Steering control system

Abstract

To provide a steering control device which makes it possible to inhibit a change amount of a correction amount for a target steering angle upon a change in steering direction from becoming excessively large.SOLUTION: When a steering direction, as a change direction of a target angle set by a host ECU, is changed to a right steering direction, a PU 62 corrects the target angle by a right play compensation amount. Then, the PU 62 executes control with a steering angle as a controlled variable and with the corrected target angle as a target value of the controlled variable. When the steering direction is changed from a left steering direction to the right steering direction, the PU 62 gradually increases a correction amount for the target angle to the right play compensation amount.SELECTED DRAWING: Figure 1

Description

【Technical Field】 【0001】 The present invention relates to a steering control device. 【Background Art】 【0002】 For example, Patent Document 1 below describes a control device that corrects a target steering angle according to the steering direction. In this device, when the planned steering direction is the right steering direction, the target steering angle is corrected by the amount of play, which is a value in the right steering direction. The amount of play is the maximum value of the amount by which the steering angle of the steering wheel does not change even when the steering angle changes. 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2022-68056 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 When correcting the target steering angle according to the steering direction as described above, there is a risk that the magnitude of the change in the correction amount of the target steering angle when the steering direction changes becomes excessively large. 【Means for Solving the Problems】 【0005】 Hereinafter, the means for solving the above problems and their effects will be described. 1. A steering control device that controls a steering system, wherein the steering system comprises a steering shaft, steering wheels of a vehicle that steer in accordance with the rotation of the steering shaft, and a motor that rotates the steering shaft, and is configured to perform target steering angle variable acquisition processing, target steering angle correction processing, gradual change processing, and steering angle control processing, wherein the target steering angle variable acquisition processing is the process of acquiring the value of the target steering angle variable, the target steering angle variable is a variable that indicates the target value of the steering angle of the steering wheel, and the target steering angle correction processing is performed according to the steering direction The steering control device is a process that corrects the value of the target steering angle variable by a play compensation amount, the steering direction is the direction in which the value of the target steering angle variable changes, the gradual change process is a process that gradually changes the magnitude of the play compensation amount set to correct the value of the target steering angle variable in accordance with the change in the steering direction, and the steering angle control process is a process that operates the motor by controlling the steering angle corresponding to the rotation angle of the steering shaft as a control amount and setting the value of the target steering angle variable as the target value of the control amount. 【0006】 The above gradual change process causes the amount of play compensation to change gradually when the steering direction changes. Therefore, compared to the case where the amount of play compensation changes in a step-like manner when the steering direction changes, the rate of change in the magnitude of the correction amount of the target steering variable can be limited to the smaller side. 【0007】 2. The steering control device according to paragraph 1 above, wherein the gradual change processing is a process that determines the rate of change of the magnitude of the play compensation amount according to the magnitude of the rate of change of the value of the target rudder angle variable, and further includes a process that sets the rate of change of the magnitude of the play compensation amount when the magnitude of the rate of change of the value of the target rudder angle variable is large to be equal to or greater than the rate of change of the magnitude of the play compensation amount when the magnitude of the rate of change of the value of the target rudder angle variable is small. 【0008】 In the above configuration, the rate of change of the magnitude of the play compensation amount is set to have a positive correlation with the rate of change of the value of the target steering variable. The larger the rate of change of the magnitude of the play compensation amount, the higher the responsiveness of the steering angle to steering. On the other hand, when the rate of change of the value of the target steering angle variable is large, a faster change in the steering angle is required than when it is small. Therefore, the above configuration can meet the requirements in situations where a rapid change in the steering angle is required. 【0009】 3. The steering control device according to 1 or 2 above includes a process that gradually increases the rate of change of the magnitude of the play compensation amount in accordance with the change in the steering direction. In the above configuration, the rate of change of the play compensation amount set in response to changes in steering direction gradually increases. Therefore, while suppressing abrupt changes in the correction amount of the target rudder angle variable in response to changes in steering direction, the play compensation amount can be moved to the desired value as quickly as possible. 【0010】 4. A steering control device according to any one of 1 to 3 above, configured to perform the steering angle control process in automatic steering mode and to perform a play displacement calculation process and a basic amount setting process, wherein the play displacement calculation process is a process that calculates the play displacement in accordance with the change in the steering angle each time, the play displacement is an amount that identifies the position in the region in which the steering angle does not change with respect to the change in the steering angle, the basic amount setting process is a process that sets a basic amount of play corresponding to the right steering direction and a basic amount of play corresponding to the left steering direction to an amount that makes the steering angle a value at the end of the region, according to the play displacement at the time the automatic steering mode is activated, and the gradual change process is a process that gradually changes the play compensation amount to the basic amount of play. 【0011】 The basic amount of play corrects the value of the target rudder angle variable to the edge of the region where the steering angle does not change in response to a change in steering angle, and is therefore an appropriate compensation amount for controlling the steering angle in response to steering. Furthermore, the play compensation amount can be gradually brought closer to the basic amount of play through the above gradual change processing. Therefore, with the above configuration, the play compensation amount can be brought closer to an appropriate compensation amount for controlling the steering angle in response to steering. [Brief explanation of the drawing] 【0012】 [Figure 1] This is a block diagram showing the configuration of the steering system according to the first embodiment. [Figure 2] This figure shows the relationship between steering angle and steering angle according to the same embodiment. [Figure 3] This is a flowchart showing the procedure of processing performed by the control device according to the embodiment. [Figure 4] This is a flowchart showing the procedure of processing performed by the control device according to the embodiment. [Figure 5] This figure illustrates the deviation avoidance control according to the same embodiment. [Figure 6] This is a flowchart showing the procedure of processing performed by the control device according to the embodiment. [Figure 7] This is a flowchart showing the procedure of processing performed by the control device according to the second embodiment. [Figure 8] This is a flowchart showing the procedure of processing performed by the control device according to the third embodiment. [Modes for carrying out the invention] 【0013】 <First Embodiment> The first embodiment will be described below with reference to the drawings. "Prerequisite configuration" The steering system 10 shown in Figure 1 includes a steering wheel 12. A steering shaft 14 is connected to the steering wheel 12. The end of the steering shaft 14 opposite to the steering wheel 12 is connected to the input shaft of a bevel gear section 16. The output shaft of the bevel gear section 16 is connected to the input shaft of a hydraulic power steering system 20 via a power transmission shaft 18. The sector shaft of the hydraulic power steering system 20 is connected to one end of a pitman arm 22. The other end of the pitman arm 22 is connected to one end of a drag link 24. The other end of the drag link 24 is connected to one end of a knuckle arm 26. The other end of the knuckle arm 26 is connected to the kingpin shaft 28 of the right steering wheel 40(R). The kingpin shaft 28 of the right steering wheel 40(R) and the kingpin shaft 28 of the left steering wheel 40(L) are connected by a tie rod arm 30 and a tie rod 32. 【0014】 The rotational power of the motor 50 is transmitted to the steering shaft 14. The motor 50 is, for example, a synchronous motor. The output voltage of the inverter 52 is applied to the terminals of the motor 50. 【0015】 The steering control device 60 controls the steering device 10. For the control of the controlled device, the steering control device 60 refers to the rotation angle θm of the motor 50 detected by the rotation angle sensor 70. The steering control device 60 also refers to the currents iu, iv, and iw flowing through each terminal of the motor 50. The currents iu, iv, and iw may be detected, for example, as the voltage drop across the shunt resistors provided on each leg of the inverter 52. The steering control device 60 refers to the vehicle speed V detected by the vehicle speed sensor 84 via the network 72. 【0016】 The steering control device 60 can communicate with the upper ECU 80 via the network 72. The upper ECU 80 executes a process of generating a command for intervening in the steering of the vehicle independently of the steering instruction by the operation of the steering wheel 12. In other words, the upper ECU 80 executes an automatic steering process. The automatic steering process of the present embodiment is a process of intervening in the steering to eliminate the situation when the vehicle is likely to deviate from the lane due to the operation of the steering wheel 12 by the driver. The upper ECU 80 acquires the image data in front of the vehicle captured by the camera 82 in order to execute the automatic steering process. Further, the upper ECU 80 grasps the driver's indication of whether to execute the automatic steering process input via the interface 86 and the like. 【0017】 The steering control device 60 includes a PU 62 and a storage device 64. The PU 62 is a software processing device such as a CPU, a GPU, and a TPU. The storage device 64 may be a non-volatile memory that cannot be electrically rewritten. Further, the storage device 64 may be a non-volatile memory that can be electrically rewritten and a storage medium such as a disk medium. The steering control device 60 executes a process of controlling the control target by the PU 62 executing the program stored in the storage device 64. 【0018】 "Characteristics of the steering device 10" Due to having a complex link mechanism, the above-described steering device 10 has a so-called large play in which the steered wheels 40 do not rotate with respect to the rotation of the steering shaft 14. 【0019】 Fig. 2 shows the relationship between the steering angle θh and the steered angle θt. Here, the steering angle θh is the rotation angle of the steering shaft 14. On the other hand, the steered angle θt is the cut angle of the tire with respect to the steered wheels 40. Further, the neutral position O shown in Fig. 2 is a point where both the steering angle θh and the steered angle θt are zero. This means that both the steering angle θh and the steered angle θt indicate the straight-ahead direction. In the following, the rotation angle in the right-turning direction is taken as positive and the rotation angle in the left-turning direction is taken as negative. 【0020】 As shown in Figure 2, even if the steering angle θh is changed in the rightward turning direction from the neutral position O, the steering angle θt does not change until point A is reached. Then, when the steering angle θh becomes larger than the value at point A, the steering angle θt increases. 【0021】 Furthermore, even if the steering angle θh is decreased at point B, the steering angle θt does not change. In other words, even if the steering direction is switched to the left at point B, the steering angle θt does not change. Note that the steering direction is the direction indicated by the rotational speed of the steering shaft 14. When the steering angle θh becomes even smaller than the value at point C, the steering angle θt decreases. In other words, if the steering angle θh is a negative value and its absolute value is increased further beyond point C, the steering angle θt decreases. 【0022】 Then, at point D where the steering angle θt is zero, the steering angle θh becomes a negative value. Point E is the value obtained by further displacing the steering angle θh in the leftward direction after the steering angle θt has become zero. Even if the steering angle θh is increased at point E, the steering angle θt does not change until the steering angle θh reaches point F. When the steering angle θh becomes larger beyond point F, the steering angle θt increases. 【0023】 Thus, for example, when positioned at point B, the steering angle θt does not change even if the steering angle θh changes between point B and point C. Similarly, when positioned at point E, the steering angle θt does not change even if the steering angle θh changes between point E and point F. In this way, due to the play in the steering device 10, there exists a region in which the steering angle θt does not change in response to a change in the steering angle θh. However, this region is not a region with a fixed value for the steering angle θh, but rather a region that can change depending on the history of changes in the steering angle θh. 【0024】 The displacement of the steering angle θh from point B to point C occurs during a corrective turn from a right turn. Similarly, the displacement of the steering angle θh from point E to point F occurs during a corrective turn from a left turn. In Figure 2, the length of the region in which the steering angle θt does not change in response to the change in steering angle θh during these corrective turns is indicated as "α". "α" is pre-stored in the memory device 64. "α" may be a fixed value, for example. Alternatively, "α" may be a value that is updated each time. The update process for "α" can be performed, for example, as follows. 【0025】 1. When the vehicle is stopped, PU62 controls the rotation angle of motor 50 to rotate the steering shaft 14. 2. PU62 identifies the end of the above region by the rotation angle of the motor 50 just before the current flowing to the motor 50 exceeds a threshold value in relation to the rotation of the motor 50. 【0026】 PU62 estimates "α" by controlling the rotation angle of the motors 50 described in "1" and "2" above, both clockwise and counterclockwise. PU62 updates the "α" stored in the memory device 64 with the estimated "α". PU62 may, for example, store the estimated "α" in the memory device 64. Alternatively, PU52 may newly store in the memory device 64 a weighted average of the estimated "α" and the "α" previously stored in the memory device 64. 【0027】 "Setting the basic amount of play time" The above region is a factor that reduces the responsiveness of the change in steering angle θt to the change in steering angle θh. Therefore, in this embodiment, the reduction in responsiveness is suppressed by the amount of play compensation. Here, we will first explain how to set the basic amount of play, which is the basic quantity for calculating the amount of play compensation. 【0028】 Figure 3 shows the procedure for setting the basic amount of play. The process shown in Figure 3 is realized by the PU 62 repeatedly executing a program stored in the memory device 64, for example, at a predetermined period. In the following, the step number of each process is represented by a number preceded by "S". 【0029】 In the series of processes shown in Figure 3, PU62 obtains the steering angle θh (S10). The steering angle θh is calculated by PU62 through the integration of the rotation angles θm. Next, PU62 calculates the variable X for calculating the play displacement using the following formula (S12). 【0030】 X ← Δα(n-1) + (θh - θh(n-1)) In the above equation, "n-1" means the value at the previous execution timing of the series of processes shown in Figure 3. That is, "Δα(n-1)" means the play displacement Δα at the previous execution timing of the series of processes shown in Figure 3. Also, "θh(n-1)" means the value obtained in process S10 at the previous execution timing of the series of processes shown in Figure 3. 【0031】 Figure 2 illustrates the play displacement Δα. Figure 2 shows the state where the steering angle θh reaches the position of point P after the steering angle θh has been turned to the right by a play displacement Δα from the neutral position O. Returning to Figure 3, PU62 determines whether the value of variable X is greater than or equal to "-α / 2" and less than or equal to "α / 2" (S14). If PU62 determines that this is true in the process of S14, it assigns the value of variable X to the play displacement Δα (S16). 【0032】 On the other hand, if PU62 makes a negative determination in the process of S14, it determines whether the value of variable X is greater than "α / 2" (S18). If PU62 determines that the value of variable X is greater than "α / 2" (S18: YES), it substitutes "α / 2" for the play displacement Δα (S20). This process corresponds, for example, to a situation in Figure 2 where the steering angle θh is turned significantly to the right beyond point A. In that case, the play displacement Δα is located at the right steering end of the region where the steering angle θt does not change with respect to the change in steering angle θh. If the length of the region is "α" and the center of the region is defined as "0", then the play displacement Δα at the right steering end of the above region is "α / 2". 【0033】 On the other hand, if PU62 determines that the result is negative in the processing of S18, it substitutes "-α / 2" for the play displacement Δα (S22). When PU62 completes the processes in S16, S20, and S22, it determines whether or not it has switched to automatic steering mode (S24). Automatic steering mode is a mode in which the automatic steering process described above is executed. In automatic steering mode, the higher-level ECU80 outputs the target angle θt* to the steering control device 60. The target angle θt* is a variable that indicates the target value of the steering angle of the steering wheel 40. However, the amount of change in the target angle θt* is quantified so that it is equal to the amount of change in the steering angle θh between points F and B, or between points C and E, as shown in Figure 2. 【0034】 If PU62 determines that a switch has occurred (S24: YES), it sets the basic right play quantity αR0 and the basic left play quantity αL0 (S26). Specifically, PU62 substitutes "α / 2-Δα" for the basic right play quantity αR0. Also, PU62 substitutes "-α / 2-Δα" for the basic left play quantity αL0. 【0035】 When the system switches to automatic steering mode, for example, if the play displacement Δα is located at point P shown in Figure 2, the steering angle will not change until the steering angle θh changes by "α / 2-Δα", even if the target angle θt* changes in the rightward steering direction. Therefore, in order to improve the responsiveness of the steering angle to changes in the target angle θt*, it is desirable to correct the target angle θt* by "α / 2-Δα" using open-loop control as the target angle θt* changes in the rightward steering direction. For this reason, PU62 substitutes "α / 2-Δα" into the basic rightward play amount αR0. Also, when the play displacement Δα is located at point P, the steering angle will not change until the steering angle θh changes by "-α / 2-Δα", even if the target angle θt* changes in the leftward steering direction. Therefore, in order to improve the responsiveness of the steering angle to changes in the target angle θt*, it is desirable to correct the target angle θt* by "-α / 2-Δα" using open-loop control as the target angle θt* changes in the left steering direction. For this reason, PU62 substitutes "-α / 2-Δα" into the basic rightward play amount αR0. 【0036】 When PU62 completes the process in S26, or when it makes a negative determination in the process in S24, it temporarily terminates the series of processes shown in Figure 3. "Setting the amount of play compensation" Figure 4 shows the procedure for setting the amount of play compensation. The process shown in Figure 4 is achieved in automatic steering mode by the PU 62 repeatedly executing a program stored in the memory device 64, for example, at a predetermined period. 【0037】 In the series of processes shown in Figure 4, PU62 first determines whether flag F is "1" (S30). If flag F is "1", it indicates that steering intervention processing is being performed to prevent the vehicle from deviating from its lane. If flag F is "0", it indicates that the above steering intervention processing is not being performed. 【0038】 If PU62 determines that flag F is "0" (S30: NO), it determines whether or not it has received a notification from the higher-level ECU 80 to initiate lane departure avoidance control (S32). The start notification is issued when control to suppress lane departure through steering intervention is initiated. At this time, the higher-level ECU 80 also notifies the steering direction for lane departure avoidance. If PU62 determines that it has received a start notification (S32: YES), it assigns "1" to flag F (S34). Then, PU62 determines whether or not the steering direction for lane departure avoidance by the higher-level ECU 80 is a rightward steering direction (S36). 【0039】 If PU32 determines that the steering direction is to the right (S36: YES), it proceeds to process S38. In process S38, PU62 substitutes the basic right play amount αR0 for the right play compensation amount αR and substitutes "0" for the left play compensation amount αL. On the other hand, if PU32 determines that the steering direction is to the left (S36: NO), it proceeds to S40. In process S40, PU62 substitutes "0" for the right play compensation amount αR and substitutes the basic left play amount αL0 for the left play compensation amount αL. 【0040】 On the other hand, if PU62 determines that flag F is "1" (S30: YES), it determines whether or not it has received a departure avoidance control completion notification from the higher-level ECU80 (S42). The departure avoidance control completion notification is output from the higher-level ECU80 when steering intervention for departure avoidance has ended. The departure avoidance control completion notification does not notify that the steering intervention itself has ended. This will be explained below with reference to Figure 5. 【0041】 Figure 5 shows a case where the vehicle VC (Vehicle Control Center) is too far to the right and about to deviate from the lane. In other words, it shows a case where the vehicle VC is too close to the right-hand white line 100. In this case, at time t1, the higher-level ECU 80 outputs a notification to start lane departure avoidance control. At time t2, the higher-level ECU 80 outputs a notification to end lane departure avoidance control. The period from time t1 to t2 is the period when the steering direction is to the left or the steering angle is at the value of a left turn and the steering angle is constant. However, minute fluctuations in the steering angle due to feedback control are ignored. If the steering angle at time t2 is maintained, the vehicle VC will move closer to the left side of the lane. Therefore, the higher-level ECU 80 performs further steering intervention from time t2 to t3 in order to keep the vehicle VC along the lane. However, the period from time t2 to t3 is the processing after the end of lane departure avoidance control. That is, the period from time t1 to t2 shows the period when the higher-level ECU 80 is performing control to move the vehicle VC to the left. On the other hand, the period from time t2 to t3 indicates the time during which the higher-level ECU 80 performs control to move the vehicle VC straight in the lane after initially controlling it to move to the left. 【0042】 Returning to Figure 4, if PU62 determines that it has received a notification that the deviation avoidance control has ended (S42: YES), it assigns "0" to flag F (S44). If PU42 completes the process in S44, or if it determines that the process in S32 is negative, it proceeds to the process in S46. In the process in S46, PU62 assigns the basic right play amount αR0 to the right play compensation amount αR and the basic left play amount αL0 to the left play compensation amount αL (S46). 【0043】 Furthermore, when PU62 completes the processes in S38, S40, and S46, it temporarily terminates the series of processes shown in Figure 4. "Control of steering angle in automatic steering mode" Figure 6 shows the procedure for controlling the steering angle. The process shown in Figure 6 is achieved in automatic steering mode by the PU 62 repeatedly executing a program stored in the memory device 64, for example, at a predetermined period. 【0044】 In the series of processes shown in Figure 6, PU62 first obtains the target angle θt* output by the higher-level ECU80 (S50). Next, PU62 determines whether the change in the target angle θt* is positive or negative (S52). In other words, PU62 determines whether the direction of change in the target angle θt* is to the right. If the direction of change in the target angle θt* is to the right, it means that the higher-level ECU80 is instructing to steer to the right through the target angle θt*. In Figure 6, the target angle θt* obtained by the process in S50 at the execution timing immediately preceding the series of processes shown in Figure 6 is written as "θt*(n-1)". 【0045】 If PU62 determines that the change in the target angle θt* is positive (S52: YES), it substitutes the rightward play compensation amount αR for the play compensation amount Δ0 (S54). On the other hand, if PU62 determines that the change in target angle θt* is negative in the processing of S52, it determines whether the change in target angle θt* is negative or not (S56). In other words, PU62 determines whether the direction of change in target angle θt* is in the left steering direction or not. If PU62 determines that the change in target angle θt* is negative (S56: YES), it substitutes the left play compensation amount αL into the play compensation amount Δ0 (S58). 【0046】 If PU62 determines that the result is negative in the processing of S56, it substitutes "0" for the play compensation amount Δ0 (S60). When PU62 completes the processes in S54, S58, and S60, it performs a guard process (S62) that limits the magnitude of the change rate of the play compensation amount Δ0 to the smaller side. The value after the guard process is the play compensation amount Δ. If the play compensation amount Δ at the previous execution timing of the series of processes shown in Figure 6 is "Δ(n-1)", then the output of the process in S62 is as follows. 【0047】 (Δ0 / |Δ0|)·MIN(Δth |Δ0-Δ(n-1)|)+Δ(n-1) Here, the upper limit Δth defines the maximum value of the change in the amount of play compensation Δ per execution cycle of the process shown in Figure 6. 【0048】 Next, PU62 adds the play compensation amount Δ to the target angle θt* and substitutes that value into the target angle θt* (S64). Next, PU62 obtains the steering angle θh (S66). Then, PU62 calculates a manipulated variable for feedback control, where the steering angle θh is the controlled variable and the target angle θt* is the target value of the controlled variable (S68). The manipulated variable may be the torque of the motor 50. Next, PU62 outputs an operation signal MS to the inverter 52 in order to control the motor 50 according to the manipulated variable (S70). As a result, for example, if the manipulated variable is the torque of the motor 50, the output voltage of the inverter 52 is operated so that the torque of the motor 50 becomes the manipulated variable. This process may be performed, for example, with currents iu, iv, and iw as inputs. 【0049】 Furthermore, when PU62 completes the process in S70, it terminates the series of processes shown in Figure 6. Incidentally, it is also possible to execute the processes in S62 to S70 multiple times within the cycle in which the processes in S50 to S60 are executed. In that case, the amount of play compensation Δ at the time of the previous execution of the process in S62 is set to "Δ(n-1)". This increases the certainty that the amount of play compensation Δ converges to the amount of play compensation Δ0 before the target angle θt* stops changing. 【0050】 "The operation and effects of this embodiment" When the PU62 switches to automatic steering mode, it sets the basic rightward play amount αR0 and the basic leftward play amount αL0. Then, when the target angle θt* changes in the rightward steering direction, it corrects the target angle θt* according to the rightward play compensation amount αR corresponding to the basic rightward play amount αR0. Similarly, when the target angle θt* changes in the leftward steering direction, it corrects the target angle θt* according to the leftward play compensation amount αL corresponding to the basic leftward play amount αL0. 【0051】 However, if the play compensation amount Δ is changed stepwise to either the right play compensation amount αR or the left play compensation amount αL when the steering direction is changed, the change in the target angle θt* becomes excessively large. This raises concerns about reducing the stability and reliability of the control. There are also concerns that the rotation of the steering wheel 12 will become abrupt, causing discomfort to the driver. 【0052】 In response to this, PU62 gradually adjusts the play compensation amount Δ to a newly set play compensation amount Δ0 as the steering direction changes. This process, when play compensation amount Δ0 is considered positive, results in a gradual increase in play compensation amount Δ. This suppresses the aforementioned concerns. 【0053】 In particular, in this embodiment, the magnitude of the change rate of the play compensation amount Δ during steering intervention by the lane departure avoidance control is limited to the smaller side. This helps to suppress the driver from feeling uncomfortable with the steering intervention. 【0054】 Furthermore, according to this embodiment, the following effects and advantages can be obtained. (1-1) If the rightward play compensation amount αR is set to the basic rightward play amount αR0 and the leftward play compensation amount αL is set to the basic leftward play amount αL0, then by controlling the steering angle θh to the target angle θt*, the steering angle can be controlled with high precision according to the target angle θt*. On the other hand, for example, in the period from time t1 to t2 as illustrated in Figure 5, fine adjustment of the control may cause the change in the target angle θt* to be in the direction of rightward steering. In that case, if the play compensation amount Δ is set to the basic rightward play amount αR0, there is a concern that the control to suppress lane departure will lack stability. Therefore, PU62 sets the rightward play compensation amount αR to zero in that case. This ensures the stability of the control to suppress lane departure. 【0055】 <Second Embodiment> The second embodiment will be described below, focusing on the differences from the first embodiment, with reference to the drawings. 【0056】 In this embodiment, the method of limiting the rate of change of the play compensation amount Δ is changed. Figure 7 shows the procedure for controlling the steering angle according to this embodiment. The process shown in Figure 7 is realized in automatic steering mode by the PU 62 repeatedly executing a program stored in the memory device 64, for example, at a predetermined period. In Figure 7, for convenience, the same step numbers are assigned to the processes corresponding to the processes shown in Figure 6. 【0057】 In the series of processes shown in Figure 7, if processes S54, S58, and S60 are completed, PU62 applies a guard process (S62a) that limits the magnitude of the rate of change of the play compensation amount Δ0 to the smaller side. The difference between the process in S62a and the process in S62 lies in the setting of the upper limit value Δth. In the process in S62, the upper limit value Δth was a fixed value. In contrast, in the process in S62a, the upper limit value Δth is changed according to the rate of change of the target angle θt*. 【0058】 More specifically, PU62 sets the upper limit Δth when the rate of change of the target angle θt* is large to be greater than or equal to the upper limit Δth when the rate of change of the target angle θt* is small. This process may also be performed by PU62 performing a map calculation on the upper limit Δth while the map data is stored in the storage device 64. Here, the map data is data in which the absolute value of the rate of change of the target angle θt* is the input variable and the upper limit Δth is the output variable. 【0059】 Map data is a set of data consisting of discrete values ​​of input variables and corresponding values ​​of output variables for each of the input variable values. The map operation can be performed by taking the value of the corresponding output variable of the map data as the calculation result if the value of the input variable matches any of the input variable values ​​of the map data. Alternatively, if the value of the input variable does not match any of the input variable values ​​of the map data, the map operation can be performed by taking the value obtained by interpolating the values ​​of multiple output variables included in the map data as the calculation result. Or, if the value of the input variable does not match any of the input variable values ​​of the map data, the map operation can be performed by taking the value of the output variable of the map data corresponding to the closest value among the multiple input variable values ​​included in the map data as the calculation result. 【0060】 The output variables of the map data described above have several values ​​that are different from each other. When the rate of change of the target angle θt* is large, a quicker change in steering direction is required compared to when the rate of change is small. Therefore, the process in S62a can strike a suitable compromise between responding to the requirement for a quick change in steering direction and suppressing the rapid rotation of the steering shaft 14. 【0061】 <Third Embodiment> The third embodiment will be described below, focusing on the differences from the first embodiment, with reference to the drawings. 【0062】 In this embodiment, the method of limiting the rate of change of the play compensation amount Δ is changed. Figure 8 shows the procedure for controlling the steering angle according to this embodiment. The process shown in Figure 8 is realized in automatic steering mode by the PU 62 repeatedly executing a program stored in the memory device 64, for example, at a predetermined period. In Figure 8, for convenience, the same step numbers are assigned to the processes corresponding to the processes shown in Figure 6. 【0063】 In the series of processes shown in Figure 8, if processes S54, S58, and S60 are completed, PU62 applies a guard process (S62b) that limits the magnitude of the rate of change of the play compensation amount Δ0 to the smaller side. The difference between the process in S62b and the process in S62 lies in the setting of the upper limit value Δth. In the process in S62, the rate of change of the upper limit value Δth was constant. In contrast, in the process in S62b, the rate of change of the upper limit value Δth is a function of time. 【0064】 More specifically, PU62 gradually increases the rate at which the upper limit value Δth increases over time. That is, PU62 considers the acceleration of the increase in the upper limit value Δth to be positive. Specifically, for example, the upper limit value Δth may be increased exponentially with respect to time. This process may also be a process in which PU62 performs a mapping calculation on the upper limit value Δth while the map data is stored in the memory device 64. Here, the map data is data in which time is the input variable and the upper limit value Δth is the output variable. Alternatively, this process may be a process in which the value of the dependent variable of an exponential function with time as the independent variable is substituted for the upper limit value Δth. 【0065】 In this way, by gradually increasing the rate at which the upper limit Δth increases, the change in the amount of play compensation Δ is small immediately after switching to the amount of play compensation Δ0. Then, as the change in the amount of play compensation Δ gradually increases, it is possible to suppress the impression of a sudden change on the driver. 【0066】 <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the "Means for Solving the Problems" section is as follows. Below, the correspondence is shown for each number of the solution means described in the "Means for Solving the Problems" section. [1] The target steering angle variable acquisition process corresponds to the process in S50. The target steering angle correction process corresponds to the process in S64. The gradual change process corresponds to the processes in S62, S62a, and S62b. The steering angle control process corresponds to the processes in S68 and S70. [2] This corresponds to the process in S62a. [3] This corresponds to the process in S62b. [4] The play displacement calculation process corresponds to the processes in S10 to S22. The basic quantity setting process corresponds to the processes in S24 and S2. 【0067】 <Other Embodiments> Furthermore, this embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically. 【0068】 "Regarding target steering angle variables" The target steering angle variable is not limited to the value obtained by converting the steering angle of the steering wheel 40 into the rotation angle of the steering shaft 14. For example, the steering angle itself may be used. In that case, in the processing of S68, the control variable should be the value obtained by converting the steering angle θh into a steering angle, and the target angle should be set as the target value of the control variable. 【0069】 "Regarding gradual change processing" For example, if the play compensation amount Δ has not reached the play compensation amount Δ0 when the target angle θt* stops changing, the play compensation amount Δ may be changed until it reaches the play compensation amount Δ0. This means, for example, that when the target angle θt* transitions from changing in the right steering direction to stopping changing, the play compensation amount Δ will be changed to the right play compensation amount αR. 【0070】 In the S62b process, the rate of change of the gradual increase rate of the upper limit Δth was set to a predetermined rate of change, but this is not limited to this. For example, the rate of change of the gradual increase rate of the upper limit Δth may be changed according to the rate of change of the target angle θt*. 【0071】 "Regarding compensation for play time" In processing S38, it is not mandatory to set the leftward play compensation amount αL to zero. For example, the absolute value of the leftward play compensation amount αL may be greater than zero, while being smaller than the absolute value of the basic leftward play amount αL0. 【0072】 In the S40 process, it is not mandatory to set the rightward play compensation amount αR to zero. For example, the absolute value of the rightward play compensation amount αR may be greater than zero, while being smaller than the absolute value of the basic rightward play amount αR0. 【0073】 The process illustrated in Figure 4 is not essential for setting the right play compensation amount αR and the left play compensation amount αL. For example, the right play compensation amount αR and the left play compensation amount αL may always be set to match the basic right play amount αR0 and the basic left play amount αL0, respectively. 【0074】 It is not essential to determine the steering direction based on the processing in S52 and S56. For example, instead of the target angle θt* in processing S52, a filtered value of the target angle θt* may be used. This can suppress the determination that the steering direction is frequently reversing due to the influence of noise. 【0075】 "About the auto-steering mode" In the above embodiment, an example was given in which the higher-level ECU 80 intervenes in steering when the vehicle is about to deviate from its lane while the driver is operating the steering wheel 12. However, the automatic steering process performed in automatic steering mode is not limited to this process. For example, the higher-level ECU 80 may perform steering even when the driver is not operating the steering wheel 12. Alternatively, for example, the higher-level ECU 80 may intervene in steering when the vehicle is about to collide with an obstacle while the driver is operating the steering wheel 12. 【0076】 "Regarding steering angle control processing" It is not mandatory for the steering angle control process to include a process for calculating a manipulated variable for feedback control, where the steering angle θh is the controlled variable and the target angle θt* is the target value of the controlled variable. For example, it may include a process for calculating a manipulated variable for open-loop control, where the steering angle θh is the controlled variable and the target angle θt* is the target value of the controlled variable. Alternatively, it may include a process for calculating both the manipulated variable for feedback control and the manipulated variable for open-loop control. 【0077】 "Regarding steering control systems" The steering control device is not limited to a device that acquires the target angle θt* set by the higher-level ECU 80. For example, the steering control device 60 and the higher-level ECU 80 may be integrated into a single device. 【0078】 The steering control device 60 is not limited to one that includes a PU 62 and a storage device 64 to perform software processing. For example, it may include a dedicated hardware circuit (e.g., an ASIC) to perform hardware processing for at least a portion of what is processed by software in the above embodiment. In other words, the steering control device may have any of the following configurations (a) to (c): (a) It includes a processing unit that performs all of the above processing according to a program and a program storage device such as a ROM that stores the program. (b) It includes a processing unit and a program storage device that perform a portion of the above processing according to a program and a dedicated hardware circuit that performs the remaining processing. (c) It includes a dedicated hardware circuit that performs all of the above processing. Here, there may be multiple software processing circuits equipped with a processing unit and a program storage device, or multiple dedicated hardware circuits. In other words, the above processing may be performed by a processing circuit that includes at least one of one or more software processing circuits and one or more dedicated hardware circuits. [Explanation of symbols] 【0079】 10… Steering gear 12… Steering wheel 14… Steering axis 16... Bevel Gear Section 18…Power transmission shaft 20… Hydraulic power steering system 22... Pitman Arm 24... Drag Link 26... Knuckle Arm 28... Kingpin shaft 30...Tie rod arm 32...Tie rod 40... Steering wheel 50...motor 52…Inverter 60... Steering control device 80…Upper ECU

Claims

[Claim 1] A steering control device that controls the steering system, The steering device is The steering axis and The steering wheels of a vehicle that steer in conjunction with the rotation of the aforementioned steering shaft, A motor that rotates the steering shaft, Equipped with, It is configured to perform target steering angle variable acquisition processing, target steering angle correction processing, gradual change processing, and steering angle control processing. The aforementioned target rudder angle variable acquisition process is a process for acquiring the value of the target rudder angle variable. The aforementioned target steering angle variable is a variable that indicates the target value of the steering angle of the steering wheel. The aforementioned target rudder angle correction process is a process that corrects the value of the target rudder angle variable by the amount of play compensation corresponding to the steering direction. The steering direction is the direction in which the value of the target rudder angle variable changes. The aforementioned gradual change process is a process that gradually changes the magnitude of the play compensation amount, which is set in order to correct the value of the target rudder angle variable in accordance with the change in the steering direction. The steering angle control process is a steering control device that operates the motor by controlling the steering angle corresponding to the rotation angle of the steering shaft as a control variable and setting the value of the target steering angle variable to the target value of the control variable. [Claim 2] The steering control device according to claim 1, wherein the gradual change processing is a process that determines the rate of change of the magnitude of the play compensation amount according to the magnitude of the rate of change of the value of the target rudder angle variable, and further includes a process that makes the rate of change of the magnitude of the play compensation amount when the magnitude of the rate of change of the value of the target rudder angle variable is large equal to or greater than the rate of change of the magnitude of the play compensation amount when the magnitude of the rate of change of the value of the target rudder angle variable is small. [Claim 3] The steering control device according to claim 1, wherein the gradual change processing includes a process of gradually increasing the rate of change of the magnitude of the play compensation amount in accordance with the change in the steering direction. [Claim 4] The steering angle control process is configured to be performed in automatic steering mode, and the system is configured to perform the play displacement calculation process and the basic quantity setting process. The aforementioned play displacement calculation process is a process that calculates the play displacement in accordance with the change in the steering angle each time, The aforementioned play displacement is a quantity that identifies the position in the region where the steering angle does not change with respect to the change in the steering angle. The aforementioned basic quantity setting process is a process that sets the basic quantity of play corresponding to the right steering direction and the basic quantity of play corresponding to the left steering direction, according to the play displacement at the time the automatic steering mode is activated, to an amount that sets the steering angle to the value at the end of the region. The steering control device according to claim 1, wherein the gradual change processing is a process of gradually changing the amount of play compensation to the amount of play base.

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