may be omitted. Other embodiments described herein can also be applied to the second embodiment.

[0088] In the first embodiment, static components that appear steadily due to the vehicle specifications and are included in the system output compensation component Fs may be considered by the reference axial force calculation unit 802 rather than by the system output compensation component calculation unit 803. Also, dynamic components included in the system output compensation component Fs may be considered by the reference axial force calculation unit 802 rather than by the system output compensation component calculation unit 803. In this case, the dynamic components considered by the reference axial force calculation unit 802 may be only those components related to the specifications of the steering system 2 that appear to transiently affect the axial force of the rack axis 22 in response to changes in the reference model. Other embodiments described herein can also be applied to the second embodiment.

[0089] In the first embodiment, it is not essential to consider the system output compensation component Fs in the abnormality detection process. The other embodiments described herein can also be applied to the second embodiment.

[0090] In the first embodiment, the system output compensation component calculation unit 803 may output a system output compensation component Fs calculated by simulation or the like, for example, a value that has been stored in a memory unit in advance as a fixed value. In this case, the memory unit that stores the fixed value system output compensation component Fs is a predetermined memory area of ​​a memory (not shown). The threshold calculation unit 807 may also output a steering torque cross determination threshold Fth calculated by simulation or the like, for example, a value that has been stored in a memory unit in advance as a fixed value. The memory unit that stores the fixed value steering torque cross determination threshold Fth is a predetermined memory area of ​​a memory (not shown). The other embodiments described herein can also be applied to the second embodiment.

[0091] In the first embodiment, the pinion angle θp was used as the steering axis-related value, but it is not limited to this. For example, the target pinion angle θp* or the steering angle θs may be used as the steering axis-related value. More specifically, the target pinion angle θp* is the target control quantity that is the target of the pinion angle θp. The target pinion angle θp* is calculated based on the converted angle θvg. The converted angle θvg is calculated based on the steering angle θs. As described above, there is a correlation between the target pinion angle θp* and the steering angle θs. That is, the target pinion angle θp* obtained based on the steering angle θs is a value that reflects the reaction force side rotation angle θa. Also, the pinion angle θp is controlled based on the target pinion angle θp*. For this reason, there is also a correlation between the pinion angle θp and the target pinion angle θp*. Furthermore, considering the correlation with the pinion angle θp, for example, the axial movement of the rack shaft 22 or the steering angle θi of the steering wheel 5 are appropriate values ​​related to the steering axis. The other embodiments described here can also be applied to the second embodiment.

[0092] In the first embodiment, the comparison unit 806 of the abnormality determination unit 85 includes a process for generating two types of flags, but it is not limited to this. For example, the comparison unit 806 may include a process for generating one type of flag, or it may include a process for generating three or more types of flags. In other words, the threshold calculation unit 807 only needs to set thresholds corresponding to the flags.

[0093] In the first embodiment, a steering lock state and a preceding steering lock precursor state were assumed as abnormalities of the steering unit 6, but the embodiment is not limited to this. For example, a steering ice state and a steering ice precursor state may be assumed, in which the steering unit 6 ceases to operate normally due to freezing. Other embodiments described herein can also be applied to the second embodiment.

[0094] In the first embodiment, the warning process was performed as a process of a warning device 51 connected to the steering control device 1, but the warning process may also be performed as a process within the steering control device 1. In this case, as a method of warning, for example, the reaction force control unit 70 may be controlled to apply an additional reaction force to the reaction force motor 13 according to the abnormality determination flag Flag. In this case, a small reaction force can be applied for abnormality determination flag Flag 1, and a large reaction force for abnormality determination flag Flag 2. Alternatively, for example, a small vibration can be applied to the steering wheel 3 for abnormality determination flag Flag 1, and a small vibration for abnormality determination flag Flag 2. Other embodiments described herein can also be applied to the second embodiment. [Explanation of Symbols]

[0095] 1... Steering control device 2… Steering system 3… Steering wheel 4…Reaction unit 5… Steering wheel 6… Steering unit 13… Reaction motor 14…Reaction force transmission mechanism 22... Rack axis (steering axis) 32... Steering motor 33... Power transmission mechanism 70…Reaction Force Control Unit 72... Reaction force control amount calculation unit 80... Steering control unit 85...Abnormality determination section 801... Steering current axial force calculation unit 802…Reference axial force calculation section 803...System output compensation component calculation unit 804... Addition and Subtraction Section 806...Comparison section 807...Threshold calculation unit 810...Extremely low speed judgment section

Claims

1. A steering control device that controls a steering system, which is mounted on a vehicle and includes a steering unit comprising a steering motor, a steering shaft connected to the steering wheels of the vehicle, and a power transmission mechanism that transmits the torque of the steering motor to the steering shaft, The steering control device is A steering current acquisition process that acquires the steering current value, which is the current generated in the steering motor, from the steering system. A steering axis-related value acquisition process that obtains steering axis-related values ​​from the steering system, which are values ​​that can be converted into the amount of movement of the steering axis, The system is configured to perform an abnormality determination process that determines whether an abnormality has occurred in the steering unit based on the steering current value and the steering shaft related value. The aforementioned abnormality determination process is: A steering current axial force calculation process that calculates the steering current axial force based on the steering current value, A reference axial force calculation process is performed to calculate a reference axial force, which is a reference axial force for the amount of movement of the steering axis, based on the steering axis-related values, A comparison process that compares the steering current axial force with the reference axial force, A steering control device including a determination process that determines, based on the results of the comparison process, that an abnormality has occurred in the steering unit.

2. The steering control device according to claim 1, wherein the reference axial force is an axial force defined by a function that takes the steering axis-related values ​​as input and outputs the axial force acting on the steering axis.

3. The steering control device according to claim 2, wherein the function is defined by an axial force map that defines the relationship between the steering axis-related values ​​and vehicle speed and the axial force acting on the steering axis.

4. The steering control device according to claim 1, wherein the abnormality determination process is performed when the vehicle is at an extremely low speed, including when it is stopped.

5. The abnormality detection process is configured to derive multiple determination results regarding the abnormality of the steering unit. The steering control device according to claim 1, wherein the plurality of determination results are divided according to the severity of the abnormality of the steering unit.

6. The abnormality determination process includes a process for calculating a system output compensation component, which is a component that appears in the vehicle according to the characteristics of the vehicle and is not included in the reference axial force. The steering control device according to claim 1, wherein the system output compensation component is taken into account during the comparison process.

7. The steering control device according to claim 6, wherein the comparison process includes a process of comparing the magnitude of the difference obtained by subtracting the reference axial force and the system output compensation component from the steering current axial force with a first threshold.

8. The steering system includes a reaction force unit with a power transmission path separated from the steering unit, The steering control device according to claim 1, wherein the reaction force unit includes a reaction force motor, a steering shaft connected to the steering wheel of the vehicle, and a reaction force transmission mechanism that transmits a reaction force torque, which is the torque of the reaction force motor and is a reaction force that opposes the driver's operation, to the steering wheel via the steering shaft.

9. The steering control device according to claim 8, wherein the steering control device includes a reaction force calculation process that calculates the reaction force torque based on the steering current axial force.

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