Steering control device and steering control method

Abstract

This steering control device (70, 90) executes a target steering-wheel angle calculation process, a lower-side angle acquisition process, a steering-side feedback process, a reaction force operation process, and a compensation process. The target steering-wheel angle calculation process is a process for calculating a target steering-wheel angle. The lower-side angle acquisition process is a process for acquiring a lower-side angle, which is an angle on the opposite side of a torsion bar from a steering wheel in a steering shaft. The steering-side feedback process is a process for calculating an operation amount for feedback control in which the lower-side angle is a control variable and the target steering-wheel angle is a target value for the control variable. The reaction force operation process is a process for controlling the torque of a reaction force motor on the basis of the operation amount. The compensation process is a process for correcting the operation amount, which is an input of the reaction force operation process, by a compensation amount based on a detected steering-torque value, which is detected as a value based on the torsion of the torsion bar.

Description

Steering control device and steering control method

[0001] The present disclosure relates to a steering control device and a steering control method.

[0002] For example, Japanese Patent Application Laid-Open No. 2003-144992 (Patent Document 1) describes a device in which an assist motor is provided on the opposite side of a torsion bar on a steering shaft from the steering wheel. A control device that controls this device controls the torque of the assist motor to assist the driver in turning the steering wheel. The control device sets the torque of the assist motor through feedback control using a pinion angle based on the rotation angle of the assist motor as a control variable.

[0003] Furthermore, Patent Document 2 listed below describes a control device that applies a reaction torque to the steering wheel when power transmission between the steering wheel and the steered wheels is interrupted. Specifically, the control device controls the torque of a reaction motor to control the reaction torque that resists the rotational force applied to the steering wheel by the driver.

[0004] JP 2017-154698 A JP 2018-52205 A

[0005] The inventors have considered including feedback control in which the rotation angle is the control variable in controlling the torque of the reaction motor. However, when the rotation angle of the reaction motor is used as the control variable as in Patent Document 1, this means controlling a rotation angle that is different from the rotation angle of the steering wheel, which is the rotation angle perceived by the driver.

[0006] One aspect of the present disclosure provides a steering control device in which a steering device is a control target. The steering device includes a steering shaft provided with a torsion bar, a steering wheel connected to a first side of the steering shaft relative to the torsion bar, a reaction motor that applies torque to a second side of the steering shaft opposite the first side of the torsion bar, and steered wheels. The steering control device is configured to execute a target steering wheel angle calculation process, a lower side angle acquisition process, a steering side feedback process, a reaction force operation process, and a compensation process when power transmission between the steering shaft and the steered wheels is interrupted. The target steering wheel angle calculation process is a process for calculating a target steering wheel angle. The target steering wheel angle is a target value of the steering wheel angle, which is the rotation angle of the steering wheel. The lower side angle acquisition process is a process for acquiring a lower side angle, which is the angle on the second side of the steering shaft. The steering side feedback process is a process for calculating an operation amount of feedback control in which the lower side angle is a control amount and the target steering wheel angle is a target value of the control amount. The reaction force operation process is a process for controlling the torque of the reaction force motor in accordance with the amount of operation, and the compensation process is a process for correcting the amount of operation, which is an input to the reaction force operation process, with a compensation amount in accordance with a detection value of steering torque detected as a value in accordance with the torsion of the torsion bar.

[0007] Another aspect of the present disclosure provides a steering control method in which a steering device is a control target. The steering device includes a steering shaft provided with a torsion bar, a steering wheel connected to a first side of the steering shaft relative to the torsion bar, a reaction motor that applies torque to a second side of the steering shaft opposite the first side of the torsion bar, and steered wheels. The steering control device is configured to execute a target steering wheel angle calculation process, a lower side angle acquisition process, a steering side feedback process, a reaction force operation process, and a compensation process in a state in which power transmission between the steering shaft and the steered wheels is interrupted. The target steering wheel angle calculation process is a process for calculating a target steering wheel angle. The target steering wheel angle is a target value of the steering wheel angle, which is the rotation angle of the steering wheel. The lower side angle acquisition process is a process for acquiring a lower side angle, which is the angle on the second side of the steering shaft. The steering side feedback process is a process for calculating an operation amount of feedback control in which the lower side angle is a control amount and the target steering wheel angle is a target value of the control amount. The reaction force operation process is a process for controlling the torque of the reaction force motor in accordance with the amount of operation, and the compensation process is a process for correcting the amount of operation, which is an input to the reaction force operation process, with a compensation amount in accordance with a detection value of steering torque detected as a value in accordance with the torsion of the torsion bar.

[0008] Fig. 1 is a diagram showing the configuration of a vehicle according to a first embodiment. Fig. 2 is a block diagram showing part of the processing executed by the steering ECU and the turning ECU shown in Fig. 1. Fig. 3 is a flowchart showing the procedure of the processing executed by the steering ECU according to a second embodiment. Fig. 4 is a block diagram showing part of the processing executed by the steering ECU and the turning ECU shown in Fig. 1. Fig. 5 is a flowchart showing the procedure of the processing executed by the turning ECU shown in Fig. 1. Fig. 6 is a block diagram showing part of the processing executed by the steering ECU and the turning ECU shown in Fig. 1. Fig. 7 is a flowchart showing the procedure of the processing executed by the turning ECU shown in Fig. 1.

[0009] <First embodiment> A first embodiment will be described below with reference to the drawings. "Prerequisite configuration" As shown in Fig. 1, a vehicle steering device 10 is a steer-by-wire type steering device. The steering device 10 includes a reaction force actuator Ar and a turning actuator At. The steering device 10 of this embodiment has a structure in which the power transmission path between the steering wheel 12 and the steered wheels 44 is mechanically always interrupted.

[0010] A steering shaft 14 is connected to the steering wheel 12. A torsion bar 14a is provided on the steering shaft 14. One of the two sides of the torsion bar 14a on either side of the steering shaft 14 is a first side, and the other is a second side. The steering wheel 12 is connected to the first side of the steering shaft 14. The reaction force actuator Ar is an actuator for applying a steering reaction force to the steering wheel 12. The steering reaction force is a force that acts in the opposite direction to the direction of operation of the steering wheel 12 by the driver. By applying the steering reaction force to the steering wheel 12, it is possible to give the driver an appropriate sense of response. The reaction force actuator Ar includes a reduction mechanism 16, a reaction force motor 20, and a reaction force inverter 22.

[0011] Reaction motor 20 is a three-phase brushless motor. The rotating shaft of reaction motor 20 is connected to a second side of steering shaft 14 via speed reducer 16. Meanwhile, steered shaft 40 extends along the vehicle width direction, which is the left-right direction in FIG. 1 . Left and right steered wheels 44 are connected to both ends of steered shaft 40 via tie rods 42, respectively. The steered angle of steered wheels 44 is changed by linear movement of steered shaft 40.

[0012] Steering actuator At includes speed reducer 56, steering motor 60, and steering inverter 62. Steering motor 60 is a three-phase brushless motor. As an example, steering motor 60 is a surface permanent magnet synchronous motor. The rotating shaft of steering motor 60 is connected to pinion shaft 52 via speed reducer 56. Pinion teeth of pinion shaft 52 mesh with rack teeth 54 of steering shaft 40. Pinion shaft 52 and steering shaft 40 on which rack teeth 54 are formed constitute rack-and-pinion mechanism 50. Torque of steering motor 60 is applied as a steering force to steering shaft 40 via pinion shaft 52. In response to the rotation of steering motor 60, steering shaft 40 moves in the vehicle width direction, which is the left-right direction in FIG. 1 .

[0013] The steering device 10 includes a reaction force ECU 70 and a steering ECU 90. The reaction force ECU 70 includes a PU 72 and a storage device 74. The PU 72 is a software processing device such as a CPU or a GPU. The storage device 74 may be an electrically non-rewritable non-volatile memory. Alternatively, the storage device 74 may be an electrically rewritable non-volatile memory or a storage medium such as a disk medium. The reaction force ECU 70 controls a control variable by the PU 72 executing a program stored in the storage device 74.

[0014] The control object of the reaction force ECU 70 is the steering wheel 12. The reaction force ECU 70 operates the reaction force actuator Ar to control the steering reaction force as a control amount of the control object. Fig. 1 shows an operation signal MSs to the reaction force inverter 22.

[0015] In order to control the control variable, the reaction force ECU 70 refers to the steering torque Th, which is the input torque to the steering shaft 14, detected by the torque sensor 80. The torque sensor 80 is a sensor that detects the steering torque Th in accordance with the torsion of the torsion bar 14a. The reaction force ECU 70 also refers to the rotation angle θs of the rotation shaft of the reaction force motor 20, detected by a rotation angle sensor 82. The reaction force ECU 70 also refers to the vehicle speed V, detected by a vehicle speed sensor 84. The reaction force ECU 70 also refers to the currents ius, ivs, and iws that flow through the reaction force motor 20. The currents ius, ivs, and iws are quantified as the voltage drops across shunt resistors provided in each leg of the reaction force inverter 22.

[0016] The steering ECU 90 includes a PU 92 and a storage device 94. The PU 92 is a software processing device such as a CPU and a GPU. The storage device 94 may be an electrically non-rewritable non-volatile memory. Alternatively, the storage device 94 may be an electrically rewritable non-volatile memory or a storage medium such as a disk medium. The steering ECU 90 controls the control variables by the PU 92 executing a program stored in the storage device 94.

[0017] The control object of the steering ECU 90 is the steered wheels 44. The steering ECU 90 operates the steering actuator At to control the steering angle of the steered wheels 44, which is the control amount of the control object. An operation signal MSt to the steering inverter 62 is shown in FIG.

[0018] To control the control amount, steering ECU 90 references the rotation angle θt of the rotary shaft of steering motor 60 detected by rotation angle sensor 83. Also, steering ECU 90 references the currents iut, ivt, iwt that flow through steering motor 60. Currents iut, ivt, iwt are quantified as the amount of voltage drop across shunt resistors provided in each leg of steering inverter 62.

[0019] "Control" Figure 2 shows the processes executed by reaction force ECU 70 and steering ECU 90. The processes enclosed by the dashed dotted line in Figure 2 are realized by PU 72 repeatedly executing a program stored in storage device 74, for example, at a predetermined cycle. Also, the processes enclosed by the dashed two dotted line in Figure 2 are realized by PU 92 repeatedly executing a program stored in storage device 94, for example, at a predetermined cycle.

[0020] The target steering torque setting process M10 is a process for calculating a target steering torque Th*, which is a target value of the steering torque Th, based on the axial force Taf0 as an input variable. The axial force Taf0 is a variable that simulates the force that would be applied to the steered shaft 40 if it were assumed that power transmission between the steering wheel 12 and the steered shaft 40 is possible. The axial force Taf0 is an amount converted into the torque of the steering shaft 14. The target steering torque setting process M10 includes a process for setting the target steering torque Th* to a different value depending on the vehicle speed V, even if the axial force Taf0 is the same. This setting is intended to allow the driver to experience an optimal steering feel depending on the vehicle speed V.

[0021] The steering operation amount calculation process M12 is a process for calculating a steering operation amount Ts*, which is a control operation amount for which the steering torque Th is a control amount. The steering operation amount calculation process M12 includes a process for calculating a control operation amount for feedback control in which the steering torque Th is a control amount and the target steering torque Th* is a target value of the control amount, thereby calculating the steering operation amount Ts* in accordance with the control operation amount. The steering operation amount calculation process M12 may further include a process for calculating a control operation amount for open-loop control in which the target steering torque Th* is a target value of the control amount, thereby calculating the steering operation amount Ts* in accordance with the control operation amount. The control amount for feedback control is, for example, an amount for reducing the absolute value of the torque required for the reaction force motor 20 when the signs of the steering torque Th and the target steering torque Th* are both positive and the steering torque Th is greater than the target steering torque Th*. Note that the steering operation amount Ts* is, for example, an amount converted into a torque applied to the steering shaft 14.

[0022] The axial force calculation process M14 is a process for calculating the axial force Taf0 by adding the steering torque Th to the steering operation amount Ts*. The correction process M62 is a process for substituting the value obtained by adding the correction amount Fi to the axial force Taf0 for the axial force Taf.

[0023] The reference model calculation process M16 is a process for calculating a target steering angle θh*, which is a target value of the steering angle θh, based on the axial force Taf as an input variable. More specifically, the reference model calculation process M16 is a process for calculating the target steering angle θh* using an equation in which the steering angle θh in the model equation expressed by the following equation (c1) is replaced with the target steering angle θh*.

[0024] Taf=K·θh+C·θh′+J·θh″ (c1) The model expressed by the above equation (c1) models the value that the steering wheel angle θh indicates when a torque equal to the axial force Taf is input to the steering shaft 14. The steering wheel angle θh is a variable that indicates the rotation angle of the steering shaft 14.

[0025] In the above formula (c1), the viscosity coefficient C models the friction of the steering device 10, etc. The inertia coefficient J models the inertia of the steering device 10. The elastic coefficient K models the specifications of the suspension, wheel alignment, etc. of the vehicle on which the steering device 10 is installed. This model does not need to accurately represent the actual steering device 10 or the vehicle on which the steering device 10 is installed. This model may be a reference model designed to make the behavior of the steering wheel angle in response to input ideal. When a reference model is used, the steering feel can be adjusted by designing the reference model.

[0026] The lower side angle calculation process M20 is a process for calculating a lower side angle θd based on the rotation angle θs as an input variable. The lower side angle θd is the rotation angle of the torsion bar 14a of the steering shaft 14 on the side opposite to the steering wheel 12. The lower side angle calculation process M20 includes a process for integrating the rotation angle θs. Note that this integration process includes a process for setting the lower side angle θd to zero at the neutral position.

[0027] The target reaction torque calculation process M30 calculates the target reaction torque Tr* based on the bottom angle θd and the target steering wheel angle θh* as input variables. The target reaction torque calculation process M30 includes a steering-side feedback process M32 that calculates a steering-side feedback operation amount Mfb, which is an operation amount of feedback control in which the bottom angle θd is the control amount and the target steering wheel angle θh* is the target value of the control amount. The steering-side feedback operation amount Mfb is the sum of the output value of a proportional element and the output value of a derivative element, in which the difference between the target steering wheel angle θh* and the bottom angle θd is the input. The target reaction torque calculation process M30 includes an open-loop operation amount calculation process M34 that calculates an open-loop operation amount Mff, which is an operation amount of open-loop control in which the target steering wheel angle θh* is the target value of the control amount. The target reaction torque calculation process M30 includes a compensation process M36 that multiplies the steering torque Th by a gain G and assigns the result to a compensation amount Tc. The gain G is positive. The compensation amount Tc will be described in detail later. The target reaction torque calculation process M30 includes an addition process M38 that assigns the sum of the steering side feedback operation amount Mfb, the open loop operation amount Mff, and the compensation amount Tc to the target reaction torque Tr*.

[0028] The steering operation signal generation process M40 is a process for operating the reaction force inverter 22 based on the target reaction force torque Tr* as an input variable. The steering operation signal generation process M40 includes a process for calculating a control operation amount in which the torque of the reaction force motor 20 is the control amount and the target reaction force torque Tr* is the target value of the control amount. The calculation of the operation amount references the rotation angle θs and the currents ius, ivs, and iws. The steering operation signal generation process M40 also includes a process for operating the reaction force inverter 22 in accordance with the operation amount. FIG. 4 shows an operation signal MSs of the reaction force inverter 22. Note that in reality, the operation signal MSs is a separate operation signal for each switching element of the reaction force inverter 22.

[0029] The target steering equivalent angle setting process M52 is a process for calculating the target steering equivalent angle θp* based on the input variables of the target steering wheel angle θh* and the vehicle speed V. The PU 92 changes the target steering equivalent angle θp* in accordance with the target steering wheel angle θh* under the condition that the absolute value of the target steering equivalent angle θp* when the absolute value of the target steering wheel angle θh* is large is equal to or greater than the absolute value of the target steering equivalent angle θp* when the absolute value of the target steering wheel angle θh* is small.

[0030] In the description "changing B according to A under the condition that when A is large, B is equal to or greater 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 magnitude 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." According to the above description, depending on the settings of the first and second values, B when A is the first value may be larger than B when A is the second value. Furthermore, 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.

[0031] The steering equivalent angle feedback process M54 is a process for calculating a target steering torque Tt* based on the steering equivalent angle θp and the target steering equivalent angle θp* as input variables. The target steering torque Tt* is a quantity corresponding to the operation quantity of feedback control in which the steering equivalent angle θp is the control quantity and the target steering equivalent angle θp* is the target value of the control quantity.

[0032] The steering operation signal generation process M56 is a process for operating the steering inverter 62 based on the target steering torque Tt* as an input variable. The steering operation signal generation process M56 may be a process for calculating a control operation amount in which the torque of the steering motor 60 is the control amount and the value obtained by converting the target steering torque Tt* into the torque of the steering motor 60 is the target value of the control amount. The calculation of the operation amount references the rotation angle θt and the currents iut, ivt, and iwt. The steering operation signal generation process M56 also includes a process for operating the steering inverter 62 in accordance with the operation amount. FIG. 2 shows an operation signal MSt for the steering inverter 62. Note that in reality, the operation signal MSt is a separate operation signal for each switching element of the steering inverter 62.

[0033] The correction amount calculation process M60 is a process for calculating a correction amount Fi based on the q-axis current iqt and vehicle speed V as input variables. The correction amount Fi is a quantity for transmitting state information of the steered wheels 44 to the steering wheel 12. The q-axis current iqt is the q-axis current of the turning motor 60. The q-axis current iqt is calculated by the PU 92 based on the currents iut, ivt, iwt and the rotation angle θt. The q-axis current iqt is a physical quantity that indicates the state of the steered wheels 44, such as the force applied to the steered wheels 44.

[0034] <Functions and Effects of the Present Embodiment> The PU 72 calculates the target steering wheel angle θh* by the reference model calculation process M16. The target steering wheel angle θh* is a target value for the steering wheel angle θh, which is the rotation angle of the steering wheel 12. In other words, it is a target value for the steering wheel angle θh perceived by the driver. According to control in which the target steering wheel angle θh* is a target value for the controlled variable, it is possible to control the steering wheel angle θh perceived by the driver as desired.

[0035] The control operation amount for which the target steering wheel angle θh* is the target value of the control amount is the target reaction torque Tr*. The target reaction torque Tr* is generated by the reaction motor 20. The reaction motor 20 applies torque to the torsion bar 14a of the steering shaft 14 on the side opposite to the steering wheel 12. The behavior of the steering wheel angle θh when torque is applied to the torsion bar 14a is difficult to predict due to the torsion of the torsion bar 14a. Therefore, if the torque of the reaction motor 20 is controlled by the operation amount of feedback control in which the steering wheel angle θh is the control amount and the target steering wheel angle θh* is the target value of the control amount, it is difficult to make the steering wheel angle θh follow the target steering wheel angle θh*. As a result, the steering wheel angle θh is likely to vibrate.

[0036] In contrast, if the torque of the reaction force motor 20 is controlled by a feedback control operation amount in which the lower side angle θd is a controlled variable and the target value of the lower side angle θd is the controlled variable target value, the feedback control can be performed appropriately. The reason for this is that whether the torque of the reaction force motor 20 should be increased or decreased is uniquely determined depending on whether the lower side angle θd is displaced toward the right turn side or the left turn side. However, because the lower side angle θd and the steering wheel angle θh generally do not coincide due to the torsion of the torsion bar 14a, the lower side angle θd is not an angle that the driver directly senses.

[0037] Therefore, the PU 72 sets the target reaction torque Tr* in accordance with the steering-side feedback operation amount Mfb, which is an operation amount for feedback control in which the lower side angle θd is the control amount and the target steering wheel angle θh* is the target value of the control amount. The PU 72 also superimposes a compensation amount Tc on the target reaction torque Tr* to compensate for the responsiveness of the steering wheel angle θh to the target steering wheel angle θh*. This improves the controllability of the steering wheel angle θh to the target steering wheel angle θh*, even when the steering-side feedback operation amount Mfb employing the lower side angle θd as the control amount is used.

[0038] According to the present embodiment described above, the following further actions and effects can be obtained. (1-1) The PU 92 sets the target steering equivalent angle θp* in accordance with the target steering wheel angle θh*. In other words, the PU 92 sets the target steering equivalent angle θp* in accordance with the target value of the steering wheel angle θh perceived by the driver. This allows the steering angle of the steered wheels 44 to be set in accordance with the steering wheel angle θh that can be perceived by the driver.

[0039] Second Embodiment A second embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment.

[0040] In this embodiment, when the stability of feedback control in which the target steering wheel angle θh* is the target value of the controlled variable decreases, the control is changed to feedback control in which the target value of the lower angle θd is the target value of the controlled variable.

[0041] The processing procedure for the above change is shown in Figure 3. The series of processes shown in Figure 3 is realized by the PU 72 repeatedly executing a program stored in the storage device 74, for example, at a predetermined interval. Note that, below, the step number of each process is represented by a number preceded by "S."

[0042] In the series of processes shown in FIG. 3 , the PU 72 first acquires the vehicle speed V (S10). Next, the PU 72 determines, based on the vehicle speed V, whether or not there is a risk of instability in feedback control, in which the target steering angle θh* is the target value of the controlled variable (S12). If the PU 12 determines that there is no risk of instability in the feedback control (S12: NO), the PU 12 assigns values ​​for setting the target steering angle θh* to the prescribed parameters that define a predetermined model in the reference model calculation process M16 (S14). That is, the PU 12 assigns values ​​for setting the target steering angle θh* to the elastic coefficient K, the inertia coefficient J, and the viscosity coefficient C. The values ​​for setting the target steering angle θh* are the elastic coefficient K, the inertia coefficient J, and the viscosity coefficient C in the first embodiment. Next, the PU 72 assigns a steering angle control set value G0 to the gain G (S16). The steering angle control set value G0 is a positive value.

[0043] On the other hand, if the PU 72 determines that there is a risk of the feedback control becoming unstable (S12: YES), it substitutes values ​​for setting a target value of the lowering angle θd into the prescribed parameters that define a predetermined model in the reference model calculation process M16 (S18). That is, the PU 72 substitutes values ​​for setting a target value of the lowering angle θd into the elastic coefficient K, the inertia coefficient J, and the viscosity coefficient C. The PU 72 then substitutes zero into the gain G (S20). The process of S20 is a stop process that stops the compensation process M36.

[0044] As a result, the reference model calculation process M16 is changed to a process of calculating a target value of the lower-side angle θd based on the axial force Taf as an input variable, and the steering-side feedback process M32 is changed to a process of substituting the operation amount of the feedback control, in which the lower-side angle θd is the controlled variable and the target value of the lower-side angle θd is the controlled variable, for the steering-side feedback operation amount Mfb.

[0045] When the PU 72 completes the processes of S16 and S20, it temporarily ends the series of processes shown in Fig. 3. The processes of S12, S14, and S18 constitute steering side switching processing. <Third Embodiment> Hereinafter, a third embodiment will be described with reference to the drawings, focusing on differences from the second embodiment.

[0046] Figure 4 shows the processes executed by reaction force ECU 70 and steering ECU 90. The processes enclosed by the dashed dotted line in Figure 4 are realized by PU 72 repeatedly executing a program stored in storage device 74, for example, at a predetermined cycle. The processes enclosed by the two-dotted line in Figure 4 are realized by PU 92 repeatedly executing a program stored in storage device 94, for example, at a predetermined cycle. For convenience, the processes in Figure 4 that correspond to the processes shown in Figure 2 are denoted by the same reference numerals.

[0047] The target steering wheel angle θh* and the lower side angle θd are input to the switching process M70 shown in Fig. 4. The switching process M70 is a process for selectively inputting either the target steering wheel angle θh* or the lower side angle θd to the target steering equivalent angle setting process M52.

[0048] FIG. 5 shows the procedure of the switching process M70. The process shown in FIG. 5 is realized by the PU 92 repeatedly executing a program stored in the storage device 94, for example, at a predetermined interval. In the series of processes shown in FIG. 5, the PU 92 first acquires the vehicle speed V (S30). Next, the PU 92 determines whether or not there is a concern that control using the target steering equivalent angle θp* set in accordance with the target steering wheel angle θh* will become unstable (S32). If the PU 92 determines that there is no concern that control will become unstable (S32: NO), it outputs the target steering wheel angle θh* to the target steering equivalent angle setting process M52 (S34). In this case, the target steering equivalent angle setting process M52, like the second embodiment, is a process for calculating the target steering equivalent angle θp* based on the target steering wheel angle θh* and the vehicle speed V as input variables.

[0049] On the other hand, when the PU 92 determines that there is a risk of control becoming unstable (S32: YES), it outputs the lower side angle θd to the target steering equivalent angle setting process M52 (S36). In this case, the target steering equivalent angle setting process M52 is changed to a process for calculating the target steering equivalent angle θp* based on the lower side angle θd and the vehicle speed V as input variables.

[0050] When the PU 92 completes the processes of S34 and S36, it temporarily ends the series of processes shown in Figure 5. The processes of S32 to S36 constitute a steering side switching process. <Fourth Embodiment> Hereinafter, a fourth embodiment will be described with reference to the drawings, focusing on the differences from the third embodiment.

[0051] Figure 6 shows the processes executed by reaction force ECU 70 and steering ECU 90. The processes enclosed by the dashed dotted line in Figure 6 are realized by PU 72 repeatedly executing a program stored in storage device 74, for example, at a predetermined cycle. The processes enclosed by the two-dotted line in Figure 6 are realized by PU 92 repeatedly executing a program stored in storage device 94, for example, at a predetermined cycle. For convenience, the processes in Figure 6 that correspond to the processes shown in Figure 4 are denoted by the same reference numerals.

[0052] 6 is a process for calculating a torsion correction amount Δθh based on input variables, ie, the steering torque Th and the vehicle speed V. The torsion correction amount Δθh is an estimated value of the torsion angle of the torsion bar 14a.

[0053] The steering wheel angle calculation process M74 calculates the steering wheel angle θh by adding the torsion correction amount Δθh to the lower side angle θd. The steering wheel angle θh in this embodiment is an estimated value of the rotation angle of the steering wheel 12.

[0054] In the switching process M70, either the steering wheel angle θh or the lower side angle θd is selectively input to the target steering equivalent angle setting process M52. The procedure of the switching process M70 is shown in Figure 7. The process shown in Figure 7 is realized by the PU 92 repeatedly executing a program stored in the storage device 94, for example, at a predetermined interval. In Figure 7, processes corresponding to those shown in Figure 5 are denoted by the same step numbers for convenience.

[0055] 7, if the determination in S32 is negative, the PU 92 outputs the steering wheel angle θh to the target steering equivalent angle setting process M52 (S34a). In this case, the target steering equivalent angle setting process M52 is a process for calculating the target steering equivalent angle θp* based on the steering wheel angle θh and the vehicle speed V as input variables.

[0056] When the PU 92 completes the processing of S34a, it temporarily ends the series of processing shown in Figure 7. The processing of S32, S34a, and S36 constitutes steering side switching processing. <Other Embodiments> This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be implemented in combination with each other to the extent that there is no technical contradiction.

[0057] Regarding the compensation process, the compensation process is not limited to substituting the value obtained by multiplying the steering torque Th by the gain G for the compensation amount Tc. For example, the compensation process may be a process in which the PU 72 calculates the compensation amount Tc based on a map in accordance with the steering torque Th, with map data stored in the storage device 74. Here, the map data is data in which the steering torque Th is an input variable and the compensation amount Tc is an output variable.

[0058] Note that map data is a set of data consisting of discrete values ​​of input variables and values ​​of output variables corresponding to each of the input variable values. Furthermore, map calculation may be a process in which, when the value of an input variable matches one of the input variable values ​​in the map data, the value of the corresponding output variable in the map data is the calculation result. Furthermore, map calculation may be a process in which, when the value of an input variable does not match any of the input variable values ​​in the map data, the calculation result is a value obtained by interpolating the values ​​of multiple output variables included in the map data. Alternatively, map calculation may be a process in which, when the value of an input variable does not match any of the input variable values ​​in the map data, the calculation result is the value of the output variable in the map data that corresponds to the closest value of the multiple input variables included in the map data.

[0059] "Regarding Steering Side Feedback Processing" The steering side feedback processing is not limited to processing in which the sum of the output value of a proportional element and the output value of a differential element is assigned to the steering side feedback manipulation amount Mfb. For example, the steering side feedback processing may be processing in which the sum of the output value of a proportional element and the output value of a differential element and the sum of the output value of a disturbance observer are assigned to the steering side feedback manipulation amount Mfb. Furthermore, for example, the steering side feedback processing may be processing in which the steering side feedback manipulation amount Mfb is calculated using an integral element in addition to a proportional element, a differential element, etc. Note that the steering side feedback processing does not necessarily have to be processing in which the steering side feedback manipulation amount Mfb is calculated using a proportional element and a differential element. For example, the steering side feedback processing may be processing in which the steering side feedback manipulation amount Mfb is calculated using a proportional element without using a differential element.

[0060] 2 shows an example in which the input to the target steering equivalent angle setting process M52 is the target steering wheel angle θh*, but this is not limiting. For example, the input to the target steering equivalent angle setting process M52 may be the steering wheel angle θh.

[0061] It is not essential that the vehicle speed V be included in the input of the target steering equivalent angle setting process. "Regarding the Steering Wheel Angle θh" Although Fig. 6 illustrates the process of estimating the steering wheel angle θh based on the steering torque Th and the vehicle speed V as input variables, the method of acquiring the steering wheel angle θh is not limited to this. The steering wheel angle θh may be, for example, a detection value of a sensor that detects the rotation angle of the steering shaft 14 on the steering wheel 12 side relative to the torsion bar 14a.

[0062] 6 illustrates a process in which the torsion correction amount Δθh is used as an estimated value of the torsion angle of the torsion bar 14a, but this is not limiting. For example, the torsion correction amount Δθh may be an amount that is artificially determined depending on the steering feel that is desired to be given to the driver.

[0063] Regarding the steering side switching process: The input of the steering side switching process, which is a process for switching the input variable of the target steering equivalent angle setting process M52, is not limited to vehicle speed V. The input of the steering side switching process may be, for example, a variable indicating the torque of the steering motor 60, such as q-axis current iqt.

[0064] Regarding the Steering Side Switching Process: The input referenced to switch the input variable of the steering side feedback process from the target steering wheel angle to the target lower side angle is not limited to the vehicle speed V. For example, it may be a variable indicating the torque of the steering motor 60, such as the q-axis current iqt.

[0065] Regarding the predetermined model: The predetermined model for calculating the target steering angle according to the axial force is not limited to the model exemplified in the above embodiment. For example, the predetermined model may be a model in which the specified parameters defining the model do not include any one of the elastic coefficient K, the inertia coefficient J, and the viscosity coefficient C.

[0066] Regarding the target steering angle calculation process: The target steering angle calculation process is not limited to the process of calculating the target steering angle θh* using the reference model calculation process M16. The target steering angle calculation process may be, for example, a process in which the PU 72 calculates the target steering angle θh* based on the axial force Taf using a map while map data is stored in the storage device 74. Here, the map data is data in which the axial force Taf is an input variable and the target steering angle θh* is an output variable.

[0067] Regarding the Axial Force Setting Process: The axial force Taf is not limited to the value obtained by adding the steering torque Th and the correction amount Fi to the steering operation amount Ts*. For example, the axial force Taf may be the value obtained by adding the steering torque Th to the steering operation amount Ts*.

[0068] It is not essential that the axial force Taf be set based on the manipulated variable of feedback control in which the steering torque Th is the controlled variable and the target steering torque Th* is the target value of the controlled variable. For example, the axial force Taf may be a weighted average value of the angle axial force and the current axial force. Here, the angle axial force may be calculated by the PU 72 in accordance with, for example, the target steering equivalent angle θp* and the vehicle speed V. The current axial force may be calculated by the PU 72 in accordance with, for example, the q-axis current iqt.

[0069] Regarding the reaction force operation processing, it is not essential that the reaction force operation processing be configured by the steering operation signal generation processing M40 including processing for calculating a control operation amount in which the torque of the reaction force motor 20 is the control amount and the target reaction force torque Tr* is the target value of the control amount. The reaction force operation processing may be, for example, processing for controlling the torque of the reaction force motor 20 by an open-loop operation amount in which the target reaction force torque Tr* is the target value of the control amount.

[0070] "Regarding the steering-side feedback processing" The steering-side feedback processing is not limited to processing configured by the steering equivalent angle feedback processing M54 and the steering operation signal generation processing M56. The steering-side feedback processing may be, for example, processing that controls the torque of steering motor 60 in accordance with the sum of the output value of the steering equivalent angle feedback processing M54 and the operation amount of open-loop control in which the target steering equivalent angle θp* is the target value of the control amount.

[0071] Regarding the Steering Control Device The steering control device is not limited to the reaction force ECU 70 and the turning ECU 90. For example, they may be formed integrally.

[0072] The steering control device is not limited to one that includes a PU and a storage device and executes software processing. For example, it may include a dedicated hardware circuit, such as an ASIC, that executes at least some of the various processes executed in the above embodiments. That is, the control device may include any of the following processing circuits (a) to (c): (a) A processing circuit that includes a processing device that executes all of the above processes in accordance with a program and a program storage device, such as a storage device, that stores the program. (b) A processing circuit that includes a processing device and program storage device that executes some of the above processes in accordance with a program, and a dedicated hardware circuit that executes the remaining processes. (c) A processing circuit that includes a dedicated hardware circuit that executes all of the above processes. Here, there may be multiple software execution devices that include a processing device and a program storage device, and multiple dedicated hardware circuits.

[0073] Regarding the steering actuator: As the steering actuator At, for example, one in which steering motor 60 is arranged coaxially with steering shaft 40 may be used. Alternatively, for example, one connected to steering shaft 40 via a belt-type reducer using a ball screw mechanism may be used.

[0074] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A steering control device for which a steering device is a control target, the steering device including a steering shaft provided with a torsion bar, a steering wheel connected to a first side of the steering shaft with respect to the torsion bar, a reaction force motor that applies torque to a second side of the steering shaft with respect to the torsion bar opposite to the first side, and a steering wheel. When power transmission between the steering shaft and the steering wheel is interrupted, the device is configured to execute a target steering wheel angle calculation process, a lower side angle acquisition process, a steering side feedback process, a reaction force operation process, and a compensation process. The target steering wheel angle calculation process is a process for calculating a target steering wheel angle, and the target steering wheel angle is a target value of a steering wheel angle that is a rotation angle of the steering wheel. The lower side angle acquisition process is a process for acquiring a lower side angle that is an angle on the second side of the steering shaft. The steering side feedback process is a process for calculating an operation amount of feedback control in which the lower side angle is a control amount and the target steering wheel angle is a target value of the control amount. The reaction force operation process is a process for controlling the torque of the reaction force motor according to the operation amount. The compensation process is a process for correcting the operation amount that is an input of the reaction force operation process by a compensation amount according to a detected value of a steering torque detected as a value corresponding to the torsion of the torsion bar. A steering control device.

2. The steering control device according to claim 1, configured to execute a target lower side angle calculation process, a steering side switching process, and a stop process. The target lower side angle calculation process is a process for calculating a target lower side angle that is a target value of the lower side angle. The steering side switching process is a process for switching the target value of the control amount of the feedback control from the target steering wheel angle to the target lower side angle by switching an input variable of the steering side feedback process from the target steering wheel angle to the target lower side angle. The stop process is a process for stopping the compensation process when the input variable of the steering side feedback process is the target lower side angle.

3. The steering device includes a steering motor for steering the steering wheel, and is configured to execute a target steering equivalent angle setting process and a steering side feedback process. The target steering equivalent angle setting process is a process of setting a target steering equivalent angle based on the target steering wheel angle. The target steering equivalent angle is a target value of the steering equivalent angle, which is a variable indicating the steering angle of the steering wheel. The steering side feedback process is a process of controlling the torque of the steering motor by an operation amount of feedback control in which the steering equivalent angle is a control amount and the target steering equivalent angle is a target value of the control amount. The steering control device according to claim 1.

4. It is configured to execute a steering side switching process. The steering side switching process is a process of switching the input variable of the target steering equivalent angle setting process from the target steering wheel angle to the lower angle. The steering control device according to claim 3.

5. The steering device includes a steering motor for steering the steering wheel, and is configured to execute a correction process, a target steering equivalent angle setting process, and a steering side feedback process. The correction process is a process of correcting the lower angle according to the steering torque. The target steering equivalent angle setting process is a process of setting a target steering equivalent angle using the lower angle corrected by the correction process as an input variable. The target steering equivalent angle is a target value of the steering equivalent angle, which is a variable indicating the steering angle of the steering wheel. The steering side feedback process is a process of controlling the torque of the steering motor by an operation amount of feedback control in which the steering equivalent angle is a control amount and the target steering equivalent angle is a target value of the control amount. The steering control device according to claim 1.

6. It is configured to execute a steering side switching process. The steering side switching process is a process of switching the input variable of the target steering equivalent angle setting process from the lower angle corrected by the correction process to the lower angle not corrected by the correction process. The steering control device according to claim 5.

7. A steering control device according to claim 2, configured to execute axial force setting processing, wherein the axial force setting processing is processing for setting an axial force that is an input to the target steering wheel angle calculation processing, the target steering wheel angle calculation processing is processing for calculating the target steering wheel angle according to a predetermined model according to the axial force, the target lower angle calculation processing is processing for calculating the target lower angle according to the predetermined model in which the value of a specified parameter is changed according to the axial force, and the specified parameter is a parameter that defines the predetermined model.

8. A steering control method in which a steering device is a control target, the steering device including a steering shaft provided with a torsion bar, a steering wheel connected to a first side of the torsion bar among the steering shafts, a reaction force motor that applies torque to a second side of the torsion bar among the steering shafts, which is opposite to the first side, and a steering wheel, and including executing target steering wheel angle calculation processing, lower angle acquisition processing, steering side feedback processing, reaction force operation processing, and compensation processing in a state where power transmission between the steering shaft and the steering wheel is interrupted, the target steering wheel angle calculation processing being processing for calculating a target steering wheel angle, the target steering wheel angle being a target value of a steering wheel angle that is a rotation angle of the steering wheel, the lower angle acquisition processing being processing for acquiring a lower angle that is an angle on the second side of the steering shaft, the steering side feedback processing being processing for calculating an operation amount of feedback control in which the lower angle is a control amount and the target steering wheel angle is a target value of the control amount, the reaction force operation processing being processing for controlling the torque of the reaction force motor according to the operation amount, and the compensation processing being processing for correcting the operation amount that is an input to the reaction force operation processing with a compensation amount according to a detected value of a steering torque detected as a value according to the torsion of the torsion bar.

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