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 is configured to perform a steering current acquisition process to acquire a steering current value Ib, which is the current generated in the steering motor, from the steering system; a turning-related value acquisition process to acquire a lateral acceleration LA, which is a value that can be converted into a force acting on the vehicle during turning, from the vehicle; and an abnormality determination process to determine whether an abnormality has occurred in the steering unit based on the steering current value Ib and the lateral acceleration LA. The abnormality determination process includes a comparison process to compare the relationship between the steering current value Ib and the lateral acceleration LA based on whether the vehicle is turning; and a determination process to determine 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 that controls 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 a steering means including a steering unit to determine 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 the steering device, the technology related to the abnormality determination of the steering unit is important. Therefore, development from various viewpoints is required for a method capable of determining an abnormality in the steering unit. This is not limited to the steering unit constituting a steer-by-wire type steering device, but 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 turning-related value acquisition process to acquire a turning-related value, which is a value that can be converted into a force acting on the vehicle during turning, from the vehicle; and an abnormality determination process to determine whether an abnormality has occurred in the steering unit based on the steering current value and the turning-related value. The abnormality determination process includes a comparison process to compare the relationship between the steering current value and the turning-related value based on whether the vehicle is turning; and a determination process to determine whether an abnormality has occurred in the steering unit based on the result of the comparison process.

[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 actual steering current value, which is based on whether the vehicle is turning, with the turning-related value, in a state where the relationship is inappropriate.

[0007] In the steering control device described above, the comparison process includes a first comparison process that compares the magnitude relationship between the steering current value and a first threshold value, and a second comparison process that compares the magnitude relationship between the turning-related value and a second threshold value. The determination process may include a process that determines whether an abnormality has occurred in the steering unit based on the results of the first comparison process and the results of the second comparison process.

[0008] According to the steering control device described above, individual comparison processing is performed using individual thresholds. Therefore, even if the dimensions of the steering current value and the turning-related value are different, abnormality detection processing can be appropriately performed based on the results of individual comparison processing using thresholds appropriate for each value.

[0009] In the steering control device described above, the first threshold and the second threshold are fixed values ​​set from the perspective of determining whether the steering current value is within the range indicating that the vehicle is turning, even though the turning-related value is within the range indicating that the vehicle is turning. The first comparison process derives a result indicating that the first condition is met when the steering current value is greater than the first threshold, and the second comparison process derives a result indicating that the second condition is met when the turning-related value is less than the second threshold. The determination process may determine that an abnormality has occurred in the steering unit if it indicates that both the first and second conditions are met.

[0010] The steering control device described above is effective in reducing the occurrence of misjudgments due to abnormality detection processing. In the steering control device described above, 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, and a reference axial force calculation process that calculates a reference axial force, which is calculated based on the turning-related value and is a reference axial force for the force acting on the vehicle during turning. The comparison process may include an axial force comparison process that compares the steering current axial force with the reference axial force.

[0011] 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 that acts on the rack shaft via the power transmission mechanism and the road surface in relation to the turning-related value, in which case the relationship is inappropriate.

[0012] 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 turning-related values ​​as input and outputs the axial force acting on the vehicle. In the steering control device described above, the function may be defined by an axial force map that defines the relationship between the turning-related values ​​and vehicle speed and the axial force acting on the steering axis.

[0013] 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.

[0014] In the steering control device described above, the abnormality detection process may be performed when the vehicle is in motion at low, medium, or high speeds. According to the steering control device described above, the conditions under which abnormality detection processing is performed can be optimized.

[0015] 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.

[0016] 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.

[0017] 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 axial force comparison process.

[0018] 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 axial force 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 third threshold.

[0019] 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 a power transmission path to the steering unit is separated, and 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 against the operation of the driver, to the steering wheel via the steering shaft.

[0020] According to the above-described steering control device, even for a steering unit mounted on a steer-by-wire vehicle, an abnormality determination process can be suitably performed. In the above-described steering control device, it may include a reaction force calculation process for calculating the reaction force torque based on the steering current axial force.

[0021] 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 vehicle, the scale of design changes can be kept small.

Effects of the Invention

[0022] 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

[0023] [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] It is a block diagram showing the functions of the abnormality determination unit according to the second embodiment. [Figure 6] It is a graph showing the general relationship between the axial force and lateral acceleration at the vehicle speed. [Modes for carrying out the invention]

[0024] <First Embodiment> The first embodiment of the present invention will be described below. <Overall Structure> As shown in Figure 1, the steering control device 1 controls the steering system 2. The steering system 2 is, for example, a steering device for a steer-by-wire vehicle. The steering system 2 comprises a reaction force unit 4 and a steering unit 6. The reaction force unit 4 is steered by the 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 from the driver to the reaction force unit 4. The steering system 2 has a structure in which, for example, the power transmission path between the reaction force unit 4 and the steering unit 6 is mechanically and permanently separated. The power transmission path between the reaction force actuator 12 (described later) and the steering actuator 31 (described later) is mechanically and permanently separated.

[0025] The reaction force unit 4 comprises 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 able to rotate integrally with the steering wheel 3. The reaction force actuator 12 comprises 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 steering wheel 3 by the driver. 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] <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.

[0031] The steering control device 1 is connected to the reaction motor 13 and the steering motor 32, and performs processing to operate the reaction motor 13 and the steering motor 32, respectively. The steering control device 1 also performs abnormality detection processing to determine if there is an abnormality in the steering unit 6 when the relationship between the steering-side actual current value Ib and the lateral acceleration LA is not appropriate. The steering-side actual current value Ib is the actual current value supplied to the steering motor 32. The lateral acceleration LA is a value that can be converted into the force acting on the vehicle during turning. 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.

[0032] 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, a steering side current sensor 58, and a lateral acceleration sensor 59.

[0033] 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.

[0034] The reaction force side current sensor 57 detects the reaction force side actual current value Ia, which is the actual current value supplied to the reaction force motor 13. The reaction force side actual current value Ia indicates the magnitude of the reaction force torque output by the reaction force motor 13. For example, the reaction force side actual 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 steering side actual current value Ib. The steering side actual current value Ib indicates the magnitude of the steering torque output by the steering motor 32. For example, the steering side actual 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.

[0035] The lateral acceleration sensor 59 detects the lateral acceleration LA occurring in the vehicle. Lateral acceleration LA is the lateral acceleration acting on the vehicle during turning. 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 lateral acceleration LA is an example of a turning-related value, which is a value that can be converted into the force acting on the vehicle during turning. The input of detection results from various sensors to the steering control device 1 is an example of the process by which the steering control device 1 acquires detection values ​​from 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. Also, the process by which the steering control device 1 acquires the detected lateral acceleration LA is an example of a turning-related value acquisition process.

[0036] <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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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*.

[0042] 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.

[0043] 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, assuming that the torque applied to the rack shaft 22 by the steering motor 32 and the torque corresponding to the force applied to the rack shaft 22 through the steering wheels 5 are balanced, 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.

[0044] 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.

[0045] 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 ​​the memory (not shown).

[0046] 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.

[0047] 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.

[0048] 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.

[0049] <Functions of the steering control unit> The steering control unit 80 receives the vehicle speed V, the steering angle θb, the steering angle θs, and the lateral acceleration LA as input. Based on the vehicle speed V, the steering angle θb, the steering angle θs, and the lateral acceleration LA, the steering control unit 80 controls the power supply to the steering motor 32.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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*.

[0055] The abnormality detection unit 85 receives the vehicle speed V, lateral acceleration LA, and steering-side actual current value Ib as input. Based on the vehicle speed V, lateral acceleration LA, 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. The abnormality detection unit 85 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.

[0056] <About abnormality detection processing> As shown in Figure 4, the abnormality determination unit 85 includes a first threshold calculation unit 811, a second threshold calculation unit 812, a first comparison unit 813, a second comparison unit 814, a flag arbitration unit 815, a steering current axial force calculation unit 816, and a driving determination unit 817.

[0057] The first threshold calculation unit 811 outputs a steering current threshold Fthi, which is the first threshold value. The steering current threshold Fthi is set to a value within a range experimentally determined by simulation, etc., based on the actual steering current value Ib, which allows for the determination that the vehicle is turning. The first threshold calculation unit 811 reads the steering current threshold Fthi from a predetermined storage area of ​​memory (not shown) and outputs it.

[0058] The second threshold calculation unit 812 outputs a lateral acceleration threshold Fthl, which is the second threshold. The lateral acceleration threshold Fthl is set to a value within a range experimentally determined by simulation, etc., based on the assumption that the vehicle is turning based on the lateral acceleration LA. The second threshold calculation unit 812 reads the lateral acceleration threshold Fthl from a predetermined storage area of ​​memory (not shown) and outputs it.

[0059] Here, the steering current threshold Fthi and the lateral acceleration threshold Fthl are values ​​of different dimensions. For example, the steering current threshold Fthi has the dimension of amperes (A), and the lateral acceleration threshold Fthl has the dimension of acceleration (m / (s·s)).

[0060] The first comparison unit 813 receives the steering-side actual current value Ib and the steering current threshold Fthi as input. The first comparison unit 813 performs a first comparison process to compare the magnitude relationship between the steering-side actual current value Ib and the steering current threshold Fthi. Based on the comparison result of the first comparison process, the first comparison unit 813 performs a first flag generation process to generate a first flag F1. The first flag F1 thus obtained is output to the flag arbitration unit 815.

[0061] More specifically, in the first flag generation process, the first comparison unit 813 includes a process to output a first flag F1 (F1=0) which is "0" if the first comparison process derives a result in which the steering-side actual current value Ib is less than or equal to the steering current threshold Fthi. On the other hand, if the first comparison unit 813 derives a result in which the steering-side actual current value Ib is greater than the steering current threshold Fthi, the first condition is met and the first flag F1 (F1=1) which is "1" is output.

[0062] The second comparison unit 814 receives the lateral acceleration LA and the lateral acceleration threshold Fthl as input. The second comparison unit 814 performs a second comparison process to compare the magnitude relationship between the lateral acceleration LA and the lateral acceleration threshold Fthl. Based on the comparison result of the second comparison process, the second comparison unit 814 performs a second flag generation process to generate a second flag F2. The second flag F2 thus obtained is output to the flag arbitration unit 815.

[0063] More specifically, in the second flag generation process, the second comparison unit 814 includes a process to output a second flag F2 (F2=0) which is "0" if the second comparison process derives a result in which the lateral acceleration LA is greater than or equal to the lateral acceleration threshold Fthl. On the other hand, if the second comparison unit 814 derives a result in which the lateral acceleration LA is less than the lateral acceleration threshold Fthl if the second comparison process derives a result in which the second condition is met, it includes a process to output a second flag F2 (F2=1) which is "1". In this embodiment, the first comparison process and the second comparison process are examples of comparison processes.

[0064] The flag arbitration unit 815 receives the first flag F1 and the second flag F2 as input. The flag arbitration unit 815 arbitrates the first flag F1 and the second flag F2. The flag arbitration unit 815 performs a logical AND operation to calculate the logical AND of the first flag F1 and the second flag F2. Based on the result of the logical AND operation, the flag arbitration unit 815 performs an abnormality determination flag generation operation to generate an abnormality determination flag Flag. The abnormality determination flag Flag thus obtained is output to the warning device 51.

[0065] More specifically, in the abnormality determination flag generation process, the flag arbitration unit 815 includes a process to generate an abnormality determination flag, Flag, when the logical AND operation results in "1" because both the first flag F1 and the second flag F2 are "1". On the other hand, the flag arbitration unit 815 includes a process not to generate an abnormality determination flag, Flag, when the logical AND operation results in "0" because both the first flag F1 and the second flag F2 are not "1".

[0066] The steering current axial force calculation unit 816 receives the steering-side actual current value Ib as input. The steering current axial force calculation unit 816 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 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 816 is an example of steering current axial force calculation processing.

[0067] The driving determination unit 817 receives the vehicle speed V as input. The driving determination unit 817 includes a process to determine whether the input vehicle speed V is low-medium-high speed, which indicates that the vehicle is traveling at a sufficient speed. This is based on the fact that a situation in which the vehicle is traveling at a sufficient speed can occur. The flag arbitration unit 815 of the abnormality determination unit 85 includes a process to generate an abnormality determination flag Flag if the driving determination unit 817 determines that the vehicle speed V is low-medium-high speed. On the other hand, the flag arbitration unit 815 of the abnormality determination unit 85 includes a process to not generate an abnormality determination flag Flag if the driving determination unit 817 determines that the vehicle speed V is not low-medium-high speed, that is, that the vehicle speed V is at an extremely low speed, including when the vehicle is stopped.

[0068] <Warning Processing> As shown in Figure 1, the warning device 51 receives an abnormality judgment flag (Flag). When the warning device 51 receives an abnormality judgment flag (Flag), it controls the operation of warning lights, speakers, etc. For example, the warning device 51 controls the warning lights to illuminate in a color corresponding to the abnormality judgment flag (Flag). For example, when the warning device 51 receives an abnormality judgment flag (Flag), it controls the warning lights to illuminate in yellow.

[0069] <Operation of the First Embodiment> The steering control unit 80 determines an abnormality due to excessive output loss by comparing the actual steering current value Ib with the lateral acceleration LA. 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.

[0070] More specifically, the abnormality determination unit 85 includes a first threshold calculation unit 811, a second threshold calculation unit 812, a first comparison unit 813, a second comparison unit 814, and a flag arbitration unit 815. The first threshold calculation unit 811 outputs a steering current threshold Fthi as the first threshold. The second threshold calculation unit 812 outputs a lateral acceleration threshold Fthl as the second threshold. The first comparison unit 813 performs a first comparison process that compares the magnitude relationship between the steering side actual current value Ib and the steering current threshold Fthi, thereby determining whether the vehicle is turning based on the steering side actual current value Ib. The second comparison unit 814 performs a second comparison process that compares the magnitude relationship between the lateral acceleration LA and the lateral acceleration threshold Fthl, thereby determining whether the vehicle is turning based on the lateral acceleration LA. The flag arbitration unit 815 determines whether the relationship between the steering-side actual current value Ib and the lateral acceleration LA matches by arbitrating whether both the first flag F1 and the second flag F2 are 1. Through this series of processes, it is possible to compare the relationship between the steering-side actual current value Ib and the lateral acceleration LA based on whether the vehicle is turning.

[0071] For example, in the first comparison process, if it is determined that the steering-side actual current value Ib is greater than the steering current threshold Fthi, it is possible that the vehicle is in a turning state. In the second comparison process, if it is determined that the lateral acceleration LA is less than the lateral acceleration threshold Fthl, it is possible that the vehicle is not in a turning state. If the relationship between these states determined from the steering-side actual current value Ib and the lateral acceleration LA is inappropriate, for example, it is possible that the steering torque generated by the steering motor 32 is excessive even though the vehicle is not turning. This is a state in which the relationship between the steering-side actual current value Ib and the lateral acceleration LA, based on whether the vehicle is turning or not, is inappropriate. Such an inappropriate relationship can occur in cases of excessive output loss, where the steering torque is generated by the steering motor 32, but is not correctly transmitted to the reciprocating motion of the rack shaft 22 via the power transmission mechanism 33. An excessive output loss abnormality includes cases caused by the occurrence of a steering lock precursor condition, such as jamming of the balls 45 in the ball screw mechanism 35 or partial damage to the ball screw nut 46. Furthermore, an excessive output loss abnormality also includes cases where the steering lock precursor condition persists, for example, when the ball screw mechanism 35 of the power transmission mechanism 33 becomes stuck and stops operating. Compared to the steering lock precursor condition, the steering lock condition is a state in which the output loss is particularly large among the excessive output loss abnormalities. An excessive output loss abnormality is an example of an abnormality in the steering unit 6.

[0072] The steering control device 1 of this embodiment determines such excessive output loss abnormalities through abnormality determination processing, from the perspective of the relationship between the steering-side actual current value Ib and the lateral acceleration LA, based on whether the vehicle is turning. Therefore, the steering control device 1 of this embodiment can suitably determine that an abnormality such as excessive output loss has occurred in the steering unit 6.

[0073] <Effects of the First Embodiment> According to the embodiment described above, the following further effects can be obtained. (1-1) The abnormality determination unit 85 performs individual comparison processing using individual thresholds for the steering-side actual current value Ib and the lateral acceleration LA, which have different dimensions, through the processing of the first comparison unit 813 and the second comparison unit 814. Therefore, even if the dimensions of the steering-side actual current value Ib and the lateral acceleration LA are different, the steering control device 1 of this embodiment can suitably perform abnormality determination processing based on the results of individual comparison processing using thresholds appropriate for each value.

[0074] (1-2) The first comparison unit 813 and the second comparison unit 814 in the abnormality determination unit 85 perform a comparison process using the steering current threshold Fthi and the lateral acceleration threshold Fthl. These steering current threshold Fthi and lateral acceleration threshold Fthl are set based on the ability to determine whether the vehicle is turning or not. This is effective in reducing the occurrence of false judgments due to the abnormality determination process.

[0075] (1-3) The abnormality detection unit 85 includes a driving detection unit 817. Therefore, the abnormality detection unit 85 can generate an abnormality detection flag when the vehicle speed V is low, medium, or high, which indicates a high probability that the vehicle is turning. Thus, the conditions under which the abnormality detection flag is generated can be optimized.

[0076] <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 determination 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.

[0077] The steering control device 1 of this embodiment performs an abnormality determination process to determine if the relationship between the steering current axial force Fi and the reference axial force Fb is inappropriate, thereby determining an abnormality in the steering unit 6. 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 due to the lateral acceleration LA when the vehicle is turning. The abnormality in the steering unit 6 includes an abnormality due to excessive output loss, similar to the first embodiment. The steering control device 1 is also connected to an on-board warning device 51 consisting of a warning light and a speaker, and performs a process to output an abnormality determination flag Flag to the warning device 51 indicating the result of the abnormality determination process.

[0078] As shown in Figure 5, the abnormality determination unit 85 of this embodiment includes a steering current axial force calculation unit 816, 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 third comparison unit 806, a third threshold calculation unit 807, and a driving determination unit 817. The steering current axial force calculation unit 816 has the same configuration as the first embodiment except that it outputs the calculated steering current axial force Fi to the addition / subtraction unit 804, so a detailed explanation thereof is omitted.

[0079] The reference axial force calculation unit 802 receives vehicle speed V and lateral acceleration LA as input. The reference axial force calculation unit 802 calculates the reference axial force Fb based on the vehicle speed V and lateral acceleration LA. The reference axial force calculation unit 802 has an axial force map that defines the relationship between lateral acceleration LA 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 lateral acceleration LA 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 should be 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.

[0080] More specifically, the reference axial force Fb is the reference axial force acting on the rack 22 axis via the power transmission mechanism 33 and the road surface with respect to the lateral acceleration LA. The reference axial force Fb is calculated in torque dimensions (N·m).

[0081] Next, the shape of the axial force map will be explained. The axial force map is defined by a normative model that relates the lateral acceleration LA to the axial force acting on the rack axis 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 Figure 6, it is generally known that the relationship between lateral acceleration and the axial force acting on the rack axis changes as follows. That is, until the lateral acceleration becomes greater than the value LA1, the axial force acting on the rack axis increases linearly with increasing lateral acceleration, as shown by the dashed line in Figure 6. When the lateral acceleration becomes greater than the value LA1, the steering wheels slip, and as the lateral acceleration increases, the axial force eventually saturates, as shown by the solid line in Figure 6, and the axial force acting on the rack axis becomes less likely to change even if the lateral acceleration increases. Also, as shown in Figure 6, it is generally known that the relationship between lateral acceleration and the axial force acting on the rack axis changes depending on the vehicle speed V. That is, when the vehicle speed V is high, the gradient, which is the rate of change of axial force with respect to the change in lateral acceleration, is larger than when the vehicle speed V is low. This relationship can serve as a reference for lateral acceleration and axial force acting on the rack axis. The resulting axial force can then be used as an indicator in anomaly detection processing.

[0082] The axial force map of this embodiment is set with the lateral acceleration LA on the horizontal axis and the reference axial force Fb on the vertical axis, taking into consideration the relationship between the general lateral acceleration and the axial force acting on the rack axis. In this embodiment, there are two types of axial force maps: a low-speed axial force map designed considering the relationship at low speeds as illustrated in Figure 6, and a medium-to-high speed axial force map designed considering the relationship at medium-to-high speeds.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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 third comparison unit 806.

[0087] The third 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 third 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 third 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.

[0088] More specifically, the abnormality determination flag Flag includes abnormality determination flag Flag1 and abnormality determination flag Flag2. In the flag generation process, the third 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 third threshold Fth3. On the other hand, the third 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 third threshold Fth3 and less than the fourth threshold Fth4. On the other hand, the third 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 fourth threshold Fth4.

[0089] The third threshold calculation unit 807 outputs a steering torque cross determination threshold Fth to the third 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 lateral acceleration LA is inappropriate. The third 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.

[0090] 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 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. The steering torque loss judgment threshold Fth is set as a value within a range experimentally determined by simulation, etc., based on the viewpoint of determining excessive output loss abnormality, including the steering lock state and the steering lock precursor state.

[0091] More specifically, the steering torque loss determination threshold Fth includes a third threshold Fth3 and a fourth threshold Fth4, which is a value greater than the third threshold Fth3. The third threshold Fth3 is the threshold for determining a pre-steering lock state. The fourth threshold Fth4 is the threshold for determining a steering lock state. The third threshold Fth3 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 third threshold Fth3 is the value obtained by adding the predetermined value To and the fixed value Fth0. The fixed value Fth0 is a range of values ​​that has been experimentally determined to be able to suppress misjudgments.

[0092] 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.

[0093] 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.

[0094] Considering the above, in this embodiment, the third threshold Fth3 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 third threshold Fth3, it is possible to determine that the output loss is excessive, that is, that the steering lock is in a precursor state or in 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 third threshold Fth3 and less than the fourth threshold Fth4, it is possible to determine that the steering lock is in a precursor 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 fourth threshold Fth4, it is possible to determine that the steering lock is in a 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 steering lock precursor state and a steering lock state.

[0095] The driving determination unit 817 receives the vehicle speed V as input. The driving determination unit 817 includes a process to determine whether the input vehicle speed V is low-medium-high speed, which indicates that the vehicle is traveling at a sufficient speed. This is based on the fact that the situation in which the vehicle is turning can occur when the vehicle is traveling at a sufficient speed. The third comparison unit 806 of the abnormality determination unit 85 includes a process to generate an abnormality determination flag Flag if the driving determination unit 817 determines that the vehicle speed V is low-medium-high speed. On the other hand, the flag arbitration unit 815 of the abnormality determination unit 85 includes a process to not generate an abnormality determination flag Flag if the driving determination unit 817 determines that the vehicle speed V is not low-medium-high speed, that is, that the vehicle speed V is at an extremely low speed, including when the vehicle is stopped. In this embodiment, the series of processes performed by the addition / subtraction unit 804, the absolute value processing unit 805, the third comparison unit 806, and the third threshold calculation unit 807 is an example of an axial force comparison process that compares the steering current axial force Fi with the reference axial force Fb.

[0096] <Warning Processing> In this embodiment, the warning device 51 controls the operation of warning lights, speakers, etc., in accordance with the type of abnormality determination flag Flag1 and Flag2 when an abnormality determination flag Flag is input. For example, the warning device 51 controls the warning lights to illuminate in a color corresponding to the type of abnormality determination flag Flag1 and Flag2. In this case, the warning device 51 controls the warning lights to illuminate yellow when abnormality determination flag Flag1 is input, and to illuminate red when abnormality determination flag Flag2 is input.

[0097] <Operation and Effects of the Second 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.

[0098] More specifically, the abnormality determination unit 85 includes a steering current axial force calculation unit 816, a reference axial force calculation unit 802, an addition / subtraction unit 804, a third comparison unit 806, and a third threshold calculation unit 807. The steering current axial force calculation unit 816 calculates the steering current axial force Fi based on the actual steering 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 lateral acceleration LA generated in the vehicle. 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 lateral acceleration LA generated in the vehicle, and can be used as a reference for the lateral acceleration LA generated in the vehicle. 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 third comparison unit 806. The third comparison unit 806 compares the absolute value of the system internal steering torque cross amount Flabs with the steering torque cross determination threshold Fth (Fth3, Fth4) output from the third 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.

[0099] 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 properly 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 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 lateral acceleration LA generated in the vehicle, 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.

[0100] <Effects of the second embodiment> According to the embodiment described above, the following further effects can be obtained. (2-1) 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 lateral acceleration LA 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.

[0101] (2-2) In the abnormality determination unit 85, the third comparison unit 806 can determine whether the output loss is excessive and distinguish between the severity of the abnormality of the steering unit 6, such as a pre-steering lock state and a steering lock state. Therefore, in the vehicle, measures can be taken according to the result of the third 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's 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's driver or maintenance personnel before it reaches the steering lock state, and the need for maintenance inspection can be made clear.

[0102] (2-3) 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 not defined by the normative model. Therefore, the third 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 indicator 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.

[0103] (2-4) The third 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 with 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.

[0104] (2-5) 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.

[0105] <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.

[0106] 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. Other embodiments described herein can also be applied to the second embodiment.

[0107] In the second embodiment, in the above 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 816. Such a configuration corresponding to the steering current axial force calculation unit 816 can calculate the steering current axial force Fi based on the current value generated in the assist motor. In this case, 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.

[0108] 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.

[0109] In the first embodiment, the configuration of the driving determination unit 817 may be omitted. In this case, the abnormality determination unit 85 performs abnormality determination processing regardless of the magnitude of the vehicle speed V. The other embodiments described herein can also be applied to the second embodiment.

[0110] In the first embodiment, a turning-driving determination unit may be provided instead of the second threshold calculation unit 812 and the second comparison unit 814. The turning-driving determination unit performs a turning-driving determination to determine whether the vehicle is turning. For example, the turning-driving determination takes lateral acceleration LA and steering angle θs as input, and determines that the vehicle is turning if the lateral acceleration LA and steering angle θs are each above a predetermined threshold. In this case, the flag arbitration unit 815 includes a process to generate an abnormality determination flag Flag if the first comparison unit 813 determines that both the first flag F1 (F1=1) and the vehicle is determined to be turning are true. On the other hand, the flag arbitration unit 815 does not include a process to generate an abnormality determination flag Flag if the first comparison unit 813 does not determine that both the first flag F1 (F1=1) and the vehicle is determined to be turning are true.

[0111] In the first embodiment, the yaw rate may be used as a turning-related value instead of the lateral acceleration LA, or in addition to the lateral acceleration LA. In this case, the steering control device 1 can calculate the yaw rate based on the lateral acceleration LA, or it may input the detection result of the yaw rate sensor instead of the lateral acceleration sensor 59, or in addition to the lateral acceleration sensor 59. Furthermore, in the abnormality determination processing in the abnormality determination unit 85, various thresholds that take the yaw rate into consideration may be used instead of the lateral acceleration LA. The other embodiments described herein can also be applied to the second embodiment. In this case, the reference axial force calculation unit 802 of the second embodiment may calculate the reference axial force Fb by applying an axial force map defined by a function that outputs the axial force acting on the rack axis 22 based on the yaw rate.

[0112] In the first embodiment, the lateral acceleration threshold Fthl may be a variable value. In this case, the lateral acceleration threshold Fthl can be varied according to the vehicle speed V or the pinion angle θp. Similarly, the steering current threshold Fthi may be varied according to the vehicle speed V or the pinion angle θp.

[0113] In the first embodiment, the steering current threshold Fthi and the lateral acceleration threshold Fthl were set to values ​​within a range experimentally determined by simulation or the like, based on the assumption that the vehicle is turning, but this is not limited to this. For example, the steering current threshold Fthi and the lateral acceleration threshold Fthl may be set to the values ​​of the actual steering current and lateral acceleration LA, respectively, when the vehicle turns at a specific vehicle speed V and turning radius R. In this case, the abnormality determination unit 85 can determine that an abnormality has occurred in the steering unit 6 by executing an abnormality determination process when the vehicle turns in a circle at a specific vehicle speed V and turning radius R, for example.

[0114] In the second 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 third 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.

[0115] In the second 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 shaft 22 in response to changes in the reference model.

[0116] In the second embodiment, it is not essential to consider the system output compensation component Fs in the abnormality detection process. In the second embodiment, the system output compensation component calculation unit 803 may output a value of the system output compensation component Fs calculated by simulation or the like, which has been previously stored in a memory unit as a fixed value. In this case, the memory unit that stores the fixed value of the system output compensation component Fs is a predetermined memory area of ​​a memory (not shown). The third threshold calculation unit 807 may also output a value of the steering torque cross determination threshold Fth calculated by simulation or the like, which has been previously stored in a memory unit as a fixed value. The memory unit that stores the fixed value of the steering torque cross determination threshold Fth is a predetermined memory area of ​​a memory (not shown).

[0117] In the second embodiment, the third comparison unit 806 of the abnormality determination unit 85 includes a process for generating two types of flags, but is not limited to this. For example, the third 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 third threshold calculation unit 807 only needs to set thresholds corresponding to the flags.

[0118] 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 these. 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.

[0119] 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 the second embodiment, for example, a small reaction force may be applied when abnormality determination flag Flag 1 is used, and a large reaction force may be applied when abnormality determination flag Flag 2 is used. Also, for example, a small vibration may be applied to the steering wheel 3 when abnormality determination flag Flag 1 is used, and a small vibration may be applied when abnormality determination flag Flag 2 is used. [Explanation of symbols]

[0120] 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 802…Reference axial force calculation section 803...System output compensation component calculation unit 804... Addition and Subtraction Section 806...Third Comparative Section 807...Third threshold calculation unit 811...First threshold calculation unit 812...Second threshold calculation unit 813...First Comparison Section 814...Second Comparative Section 815... Flag Mediation Department 816... Steering current axial force calculation unit 817... Driving determination unit

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 turning-related value acquisition process that obtains turning-related values ​​from the vehicle, which are values ​​that can be converted into forces acting on the vehicle during turning, 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 turning-related value. The aforementioned abnormality determination process is: A comparison process that compares the relationship between the steering current value and the turning-related value, based on whether the vehicle is turning or not, 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 comparison process includes a first comparison process that compares the magnitude relationship between the steering current value and a first threshold value, and a second comparison process that compares the magnitude relationship between the turning-related value and a second threshold value. The steering control device according to claim 1, wherein the determination process includes a process of determining that an abnormality has occurred in the steering unit based on the result of the first comparison process and the result of the second comparison process.

3. The first threshold and the second threshold are fixed values ​​set from the perspective of determining whether the steering current value is within the range indicating that the vehicle is turning, even though the turning-related value is within the range indicating that the vehicle is turning. The first comparison process derives a result indicating that the first condition is met when the steering current value is greater than the first threshold, and the second comparison process derives a result indicating that the second condition is met when the turning-related value is less than the second threshold. The steering control device according to claim 2, wherein the determination process determines that an abnormality has occurred in the steering unit if both the first condition and the second condition are met.

4. 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, Includes a reference axial force calculation process that calculates a reference axial force, which is a reference axial force for the force acting on the vehicle during turning, based on the aforementioned turning-related values, The aforementioned comparison process is, The steering control device according to claim 1, comprising an axial force comparison process which is a process of comparing the steering current axial force with the reference axial force.

5. The steering control device according to claim 4, wherein the reference axial force is an axial force defined by a function that takes the turning-related values ​​as input and outputs the axial force acting on the vehicle.

6. The steering control device according to claim 5, wherein the function is defined by an axial force map that defines the relationship between the turning-related value and vehicle speed and the axial force acting on the steering axis.

7. The steering control device according to claim 1 or 4, wherein the abnormality determination process is performed when the vehicle is in motion at low, medium, or high speeds.

8. The abnormality determination process is configured to derive multiple determination results regarding the abnormality of the steering unit. The steering control device according to claim 4, wherein the plurality of determination results are divided according to the severity of the abnormality of the steering unit.

9. 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 4, wherein the system output compensation component is taken into account during the axial force comparison process.

10. The steering control device according to claim 9, wherein the axial force 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 third threshold.

11. 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.

12. The steering system includes a reaction force unit with a power transmission path separated from the steering unit, 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 the 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. The steering control device according to claim 4, 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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