Steering control device

Abstract

To provide a steering control device that can compensate deterioration of responsiveness of a steering angle due to the fact that a dead zone amount is not zero.SOLUTION: Feedback processing M10 is processing of calculating a feedback operation amount Tfb so that a steering angle θt approximates a target steering angle θt*. Processing to calculate position in dead zone M20 is processing of calculating a position in a dead zone Δα when the steering angle θt is within the dead zone. Dead zone compensation torque calculation processing M14 is processing of calculating dead zone compensation torque Tdz by calculating a dead zone amount in a steering direction based on the position in dead zone Δα. Addition processing M16 is processing of substituting a value obtained by adding the dead zone compensation torque Tdz to the feedback operation amount Tfb into a torque command value Trq*. Operation signal generation processing M18 is processing of generating and outputting an inverter operation signal for allowing motor torque to approximate the torque command value Trq*.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] For example, the following Patent Document 1 describes a control device that corrects a target steering angle according to the steering direction. In this device, when the planned steering direction is a right steering direction, the target steering angle is corrected by the amount of play, which is the value of the right steering direction. The amount of play is the maximum amount at which the steering angle of the steered wheels does not change even if the steering angle changes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-73790 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when correcting the target steering angle as described above, the target value deviates from the steering angle of the steered wheels to be actually controlled, and so there is a risk that an appropriate operation amount cannot be calculated. Specifically, for example, when the operation amount of the feedforward control is calculated according to the target steering angle, the magnitude of the operation amount may be excessive. [Means for solving the problem]

[0005] Means for solving the above problems and their effects will be described below. 1. A steering control device which controls a steering device, the steering device comprising a steering shaft, steerable wheels of a vehicle which turn in accordance with the rotation of the steering shaft, and a motor which rotates the steering shaft, and is configured to execute a dead zone amount calculation process and a superposition process, the dead zone amount calculation process being a process in which a steering angle is input and a dead zone amount which is the amount by which the steering angle changes without turning the steerable wheels in the steering direction, the steering angle being the rotation angle of the steering shaft, the superposition process being a process in which a dead zone compensation torque is superimposed on the torque of the motor when the magnitude of the dead zone amount is greater than zero, and the dead zone compensation torque is a torque which increases the torque of the motor in the direction which steers the steerable wheels in accordance with the rotation of the steering shaft.

[0006] In the above configuration, when the dead-zone amount is greater than zero, the dead-zone compensation torque is superimposed on the motor torque. Therefore, the deterioration in the responsiveness of the steering angle caused by the dead-zone amount being non-zero can be compensated for by designing the dead-zone compensation torque. Therefore, compared to the case where the target value of the steering angle is corrected, the deterioration in the responsiveness of the steering angle caused by the dead-zone amount being non-zero can be more directly compensated for, thereby improving the controllability of the steering angle.

[0007] 2. A steering control device as described in 1 above, wherein the superimposition process includes a dead zone compensation torque calculation process, and the dead zone compensation torque calculation process is a process for changing the magnitude of the dead zone compensation torque in accordance with the dead zone amount under the condition that the magnitude of the dead zone compensation torque when the dead zone amount is large is equal to or greater than the magnitude of the dead zone compensation torque when the dead zone amount is small.

[0008] In the above configuration, by changing the magnitude of the dead-zone compensation torque in accordance with the magnitude of the dead-zone amount, the dead-zone compensation torque can be adjusted to a more appropriate value for improving the controllability of the steering angle, compared to the case where the magnitude of the dead-zone compensation torque is fixed.

[0009] 3. A steering control device as described in claim 2, further comprising a memory device in which a dead zone width is stored for each different vehicle speed, the dead zone width being the amount by which the steering angle changes from when the rotation direction of the steering shaft is switched from either a right turning direction or a left turning direction to the other until the steered wheels are turned, the dead zone compensation torque calculation process including a dead zone width selection process, the dead zone width selection process being a process of selecting the dead zone width corresponding to the vehicle speed from among a plurality of dead zone widths stored in the memory device in accordance with the vehicle speed, and the dead zone compensation torque calculation process being a process of changing the magnitude of the dead zone compensation torque in accordance with the ratio under the condition that the magnitude of the dead zone compensation torque when the magnitude of the ratio of the dead zone amount to the dead zone width selected by the dead zone width selection process is large is equal to or greater than the magnitude of the dead zone compensation torque when the magnitude of the ratio is small.

[0010] The dead zone width can change depending on the vehicle speed. Therefore, in the above configuration, the magnitude of the dead zone compensation torque is changed depending on the ratio of the dead zone amount to the dead zone width. This makes it possible to fix the maximum value of the magnitude of the dead zone compensation torque even if the dead zone width changes depending on the vehicle speed.

[0011] 4. A steering control device described in any one of 1 to 3 above, wherein the dead zone amount calculation process includes a steering direction determination process, which is a process for determining whether the steering direction is a right turning direction or a left turning direction based on the direction of change of the target value of the steering angle, and the dead zone amount calculation process is a process for calculating the dead zone amount according to the steering direction determined by the steering direction determination process.

[0012] In the above-described configuration, the dead zone amount is calculated in response to a change in the target value, so that a dead zone compensation torque appropriate for improving controllability of the steering angle to the target value can be superimposed. 5. A steering control device described in any one of 1 to 3 above, wherein the dead zone amount calculation process includes a steering direction determination process, which is a process for determining whether the steering direction is a right turning direction or a left turning direction based on the sign of the difference between a target value of the steering angle and the steering angle, and the dead zone amount calculation process is a process for calculating the dead zone amount according to the steering direction determined by the steering direction determination process.

[0013] In the above-described configuration, the dead zone amount is calculated according to the sign of the difference between the target value and the steering angle, so that a dead zone compensation torque appropriate for improving controllability of the steering angle to the target value can be superimposed. 6. A steering control device as described in any one of 1 to 5 above, configured to execute a steering process, the steering process being a process of manipulating the torque of the motor in accordance with an operation amount of feedback control in which the steering angle of the steered wheels is a control amount and a target value of the steering angle is a target value of the control amount, and the superimposition process being a process of superimposing the dead zone compensation torque on the torque in accordance with the operation amount.

[0014] In the above configuration, by superimposing the dead zone compensation torque, it is possible to add a feedforward control according to the dead zone to the feedback control, thereby improving the responsiveness of the steering angle compared to the case of only feedback control.

[0015] 7. A steering control device as described in claim 6, further comprising a memory device in which a stiffness coefficient is stored for each different vehicle speed, the stiffness coefficient being a ratio of a turning angle to the steering angle, and configured to execute a stiffness coefficient selection process and a turning angle acquisition process, the stiffness coefficient selection process being a process of selecting the stiffness coefficient corresponding to the vehicle speed from among the plurality of stiffness coefficients stored in the memory device in accordance with the vehicle speed, and the turning angle acquisition process being a process of calculating an estimated value of the turning angle as the control quantity using the detected value of the steering angle and the stiffness coefficient selected by the stiffness coefficient selection process.

[0016] The stiffness coefficient changes depending on the vehicle speed, so in the above configuration, the steering angle can be estimated with high accuracy by using the stiffness coefficient according to the vehicle speed. [Brief description of the drawings]

[0017] [Figure 1] 1 is a diagram showing a configuration of a steering system according to a first embodiment. [Diagram 2] 2 is a diagram showing the relationship between the steering angle and the turning angle in the steering system shown in FIG. 1. [Diagram 3] 2 is a block diagram showing a process executed by the steering control device shown in FIG. 1. [Figure 4] 2 is a flowchart showing a procedure of a process executed by the steering control device shown in FIG. [Diagram 5] 2 is a flowchart showing a procedure of a process executed by the steering control device shown in FIG. [Figure 6] FIG. 6 is a diagram illustrating a part of the process shown in FIG. 5. [Figure 7] 2 is a flowchart showing a procedure of a process executed by the steering control device shown in FIG. [Figure 8] 2 is a flowchart showing a procedure of a process executed by the steering control device shown in FIG. [Figure 9] 2 is a flowchart showing a procedure of a process executed by the steering control device shown in FIG. [Figure 10] 2 is a time chart illustrating a process executed by the steering control device shown in FIG. 1; [Figure 11] 6 is a flowchart showing a procedure of a process executed by a steering control device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] <First embodiment> Hereinafter, the first embodiment will be described with reference to the drawings. "Prerequisite configuration" The steering device 10 shown in FIG. 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 a steering gear box 20. A sector shaft of the steering gear box 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 a kingpin shaft 28 of a right steered wheel 40(R). The kingpin shaft 28 of the right steered wheel 40(R) and the kingpin shaft 28 of the left steered wheel 40(L) are connected by a tie rod arm 30 and a tie rod 32.

[0019] 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 an inverter 52 is applied to the terminals of the motor 50.

[0020] 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, or a TPU. The storage device 64 may be an electrically non-rewritable non-volatile memory. The storage device 64 may also be an electrically rewritable non-volatile memory or a storage medium such as a disk medium. The steering control device 60 executes a process for controlling a control target by the PU 62 executing a program stored in the storage device 64.

[0021] The control target of the steering control device 60 is the steering device 10. To control the control target, 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 yaw rate γ detected by the yaw rate sensor 71. The steering control device 60 also refers to the currents iu, iv, iw flowing through each terminal of the motor 50. The currents iu, iv, iw may be detected as voltage drops across shunt resistors provided in each leg of the inverter 52, for example. The steering control device 60 refers to the vehicle speed V detected by the vehicle speed sensor 84 via the network 72.

[0022] The steering control device 60 is capable of communicating with a host ECU 80 via a network 72. The host ECU 80 executes a process of generating a command for intervening in the steering of the vehicle, independent of a steering command by the operation of the steering wheel 12. In other words, the host ECU 80 executes the automatic steering process. In order to execute the automatic steering process, the host ECU 80 acquires image data of the surroundings of the vehicle captured by a camera 82. The host ECU 80 also grasps an indication of intent, input by the driver via an interface 86, as to whether or not to execute the automatic steering process.

[0023] "Characteristics of steering device 10" The above-described steering device 10 has a complex link mechanism, which results in a large amount of play in which the steered wheels 40 do not rotate relative to the rotation of the steering shaft 14.

[0024] FIG. 2 shows the relationship between the steering angle θh and the turning angle θt. Here, the steering angle θh is the rotation angle of the steering shaft 14. Meanwhile, the turning angle θt is the turning angle of the tires with respect to the steered wheels 40. The neutral position O shown in FIG. 2 is a point where both the steering angle θh and the turning angle θt are zero. This means that both the steering angle θh and the turning 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.

[0025] As shown in Fig. 2, even if the steering angle θh is changed in the right turning direction from the neutral position O, the turning angle θt does not change until it reaches point A. Then, when the steering angle θh becomes a value larger than point A, the turning angle θt increases.

[0026] Furthermore, even if the steering angle θh is reduced at point B, the turning angle θt does not change. In other words, even if the steering direction is switched to the left at point B, the turning angle θt does not change. Note that the steering direction is the rotation direction of steering shaft 14. Then, when the steering angle θh exceeds point C and becomes even smaller, the turning angle θt decreases.

[0027] Then, at point D, the steering angle θt becomes zero. Point E is a value obtained by further displacing the steering angle θh in the left steering direction even after the steering angle θt becomes 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 even larger beyond point F, the steering angle θt increases.

[0028] In this way, for example, when the steering device 10 is located at point B, the turning angle θt does not change even if the steering angle θh changes between point B and point C. Also, for example, when the steering device 10 is located at point E, the turning angle θt does not change even if the steering angle θh changes between point E and point F. In this way, due to play in the steering device 10, there is a dead zone where the turning angle θt does not change with respect to changes in the steering angle θh. However, the dead zone is not a zone having a fixed value of the steering angle θh, but a zone that can change depending on the history of changes in the steering angle θh.

[0029] The change in steering angle θh from point B to point C occurs when steering back from a right turn. The change in steering angle θh from point E to point F occurs when steering back from a left turn. The dead zone width α shown in FIG. 2 is the length of the dead zone area where the steered angle θt does not change in response to the change in steering angle θh when steering back.

[0030] "Overview of Steering Control Device Control" Fig. 3 shows a part of the process executed by the steering control device 60. The process shown in Fig. 3 is realized by the PU 62 repeatedly executing a program stored in the storage device 64, for example, at a predetermined interval.

[0031] Feedback processing M10 is processing in which the target steering angle θt* and the steering angle θt are input and the feedback control input Tfb is output. The feedback control input Tfb is a feedback control input in which the steering angle θt is a control amount and the target steering angle θt* is a target value of the control amount. The target steering angle θt* is calculated by the host ECU 80. That is, when the automatic driving mode is selected by operating the interface 86, the host ECU 80 calculates a target trajectory on which the vehicle should travel based on image data of the surroundings of the vehicle captured by the camera 82. The host ECU 80 then calculates the target steering angle θt* to bring the actual driving route of the vehicle closer to the target trajectory.

[0032] The steering angle estimation process M12 is a process in which the steering angle θh is input and the steering angle θt is output. The steering angle θt is an estimated value. The steering angle θh is calculated by the PU 62 through an integration process of the rotation angle θm.

[0033] The dead-zone compensation torque calculation process M14 is a process in which the dead-zone compensation torque Tdz, which is the manipulated variable of the feedforward control in the dead-zone region, is output. The addition process M16 is a process of substituting the sum of the feedback operation amount Tfb and the dead zone compensation torque Tdz into the torque command value Trq*. The torque command value Trq* is a command value for the torque of the motor 50. The operation signal generation process M18 is a process of generating an operation signal MS for controlling the torque of the motor 50 to approach the torque command value Trq* and outputting it to the inverter 52. Note that the operation signal generation process M18 may be a process of bringing the currents iu, iv, and iw closer to a current command value corresponding to the torque command value Trq*.

[0034] The dead zone position calculation process M20 is a process for calculating the dead zone position Δα, which is a variable indicating a position within the dead zone region shown in Fig. 2. Fig. 2 illustrates an example of the dead zone position Δα when the set of the steering angle θh and the turning angle θt is located at point P.

[0035] The control constant learning process M22 is a process for learning a control constant which is a constant indicating the rotational displacement of the steered wheels 40 relative to the rotational displacement of the steering shaft 14. "Control constant learning process M20" Fig. 4 shows the procedure of pre-processing for the control constant learning process M22. The series of processes shown in Fig. 4 is realized by the PU 62 repeatedly executing a program stored in the storage device 64, for example, at a predetermined interval. In the following, the step number of each process is represented by a number preceded by "S".

[0036] In the series of processes shown in FIG. 4, the PU 62 first acquires the steering angle θh and the vehicle speed V (S10). Next, the PU 62 determines whether the absolute value of the steering angle θh is equal to or greater than a learning minimum value θL and equal to or less than a learning maximum value θH (S12). Here, the learning minimum value θL is set based on a lower limit value of the steering angle θh that allows the learning process described later to be performed with good accuracy. The learning maximum value θH is set based on an upper limit value of the steering angle θh that allows the learning process described later to be performed with good accuracy. In setting the learning maximum value θH, it is taken into consideration that if the steering angle θh is excessively large, the vehicle will not operate stably.

[0037] When the PU 62 determines that the absolute value is equal to or greater than the learning minimum value θL and equal to or less than the learning maximum value θH (S12: YES), the PU 62 determines whether or not a condition is established that the absolute value of the steering angular velocity ωh is equal to or less than a threshold value ωth1 (S14). The steering angular velocity ωh is the rate of change of the steering angle θh. The steering angular velocity ωh is calculated by the PU 62 using time-series data of the steering angle θh. The condition that the absolute value of the steering angular velocity ωh is equal to or less than a threshold value ωth1 is one of the execution conditions for the learning process described later. This condition is a condition that the steering angle θh is stable.

[0038] When PU 62 determines that the absolute value of steering angular velocity ωh is equal to or less than threshold value ωth1 (S14: YES), PU 62 determines whether or not the set of steering angle θh and turning angle θt is outside the dead zone (S16). The input for this process is the dead zone position Δα output by the dead zone position calculation process M20. When the absolute value of the dead zone position Δα is less than "1 / 2" of the dead zone width αi described later, PU 62 determines that the set of steering angle θh and turning angle θt is in the dead zone.

[0039] When it is determined that the current state is not within the dead zone (S16: YES), the PU 62 determines whether the following condition (A) is satisfied (S18). Condition (A): The condition that the absolute value of the steering angular velocity ωh from a timing that is a predetermined period back from the current execution timing of the series of processes in FIG. 4 to the present is equal to or less than a threshold value ωth2.

[0040] When it is determined that the condition (A) is satisfied (S18: YES), the PU 62 acquires the yaw rate γ (S20). Next, the PU 62 multiplies the yaw rate γ by "(1+A·V·V) / V / I" and assigns the result to the steering angle θt (S22). In this process, the PU 62 estimates the steering angle θt based on the yaw rate γ. Here, the stability factor A and the wheelbase I are used.

[0041] Next, the PU 62 stores the steering angle θt estimated by the process of S22 in the storage device 64 in association with the turning direction, the vehicle speed V, and the steering angle θh (S24). When the process of S24 is completed or when a negative determination is made in the processes of S12, S14, S16, or S18, the PU 62 temporarily ends the series of processes shown in FIG.

[0042] The procedure of the control constant learning process M22 is shown in Fig. 5. The series of processes shown in Fig. 5 is realized by the PU 62 repeatedly executing a program stored in the storage device 64, for example, at a predetermined interval.

[0043] 5, the PU 62 judges whether the data stored in the storage device 64 by the process of S24 is sufficient to satisfy the learning condition (S30). As an example, the learning condition is that the number of values ​​stored by the process of S24 in each of the following states 1 to 4 is a predetermined number. Here, the predetermined number may be more than one.

[0044] State 1: When the steering direction is a right turning direction, the steering angle θh is equal to or larger than the learning minimum value θL and equal to or smaller than the learning maximum value θH. State 2: When the steering direction is a right turning direction, the steering angle θh is equal to or larger than "-θH" and equal to or smaller than "-θL".

[0045] State 3: When the steering direction is a left turning direction, the steering angle θh is equal to or greater than the learning minimum value θL and equal to or less than the learning maximum value θH. State 4: When the steering direction is a left turning direction, the steering angle θh is equal to or larger than "-θH" and equal to or smaller than "-θL".

[0046] When the PU 62 determines that the data has been secured in an amount sufficient to satisfy the learning conditions (S30: YES), it assigns "1" to the variable i that identifies the data (S32). Next, PU 62 reads out data in which the vehicle speed V falls within region Ai from among the sampling data stored in storage device 64 by the process of S24 (S34). Region Ai indicates one of regions A1, A2, ... according to variable i. Regions A1, A2, ... are regions of different vehicle speeds V. For example, region A3 is 30 to 40 km / h, region A4 is 40 to 50 km / h, etc. Then, PU 62 calculates stiffness coefficient ki (S36). The stiffness coefficient is a coefficient that determines the ratio of the amount of change in steering angle θt to the amount of change in steering angle θh when the set of steering angle θh and steering angle θt is not in the dead zone region.

[0047] The black circles in Fig. 6 indicate pairs of steering angle θh and turning angle θt stored by the process of S24. As an example, PU 62 uses the least squares method to find a straight line that minimizes the deviation from the sampling points consisting of the pairs of steering angle θh and turning angle θt. Then, PU 62 substitutes the slope of the straight line for stiffness coefficient ki. Stiffness coefficient ki is a learned value when vehicle speed V is a value within region Ai.

[0048] Returning to FIG. 5, the PU 62 extracts data when the steering direction is a right turning direction from the data read out by the process of S34 (S38). Then, the PU 62 calculates a right turning straight line L1 shown in FIG. 6 based on the data extracted by the process of S38 (S40). The right turning straight line L1 is a straight line whose slope is the stiffness coefficient ki calculated by the process of S36 and has an intercept b1. The process of S40 is a process of obtaining an intercept b1 that minimizes the difference between the extracted data and the right turning straight line L1. The right turning straight line L1 is an approximation equation that approximates the relationship between the steering angle θh and the steered angle θt when the steering direction is a right turning direction.

[0049] Next, the PU 62 extracts data when the steering direction is a left turning direction from the data read out by the process of S34 (S42). The PU 62 then calculates a left turning straight line L2 based on the data extracted by the process of S42 (S44). The left turning straight line L2 is a straight line whose slope is the stiffness coefficient ki calculated by the process of S42 and has an intercept b2. The process of S44 is a process of obtaining the intercept b2 that minimizes the difference between the extracted data and the left turning straight line L2. The left turning straight line L2 is an approximation equation that approximates the relationship between the steering angle θh and the steered angle θt when the steering direction is a left turning direction.

[0050] Next, the PU 62 substitutes the absolute value of the difference between the intercepts b1 and b2 into the dead zone width αi (S46). The dead zone width αi is a learned value when the vehicle speed V is within the region Ai. Then, the PU 62 judges whether or not learning of the stiffness coefficients k1, k2, ... and the dead-band widths α1, α2, ... has been completed in all the regions A1, A2, ... related to the vehicle speed V (S48). If the PU 62 judges that there is a region for which learning has not yet been completed (S48: NO), the PU 62 increments the variable i (S50) and returns to the process of S34.

[0051] On the other hand, when the PU 62 determines that learning has been completed for all areas (S48: YES), it stores the learned data in a predetermined area of ​​the storage device 64 (S52). When the process of S52 is completed or when a negative determination is made in the process of S30, the PU 62 temporarily ends the series of processes shown in FIG.

[0052] Incidentally, until the above learning is completed, the PU 62 uses predetermined default values ​​as the stiffness coefficient ki and the dead zone width αi. The default values ​​are stored in the storage device 64 in advance. Also, for example, a region A0 where the vehicle speed V is zero and is not subject to learning by the process of FIG. 6 may be provided. In this case, the dead zone width α0 in the region A0 may be learned by using a separately known technique.

[0053] "Steering angle estimation processing" The procedure of the steering angle estimation process M12 is shown in Fig. 7. The process shown in Fig. 7 is realized by the PU 62 repeatedly executing a program stored in the storage device 64, for example, at a predetermined interval.

[0054] 7, the PU 62 first acquires the steering angle θh and the vehicle speed V (S60). Next, the PU 62 selects the stiffness coefficient ki based on the vehicle speed V acquired by the process of S60 (S62). For example, when the vehicle speed V is a value within the region A2, the PU 62 selects the stiffness coefficient k2.

[0055] Next, PU 62 assigns a value obtained by dividing steering angle θh by stiffness coefficient ki to steering angle θt0 (S64). Next, PU 62 calculates steering angle θt by appropriately correcting steering angle θt0 (S66). That is, when steering angle θt0 is located in the dead zone, PU 62 assigns the previous value of steering angle θt to steering angle θt. On the other hand, when steering angle θt0 is not located in the dead zone, PU 62 assigns a value obtained by adding the difference between the current value of steering angle θt0 and the previous value of steering angle θt to the previous value of steering angle θt to the current value of steering angle θt. Note that whether steering angle θt0 is located in the dead zone is determined by whether the magnitude of inside-dead zone position Δα calculated by inside-dead zone position calculation process M20 is smaller than "1 / 2" of dead zone width αi. That is, the process of S66 uses the dead zone position Δα as an input.

[0056] When the PU 62 completes the process of S66, the PU 62 temporarily ends the series of processes shown in FIG. "Dead zone position calculation process M20" The procedure of the dead zone position calculation process M20 is shown in Fig. 8. The process shown in Fig. 8 is realized by the PU 62 repeatedly executing a program stored in the storage device 64, for example, at a predetermined interval.

[0057] 8, the PU 62 first acquires the vehicle speed V (S70). Next, the PU 62 selects the dead zone width αi corresponding to the vehicle speed V acquired by the process of S70 (S72). For example, when the vehicle speed V is a value within the area A2, the PU 62 selects the dead zone width α2.

[0058] Next, PU 62 assigns a value obtained by adding a value obtained by subtracting the previous value "θh(n-1)" of steering angle θh from the current value "θh(n)" of steering angle θh to the previous value "Δα(n-1)" of the dead-zone position Δα, to a tentative position X (S74). Next, PU 62 determines whether or not tentative position X is equal to or greater than "(-1)·αi / 2" and equal to or less than "αi / 2" (S76). This process is a process for determining whether or not the set of steering angle θh and turning angle θt is in the dead-zone region. When PU 62 determines that tentative position X is equal to or greater than "(-1)·αi / 2" and equal to or less than "αi / 2" (S76: YES), it assigns tentative position X to the dead-zone position Δα (S77).

[0059] On the other hand, if the PU 62 makes a negative determination in the process of S76, it determines whether or not the tentative position X is greater than "αi / 2" (S78). If the PU 62 determines that the tentative position X is greater than "αi / 2" (S78: YES), it assigns "αi / 2" to the in-dead-zone position Δα (S80). On the other hand, if the PU 62 determines that the tentative position X is smaller than "αi / 2" (S78: NO), it assigns "(-1)·αi / 2" to the in-dead-zone position Δα (S82).

[0060] When the PU 62 completes the processes of S77, S80, and S82, it temporarily ends the series of processes shown in FIG. "Dead zone compensation torque calculation process M14" The procedure of the dead-zone compensation torque calculation process M14 is shown in Fig. 9. The process shown in Fig. 9 is realized by the PU 62 repeatedly executing a program stored in the storage device 64, for example, at a predetermined interval.

[0061] 9, the PU 62 first acquires the vehicle speed V (S90). Next, the PU 62 selects the dead-band width αi corresponding to the vehicle speed V selected by the process of S90 (S92).

[0062] PU 62 determines whether the value obtained by subtracting the previous value "θt*(n-1)" of target steering angle θt* from the current value "θt*(n)" is positive (S94). This process is to determine whether the steering direction is a right turning direction. If PU 62 determines that the above subtracted value is positive (S94: YES), it assigns a value obtained by subtracting the dead-band position Δα from "1 / 2" of the dead-band width αi selected by the process of S92 to the dead-band amount Dα (S96). The dead-band amount Dα by the process of S96 is the maximum amount by which the steering angle θt does not change when the steering angle θh is changed in the right turning direction.

[0063] Next, the PU 62 judges whether the dead-band amount Dα is greater than zero (S98). When the PU 62 judges that the dead-band amount Dα is greater than zero (S98: YES), the PU 62 assigns the sum of the offset amount TdzB and the value obtained by dividing the dead-band amount Dα by the dead-band width αi and adding the specified torque TdzA to the value, to the dead-band compensation torque Tdz (S100).

[0064] On the other hand, when the PU 62 makes a negative determination in the process of S94, it determines whether or not a value obtained by subtracting the previous value "θt*(n-1)" of the target steering angle θt* from the current value "θt*(n)" is negative (S102). This process is a process for determining whether or not the steering direction is a left turning direction. When the PU 62 determines that the subtracted value is negative (S102: YES), it assigns a value obtained by subtracting the inside-dead-band position Δα from "-1 / 2" of the dead-band width αi selected in the process of S92 to the dead-band amount Dα (S104). The absolute value of the dead-band amount Dα in the process of S104 is the maximum amount by which the steering angle θt does not change when the steering angle θh is changed in the left turning direction, and the maximum amount means that the absolute value is maximum. However, the dead-band amount Dα here is equal to or less than zero.

[0065] When the PU 62 determines that the dead band amount Dα is smaller than zero (S106: YES), the PU 62 assigns a value obtained by subtracting an offset amount TdzB from a value obtained by dividing the dead band amount Dα by the dead band width αi and adding the specified torque TdzA to the value, to the dead band compensation torque Tdz (S108).

[0066] On the other hand, if a negative determination is made in the processes of S98 and S106, the PU 62 assigns "0" to the dead zone compensation torque Tdz (S110). When the processes of S100, S108, and S110 are completed, or when a negative determination is made in the process of S102, the PU 62 temporarily ends the series of processes shown in FIG.

[0067] "Actions and Effects of the Present Embodiment" FIG. 10 illustrates the transition of the dead zone compensation torque Tdz according to this embodiment. As shown in FIG. 10, the PU 62 sets the dead zone compensation torque Tdz to a torque for turning left at time t1 when it is determined that the steering direction has changed from a right turning direction to a left turning direction based on the target turning angle θt*. In FIG. 10, it is assumed that the turning angle θt is not in the dead zone area immediately before time t1. Therefore, the dead zone amount Dα at time t1 is "-αi". Therefore, the PU 62 changes the dead zone compensation torque Tdz in a stepwise manner from "0" to "-TdzA-TdzB" at time t1. Then, the PU 62 gradually reduces the magnitude of the dead zone compensation torque Tdz until the dead zone amount Dα becomes zero. At time t2 when the dead-band amount Dα becomes zero, the PU 62 changes the dead-band compensation torque Tdz from "-TdzB" to "0" in a stepped manner.

[0068] Thereafter, at time t3 when it is determined that the steering direction has changed from a left turning direction to a right turning direction based on the target steering angle θt*, the PU 62 sets the dead zone compensation torque Tdz to a torque for turning right. The dead zone amount Dα at time t3 is "αi". Therefore, at time t3, the PU 62 changes the dead zone compensation torque Tdz in a stepwise manner from "0" to "TdzA+TdzB". Then, the PU 62 gradually decreases the magnitude of the dead zone compensation torque Tdz until the dead zone amount Dα becomes zero. At time t4 when the dead zone amount Dα becomes zero, the PU 62 changes the dead zone compensation torque Tdz in a stepwise manner from "TdzB" to "0".

[0069] In this way, when the steering angle θt falls within the dead zone, PU 62 uses the dead zone compensation torque Tdz as the manipulated variable for feedforward control to control the torque of motor 50. Therefore, the responsiveness of the steering angle θt can be improved compared to the case where the torque of motor 50 is controlled only by the feedback manipulated variable Tfb.

[0070] In particular, since the dead zone compensation torque Tdz is an operation amount for feedforward control, it is easier to design the torque command value Trq* to an appropriate amount compared to the case where the steering angle θt is in the dead zone region by correcting the target steering angle θt*.

[0071] According to the present embodiment described above, the following actions and effects can be obtained. (1-1) The dead-zone compensation torque Tdz is determined according to the value obtained by dividing the dead-zone amount Dα by the dead-zone width αi. This makes it possible to keep the maximum absolute value of the dead-zone compensation torque Tdz constant regardless of the size of the dead-zone width αi.

[0072] (1-2) The PU 62 determines the steering direction according to the direction of change in the target steering angle θt*. This improves the controllability of the steering angle θt according to the steering direction intended by the host ECU 80.

[0073] (1-3) PU 62 estimates the turning angle θt in accordance with the stiffness coefficient ki in accordance with the vehicle speed V. This allows the stiffness coefficient ki to be set to an appropriate value in accordance with the vehicle speed V, thereby improving the estimation accuracy of the turning angle θt.

[0074] (1-4) The PU 62 learns the dead-band width αi according to the vehicle speed V. This makes it possible to calculate the dead-band position Δα with higher accuracy than when the dead-band width αi is set to a value independent of the vehicle speed V.

[0075] <Second embodiment> The second embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment.

[0076] Fig. 11 shows the procedure of the dead-zone compensation torque calculation process M14 according to this embodiment. The process shown in Fig. 11 is realized by repeatedly executing a program stored in the storage device 64 by the PU 62, for example, at a predetermined interval. For convenience, the same step numbers are given to the processes in Fig. 11 that correspond to the processes shown in Fig. 9.

[0077] In the series of processes shown in Fig. 11, when completing the process of S92, the PU 62 judges whether or not a value obtained by subtracting the steering angle θt from the target steering angle θt* is positive (S94a). The process of S94a is a process for judging whether or not the steering direction is a right turning direction. When the PU 62 judges that the above-mentioned subtracted value is positive (S94a: YES), the PU 62 proceeds to the process of S96.

[0078] On the other hand, when the PU 62 determines that the subtracted value is equal to or less than zero (S94a: NO), the PU 62 determines whether or not the value obtained by subtracting the steering angle θt from the target steering angle θt* is negative (S102a). The process of S102a is a process for determining whether or not the steering direction is a left turning direction. When the PU 62 determines that the subtracted value is negative (S102a: YES), the PU 62 proceeds to the process of S104. On the other hand, when the PU 62 makes a negative determination in the process of S102a, the PU 62 temporarily ends the series of processes shown in FIG.

[0079] <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the above "Means for solving the problem" is as follows. In the following, the correspondence is shown for each number of the solving means described in the "Means for solving the problem" column. [1, 2] The dead zone amount calculation process corresponds to the dead zone inside position calculation process M20, and the processes of S92 to S96, S102, and S104. The dead zone amount calculation process corresponds to the dead zone inside position calculation process M20, and the processes of S92, S94a, S96, S102a, and S104. The superposition process corresponds to the dead zone compensation torque calculation process M14 and the addition process M16. [3] The dead zone width selection process corresponds to the processes of S72 and S92. [4] The steering direction determination process corresponds to the processes of S94 and S102. [5] The steering direction determination process corresponds to the processes of S94a and S102a. [6] The steering process corresponds to the feedback process M10 and the operation signal generation process M18. [7] The stiffness coefficient selection process corresponds to the process of S62. The steering angle acquisition process corresponds to the processes of S64 and S66.

[0080] <Other embodiments> This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0081] "Dead zone compensation torque calculation process" The dead-zone compensation torque calculation process does not necessarily need to calculate the dead-zone compensation torque Tdz using the offset amount TdzB.

[0082] It is not essential that the dead-zone compensation torque calculation process calculates the dead-zone compensation torque Tdz as a value proportional to the value obtained by dividing the dead-zone amount Dα by the dead-zone width αi. For example, the dead-zone compensation torque calculation process may calculate the dead-zone compensation torque Tdz as a value proportional to the square of the above-mentioned divided value.

[0083] The dead-zone compensation torque calculation process does not necessarily have to be a process of calculating a value by inputting the above-mentioned divided value into an elementary function. The dead-zone compensation torque calculation process may be, for example, a process of map-calculating the dead-zone compensation torque Tdz by the PU 62 in a state where map data is prestored in the storage device 64. In that case, the relationship between the divided value and the dead-zone compensation torque Tdz can be adjusted to an arbitrary relationship that cannot be expressed by an elementary function.

[0084] Even in this case, the dead-zone compensation torque calculation process may be a process for changing the dead-zone compensation torque Tdz in accordance with the dead-zone amount Dα under the following condition: the magnitude of the dead-zone compensation torque Tdz when the dead-zone amount Dα is large is equal to or greater than the magnitude of the dead-zone compensation torque Tdz when the dead-zone amount Dα is small.

[0085] In the description "changing B according to A under the condition that B when A is large is equal to or larger than B when A is small," the case where A is large and the case where A is small refer to the relative relationship of size when comparing the two. For example, "when A is large" corresponds to the case where "A is a first value," and "when A is small" corresponds to the case where "A is a second value smaller than the first value." And according to the above description, depending on the settings of the first value and the second value, B when A is the first value may be larger than B when A is the second value. Also, the above description means that B is changed according to A so that A when B is large is larger than A when B is small.

[0086] Incidentally, the map data may have the divided value as the input variable, but the dead zone amount Dα and the dead zone width αi may also be the input variables. It is not essential that the dead-zone compensation torque calculation process calculates the dead-zone compensation torque Tdz taking into account the dead-zone width αi. For example, the dead-zone compensation torque calculation process may be a process of calculating the dead-zone compensation torque Tdz based on the dead-zone amount Dα without referring to the dead-zone width αi.

[0087] "About the calculation process for position within the dead zone" The process M20 for calculating the position within the dead zone does not necessarily have to calculate the position within the dead zone Δα using the dead zone width αi according to the vehicle speed. For example, the process may calculate the position within the dead zone Δα using a single dead zone width that is not dependent on the vehicle speed.

[0088] "About the steering angle θt" The steering angle estimation process M12 does not necessarily have to be a process for estimating the steering angle using the stiffness coefficient ki learned according to the vehicle speed V. For example, the steering angle may be estimated using the stiffness coefficient ki that is not dependent on the vehicle speed.

[0089] The steering angle θt as a control amount in the feedback control does not necessarily have to be an estimated value. For example, the steering angle θt may be a detected value of a sensor that detects the steering angle. "Motor torque control" It is not essential that the drive circuit of motor 50 is operated according to the manipulated variable of control in which the steering angle is the controlled variable and the target value of the steering angle is the target value of the controlled variable. For example, the drive circuit of motor 50 may be operated according to the manipulated variable of feedforward control according to the target value. In that case, in the dead zone, PU 62 may superimpose the dead zone compensation torque Tdz on the manipulated variable of feedforward control that is calculated even outside the dead zone region.

[0090] "About autonomous driving mode" In the autonomous driving mode, the sensing member used to acquire information about the outside of the vehicle, including the lane, is not limited to the camera 82. For example, it may be a LIDAR.

[0091] "About driving modes" The driving mode in which the dead zone compensation torque Tdz is superimposed on the torque of the motor 50 is not limited to the automatic driving mode. For example, it may be a manual driving mode in which the driver performs steering. In that case, for example, in the processing of S94 and S102, the steering angle θh may be used instead of the target steering angle θt*.

[0092] "About steering control devices" The host ECU 80 and the steering control device 60 may be integrated into one unit. The steering control device is not limited to one that executes software processing. For example, it may be equipped with a dedicated hardware circuit such as an ASIC that executes at least a part of the processing executed in the above embodiment. That is, the steering control device may include a processing circuit having any of the following configurations (a) to (c). (a) A processing circuit equipped with a processing device that executes all of the above processing according to a program, and a program storage device such as a memory device that stores the program. (b) A processing circuit equipped with a processing device and a program storage device that executes part of the above processing according to a program, and a dedicated hardware circuit that executes the remaining processing. (c) A processing circuit equipped with a dedicated hardware circuit that executes all of the above processing. Here, there may be multiple software execution devices equipped with a processing device and a program storage device. Also, there may be multiple dedicated hardware circuits. [Explanation of symbols]

[0093] 10...Steering gear 12…Steering wheel 14…Steering shaft 20…Steering gear box 22…Pitman arm 24…Drag Link 26…Knuckle arm 28…Kingpin axis 30…Tie rod arm 32…Tie rod 40…Steering wheel 50…Motor 52…Inverter 60...Steering control device

Claims

1. A steering control device that controls a steering device, The steering device is A steering shaft; a steered wheel of a vehicle that is steered in accordance with the rotation of the steering shaft; A motor that rotates the steering shaft; Equipped with The apparatus is configured to execute a dead zone amount calculation process and a superposition process, The dead zone amount calculation process is a process in which a steering angle is input, and a dead zone amount is calculated, which is an amount by which the steering angle changes without turning the steered wheels in a steering direction, The steering angle is a rotation angle of the steering shaft. the superimposition process is a process of superimposing a dead-zone compensation torque on the torque of the motor when the magnitude of the dead-zone amount is greater than zero; A steering control device, wherein the dead zone compensation torque is a torque that increases the torque of the motor in a direction in which the steered wheels are turned in response to the rotation of the steering shaft.

2. The superimposition process includes a dead zone compensation torque calculation process, 2. A steering control device according to claim 1, wherein the dead zone compensation torque calculation process changes the magnitude of the dead zone compensation torque in accordance with the dead zone amount under the condition that the magnitude of the dead zone compensation torque when the dead zone amount is large is equal to or greater than the magnitude of the dead zone compensation torque when the dead zone amount is small.

3. A storage device is provided, The storage device stores a dead zone width for each different vehicle speed, the dead zone width is an amount by which the steering angle changes from when the rotation direction of the steering shaft is switched from one of the right turning direction and the left turning direction to the other until the steered wheels are turned, The dead zone compensation torque calculation process includes a dead zone width selection process, the dead zone width selection process is a process of selecting a dead zone width corresponding to a vehicle speed from among a plurality of dead zone widths stored in the storage device according to a vehicle speed, 3. A steering control device according to claim 2, wherein the dead zone compensation torque calculation process changes the magnitude of the dead zone compensation torque in accordance with the ratio under the condition that the magnitude of the dead zone compensation torque when the ratio of the dead zone amount to the dead zone width selected by the dead zone width selection process is large is equal to or greater than the magnitude of the dead zone compensation torque when the ratio is small.

4. The dead zone amount calculation process includes a steering direction determination process, the steering direction determination process is a process for determining whether the steering direction is a right turning direction or a left turning direction based on a changing direction of a target value of a steering angle, 2. The steering control device according to claim 1, wherein the dead-zone amount calculation process calculates the dead-zone amount in accordance with the steering direction determined by the steering direction determination process.

5. The dead zone amount calculation process includes a steering direction determination process, the steering direction determination process is a process for determining whether the steering direction is a right-turning direction or a left-turning direction based on a sign of a difference between a target value of a steering angle and the steering angle, 2. The steering control device according to claim 1, wherein the dead-zone amount calculation process calculates the dead-zone amount in accordance with the steering direction determined by the steering direction determination process.

6. configured to execute a steering process; the steering process is a process of manipulating a torque of the motor in response to an operation amount of a feedback control in which a steering angle of the steered wheels is a control amount and a target value of the steering angle is a target value of the control amount, 2. The steering control device according to claim 1, wherein the superimposition process is a process of superimposing the dead zone compensation torque on a torque corresponding to the operation amount.

7. A storage device is provided, The storage device stores stiffness coefficients for different vehicle speeds, The stiffness coefficient is a ratio of a turning angle to the steering angle, A stiffness coefficient selection process and a steering angle acquisition process are configured to be executed, the stiffness coefficient selection process is a process of selecting, in response to a vehicle speed, the stiffness coefficient corresponding to the vehicle speed from among a plurality of stiffness coefficients stored in the storage device; 7. The steering control device according to claim 6, wherein the steering angle acquisition process calculates an estimated value of the steering angle as the controlled variable by using the detected value of the steering angle and the stiffness coefficient selected by the stiffness coefficient selection process.

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