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] When the vehicle's start switch is turned on, the steering control device performs an abnormality determination process to determine if an abnormality has occurred in the steering unit while executing the start sequence. The abnormality determination process includes a feedback control process that controls the torque generated by the steering motor to eliminate the deviation between the target pinion angle θp* and the pinion angle θp, and a first determination process that determines whether or not a first abnormality condition is met. The first abnormality condition is a condition for determining that a first abnormality has occurred, and includes a first condition where the difference between the target pinion angle θp* and the pinion angle θp is less than a first threshold Th1, and a second condition where the steering side actual current value Ib is greater than the steering current upper limit value Ibmax. The first determination process includes a process to determine that a first abnormality has occurred if both the first and second conditions are met.

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 executes control to steer a steered wheel in conjunction with the rotation of a steering wheel. The steering control device uses a detection value detected from steering means including a steering unit to perform an abnormality determination as to whether an abnormality has occurred in the steering unit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In ensuring the reliability of a steering device, a technique regarding the abnormality determination of a steering unit is important. Therefore, development from various viewpoints is required for a method capable of determining an abnormality of a steering unit. This is the same not only for a steering unit constituting a steer-by-wire type steering device but also, for example, for a 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 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 execute a startup sequence, which is the initial operation at startup, when the power switch of the vehicle is turned on, and after the completion of the startup sequence, while waiting for the vehicle to be ready to drive, to execute an abnormality determination process to determine if an abnormality has occurred in the steering unit during the execution of the startup sequence. The abnormality determination process includes a feedback control process that calculates a steering target value, which is a target value of a steering shaft-related value that can be converted into a value of the amount of movement of the steering shaft, and controls the torque generated by the steering motor so as to eliminate the deviation between the steering target value and the actual steering measured value, which is the actual value of the steering shaft-related value, and a first determination process that determines whether or not a first abnormality condition is met during the feedback control process. The first abnormality condition is a condition for determining that a first abnormality has occurred in the steering unit, and includes a first condition indicating that the difference between the steering target value and the measured steering value is less than a first threshold, and a second condition indicating that the steering current value, which is the current generated in the steering motor, is equal to or greater than the upper limit of the steering current value for which the steering motor can operate normally. The first determination process includes a process for determining that the first abnormality has occurred if both the first and second conditions are met.

[0006] In the steering control device described above, if the second condition is met while the first condition is met, it is assumed that the relationship between the difference between the measured steering value and the steering target value and the steering current value is inappropriate. This inappropriate relationship can occur in cases of excessive output loss, where the steering motor generates steering torque, but the steering torque is not properly transmitted to the reciprocating motion of the steering shaft via the power transmission mechanism. In response to this, the abnormality detection process can detect excessive output loss while keeping the difference between the measured steering value and the steering target value as small as possible, through processing the first and second conditions. As a result, the steering control device can determine that there is an excessive output loss abnormality. Therefore, it is possible to suitably determine that an abnormality has occurred in the steering unit.

[0007] In a steering control device capable of solving the above problems, the abnormality determination process includes a second determination process that determines whether a second abnormality condition is met during the feedback control process. The second abnormality condition is a condition for determining that a second abnormality has occurred in the steering unit, and includes a third condition indicating that the difference between the steering target value and the measured steering value is greater than or equal to a second threshold value, and a fourth condition indicating that the state in which the third condition is met has continued for a threshold time. The second determination process includes a process that determines that the second abnormality has occurred if both the third condition and the fourth condition are met.

[0008] The steering control device described above can specialize in determining a steering lock state, which is a condition where a precursor to steering lock has persisted for a sufficient period, even among abnormalities involving excessive output loss, such as jamming of balls in the ball screw mechanism or partial damage to the ball screw nut. This is effective in reliably determining that the steering unit 6 is malfunctioning.

[0009] In a steering control device that can solve the above problems, the first threshold and the second threshold are the same value. According to the steering control device described above, for example, if the first abnormality is a premonitory state of steering lock and the second abnormality is a steering lock state, these two abnormalities can be suitably determined without overlap.

[0010] In a steering control device that can solve the above problems, 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 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.

[0011] According to the steering control device described above, it is possible to detect mechanical abnormalities in the steering unit of a steer-by-wire steering system. In a steering control device capable of solving the above problems, the startup sequence includes a steering control preparation process to enable a linked steering control process, which is a process that executes steering control to steer the steering wheel according to a steering target value calculated in conjunction with the rotation of the steering wheel, and the abnormality determination process is executed after the steering control preparation process is completed successfully.

[0012] According to the steering control device described above, if the steering wheel is rotating but the vehicle's steering wheels are not turning, it can give the driver a sense of unease, thereby allowing the driver to realize that there is a problem with the steering unit.

[0013] In a steering control device capable of solving the above problems, the steering target value calculated in the abnormality determination process is calculated according to the rotation angle of the steering wheel, which changes as the steering wheel is automatically rotated by driving the reaction force motor.

[0014] According to the steering control device described above, by ensuring stable rotation of the steering wheel, it is possible to determine with high accuracy if there is an abnormality in the steering unit. [Effects of the Invention]

[0015] According to the present invention, it is possible to suitably determine that an abnormality has occurred in the steering unit. [Brief explanation of the drawing]

[0016] [Figure 1] This diagram shows the overall configuration of the steering system according to the embodiment. [Figure 2] Figure 1 is a flowchart showing the startup process for the steering control device. [Figure 3] Figure 2 shows the startup sequence flow for the startup process. [Figure 4] Figure 3 is a flowchart showing the flow of the abnormality detection process. [Modes for carrying out the invention]

[0017] The following describes one embodiment of the present invention. 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.

[0018] The reaction force unit 4 includes a steering shaft 11 and a reaction force actuator 12. The steering shaft 11 is connected to the steering wheel 3 so as to be rotatable integrally with the steering wheel 3. The reaction force actuator 12 includes a reaction force motor 13 and a reaction force transmission mechanism 14. The reaction force motor 13 is connected to the steering shaft 11 via the reaction force transmission mechanism 14. The reaction force motor 13 outputs a reaction force torque, which is a torque that resists the driver's steering of the steering wheel 3. The reaction force transmission mechanism 14 transmits the reaction force torque output by the reaction force motor 13 to the steering shaft 11. The reaction force transmission mechanism 14 is, for example, a worm and wheel mechanism. The reaction force motor 13 is, for example, a three-phase brushless motor.

[0019] The steering unit 6 includes 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 in the rack housing 23 at a predetermined crossing angle. The rack housing 23 houses the rack shaft 22 so as to be reciprocally movable. The rack and pinion mechanism 24 is constituted by meshing a pinion tooth 21a formed on the pinion shaft 21 with a rack tooth 22a formed on the rack shaft 22. Thereby, the pinion shaft 21 rotates according to the reciprocal movement of the rack shaft 22. Ball joints 25 are connected to both ends of the rack shaft 22, and tie rods 26 are connected via the ball joints 25. The tip of the tie rod 26 is connected to a knuckle to which the steering wheel 5 of the vehicle is assembled. That is, the rack shaft 22 is connected to the steering wheel 5 of the vehicle.

[0020] The steering actuator 31 includes 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 a torque for steering the steering wheel 5 with respect 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.

[0021] More specifically, the power transmission mechanism 33 includes a belt mechanism 34 and a ball screw mechanism 35. The belt mechanism 34 includes a pair of pulleys 41, 42 and a belt 43 wound between the pair of pulleys 41, 42. The pair of pulleys 41, 42 are made of resin, and the belt 43 is made of rubber. The ball screw mechanism 35 includes a screw portion 22b formed on the rack shaft 22 and a ball screw nut 46 that is screwed to the screw 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 periphery of the ball screw nut 46. Thereby, 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 converts it into the reciprocating motion of the rack shaft 22 in the ball screw mechanism 35, thereby applying a steering torque to the rack shaft 22.

[0022] In the steering system 2 configured as described above, in response to the driver's steering operation of the steering wheel, a steering torque is output from the steering actuator 31 to the rack shaft 22, so that the rack shaft 22 reciprocates and the steering angle θi of the steering wheel 5 is changed. At this time, a reaction torque, which is a torque that resists the driver's steering operation, is output from the reaction actuator 12. Thereby, in the steering system 2, the steering torque Th required for the driver's steering operation is changed by the reaction force output from the reaction actuator 12. That is, it is possible to give a feeling of resistance to the driver who steers the steering wheel 3.

[0023] <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.

[0024] The steering control device 1 is connected to the reaction motor 13 and the steering motor 32, and performs steering control 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 if the relationship between the difference between the target pinion angle θp*, which is the target steering value, and the measured steering value, the pinion angle θp, and the steering current value, the steering-side actual current value Ib, which is the steering current value generated in the steering motor 32, is not appropriate. The target pinion angle θp* is the target value of the pinion angle θp, which is a value that can be converted into the amount of movement of the rack shaft 22. The pinion angle θp is a value that can be converted into the amount of movement of the rack shaft 22, which is the rotation angle of the pinion shaft 21. The steering-side actual current value Ib is the actual current value supplied to the steering motor 32. 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 referred to as 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 and display devices, and executes a process to output an abnormality flag Flag to the warning device 51 indicating the result of the abnormality determination process.

[0025] The steering control device 1 receives detection results from various sensors. These sensors include, for example, a vehicle speed sensor 52, a torque sensor 53, a reaction force side rotation angle sensor 54, a steering side rotation angle sensor 55, a reaction force side current sensor 57, and a steering side current sensor 58.

[0026] 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.

[0027] 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.

[0028] A power supply system 66 is connected to the steering control device 1. The power supply system 66 includes a battery 67. The battery 67 is a secondary battery mounted on the vehicle and serves as the power source for the reaction motor 13 and the steering motor 32 to operate. The battery 67 also serves as the power source for the steering control device 1 to operate.

[0029] A vehicle start switch 68 (indicated as "SW" in Figure 1), such as an ignition switch, is provided between the steering control device 1 and the battery 67. The start switch 68 is located in the middle of the power supply line L2, which branches off from power supply line L1, one of the two power supply lines L1 and L2 that connect the steering control device 1 and the battery 67. The start switch 68 is operated to activate various functions so that the vehicle can operate by activating the vehicle's drive source, such as the engine. The start switch 68 is, for example, an ignition switch or power switch located in the driver's seat. The conduction of power supply line L2 is turned on and off through the operation of the start switch 68. When the start switch 68 is turned on, power is supplied to the steering control device 1, and the steering control device 1 starts operating. Turning on the start switch 68 is equivalent to turning on the vehicle's power switch. Conversely, turning off the start switch 68 is equivalent to turning off the vehicle's power switch. Similarly, vehicle-side systems such as the braking control device, which controls the braking system related to the vehicle's braking, also start operating when the start switch 68 is turned on.

[0030] <About steering control processing> This section will explain the overview of the reaction force control process performed by the steering control device 1, specifically the reaction force control process through the operation of the reaction force motor 13.

[0031] The steering control process includes reaction force control processing, steering angle calculation processing, reaction force generation processing, and power supply control processing. The steering angle calculation process includes converting the reaction force 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 process also includes calculating 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 it is, for example, to the right of the steering neutral position, and negative if it is to the left.

[0032] The reaction force generation process includes a process for calculating the reaction force torque command value Ts*, which is the target value of the steering reaction force, based on the steering torque Th, vehicle speed V, and steering-side actual current value Ib. The reaction force generation process also includes a process for calculating the reaction force torque command value Ts* by adding a component calculated from the steering-side actual current value Ib to the components calculated from the steering torque Th and vehicle speed V.

[0033] The power supply control process includes a process for calculating a reaction force current command value for the reaction force motor 13 based on the reaction force torque command value Ts*. 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 process then includes a process for determining the deviation between the reaction force current command value and the current value on the dq coordinate obtained by converting the actual reaction force current value Ia detected through the reaction force side current sensor 57 based on the reaction force side rotation angle θa, and controlling the power supply to the reaction force motor 13 to eliminate this deviation. As a result, the reaction force motor 13 outputs a reaction force torque corresponding to the reaction force torque command value Ts*, and the rotation axis 13a of the reaction force motor 13 rotates by an angle corresponding to the reaction force torque command value Ts*.

[0034] This section will explain the steering control process performed by the steering control device 1, specifically the steering control process that is carried out through the operation of the steering motor 32. Of the steering control processes, the steering control process includes steering angle conversion processing, pinion angle calculation processing, pinion angle feedback processing, and power supply control processing.

[0035] The steering angle conversion process includes a process to calculate the target pinion angle θp* by multiplying the steering angle θs obtained in the steering angle calculation process by a predetermined steering angle ratio corresponding to the vehicle speed V. In this embodiment, the target pinion angle θp* is an example of an actual value of a steering axis-related value that can be converted into the amount of movement of the steering axis.

[0036] The pinion angle calculation process includes converting 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. That is, 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. Thus, the pinion angle θp can be obtained from the steering-side rotation angle θb by utilizing this correlation. Specifically, the pinion angle calculation process includes a process that 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. In this embodiment, the pinion angle θp is an example of an actual value of a steering axis-related value that can be converted into the amount of movement of the steering axis.

[0037] The pinion angle feedback process includes a process of calculating a steering torque command value T* as a target control amount for steering torque, through feedback control of the pinion angle θp to make the pinion angle θp follow a target pinion angle θp*. More specifically, the pinion angle feedback process calculates the deviation between the target pinion angle θp* and the pinion angle θp, and calculates a steering torque command value T* to eliminate this deviation by multiplying the deviation by a predetermined gain. The pinion angle feedback process can be implemented, for example, by PID control. The pinion angle feedback process is an example of feedback control processing.

[0038] The power supply control process includes a process for calculating a steering current command value for the steering motor 32 based on the steering torque command value T*. The steering current command value is the target value of the torque to be generated by the steering motor 32. The power supply control process then includes a process for determining the difference between the steering current command value and the current value on the dq coordinate obtained by converting the steering side actual current value Ib detected through the steering side current sensor 58 based on the steering side rotation angle θb, and controlling 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*.

[0039] As described above, the steering control device 1 of this embodiment includes a process to operate the reaction motor 13 so that a motor torque corresponding to the reaction torque command value Ts* is generated. This applies a steering reaction force to the reaction unit 4. The steering control device 1 also calculates the target pinion angle θp* by steering angle conversion processing in conjunction with the rotation of the steering wheel 3. The steering control device 1 can then perform steering control to steer the steering wheel 5 through pinion angle feedback processing between the target pinion angle θp* and the pinion angle θp. In this embodiment, among the steering control processes, the steering control process that is linked to the rotation of the steering wheel 3 is described as linked steering control processing, taking into consideration that the rotation of the steering wheel 3 and the steering of the steering wheel 5 are linked.

[0040] <About startup processing> As shown in Figures 2 and 3, the steering control device 1 executes startup processing when the start switch 68 is turned on. Startup processing is a series of processes that are executed when the steering control device 1 is started up.

[0041] More specifically, as shown in Figure 2, during startup, when the start switch 68 is turned on (S201), the steering control device 1 executes a startup sequence (S202). The startup sequence is an initial operation after the start switch 68 is turned on, and includes steering control preparation processing to enable the steering system 2 to execute steering control processing, i.e., linked steering control processing.

[0042] Next, once the startup sequence is complete, the steering control device 1 waits for the vehicle to be ready to drive, which is performed through the vehicle-side systems other than the steering system 2 (S203). While waiting for the vehicle to be ready to drive, the steering control device 1 transmits a startup sequence completion signal S1 to the vehicle-side system, indicating that the startup sequence (S202) has been completed. Subsequently, while waiting for the vehicle to be ready to drive, the steering control device 1 transitions to an assist start waiting state when it receives an assist start permission signal S2 from the vehicle-side system (S204). The assist start permission signal S2 is a signal that allows the steering system 2, i.e., the steering control device 1, to understand that the vehicle has been ready to drive in the vehicle-side system. The assist start waiting state is a state in which the driver is able to steer the vehicle. In the assist start waiting state, when the driver steers the vehicle, the steering control device 1 can steer the steering wheels 5 through linked steering control processing.

[0043] <About the startup sequence> As shown in Figure 3, the startup sequence is executed during the period until the driver is able to steer the vehicle. More specifically, the startup sequence includes an initial check process (S301), a midpoint learning process (S302), a steering angle synchronization process (S303), an anomaly detection process (S304), an anomaly response process (S305), and a completion signal generation process (S306).

[0044] The initial check process (S301) is an initial inspection process that is performed when the start switch 68 is turned on, and includes, for example, hardware checks, initialization of the CPU (central processing unit) of the steering control device 1, and initialization of variables or flags.

[0045] The midpoint learning process (S302) is a process for learning the steering neutral position of the steering wheel 3 when the steering neutral position, which is the midpoint of the steering angle θs, has been lost. The midpoint learning process includes a process for calculating the steering neutral position. The steering neutral position is information used when calculating the steering angle θs and is stored in a predetermined area of ​​memory (not shown). Note that the midpoint learning process is not executed when the steering neutral position has not been lost.

[0046] For example, the steering control device 1 performs a process to learn the steering neutral position of the steering wheel 3 if the information regarding the steering neutral position stored in memory is lost. This occurs, for example, when the start switch 68 is turned on for the first time after a new battery 67 has been installed in the vehicle. This is because when the battery 67 is removed from the vehicle during battery replacement work, the power supply to the steering control device 1 is cut off, causing the information regarding the steering neutral position stored in the memory of the steering control device 1 to be lost. When calculating the steering neutral position, the steering control device 1 performs a process to drive the reaction force motor 13 to rotate the steering wheel 3 in the left and right directions.

[0047] The steering angle synchronization process (S303) is a process for adjusting the relationship between the rotational position of the steering wheel 3 and the steering position of the steering wheels 5. Note that the steering angle synchronization process is not executed when there is no need to adjust the relationship between the rotational position of the steering wheel 3 and the steering position of the steering wheels 5.

[0048] For example, when the steering control device 1 is at a rotational position different from the rotational position corresponding to the steering position of the steering wheel 5, it drives the reaction force motor 13 so that the rotational position of the steering wheel 3 becomes the rotational position corresponding to the steering position of the steering wheel 5.

[0049] In this embodiment, the initial check process, midpoint learning process, and rudder angle synchronization process in the startup sequence are steering control preparation processes required to start the linked steering control process. In other words, the steering control device 1 becomes capable of executing the linked steering control process once it has completed the steering control preparation process.

[0050] Furthermore, if the steering control device 1 is unable to complete the steering control preparation process, it will execute a function shutdown process to stop the functions of the steering control device 1. Failure to complete the steering control preparation process may occur, for example, if the initial check process, the midpoint learning process, and the steering angle synchronization process do not complete within a predetermined period, i.e., if a timeout occurs. The function shutdown process includes, for example, interrupting the startup sequence and prompting the driver to turn off the start switch 68 via the warning device 51.

[0051] The abnormality detection process (S304) is a process for determining whether an abnormality has occurred in the steering unit 6 through the pinion angle feedback process. If the abnormality detection process determines that an abnormality has occurred in the steering unit 6, it includes a process for generating an abnormality flag (Flag) to indicate that fact.

[0052] For example, if the steering control device 1 determines that an abnormality has occurred in the steering unit 6, it executes a process to generate either a first abnormality flag Flag1 or a second abnormality flag Flag2, depending on the type of abnormality.

[0053] The abnormality response process (S305) is executed when the abnormality determination process determines that an abnormality has occurred in the steering unit 6, and an abnormality flag (Flag) is generated. The abnormality response process includes sending the abnormality flag (Flag) generated in the abnormality determination process to the warning device 51.

[0054] For example, the steering control device 1 performs the process of sending the generated first abnormality flag Flag1 or second abnormality flag Flag2 to the warning device 51. The completion signal generation process (S306) is executed when the abnormality determination process determines that no abnormality has occurred in the steering unit 6, and therefore no abnormality flag is generated. The completion signal generation process includes the generation of a startup sequence completion signal S1, which indicates that the startup sequence has been completed, because no abnormality flag was generated in the abnormality determination process.

[0055] In other words, the steering control device 1 completes the startup sequence (S202), i.e., the steering control preparation process, and transmits the generated startup sequence completion signal S1 to the vehicle-side system, enabling the execution of the linked steering control process.

[0056] <About abnormality detection processing> As shown in Figure 3, the abnormality detection process is performed after the steering control device 1 enables the execution of the linked steering control process. The abnormality detection process is repeatedly performed at a predetermined calculation cycle by the pinion angle feedback process.

[0057] More specifically, as shown in Figure 4, in the abnormality detection process, the steering control device 1 controls the drive of the reaction force motor 13 so that the steering wheel 3 is automatically rotated by "θn" in the left-right direction based on the current rotation position of the steering wheel 3 (S400). In step 400, the steering control device 1 calculates a target pinion angle θp* for the abnormality detection process that corresponds to the current steering angle θs obtained in the steering angle calculation process. The current steering angle θs is the rotation angle of the steering wheel 3 that changes as the steering wheel 3 is automatically rotated. Subsequently, the steering control device 1 performs pinion angle feedback processing to make the pinion angle θp follow the target pinion angle θp* for the abnormality detection process. In this case, the pinion angle feedback processing includes a process to calculate a steering torque command value T* through feedback control of the pinion angle θp in order to make the pinion angle θp follow the target pinion angle θp* for the abnormality detection process. The steering control device 1 then controls the drive of the steering motor 32 to output a steering torque corresponding to the steering torque command value T*.

[0058] Next, the steering control device 1 performs pinion angle feedback processing to make the pinion angle θp follow a target pinion angle θp* for abnormality detection processing, and determines whether the difference between the pinion angle θp and the target pinion angle θp* is less than the first threshold Th1 (S401). For example, the first threshold Th1 is the relatively small value within the range R1 of deviations between the target pinion angle θp* and the pinion angle θp that are not expected to occur due to the pinion angle feedback processing. In other words, the first threshold Th1 is a value greater than the maximum value of the range R2 of deviations between the target pinion angle θp* and the pinion angle θp that are expected to occur due to the pinion angle feedback processing. Therefore, if the boundary between range R1 and range R2 is defined as the boundary value BP, the first threshold Th1 is a value greater than the boundary value BP. The first threshold Th1 is stored in a predetermined area of ​​memory (not shown).

[0059] Next, in step 401, the steering control device 1 determines whether the steering-side actual current value Ib is greater than the steering current upper limit value Ibmax if the difference between the pinion angle θp and the target pinion angle θp* is less than the first threshold Th1 (S401: YES) (S402). For example, the steering current upper limit value Ibmax is the upper limit of the steering-side actual current value Ib that allows the steering motor 32 to operate normally. The steering current upper limit value Ibmax is a fixed value set, for example, from the viewpoint of preventing the steering motor 32 from overheating or from preventing the control stability of the steering control process from becoming unstable. In other words, the steering current upper limit value Ibmax indicates that controlling the drive of the steering motor 32 may cause the steering motor 32 to overheat or the control stability of the steering control process to become unstable. In this embodiment, the steering current upper limit value Ibmax is a value corresponding to the steering-side actual current value Ib that can be supplied to the steering motor 32 when the difference between the pinion angle θp and the target pinion angle θp* is within the range R2 and is smaller than the boundary value BP. The steering current upper limit value Ibmax is stored in a predetermined area of ​​memory (not shown).

[0060] Next, in step 402, if the steering control device 1 determines that the steering-side actual current value Ib is greater than the steering current upper limit value Ibmax (S402: YES), it executes the first abnormality determination process (S403). In step 403, the steering control device 1 executes a process to generate a first abnormality flag Flag1, which indicates that an output loss excessive abnormality has occurred in the steering unit 6, which is the first abnormality. After that, the steering control device 1 terminates the abnormality determination process. Also, in step 402, if the steering control device 1 determines that the steering-side actual current value Ib is less than or equal to the steering current upper limit value Ibmax (S402: NO), it terminates the abnormality determination process.

[0061] On the other hand, in step 401, if the steering control device 1 determines that the difference between the pinion angle θp and the target pinion angle θp* is greater than or equal to the first threshold Th1 (S401: NO), it determines whether time Tc is greater than or equal to the threshold time Tth (S404). In step 404, the steering control device 1 performs a process to count the time during which the state in which the difference between the pinion angle θp and the target pinion angle θp* is greater than or equal to the first threshold Th1 continues. The steering control device 1 has a counter function and counts time Tc by, for example, incrementing a value for the counter at each calculation cycle. After the start of counting time Tc, the steering control device 1 clears, i.e., resets the value of time Tc when it determines S401: YES. The threshold time Tth is a value shorter than the time required for the startup sequence, for example, 1 second (sec). The threshold time Tth is stored in a predetermined area of ​​memory (not shown).

[0062] Next, if the steering control device 1 determines that time Tc is greater than or equal to the threshold time Tth, i.e., that the threshold time Tth is continuing (S404: YES), it executes the second abnormality determination process (S405). In step 405, the steering control device 1 executes a process to generate a second abnormality flag Flag2, which indicates that an excessive output loss abnormality has occurred in the steering unit 6, which is the second abnormality. After that, the steering control device 1 terminates the abnormality determination process. Also, in step 404, if the steering control device 1 determines that time Tc is less than the threshold time Tth, i.e., that the threshold time Tth is not continuing (S404: NO), it terminates the abnormality determination process.

[0063] In this embodiment, the series of processes in steps 401 and 402 is an example of a first determination process. The series of processes in steps 401 and 404 is an example of a second determination process. Step 401:YES is an example of a first condition, and step 402:YES is an example of a second condition, and the first and second conditions are examples of a first abnormal condition. Step 401:NO is an example of a third condition, and step 404:YES is an example of a fourth condition, and the third and fourth conditions are examples of a second abnormal condition. The process in step 403 is an example of a process for determining that a first abnormality has occurred in the steering unit 6. The process in step 405 is an example of a process for determining that a second abnormality has occurred in the steering unit 6. The first threshold Th1, which is the threshold for determining step 401:NO, is an example of a second threshold. In other words, in this embodiment, the second threshold is the same value as the first threshold Th1.

[0064] <Warning Processing> When an abnormality flag (Flag) is input, the warning device 51 controls the operation of warning lights, speakers, etc., in a manner corresponding to the type of abnormality flag (Flag1, Flag2). For example, the warning device 51 controls the warning lights to illuminate in a color corresponding to the type of abnormality flag (Flag). In this case, the warning device 51 controls the operation of the warning lights to illuminate yellow when the first abnormality flag (Flag1) is input, and to illuminate red when the second abnormality flag (Flag2) is input.

[0065] <Operation and Effects of This Embodiment> The steering control device 1 determines an excessive output loss abnormality by comparing the relationship between the difference in the pinion angle θp relative to the target pinion angle θp* and the actual steering current value Ib. The steering control device 1 performs an abnormality determination process to determine whether or not there is an excessive output loss abnormality. More specifically, the abnormality determination process includes steps 401 and 402. Steps 401 and 402 determine that there is an excessive output loss abnormality if both of the following conditions are met: the difference in the pinion angle θp relative to the target pinion angle θp* is less than the first threshold Th1 (S401: YES) and the actual steering current value Ib is greater than the steering current upper limit value Ibmax (S402: YES).

[0066] If step 401 is YES, and then step 402 is also YES, it is assumed that the steering-side actual current value Ib is greater than the steering current upper limit Ibmax while the difference in pinion angle θp with respect to the target pinion angle θp* is within range R2. In this case, it is assumed that the relationship between the difference in pinion angle θp with respect to the target pinion angle θp* and the steering-side actual current value Ib is inappropriate. Such an inappropriate relationship can occur in the case of excessive output loss abnormality where the steering motor 32 is generating 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.

[0067] 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.

[0068] In contrast, the abnormality detection process, through steps 401 and 402, can detect an excessive output loss abnormality while keeping the difference between the pinion angle θp and the target pinion angle θp* as small as possible. As a result, the steering control device 1 can determine a pre-steering lock state, which is a transient state before a steering lock state occurs, even amidst an excessive output loss abnormality. Therefore, it can suitably determine that an abnormality has occurred in the steering unit 6.

[0069] <Effects of this embodiment> According to the embodiment described above, the following further effects can be obtained. (1-1) The abnormality detection process includes the processes in steps 401 and 404. Steps 401 and 404 determine that there is an excessive output loss abnormality when both of the following conditions are met: the difference between the pinion angle θp and the target pinion angle θp* is greater than or equal to the first threshold Th1 (S401: NO), and time Tc continues for the threshold time Tth (S404: YES).

[0070] If step 401 is NO, and step 404 is YES, then it is assumed that this state persists for a threshold time Tth while the difference in pinion angle θp relative to the target pinion angle θp* is within range R1. In this case, it is assumed that the relationship between the difference in pinion angle θp relative to the target pinion angle θp* and the steering side actual current value Ib is inappropriate. As mentioned above, this inappropriate relationship can occur in the case of excessive output loss, where the steering motor 32 is generating 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.

[0071] In response to this, the abnormality detection process can detect that an excessive output loss abnormality is occurring continuously through the processing in steps 401 and 404. As a result, the steering control device 1 can determine that even among the excessive output loss abnormalities, the steering lock state is a state in which the pre-steering lock state has continued sufficiently. In other words, the steering control device 1 can determine both the pre-steering lock state and the steering lock state. This is effective in reliably determining that the steering unit 6 is abnormal.

[0072] (1-2) Both the process of step 401:YES for determining that there is a precursor to steering lock and the process of step 401:NO for determining that there is a steering lock state use the first threshold Th1. Therefore, the precursor to steering lock state and the steering lock state can be suitably determined without overlap.

[0073] (1-3) In this embodiment, a steer-by-wire steering system is employed as the steering system 2. Therefore, mechanical abnormalities in the steering unit 6 can be detected in the steer-by-wire steering system.

[0074] (1-4) The steering control device 1 is configured to perform abnormality detection processing after it has become possible to perform linked steering control processing. Therefore, assuming that the rotational movement of the steering wheel 3 and the steering movement of the steering wheels 5 are linked, if the steering wheel 3 is rotating but the steering wheels 5 of the vehicle do not steer, it can give the driver a sense of unease. This is effective in making the driver aware that an abnormality has occurred in the steering unit 6.

[0075] (1-5) The abnormality detection process automatically rotates the steering wheel 3 by driving the reaction motor 13. Therefore, the steering wheel 3 can be rotated more stably than when the driver rotates the steering wheel 3 manually. Consequently, it is possible to determine with high accuracy that the steering unit 6 is malfunctioning.

[0076] <Other Embodiments> 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.

[0077] The steering control device 1 is configured to perform steering control processing that includes reaction force control processing and steering control processing, but is not limited to this. For example, the steering control device 1 may include a reaction force control device that performs reaction force control processing and a steering control device that performs steering control processing. In this case, the initial check processing of the startup sequence may be performed by both the reaction force control device and the steering control device, while other processing may be performed by either the reaction force control device or the steering control device.

[0078] The steering system 2 is configured as a steer-by-wire steering device, but it may also be configured as an electric power steering device. In an electric power steering device, the steering wheel 3 and the steering wheels 5 shown in Figure 1 are mechanically connected. That is, the steering shaft 11, pinion shaft 21, and rack shaft 22 function as power transmission paths between the steering wheel 3 and the steering wheels 5. As the steering wheel 3 is turned, the rack shaft 22 reciprocates, changing the steering angle θi of the steering wheels 5. The electric power steering device has an assist motor and an assist control device. The assist motor is located in the same position as the reaction motor 13 or steering motor 32 shown in Figure 1. The assist motor generates an assist force to assist in the operation of the steering wheel 3. The assist force is a torque in the same direction as the steering direction of the steering wheel 3, and is a steering torque for turning the steering wheels 5. The assist control device corresponds to the steering control device 1. The assist control device controls the drive of the assist motor, which is the object of control. In this case, the assist control device executes the abnormality detection process shown in Figure 4 above.

[0079] • While the pinion angle θp was used as the measured steering value, it is not limited to this; any value correlated with the amount of movement of the rack axis 22 is acceptable. For example, the lateral movement of the rack axis 22 detected by a separately provided rack movement sensor, or the steering angle θi of the steering wheel 5 detected by a separately provided tire angle sensor, can be used as the measured steering value. In this case, the corresponding steering target values ​​would be the target movement and target tire angle, respectively.

[0080] The startup sequence only needs to include an initial check process; it is not mandatory to include a midpoint learning process or a steering angle synchronization process. In this case, the initial check process becomes the steering control preparation process required to start the linked steering control process. In this case, the midpoint learning process or steering angle synchronization process may be performed not during the startup sequence, but triggered by a control signal from dedicated equipment installed at a dealer or vehicle factory.

[0081] In step 400 of the abnormality detection process, the steering control device 1 automatically rotates the steering wheel 3 by driving the reaction force motor 13, but is not limited to this. For example, the driver may rotate the steering wheel 3 to rotate the steering angle θs of the steering wheel 3 by ±θn relative to the position of the steering wheel 3. This is effective when the steering system 2 is configured as an electric power steering type steering device.

[0082] In step 400 of the abnormality detection process, a condition regarding the rotational position of the steering wheel 3 used as a reference may be added. The condition regarding the rotational position is, for example, that the rotational position of the steering wheel 3 is in the steering neutral position. In other words, the first abnormality condition will be the above condition added in addition to steps 401:YES and 402:YES. Similarly, the second abnormality condition will be the above condition added in addition to steps 401:NO and 404:YES.

[0083] In the abnormality detection process, the steering control device 1 performed two types of detection processes: the processes in steps 401 and 402, and the processes in steps 401 and 404, but is not limited to this. For example, the steering control device 1 may execute only one of the processes in steps 401 and 402, or the processes in steps 401 and 404.

[0084] The abnormality determination process may include, in the case of step 401: NO, a process to determine whether the difference between the pinion angle θp and the target pinion angle θp* is greater than or equal to a second threshold Th2, which is a value greater than the first threshold Th1. In this case, the steering control device 1 may execute the process of step 404 if the difference between the pinion angle θp and the target pinion angle θp* is greater than or equal to the second threshold Th2. In other words, when determining a steering lock precursor state and a steering lock state, the thresholds for determining the difference between the pinion angle θp and the target pinion angle θp* may be different from each other. According to other embodiments described herein, a dead zone exists between the first threshold Th1 and the second threshold Th2. In this case, the difference between the pinion angle θp and the target pinion angle θp* repeatedly increases and decreases near the boundary value BP, thereby suppressing the oscillation of determination results that are less than the first threshold Th1 and greater than or equal to the second threshold Th2. In addition, the abnormality detection process may include, in the case of step 401: NO, a process to determine whether the difference between the pinion angle θp and the target pinion angle θp* is greater than or equal to (or greater than) a second threshold Th2, which is a value smaller than the first threshold Th1.

[0085] The process in step 402 of the abnormality detection process may be a process that determines whether the steering current value Ib is greater than or equal to the steering current upper limit value Ibmax. The energization control process of the steering control process may include a limiting process that restricts the upper limit of the absolute value of the steering current command value. For example, the limiting process is a process that calculates a steering current command value whose absolute value is the steering current upper limit Ibmax if the absolute value of the steering current command value exceeds the steering current upper limit Ibmax. In this case, the process in step 402 of the abnormality determination process should be a process that determines whether the steering side actual current value Ib matches the steering current upper limit Ibmax.

[0086] While we have assumed steering lock and the preceding steering lock precursor state as abnormalities of the steering unit 6, we are not limited to these. For example, we may also assume a steering ice state and a steering ice precursor state in which the steering unit 6 ceases to function normally due to freezing.

[0087] • The warning process was performed as a process of the 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, a reaction force control process may be performed to apply an additional reaction force to the reaction force motor 13 according to the abnormality flag Flag. In this case, for example, a small reaction force may be applied for the first abnormality flag Flag1, and a large reaction force for the second abnormality flag Flag2. Alternatively, for example, a small vibration may be applied to the steering wheel 3 for the first abnormality flag Flag1, and a small vibration for the second abnormality flag Flag2. [Explanation of symbols]

[0088] 1... Steering control device 2… Steering system 3… Steering wheel 4…Reaction unit 5… Steering wheel 6… Steering unit 11… Steering shaft 13… Reaction motor 14…Reaction force transmission mechanism 22... Rack axis (steering axis) 32... Steering motor 33... Power transmission mechanism

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 When the vehicle's power switch is turned on, the system executes a startup sequence, which is the initial operation at startup. After the startup sequence is completed, while waiting for the vehicle to be ready to drive, the system is configured to perform an abnormality detection process to determine if an abnormality has occurred in the steering unit during the execution of the startup sequence. The aforementioned abnormality determination process is: A feedback control process that calculates a steering target value, which is a target value of the steering axis-related value that can be converted into the amount of movement of the steering axis, and controls the torque generated by the steering motor so as to eliminate the deviation between the steering target value and the actual steering measured value, which is the actual value of the steering axis-related value. The feedback control process includes a first determination process that determines whether or not a first abnormal condition is met during the feedback control process, The first abnormality condition is a condition for determining that a first abnormality has occurred in the steering unit, and includes a first condition indicating that the difference between the steering target value and the measured steering value is less than a first threshold, and a second condition indicating that the steering current value, which is the current generated in the steering motor, is equal to or greater than the upper limit of the steering current value for which the steering motor can operate normally. The steering control device includes a process for determining that the first abnormality has occurred if both the first and second conditions are met.

2. The abnormality determination process includes a second determination process that determines whether or not a second abnormality condition is met during the feedback control process. The second abnormality condition is a condition for determining that a second abnormality has occurred in the steering unit, and includes a third condition indicating that the difference between the steering target value and the measured steering value is greater than or equal to a second threshold value which is greater than or equal to the first threshold value, and a fourth condition indicating that the state in which the third condition is met has continued for a threshold time. The steering control device according to claim 1, wherein the second determination process includes a process for determining that the second abnormality has occurred when both the third condition and the fourth condition are met.

3. The steering control device according to claim 2, wherein the first threshold and the second threshold are the same value.

4. 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 or 2, 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.

5. The startup sequence includes steering control preparation processing to enable linked steering control processing, which is the process of executing steering control to steer the steering wheel according to the steering target value calculated in conjunction with the rotation of the steering wheel. The steering control device according to claim 4, wherein the abnormality determination process is executed after the steering control preparation process has been successfully completed.

6. The steering control device according to claim 5, wherein the steering target value calculated in the abnormality determination process is calculated according to the rotation angle of the steering wheel which changes as the steering wheel is automatically rotated by driving the reaction force motor.

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