Steering controller

Abstract

To provide a steering controller capable of inhibiting a magnitude of a change in reaction force torque from getting excessively large.SOLUTION: A PU sets a target turn equivalent angle θp*0 according to a steering angle regarded as an input variable. The PU calculates an offset quantity, which is a difference between a previous value of the target turn equivalent angle θp*0 and a current value, by using a predetermined condition that the target turn equivalent angle θp*0 varies discontinuously as a trigger. The PU calculates the target turn equivalent angle θp* by subtracting an offset correction quantity Δθp, which depends on the offset quantity, from the target turn equivalent angle θp*. When an absolute value of the offset correction quantity Δθp is larger than zero, the PU adjusts an axial force F which resists rotation of a steering wheel.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] For example, Patent Document 1 below describes a steering control device in a steer-by-wire system. This device executes a process of setting an axial force that resists the rotation of the steering wheel based on the target value of the steering angle of the steering wheel and the current value indicating the torque of the steering motor as input variables. This device sets the gradient of the axial force so as to maintain the stability of control.

[0003] Also, for example, Patent Document 2 below describes a steering control device that corrects a target value according to the difference between the target value of the steering angle of the steering wheel and the steering angle under predetermined conditions and then gradually changes the correction amount to zero in a steer-by-wire system.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, when executing the process of gradually changing the correction amount to zero after correcting the target value as described above, the change speed of the target value of the steering angle becomes larger compared to the case where the process is not executed. Therefore, when the axial force is designed without assuming the gradual change process, there is a risk that the gradient of the axial force becomes larger than expected.

Means for Solving the Problems

[0006] Means for solving the above problems and their effects will be described below. 1. Applied to a steer-by-wire system including a reaction force motor that applies a reaction force to a steering wheel and a steering device that steers steered wheels by a steering motor, configured to execute a target steering equivalent angle setting process, a steering operation process, a reaction force operation process, and an adjustment process, the target steering equivalent angle setting process is a process of setting a target steering equivalent angle according to a steering request, the target steering equivalent angle is a target value of a steering equivalent angle that is a variable indicating the steering angle of the steered wheels, the steering operation process is a process of operating the steering motor according to the control operation amount whose target value is the target steering equivalent angle, the reaction force operation process is a process of controlling the torque of the reaction force motor according to the state quantity of the steering device, and the adjustment process is a steering control device that adjusts the torque of the reaction force motor in a situation where the magnitude of the change in the torque of the reaction force motor with respect to the steering request may become excessively large.

[0007] In the above configuration, when the magnitude of the change in the torque of the reaction force motor with respect to the steering request may become excessively large due to circumstances not considered in the basic setting of the reaction force operation process, the torque of the reaction force motor is adjusted by the adjustment process. Therefore, it is possible to suppress the magnitude of the change in the torque of the reaction force motor from becoming excessively large.

[0008] 2. The target rudder equivalent angle setting process is configured to execute a base value setting process, an offset amount calculation process, an offset correction process, and an offset cancellation process. The base value setting process is a process of setting a base value of the target rudder equivalent angle according to a steering request. The offset amount calculation process is a process of calculating an offset amount, which is an amount equivalent to the difference between the target rudder equivalent angle and the actual rudder equivalent angle, triggered by the establishment of a predetermined condition. The offset correction process is a process of correcting the target rudder equivalent angle so as to reduce the deviation between the target rudder equivalent angle and the actual rudder equivalent angle by an offset correction amount corresponding to the offset amount. The offset cancellation process is a process of reducing the magnitude of the offset correction amount. The situation where the magnitude of the change in the torque of the reaction force motor with respect to the steering request can become excessively large is the situation where the offset cancellation process is executed. The steering control device according to the above 1.

[0009] When the offset cancellation process is executed, the change in the target rudder equivalent angle becomes larger compared to when it is not executed. Therefore, the situation where the offset cancellation process is executed is the situation where the magnitude of the change in the torque of the reaction force motor with respect to the steering request can become excessively large.

[0010] 3. The reaction force operation process includes an assist amount setting process, an axial force setting process, and a target reaction force setting process, and is a process of controlling the torque of the reaction force motor according to the target reaction force torque. The axial force setting process is a process of setting an axial force, which is a force resisting the rotational operation of the steering shaft by the driver. The assist amount setting process is a process of setting an assist amount with the steering torque as an input. The assist amount is an amount that assists the driver in rotating the steering shaft. The target reaction force setting process is a process of setting the target reaction force torque according to the value obtained by subtracting the assist amount from the axial force. The adjustment process is a process of adjusting the axial force set by the axial force setting process. The steering control device according to the above 1 or 2.

[0011] With the above configuration, by adjusting the axial force, it is possible to suppress the excessive increase in the change of the target reaction torque. Therefore, it is possible to suppress the excessive increase in the magnitude of the change in the torque of the reaction motor with respect to the steering request.

[0012] 4. The axial force setting process includes a process of setting a current axial force based on the current of the steering motor as an input variable, the axial force includes the current axial force, and the adjustment process includes a process of adjusting the current axial force. The steering control device according to item 3 above.

[0013] When the change in the target steering equivalent angle becomes large, the change in the torque of the steering motor tends to become large. This means that since the change in the current flowing through the steering motor becomes large, the change in the current axial force becomes large. Therefore, with the above configuration, by adjusting the current axial force, it is possible to suppress the excessive increase in the magnitude of the change in the torque of the reaction motor with respect to the steering request.

[0014] 5. The adjustment process includes a process of adjusting the torque of the reaction motor based on the decreasing speed of the offset amount as an input variable. The steering control device according to any one of items 2 to 4 above (excluding those not including item 2).

[0015] The larger the decreasing speed of the offset amount, the larger the change in the target steering equivalent angle. Therefore, the larger the decreasing speed of the offset amount, the more likely the magnitude of the change in the torque of the reaction motor with respect to the steering request will become excessively large. Therefore, with the above configuration, by adjusting the torque of the reaction motor based on the decreasing speed of the offset amount, it is possible to suppress the excessive increase in the magnitude of the change in the torque of the reaction motor with respect to the steering request.

[0016] 6. The adjustment process includes a process of adjusting the torque of the reaction motor based on the offset amount as an input variable. The steering control device according to any one of items 2 to 5 above (excluding those not including item 2).

[0017] The larger the offset amount, the more likely it is that the situation where the change in the target steering equivalent angle tends to be large becomes apparent. Therefore, the larger the offset amount, the more likely it is that the situation where the magnitude of the change in the torque of the reaction motor with respect to the steering demand becomes excessively large becomes apparent. Thus, in the above configuration, by adjusting the torque of the reaction motor based on the offset amount, it is possible to suppress the situation where the magnitude of the change in the torque of the reaction motor with respect to the steering demand becomes excessively large from becoming apparent.

[0018] 7. The adjustment process includes adjusting the magnitude of the reduction rate of the offset correction amount according to the steering angular velocity under the condition that the magnitude of the reduction rate of the offset correction amount when the magnitude of the steering angular velocity is large is less than or equal to the magnitude of the reduction rate of the offset correction amount when the magnitude of the steering angular velocity is small, so as to adjust the magnitude of the torque of the reaction motor. The steering control device according to any one of 2 to 6 above (excluding those not including 2 above).

[0019] The larger the magnitude of the steering angular velocity, the more likely it is that the magnitude of the target steering angular velocity tends to be large. And when the magnitude of the target steering angular velocity is large, the magnitude of the change in the torque of the reaction motor with respect to the steering demand tends to become excessively large. Thus, in the above configuration, a negative correlation is given to the magnitude of the reduction rate of the offset amount with respect to the magnitude of the steering angular velocity. Thereby, it is possible to suppress the change in the target steering equivalent angle from becoming excessively large.

[0020] 8. It is configured to execute torque prescribing processing, and the torque prescribing processing is processing for prescribing the torque to be applied to the steering shaft based on the value of the steering angle variable as an input. The adjustment processing includes adjusting the magnitude of the torque of the reaction motor so as to approach the torque prescribed by the torque prescribing processing. The steering control device according to any one of 1 to 7 above.

[0021] In an apparatus capable of transmitting power between a steering shaft and a steered wheel, the torque applied to the steering shaft is generally determined according to the steering angle such as the steering angle. Therefore, in the above configuration, the torque to be applied to the steering shaft is set according to the value of the steering angle variable. Then, by adjusting the magnitude of the change in the torque of the reaction force motor so as to approach the change in this torque, the change in the torque of the reaction force motor can be regulated by the change in torque determined by the specified torque setting process.

[0022] 9. A steering control device according to any one of 1 to 8 above, which is configured to execute a predetermined component reflection process, wherein the predetermined component reflection process is a process of reflecting a predetermined component of a frequency signal applied to the steered wheel according to a value of a torque variable of the steering motor as an input to the torque of the reaction force motor, and a situation in which the magnitude of the change in the torque of the reaction force motor with respect to the steering request can become excessively large includes a situation in which the predetermined component is reflected in the torque of the reaction force motor, and the adjustment process includes a process of adjusting the degree to which the predetermined component is reflected in the torque of the reaction force motor.

[0023] When a predetermined component is reflected in the torque of the reaction force motor, the change in the torque of the reaction force motor fluctuates due to the predetermined component. Therefore, in the above configuration, by adjusting the degree to which the predetermined component is reflected in the torque of the reaction force motor, it is possible to suppress the change in the torque of the reaction force motor from becoming excessively large.

[0024] 10. The steering control device according to any one of 2 to 9 above (excluding those not including 2 above), wherein the offset canceling process includes a process of setting a decreasing speed of the offset correction amount according to a changing speed of a target equivalent steering angle set by the target equivalent steering angle setting process, and the adjustment process includes a process of adjusting the magnitude of the torque of the reaction force motor by changing a steering angle ratio between the target equivalent steering angle and the steering angle as an input variable of the offset canceling process when the offset correction process is being executed.

[0025] In the above configuration, the rate of decrease in the magnitude of the offset correction amount is determined according to the rate of change of the target equivalent steering angle set by the target equivalent steering angle setting process. On the other hand, the rate of change of the target equivalent steering angle varies according to the steering angle ratio. Therefore, in the above configuration, by changing the steering angle ratio, the rate of decrease in the magnitude of the offset correction amount can be adjusted. And thereby, the change of the target equivalent steering angle as an input variable of the steering operation process can be adjusted.

[0026] 11. The reaction force operation process includes an assist amount setting process, an axial force setting process, and a target reaction force setting process, and is a process for controlling the torque of the reaction force motor according to the target reaction force torque. The axial force setting process is a process for setting an axial force, which is a force resisting the rotational operation of the steering shaft by the driver. The assist amount setting process is a process for setting an assist amount using the steering torque as an input. The assist amount is an amount for assisting the driver in rotating the steering shaft. The target reaction force setting process is a process for setting the target reaction force torque according to the value obtained by subtracting the assist amount from the axial force. The adjustment process includes a process for restricting the magnitude of the change in the axial force set by the axial force setting process to the smaller side, and is the steering control device according to any one of the above 1 to 10.

[0027] In the above configuration, by restricting the magnitude of the change in the axial force, it is possible to suppress the situation where the magnitude of the change in the torque of the reaction force motor becomes excessively large.

Brief Description of the Drawings

[0028]

Figure 1

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Mode for Carrying Out the Invention

[0029] <First Embodiment> Hereinafter, a first embodiment of the steering control device will be described with reference to the drawings. 「Premise Configuration」 As shown in FIG. 1, the steering device 10 of the vehicle is a steer-by-wire type steering device. The steering device 10 includes a reaction force actuator Ar and a steering actuator At. The steering device 10 of the present embodiment has a structure in which the power transmission path between the steering wheel 12 and the steered wheels 44 is mechanically interrupted.

[0030] A steering shaft 14 is connected to the steering wheel 12. The reaction force actuator Ar is an actuator for applying a steering reaction force to the steering wheel 12. The steering reaction force refers to a force acting in a direction opposite to the operation direction 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 resistance. The reaction force actuator Ar includes a reduction mechanism 16, a reaction force motor 20, and a reaction force inverter 22.

[0031] The reaction force motor 20 is, for example, a three-phase brushless motor. The rotating shaft of the reaction force motor 20 is connected to the steering shaft 14 via the reduction mechanism 16. On the other hand, the steering shaft 40 extends along the vehicle width direction which is the left-right direction in FIG. 1. Left and right steering wheels 44 are connected to both ends of the steering shaft 40 via tie rods 42 respectively. When the steering shaft 40 moves linearly, the steering angle of the steering wheels 44 is changed.

[0032] The steering actuator At includes a reduction mechanism 56, a steering motor 60, and a steering inverter 62. The steering motor 60 is, for example, a three-phase surface magnet synchronous motor. The rotating shaft of the steering motor 60 is connected to the pinion shaft 52 via the reduction mechanism 56. The pinion teeth of the pinion shaft 52 are meshed with the rack teeth 54 of the steering shaft 40. The rack and pinion mechanism 50 is constituted by the steering shaft 40 provided with the rack teeth 54 and the pinion shaft 52. The torque of the steering motor 60 is applied to the steering shaft 40 via the pinion shaft 52 as a steering force. In response to the rotation of the steering motor 60, the steering shaft 40 moves along the vehicle width direction which is the left-right direction in FIG. 1.

[0033] The steering control device 70 includes a PU 72 and a storage device 74. The PU 72 is a software processing device such as a CPU and a GPU. The steering control device 70 controls the control amount by the PU 72 executing a program stored in the storage device 74.

[0034] The steering control device 70 controls the steering wheel 12. The steering control device 70 operates the reaction force actuator Ar to control the steering reaction force as the control amount of the control target. In FIG. 1, an operation signal MSs to the inverter 22 for reaction force is described. Further, the steering control device 70 controls the steering wheel 44. The steering control device 70 operates the steering actuator At to control the steering angle of the steering wheel 44 as the control amount of the control target. In FIG. 1, an operation signal MSt to the inverter 62 for steering is described.

[0035] The steering control device 70 refers to the steering torque Th, which is the input torque to the steering shaft 14 detected by the torque sensor 80, in order to control the control amount. Further, the steering control device 70 refers to the rotation angle θa of the rotation shaft of the reaction force motor 20 detected by the rotation angle sensor 82. Further, the steering control device 70 refers to the currents iu1, iv1, iw1 flowing through the reaction force motor 20. The currents iu1, iv1, iw1 are quantified as the voltage drop amounts of the shunt resistors provided in the respective legs of the inverter 22 for reaction force. The steering control device 70 refers to the rotation angle θb of the rotation shaft of the steering motor 60 detected by the rotation angle sensor 84 in order to control the control amount. Further, the steering control device 70 refers to the currents iu2, iv2, iw2 flowing through the steering motor 60. The currents iu2, iv2, iw2 are quantified as the voltage drop amounts of the shunt resistors provided in the respective legs of the inverter 62 for steering. Further, the steering control device 70 refers to the vehicle speed V detected by the vehicle speed sensor 92.

[0036] "Control" FIG. 2 shows a part of the process executed by the steering control device 70. The assist amount setting process M10 is a process of calculating the assist amount Ta based on the steering torque Th and the vehicle speed V as input variables. The assist amount Ta is an amount in the same direction as the steering direction of the driver. The magnitude of the assist amount Ta is set to a large value when increasing the force to assist the driver's steering.

[0037] Figure 3 shows the details of the assist amount setting process M10. The basic assist amount setting process M40 is a process of setting the basic assist amount Tab based on the steering torque Th and the vehicle speed V as input variables. The basic assist amount setting process M40 sets the basic assist amount Tab to a value having a positive correlation with the steering torque Th. This process may be, for example, a process of performing a map operation on the basic assist amount Tab by the PU52 in a state where the map data is stored in advance in the storage device 74. The map data is data in which the steering torque Th and the vehicle speed V are input variables and the basic assist amount Tab is an output variable.

[0038] Note that the map data is set of data of discrete values of the input variable and values of the output variable corresponding to each of the values of the input variable. Also, the map operation may be any process as long as, when the value of the input variable matches any of the values of the input variable of the map data, the value of the output variable of the corresponding map data is the operation result. Also, the map operation may be any process as long as, when the value of the input variable does not match any of the values of the input variable of the map data, the value obtained by interpolation of the values of a plurality of output variables included in the map data is the operation result. Alternatively, the map operation may be any process as long as, when the value of the input variable does not match any of the values of the input variable of the map data, the value of the output variable of the map data corresponding to the closest value among the values of a plurality of input variables included in the map data is the operation result.

[0039] The load information processing M50 is a process for superimposing information on the road surface reaction force, which is the force applied from the road surface to the steering wheel 44, on the steering wheel 12. The load information processing M50 includes a band-pass filter M52, a filter coefficient setting process M54, and a gain multiplication process M56. The q-axis current iqt is input to the band-pass filter M52. The q-axis current iqt is the q-axis current of the steering motor 60. The q-axis current iqt is calculated by the PU72 based on the currents iu2, iv2, iw2 and the rotation angle θb as input variables. The q-axis current iqt is input to the band-pass filter M52 as a variable including the vibration component of the steering wheel 44 due to the road surface reaction force. The band-pass filter M52 is a process for selectively extracting a signal in the vibration frequency band caused by the unevenness of the road surface. The gain multiplication process M56 is a process for substituting the value obtained by multiplying the output value of the band-pass filter M52 by the gain Gb into the road surface information torque Ti. The filter coefficient setting process M54 is a process for setting the filter coefficient τi of the band-pass filter M52 according to the vehicle speed V. The filter coefficient τi is a variable for defining the frequency band transmitted by the band-pass filter M52 or a variable for defining how to attenuate. Here, the variable for defining the transmitted frequency band may be, for example, a variable for defining the center frequency. Also, the variable for defining how to attenuate may be, for example, an attenuation coefficient. Here, the filter coefficient τi is described as one variable, but actually there may be a plurality of them.

[0040] The synthesis process M60 is a process for subtracting the road surface information torque Ti from the basic assist amount Tab. The value thus calculated is the assist amount Ta. Returning to FIG. 2, the steering angle calculation process M12 is a process of calculating the steering angle θh, which is the rotation angle of the steering wheel 12, based on the rotation angle θa as an input variable. The steering angle calculation process M12 includes a process of converting the rotation angle θa into an integrated angle including a range exceeding 360° by counting the rotation speed of the reaction force motor 20 from the steering neutral position, which is the position of the steering wheel 12 when the vehicle is going straight. The steering angle calculation process M12 includes a process of calculating the steering angle θh by multiplying the obtained integrated angle by a conversion coefficient based on the rotation speed ratio of the speed reduction mechanism 16. Note that the steering angle θh is set to be positive when it is an angle on the right side of the steering neutral position and negative when it is an angle on the left side as an example.

[0041] The axial force setting process M14 is a process of setting the axial force F based on the vehicle speed V, the q-axis current iqt of the steering motor 60, and the steering angle θh as input variables. The axial force F is a value representing the force acting on the steering shaft 40 through the steered wheels 44 by control. However, it is not necessary that the axial force F is intended to accurately estimate the force acting on the steering shaft 40. The axial force F may be, for example, a virtual determination of the force acting on the steering shaft 40. The axial force F is converted into the torque applied to the steering shaft 14. That is, it is converted into the torque applied to the steering shaft 14 assuming a state where power transmission between the steered wheels 44 and the steering shaft 14 is possible.

[0042] FIG. 4 shows the details of the axial force setting process M14. The angle axial force setting process M70 is a process of calculating the angle axial force Fa based on the steering angle θh and the vehicle speed V as input variables. The angle axial force Fa is an estimated value of the axial force defined by an arbitrarily set vehicle model or the like. The angle axial force Fa is calculated as an axial force that does not reflect road surface information. Road surface information is information such as minute unevenness that does not affect the lateral behavior of the vehicle and steps that affect the lateral behavior of the vehicle. As an example, the angle axial force setting process M70 is a process of changing the angle axial force Fa according to the steering angle θh under the condition that the absolute value of the angle axial force Fa when the absolute value of the steering angle θh is large is equal to or greater than the absolute value of the angle axial force Fa when the absolute value of the steering angle θh is small. Also, as an example, the angle axial force setting process M70 may be a process of changing the angle axial force Fa according to the vehicle speed V under the condition that the absolute value of the angle axial force Fa when the vehicle speed V is large is equal to or greater than the absolute value of the angle axial force Fa when the vehicle speed V is small.

[0043] Note that in the description such as "changing B according to A under the condition that B when A is large is equal to or greater than B when A is small", "when A is large" and "when A is small" mean the relative magnitude relationship when the two are compared. For example, "when A is large" corresponds to the case where "A is the first value", and "when A is small" corresponds to the case where "A is the second value smaller than the first value". And according to the above description, it means that 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 changing B according to A such that A when B is large is larger than A when B is small.

[0044] Specifically, the angle axial force setting process M70 is a process of performing map calculation of the angle axial force Fa by the PU72 with the map data stored in the storage device 74. The map data is data in which the target steering equivalent angle θp* and the vehicle speed V are input variables and the angle axial force Fa is an output variable.

[0045] The current axial force setting process M72 is a process of calculating the current axial force Fi as the q-axis current iqt of the steering motor 60. The current axial force Fi is an estimated value of the axial force actually acting on the steering shaft 40 that operates to steer the steering wheel 44, that is, the axial force actually transmitted to the steering shaft 40. The current axial force Fi is calculated as the axial force reflecting the above road surface information. For example, the current axial force setting process M72 is a process of calculating the current axial force Fi on the assumption that the torque applied to the steering shaft 40 by the steering motor 60 and the torque corresponding to the force applied to the steering shaft 40 through the steering wheel 44 are balanced.

[0046] The distribution ratio calculation process M74 is a process of calculating the ratio Di based on the vehicle speed V and the steering angle θh as input variables. The ratio Di is the ratio of the current axial force Fi to the sum of the angular axial force Fa and the current axial force Fi. The ratio Di has a value of 0 or more and 1 or less. The distribution ratio calculation process M74 may be, for example, a process of performing a map calculation of the ratio Di by the PU72 with the map data stored in the storage device 74. Here, the map data is data in which the vehicle speed V and the steering angle θh are input variables and the ratio Di is an output variable.

[0047] The second ratio calculation process M76 is a process of calculating the second ratio "1 - Di" by subtracting the ratio Di from "1". The second ratio is the ratio of the angular axial force Fa to the sum of the angular axial force Fa and the current axial force Fi.

[0048] The first ratio multiplication process M78 is a process of multiplying the current axial force Fi by the ratio Di. The second ratio multiplication process M80 is a process of multiplying the angular axial force Fa by the second ratio. The addition process M82 is a process of substituting the value obtained by adding the output value of the first ratio multiplication process M78 and the output value of the second ratio multiplication process M80 into the axial force F. That is, the axial force F is a weighted average processed value of the angular axial force Fa and the current axial force Fi.

[0049] Returning to FIG. 2, the subtraction process M16 is a process of substituting the value obtained by subtracting the axial force F from the assist amount Ta into the target reaction torque Tr*. The target reaction torque Tr* is the target value of the torque applied by the reaction motor 20 to the steering shaft 14. When the axial force F constitutes the target reaction torque Tr*, the sign of the axial force F is inverted by the subtraction process M16. Therefore, the sign of the axial force F output by the axial force setting process M14 is opposite to the sign of the steering reaction force. This is simply a setting in terms of calculation.

[0050] The reaction force operation signal generation process M18 is a process of generating an operation signal MSs for the reaction force inverter 22 to control the torque of the reaction motor 20 so that the torque applied to the steering shaft 14 becomes the target reaction torque Tr*. Specifically, the reaction force operation signal generation process M18 includes a process of converting the target reaction torque Tr* into the target torque of the reaction motor 20. Further, the reaction force operation signal generation process M18 includes a process of calculating the operation signal MSs for the reaction force inverter 22 so as to bring the current flowing through the reaction motor 20 closer to the current determined from the target reaction torque Tr* by current feedback control. The operation signal MSs is actually the operation signal for each of the six switching elements of the reaction force inverter 22. The sign of the target reaction torque Tr* is usually opposite to the sign of the assist amount Ta.

[0051] The rudder equivalent angle calculation process M20 is a process of calculating the rudder equivalent angle θp, which is the rotation angle of the pinion shaft 52, based on the rotation angle θb as an input variable. The rudder equivalent angle calculation process M20 includes a process of converting to an integrated angle including a range exceeding 360° by counting the number of rotations of the steering motor 60 from the rack neutral position, which is the position of the steering shaft 40 when the vehicle is going straight. The rudder equivalent angle calculation process M20 includes a process of calculating the rudder equivalent angle θp, which is the actual rotation angle of the pinion shaft 52, by multiplying the converted integrated angle by a conversion coefficient based on the rotation speed ratio of the speed reduction mechanism 56. Note that the rudder equivalent angle θp is set to be positive when it is an angle on the right side of the rack neutral position and negative when it is an angle on the left side as an example. The rudder equivalent angle θp is a variable indicating the steering angle of the steered wheels 44.

[0052] The base value setting process M22 is a process of calculating the target rudder equivalent angle θp*0 based on the steering angle θh and the vehicle speed V as input variables. The target rudder equivalent angle θp*0 is the target value of the rudder equivalent angle θp corresponding to the operation of the steering wheel 12 by the driver. The base value setting process M22 includes a process of changing the target steering angle ratio, which is the ratio of the steering angle θh to the target rudder equivalent angle θp*, according to the vehicle speed V and the like.

[0053] The offset correction amount calculation process M24 is a process of calculating the offset correction amount Δθp of the target rudder equivalent angle θp*0. The offset correction process M26 is a process of calculating the target rudder equivalent angle θp* by subtracting the offset correction amount Δθp from the target rudder equivalent angle θp*0.

[0054] The steering feedback process M28 is a process of calculating the steering torque command value Tt*, which is the command value of the torque of the steering motor 60, according to the operation amount of the feedback control in which the rudder equivalent angle θp is the control amount and the target rudder equivalent angle θp* is the target value of the control amount.

[0055] The steering operation signal generation process M30 is a process that outputs an operation signal MSt for the steering inverter 62 based on the steering torque command value Tt*, the currents iu2, iv2, iw2, and the rotation angle θb as input variables. The steering operation signal generation process M30 includes a process of calculating the current command values on the dq axes based on the steering torque command value Tt*. Further, the steering operation signal generation process M30 includes a process of calculating the currents on the dq axes based on the currents iu2, iv2, iw2, and the rotation angle θb. Then, the steering operation signal generation process M30 includes a process of calculating the operation signal MSt to operate the steering inverter 62 so that the currents on the dq axes become the command values.

[0056] "Details of the Offset Correction Amount Calculation Process" FIG. 5 shows the procedure of the offset correction amount calculation process. The process shown in FIG. 5 is realized by the PU72 repeatedly executing, for example, at a predetermined period, a program stored in the storage device 74. In the following, the step numbers of each process are represented by numbers preceded by "S".

[0057] In the series of processes shown in FIG. 5, the PU72 first acquires the steering equivalent angle θp and the target steering equivalent angle θp*0 (S10). Next, the PU72 determines whether the flag FL is "1" (S12). The value of the flag FL is set to "1" when the absolute value of the offset correction amount Δθp is set to a value greater than zero. The value of the flag FL is set to "0" when the absolute value of the offset correction amount Δθp is zero.

[0058] When the PU72 determines that the flag FL is "0" (S12: NO), it determines whether a predetermined condition for starting the correction by the offset correction amount Δθp is satisfied (S14). The predetermined condition is a condition in which the deviation between the target steering equivalent angle θp* and the steering equivalent angle θp becomes large. The predetermined condition may be the following first condition or second condition. The first condition is a condition indicating that the target steering equivalent angle θp*0 is changed discontinuously.

[0059] Specifically, the first condition may be, for example, a condition indicating that an abnormality has occurred in the vehicle speed sensor 92. That is, when the vehicle speed sensor 92 is constituted by sensors that detect the speed of each of a plurality of wheels, if an abnormality occurs in any one of these wheel speed sensors, the calculation method of the vehicle speed V may be changed. And in that case, due to the discontinuous change in the vehicle speed V, the target equivalent steering angle θp*0 changes discontinuously. Also, for example, the first condition may be a condition indicating that operation intervention by the steering control device 70 has started. When the steering intervention starts, since the target equivalent steering angle θp*0 is set independently of the steering angle θh and the vehicle speed V, the target equivalent steering angle θp*0 changes discontinuously.

[0060] The second condition is a condition that the target equivalent steering angle θp*0 and the equivalent steering angle θp deviate from each other by a predetermined amount or more despite the steerable wheels 44 being capable of being steered. The second condition may be, for example, a condition indicating that the start switch of the vehicle has been switched from the off state to the on state. When the steering wheel 12 is rotated in the off state of the start switch, the steering angle θh and the equivalent steering angle θp become inconsistent. Therefore, at the time of the above switch of the start switch, despite the steerable wheels 44 being capable of being steered, the target equivalent steering angle θp*0 greatly deviates from the equivalent steering angle θp. Also, for example, the second condition may be a condition indicating that the current limit of the steering motor 60 has been released. Specifically, for example, when the steerable wheels 44 hit an obstacle such as a curb while the current limit of the steering motor 60 is being applied, it becomes difficult for the steerable wheels 44 to steer toward the side where they hit the obstacle. In this state, when the steering wheel 12 is steered toward the side where the obstacle is hit, the target equivalent steering angle θp*0 changes as the steering angle θh changes. On the other hand, the equivalent steering angle θp is maintained at a constant value. When the current limit of the steering motor 60 is released in this state, despite the steerable wheels 44 being capable of being steered, the target equivalent steering angle θp*0 and the equivalent steering angle θp deviate greatly from each other.

[0061] When determining that a predetermined condition is satisfied (S14: YES), PU72 substitutes "1" into flag FL (S16). Then, PU72 calculates an offset amount Δθp0, which is the difference equivalent amount between the target steering equivalent angle θp* and the actual steering equivalent angle θp (S18). Specifically, when PU72 determines in the process of S14 that the first condition is satisfied, it substitutes the value obtained by subtracting the previous value "θp*0(n - 1)" from the current value "θp*0(n)" of the target steering equivalent angle θp*0 into the offset amount Δθp0. Also, when PU72 determines in the process of S14 that the second condition is satisfied, it substitutes the value obtained by subtracting the steering equivalent angle θp from the target steering equivalent angle θp*0 into the offset amount Δθp0. Note that the steering equivalent angle θp immediately before the first condition is satisfied is considered to be approximately equal to the target steering equivalent angle θp*0. Therefore, the "value obtained by subtracting the previous value from the current value of the target steering equivalent angle θp*0" when the first condition is satisfied can be regarded as the difference between the target steering equivalent angle θp* and the actual steering equivalent angle θp. In other words, the "value obtained by subtracting the previous value from the current value of the target steering equivalent angle θp*0" when the first condition is satisfied is the difference equivalent amount between the target steering equivalent angle θp* and the actual steering equivalent angle θp.

[0062] Next, PU72 substitutes the offset amount Δθp0 into the offset correction amount Δθp (S20). On the other hand, when determining that flag FL is "1" (S12: YES), PU72 determines whether the offset correction amount Δθp is zero (S22). When PU72 determines that the absolute value of the offset correction amount Δθp is greater than zero (S22: NO), it calculates the target angular velocity ωp* (S24). The target angular velocity ωp* is the absolute value of the change rate of the target steering equivalent angle θp*0. The target angular velocity ωp* is calculated by PU72 based on the target steering equivalent angle θp*0 as an input variable. Specifically, the target angular velocity ωp* may be the difference between two target steering equivalent angles θp*0 separated by a unit time. Also, PU72 may provide a dead zone between the change rate of the target steering equivalent angle θp*0 and the target angular velocity ωp*. That is, for example, when the absolute value of the change rate of the target steering equivalent angle θp*0 is greater than zero and less than or equal to a threshold value, PU72 may set the target angular velocity ωp* to zero.

[0063] Next, PU72 substitutes, into the offset cancellation angle Δ, a value obtained by multiplying the target angular velocity ωp* as an input variable by the gain Gω and the period T (S26). The offset cancellation angle Δ is a variable that determines the speed at which the absolute value of the offset correction amount Δθp shifts to zero. Also, the period T is the period in which the series of processes shown in FIG. 5 is repeatedly executed. The gain Gω is calculated by PU72 based on the vehicle speed V as an input variable. PU72 calculates the gain Gω according to the vehicle speed V on the condition that the gain Gω when the vehicle speed V is high is equal to or greater than the gain Gω when the vehicle speed V is low. Specifically, with the map data stored in the storage device 74, PU72 performs a map operation on the gain Gω according to the vehicle speed V. Here, the map data is data in which the vehicle speed V is an input variable and the gain Gω is an output variable.

[0064] PU72 determines whether the offset amount Δθp0 is positive (S28). When PU72 determines that the offset amount Δθp0 is positive (S28: YES), it substitutes, into the offset correction amount Δθp, the larger of the value obtained by subtracting the offset cancellation angle Δ from the offset correction amount Δθp and zero (S30). On the other hand, when PU72 determines that the offset amount Δθp0 is not positive (S28: NO), it substitutes, into the offset correction amount Δθp, the smaller of the value obtained by adding the offset cancellation angle Δ to the offset correction amount Δθp and zero (S32).

[0065] On the other hand, when PU72 determines that the offset correction amount Δθp is zero (S22: YES), it substitutes "0" into the flag FL (S34). Also, when a negative determination is made in the process of S14, PU72 substitutes zero into the offset correction amount Δθp (S36).

[0066] Note that when PU72 completes the processes of S20, S30 to S36, it temporarily ends the series of processes shown in FIG. 5. "Details of the Axial Force Setting Process for Current" Fig. 6 shows the detailed procedure of the current axial force setting process M72. The process shown in Fig. 6 is realized by the PU72 repeatedly executing the program stored in the storage device 74 at a predetermined cycle, for example.

[0067] In the series of processes shown in Fig. 6, the PU72 first acquires the q-axis current iqt (S40). Next, the PU72 calculates the current axial force Fi based on the q-axis current iqt as an input variable (S42). Specifically, the PU72 changes the current axial force Fi according to the q-axis current iqt on the condition that the absolute value of the current axial force Fi when the absolute value of the q-axis current iqt is large is equal to or greater than the absolute value of the current axial force Fi when the absolute value of the q-axis current iqt is small. This process is realized by the PU72 performing a map operation on the current axial force Fi with the map data stored in the storage device 74. Note that the map data is data where the q-axis current iqt is the input variable and the current axial force Fi is the output variable.

[0068] Next, the PU72 determines whether the flag FL is "1" (S44). When the PU72 determines that the flag FL is "1" (S44: YES), it acquires the offset amount Δθp0 (S46). Then, the PU72 calculates the gain Gi based on the offset amount Δθp0 as an input variable (S48). The Gi is set to a value of "1" or less. The PU72 changes the gain Gi according to the offset amount Δθp0 on the condition that the gain Gi when the absolute value of the offset amount Δθp0 is large is equal to or less than the gain Gi when the absolute value of the offset amount Δθp0 is small. This process may be a process of the PU72 performing a map operation on the gain Gi with the map data stored in the storage device 74. The input variable of this map data is the offset amount Δθp0, and the output variable of this map data is the gain Gi.

[0069] Then, the PU72 substitutes the value obtained by multiplying the current axial force Fi calculated in the process of S42 by the gain Gi into the current axial force Fi (S50). Note that when the process of S50 is completed or when a negative determination is made in the process of S44, PU72 temporarily ends the series of processes shown in FIG. 6.

[0070] "Operations and Effects of the Present Embodiment" The time t1 in FIG. 7 indicates the timing when the above-described predetermined conditions are satisfied and the target rudder angle ratio for the base value setting process M22 to set the target turning equivalent angle θp*0 is changed. In that case, PU72 changes the target turning equivalent angle θp*0 step by step. Further, PU72 substitutes the difference between the previous value and the current value of the target turning equivalent angle θp*0 into the offset amount Δθp0. Then, PU72 sets the initial value of the offset correction amount Δθp to the offset amount Δθp0 and substitutes the value obtained by correcting the target turning equivalent angle θp*0 with the offset correction amount Δθp into the target turning equivalent angle θp*. PU72 gradually decreases the absolute value of the offset correction amount Δθp in order to converge the target turning equivalent angle θp* to the target turning equivalent angle θp*0. As a result, at time t2, the target turning equivalent angle θp* coincides with the target turning equivalent angle θp*0.

[0071] FIG. 7 shows the transition of the target turning equivalent angle θp* when it is assumed that the offset amount Δθp0 is zero and there is no discontinuous change in the target turning equivalent angle θp*0 at time t1, indicated by a two-dot chain line. As shown in FIG. 7, when the target turning equivalent angle θp*0 is corrected by the offset correction amount Δθp, the absolute value of the change rate of the target turning equivalent angle θp* becomes larger compared to the case where the offset amount Δθp0 is zero. Therefore, the absolute value of the change amount of the torque of the steering motor 60 per unit change amount of the turning equivalent angle θp becomes larger than the case where the offset amount Δθp0 is zero.

[0072] Here, in the present embodiment, the assist amount setting process M10, the axial force setting process M14, and the base value setting process M22 are adapted on the premise that there is no correction of the target steering equivalent angle θp*0 by the offset correction amount Δθp. Therefore, if the processes of S44 to S50 are not provided, there is a possibility that the gradient of the current axial force Fi, which is the absolute value of the current axial force Fi per unit change amount of the steering equivalent angle θp, becomes unexpectedly large. And when the gradient becomes unexpectedly large, the operation of the steering wheel 12 becomes heavy, resulting in a decrease in steering stability.

[0073] On the other hand, the PU72 corrected the magnitude of the current axial force Fi to the smaller side by the gain Gi. As a result, the gradient of the current axial force Fi becomes smaller compared to the case where no correction is made by the gain Gi. Therefore, it is possible to suppress a decrease in stability caused by the correction of the target steering equivalent angle θp*0 by the offset correction amount Δθp.

[0074] According to the present embodiment described above, the following operations and effects can be obtained. (1) The PU72 set the gain Gi according to the offset amount Δθp0. When the offset amount Δθp0 is large, the deviation between the target steering equivalent angle θp* and the target steering equivalent angle θp*0 becomes larger than when it is small. Therefore, when the offset amount Δθp0 is large, the period during which the change in the current axial force Fi with respect to the change in the target steering equivalent angle θp* becomes larger is longer than when it is small. Therefore, when the offset amount Δθp0 is large, the control is more likely to become unstable than when it is small. Therefore, by setting the gain Gi according to the offset amount Δθp0, it is possible to suppress the control from becoming unstable.

[0075] <Second Embodiment> Hereinafter, the second embodiment will be described with reference to the drawings, centering on the differences from the first embodiment.

[0076] Fig. 8 shows the detailed procedure of the current axial force setting process M72. The process shown in Fig. 8 is realized by the PU72 repeatedly executing the program stored in the storage device 74, for example, at a predetermined cycle. In Fig. 8, for the processes corresponding to the processes shown in Fig. 6, the same step numbers are given for convenience.

[0077] In the series of processes shown in Fig. 8, when the PU72 makes an affirmative determination in the process of S44, it acquires the offset cancellation angle Δ (S46a). Then, the PU72 calculates the gain Gi based on the offset cancellation angle Δ as an input variable (S48a). The PU72 changes the gain Gi according to the offset cancellation angle Δ on the condition that the gain Gi when the offset cancellation angle Δ is large is less than or equal to the gain Gi when the offset cancellation angle Δ is small. This process may be a process in which the PU72 performs a map operation on the gain Gi in a state where the map data is stored in the storage device 74. The input variable of this map data is the offset cancellation angle Δ, and the output variable of this map data is the gain Gi.

[0078] Note that when the PU72 completes the process of S48a, it proceeds to the process of S50. The larger the offset cancellation angle Δ is, the greater the decreasing speed of the absolute value of the offset correction amount Δθp becomes. Therefore, the larger the offset cancellation angle Δ is, the greater the changing speed of the target steering equivalent angle θp* becomes. Accordingly, the changing speed of the current axial force Fi calculated by the process of S42 becomes larger as the offset cancellation angle Δ becomes larger. On the contrary, the PU72 suppresses the excessive increase in the changing speed of the current axial force Fi by reducing the gain Gi when the offset cancellation angle Δ is large.

[0079] <The Third Embodiment> Hereinafter, the third embodiment will be described with reference to the drawings, centering on the differences from the first embodiment.

[0080] The current axial force setting process M72 according to this embodiment is the process of S40 and S42. That is, the current axial force setting process M72 does not have the process after S44 in FIG. 6. FIG. 9 shows the procedure of the offset correction amount calculation process. The process shown in FIG. 9 is realized by the PU72 repeatedly executing the program stored in the storage device 74, for example, at a predetermined cycle. In FIG. 9, for the processes corresponding to the processes shown in FIG. 5, the same step numbers are given for convenience.

[0081] In the series of processes shown in FIG. 9, when the PU72 makes a negative determination in the process of S22, the steering angular velocity ωh is acquired (S24a). The steering angular velocity ωh is the change rate of the steering angle θh. The steering angular velocity ωh is calculated by the PU72 based on the steering angle θh as an input variable.

[0082] Then, the PU72 calculates the offset cancellation angle Δ based on the steering angular velocity ωh as an input variable (S26a). The PU72 changes the offset cancellation angle Δ according to the steering angular velocity ωh on the condition that the offset cancellation angle Δ when the absolute value of the steering angular velocity ωh is large is less than or equal to the offset cancellation angle Δ when the absolute value of the steering angular velocity ωh is small. This process is, for example, a process in which the PU72 performs a map operation on the offset cancellation angle Δ with the map data stored in the storage device 74 in advance. The input variable of this map data is the steering angular velocity ωh, and the output variable of the map data is the offset cancellation angle Δ. Note that the offset cancellation angle Δ is a value of zero or more.

[0083] When the PU72 completes the process of S26a, it proceeds to the process of S28. When the absolute value of the steering angular velocity ωh is large, the absolute value of the change rate of the target rudder equivalent angle θp*0 also becomes large compared to when it is small. On the other hand, PU72 gives a negative correlation between the absolute value of the steering angular velocity ωh and the offset cancellation angle Δ. As a result, when the absolute value of the change rate of the target rudder equivalent angle θp*0 is large, the offset cancellation angle Δ is set to a small value. Therefore, when the absolute value of the change rate of the target rudder equivalent angle θp*0 is large, the absolute value of the change rate of the offset correction amount Δθp is set to a small value. Therefore, it is suppressed that the absolute value of the change rate of the target rudder equivalent angle θp*, which is the target rudder equivalent angle θp*0 corrected by the offset correction amount Δθp, becomes excessively large.

[0084] <Fourth Embodiment> Hereinafter, the fourth embodiment will be described with reference to the drawings, centering on the differences from the first embodiment.

[0085] The current axial force setting process M72 according to this embodiment is the processes of S40 and S42. That is, the current axial force setting process M72 does not have the processes after S44 in FIG. 6. And in this embodiment, PU72 estimates the change in the axial force applied to the rudder shaft 40 from the change in the steering angle θh. Then, PU72 regulates the change in the axial force F according to the estimated change in the axial force.

[0086] FIG. 10 shows the procedure of the process for regulating the change in the axial force F. The process shown in FIG. 10 is realized by the PU72 repeatedly executing the program stored in the storage device 74, for example, at a predetermined cycle.

[0087] In the series of processes shown in FIG. 10, the PU 72 first acquires the steering angle θh (S60). Next, the PU 72 calculates a specified axial force torque Fr based on the steering angle θh as an input variable (S62). The specified axial force torque Fr is an estimated value of the axial force applied to the steering shaft 40 when the steering shaft 14 and the steering shaft 40 are mechanically connected and power transmission is possible between them. However, the specified axial force torque Fr is an amount converted to the torque applied to the steering shaft 14 assuming that the steering wheel 44 and the steering wheel 12 are connected.

[0088] Next, the PU 72 substitutes the value obtained by subtracting the previous value "Fr(n - 1)" from the current value "Fr(n)" of the specified axial force torque Fr into the specified change amount ΔFr (S64). Then, the PU 72 acquires the axial force F (S66). The PU 72 determines whether the absolute value of the value obtained by subtracting the previous value "F(n - 1)" from the current value "F(n)" of the axial force F is greater than the absolute value of the specified change amount ΔFr (S68). When the PU 72 determines that the absolute value of the subtracted value is greater than the absolute value of the specified change amount ΔFr (S68: YES), it limits the magnitude of the change amount of the current value "F(n)" of the axial force F from the previous value "F(n - 1)" to the magnitude of the specified change amount ΔFr (S70).

[0089] Note that when the PU 72 completes the process of S70 or makes a negative determination in the process of S68, the series of processes shown in FIG. 10 is temporarily terminated. According to the above process, the magnitude of the change amount of the axial force F can be regulated by the magnitude of the change amount of the specified axial force torque Fr. The specified axial force torque Fr is the axial force assumed when the equivalent steering angle θp changes according to the steering angle θh. Therefore, the change speed of the specified axial force torque Fr does not increase due to the offset cancellation angle Δ. Accordingly, it is possible to suppress the magnitude of the change amount of the axial force F from becoming excessively large.

[0090] <Fifth Embodiment> Hereinafter, the fifth embodiment will be described with reference to the drawings, centering on the differences from the first embodiment.

[0091] In this embodiment, when the target steering equivalent angle θp*0 is corrected by the offset correction amount Δθp, a restriction is imposed on the road surface information torque Ti. FIG. 11 shows the procedure of the road information processing M50. The series of processes shown in FIG. 11 is realized by the PU72 repeatedly executing, for example, at a predetermined cycle, a program stored in the storage device 74.

[0092] In the series of processes shown in FIG. 11, the PU72 first determines whether the flag FL is "1" (S80). When the PU72 determines that the flag FL is "0" (S80: NO), the normal value GH is substituted for the gain Gb used in the gain multiplication process M56 (S82). On the other hand, when the PU72 determines that the flag FL is "1" (S80: NO), the limit value GL is substituted for the gain Gb (S84). The limit value GL is a value that is 0 or more and smaller than the normal value GH.

[0093] When the PU72 completes the processes of S82 and S84, the PU72 temporarily ends the series of processes shown in FIG. 11. The road surface information torque Ti, which is the output of the road information processing M50, affects the change in the target reaction force torque Tr*. However, since the road surface information torque Ti is a value corresponding to the state of the road surface, it is difficult to design a controller by presuming in advance the degree to which the road surface information torque Ti affects the change in the target reaction force torque Tr*. Therefore, in this embodiment, in a situation where the change in the target reaction force torque Tr* becomes large due to the gradual decrease process of the magnitude of the offset correction amount Δθp, the magnitude of the road surface information torque Ti is restricted to the smaller side. Thereby, in cooperation with the gradual decrease process of the magnitude of the offset correction amount Δθp and the road surface information torque Ti, it is possible to suppress the change in the target reaction force torque Tr* from becoming excessively large.

[0094] <Sixth Embodiment> Hereinafter, the sixth embodiment will be described with reference to the drawings, centering on the differences from the first embodiment.

[0095] The current axial force setting process M72 according to this embodiment is the process of S40 and S42. That is, the current axial force setting process M72 does not have the process after S44 in FIG. 6. On the other hand, in this embodiment, the gear ratio of the steering equivalent angle used to calculate the offset cancellation angle Δ is restricted to the smaller side.

[0096] FIG. 12 shows the procedure of the offset correction amount calculation process. The process shown in FIG. 12 is realized by the PU72 repeatedly executing the program stored in the storage device 74, for example, at a predetermined cycle. In FIG. 12, for the processes corresponding to the processes shown in FIG. 5, the same step numbers are given for convenience.

[0097] In the series of processes shown in FIG. 12, when the PU72 makes a negative determination in the process of S22, it calculates the calculation steering equivalent angle θpl* (S24b). The ratio of the calculation steering equivalent angle θpl* to the steering angle θh is set to a value smaller than the ratio of the target steering equivalent angle θp*0 to the steering angle θh. The PU72 calculates the calculation angular velocity ωpl* based on the calculation steering equivalent angle θpl* as an input variable (S24c). The calculation angular velocity ωpl* is the absolute value of the change speed of the calculation steering equivalent angle θpl*. Then, the PU72 substitutes the value obtained by multiplying the calculation angular velocity ωpl* as an input variable by the gain Gω and the period T into the offset cancellation angle Δ (S26b). Note that when the PU72 completes the process of S26b, it proceeds to the process of S28.

[0098] Since the ratio of the calculation steering equivalent angle θpl* to the steering angle θh is smaller than the ratio of the target steering equivalent angle θp*0 to the steering angle θh, the calculation angular velocity ωpl* tends to be a value smaller than the target angular velocity ωp*. Therefore, the offset cancellation angle Δ calculated using the calculation angular velocity ωpl* tends to be a value smaller than the offset cancellation angle Δ calculated using the target angular velocity ωp*. Therefore, in this embodiment, compared with the case of using the offset cancellation angle Δ calculated using the target angular velocity ωp*, the decrease speed of the absolute value of the offset correction amount Δθp can be restricted to the smaller side.

[0099] <Seventh Embodiment> Hereinafter, the seventh embodiment will be described with reference to the drawings, centering on the differences from the first embodiment.

[0100] FIG. 13 shows the detailed procedure of the current axial force setting process M72. The process shown in FIG. 13 is realized by the PU72 repeatedly executing the program stored in the storage device 74, for example, at a predetermined cycle. In FIG. 13, for the processes corresponding to the processes shown in FIG. 6, the same step numbers are given for convenience.

[0101] In the series of processes shown in FIG. 13, when the process of S40 is completed, the PU72 determines whether the flag FL is "1" (S90). When the PU72 determines that the flag FL is "0" (S90: NO), it selects normal map data as the map data used in the process of S42 (S92). On the other hand, when the PU72 determines that the flag FL is "1" (S90: YES), it selects relaxation map data as the map data used in the process of S42 (S94). The relaxation map data is set to a value with a smaller absolute value of the current axial force Fi than the absolute value of the q-axis current iqt.

[0102] When the processes of S92 and S94 are completed, the PU72 proceeds to the process of S42. Also, when the process of S42 is completed, the PU72 temporarily ends the series of processes shown in FIG. 13. The change amount of the absolute value of the current axial force Fi calculated using the relaxation map data tends to be smaller than the change amount of the absolute value of the current axial force Fi calculated using the normal map data. Therefore, the increase in the change amount of the absolute value of the current axial force Fi due to the gradual decrease process of the offset correction amount Δθp can be suppressed by the relaxation map data.

[0103] <Eighth Embodiment> Hereinafter, the eighth embodiment will be described with reference to the drawings, centering on the differences from the first embodiment.

[0104] In this embodiment, when the change in the current axial force Fi, which is grasped from the current axial force Fi calculated each time, becomes large, the PU72 corrects the current axial force Fi so as to reduce the change in the current axial force Fi.

[0105] FIG. 14 shows the detailed procedure of the current axial force setting process M72. The process shown in FIG. 14 is realized by the PU72 repeatedly executing, for example, at a predetermined cycle, the program stored in the storage device 74. In FIG. 14, for the processes corresponding to the processes shown in FIG. 6, the same step numbers are given for convenience.

[0106] In the series of processes shown in FIG. 14, when the PU72 completes the process of S42, it acquires the steering angle θh (S100). Then, the PU72 substitutes, into the current axial force gradient ΔFi, a value obtained by dividing a value obtained by subtracting the previous value "Fi(n - 1)" from the current value "Fi(n)" of the current axial force Fi by a value obtained by subtracting the previous value "θh(n - 1)" from the current value "θh(n)" of the steering angle θh. Next, the PU72 determines whether or not the absolute value of the current axial force gradient ΔFi is greater than the threshold value ΔFith (S104). The threshold value ΔFith is set to approximately the maximum value of the gradient of the current axial force Fi assumed when the correction of the target steering equivalent angle θp*0 by the offset correction amount Δθp is not performed.

[0107] When the PU72 determines that the absolute value of the current axial force gradient ΔFi is greater than the threshold value ΔFith (S104: YES), it corrects the current axial force Fi so that the absolute value of the current axial force gradient ΔFi becomes the threshold value ΔFith (S106). Note that when the PU72 makes a negative determination in the process of S104 and when it completes the process of S106, it temporarily ends the series of processes shown in FIG. 14.

[0108] According to the above process, it is possible to suppress the current axial force gradient ΔFi from becoming excessively large due to the gradual decrease process of the absolute value of the offset correction amount Δθp. <Corresponding relationship> The correspondence between the matters in the above-described embodiment and the matters described in the column of "Means for Solving the Problems" is as follows. Below, the correspondence is shown for each number of the solution means described in the column of "Means for Solving the Problems". [1] The target steering equivalent angle setting process corresponds to the base value setting process M22, the offset correction amount calculation process M24, and the offset correction process M26. The steering operation process corresponds to the steering feedback process M28 and the steering operation signal generation process M30. The reaction force operation process corresponds to the assist amount setting process M10, the axial force setting process M14, the subtraction process M16, and the reaction force operation signal generation process M18. The state quantity of the steering device corresponds to the q-axis current iqt. The adjustment process corresponds to the processes of S44 to S50 in FIG. 6, the processes of S44, S46a, S48a, S50 in FIG. 8, the processes of S24a, S26a in FIG. 9, and the processes of S68, S70 in FIG. 10. Also, the adjustment process corresponds to the process of S84 in FIG. 11, the processes of S24b, S24c, S26b in FIG. 12, the process of S94 in FIG. 13, and the processes of S104, S106 in FIG. 14. [2] The offset cancellation process corresponds to the processes of S28 to S32. [3] The target reaction force setting process corresponds to the subtraction process M16. [4] The adjustment process corresponds to the processes of S44 to S50 in FIG. 6, the processes of S44, S46a, S48a, S50 in FIG. 8, the process of S94 in FIG. 13, and the processes of S104, S106 in FIG. 14. "5" The adjustment process corresponds to the processes of S44, S46a, S48a, S50 in FIG. 8. [6] The adjustment process corresponds to the processes of S44 to S50 in FIG. 6. [7] The adjustment process corresponds to the processes of S24a, S26a in FIG. 9. [8] The torque regulation process corresponds to the process of S62. The adjustment process corresponds to the processes of S68, S70 in FIG. 10. [9] The predetermined component reflection process corresponds to the load information process M50. The adjustment process corresponds to the process of S84 in FIG. 11.

[10] The adjustment process corresponds to the processes of S24b, S24c, S26b in FIG. 12.

[11] The adjustment process corresponds to the processes of S104, S106.

[0109] <Other Embodiments> Note that this embodiment can be implemented with the following modifications. This embodiment and the following modification examples can be implemented in combination with each other within a technically non - conflicting range.

[0110] "Regarding Torque Specifying Processing" · It is not essential that the rudder angle variable as an input variable of the torque specifying process is the steering angle θh. The rudder angle variable may be, for example, the target equivalent steering angle θp*0.

[0111] "Regarding Angle Axial Force Setting Processing" · The input variables of the angle axial force setting process are not limited to the steering angle θh and the vehicle speed V. For example, instead of the steering angle θh as the variable indicating the rudder angle, the target equivalent steering angle θp*0 may be used. Also, for example, the input variables of the angle axial force setting process may not include the vehicle speed V.

[0112] "Regarding Adjustment Processing" · The process of making the change in the axial force F approach the change in the specified axial force torque Fr is not limited to the process illustrated in FIG. 10. For example, PU72 may forcibly substitute the specified axial force torque Fr for the axial force F when the flag FL is "1".

[0113] · The specified axial force torque Fr may be an amount equivalent to the current axial force Fi. In that case, the axial force F in the processes of S66 to S70 may be read as the current axial force Fi. · The gain Gi for limiting the magnitude of the current axial force Fi to the smaller side may be changed according to both the absolute value of the offset amount Δθp0 and the offset cancellation angle Δ. Also, the gain Gi may be a fixed value.

[0114] ·Both the process of restricting the magnitude of the current axial force Fi to the lower side as exemplified in FIGS. 6 and 8, etc., and the process of restricting the decreasing rate of the absolute value of the offset correction amount Δθp to the lower side as exemplified in FIG. 9, etc., may be executed. For example, both the process of restricting the decreasing rate of the absolute value of the offset correction amount Δθp to the lower side and the processes exemplified in FIGS. 10 and 14, etc., may be executed. For example, both the processes exemplified in FIGS. 6 and 8, etc., and the processes exemplified in FIGS. 10 and 14, etc., may be executed. Further, for example, both the processes exemplified in FIGS. 6 and 8, etc., the processes exemplified in FIGS. 10 and 14, etc., and the process of restricting the decreasing rate of the absolute value of the offset correction amount Δθp to the lower side may be executed.

[0115] ·The situation to be addressed by the adjustment process, where the magnitude of the change in the reaction torque with respect to the steering request can become excessively large, does not assume a situation where the magnitude of the offset correction amount Δθp is gradually reduced by the offset cancellation angle Δ.

[0116] ·The current axial force Fi in FIG. 14 may be reinterpreted as the axial force F. ·In the process of FIG. 14, the current axial force gradient ΔFi may be reinterpreted as the change amount of the current axial force Fi per unit time.

[0117] "Regarding the offset cancellation process" ·The offset cancellation angle Δ is not limited to the value obtained by multiplying the target angular velocity ωp* by the gain Gω that depends on the vehicle speed V. For example, the gain Gω may be a fixed value.

[0118] ·With the map data stored in the storage device 74, the PU 72 may perform a map calculation of the offset cancellation angle Δ according to the target angular velocity ωp* and the vehicle speed V. Here, the map data is data in which the target angular velocity ωp* and the vehicle speed V are input variables and the offset cancellation angle Δ is an output variable.

[0119] · The offset cancellation angle Δ may be the sum of the angular velocity-dependent cancellation amount Δω and the vehicle speed-dependent cancellation amount Δv. Here, PU72 may calculate the angular velocity-dependent cancellation amount Δω according to the target angular velocity ωp* under the following conditions. The condition is that the magnitude of the angular velocity-dependent cancellation amount Δω when the absolute value of the target angular velocity ωp* is large is equal to or greater than the magnitude of the angular velocity-dependent cancellation amount Δω when the absolute value of the target angular velocity ωp* is small. Also, PU72 may calculate the vehicle speed-dependent cancellation amount Δv according to the vehicle speed V under the following conditions. The condition is that the vehicle speed-dependent cancellation amount Δv when the vehicle speed V is large is equal to or greater than the vehicle speed-dependent cancellation amount Δv when the vehicle speed V is small.

[0120] · The offset cancellation angle Δ may be a value obtained by multiplying the offset amount Δθp0 by a predetermined value greater than 0 and less than 1. Thus, when the decrease amount per cycle of the offset correction amount Δθp has a positive correlation with the absolute value of the offset amount Δθp0, the process of S48 is particularly effective.

[0121] "Regarding the steering operation process" · It is not essential that the steering operation process includes the steering feedback process M28 and the steering operation signal generation process M30. For example, the steering operation process may be a process of controlling the torque of the steering motor 60 based only on the operation amount of the open-loop control whose target steering equivalent angle θp* is the target value of the control amount.

[0122] "Regarding the reaction force application process" · It is not essential that the reaction force application process includes the assist amount setting process M10 and the axial force setting process M14. For example, in a state where map data is stored in the storage device 74, a process of performing map calculation of the target reaction force torque Tr* by PU52 according to the steering torque Th, the q-axis current iqt, and the vehicle speed V as input variables may be performed. In that case, for example, the current axial force Fi in FIG. 14 may be read as the steering torque command value Tt*.

[0123] "Regarding the steering control device" ·The steering control device is not limited to one that executes various processes by a PU. For example, it may be provided with a dedicated hardware circuit such as an ASIC that executes at least a part of the processes executed in the above-described embodiment. That is, the steering control device may be provided with any of the following processing circuits (a) to (c). (a) A processing circuit including a processing device that executes all of the above processes according to a program, and a program storage device such as a storage device that stores the program. (b) A processing circuit including a processing device and a program storage device that execute a part of the above processes according to a program, and a dedicated hardware circuit that executes the remaining processes. (c) A processing circuit including a dedicated hardware circuit that executes all of the above processes. Here, there may be a plurality of software execution devices including a processing device and a program storage device, and dedicated hardware circuits.

[0124] "Regarding the steering actuator" ·As the steering actuator At, for example, one in which a steering motor 60 is arranged coaxially with the steering shaft 40 may be adopted. Also, for example, one that is connected to the steering shaft 40 via a belt type reducer using a ball screw mechanism may be adopted.

Explanation of Signs

[0125] 10... Steering device 12... Steering wheel 14... Steering shaft 16... Reduction mechanism 20... Reaction force motor 22... Inverter for reaction force 40... Steering shaft 42... Tie rod 44... Steering wheel 50... Rack and pinion mechanism 52... Pinion shaft 54... Rack teeth 56... Reduction mechanism 60... Steering motor 62... Inverter for steering 70... Steering control device

Claims

1. Applied to a steer-by-wire system including a reaction force motor that applies a reaction force to a steering wheel and a steering device that steers steered wheels by a steering motor, configured to execute a target steering equivalent angle setting process, a steering operation process, a reaction force operation process, and an adjustment process, wherein the target steering equivalent angle setting process is a process of setting a target steering equivalent angle according to a steering request, the target steering equivalent angle is a target value of a steering equivalent angle that is a variable indicating the steering angle of the steered wheels, the steering operation process is a process of operating the steering motor according to an operation amount of control in which the target steering equivalent angle is a target value of a control amount, the reaction force operation process is a process of controlling the torque of the reaction force motor according to a state amount of the steering device, the adjustment process is a steering control device that adjusts the torque of the reaction force motor in a situation where the magnitude of the change in the torque of the reaction force motor with respect to the steering request can become excessively large.

2. The target steering equivalent angle setting process is configured to execute a base value setting process, an offset amount calculation process, an offset correction process, and an offset cancellation process, wherein the base value setting process is a process of setting a base value of the target steering equivalent angle according to a steering request, the offset amount calculation process is a process of calculating an offset amount that is an amount equivalent to the difference between the target steering equivalent angle and the actual steering equivalent angle triggered by the establishment of a predetermined condition, the offset correction process is a process of correcting the target steering equivalent angle so as to reduce the deviation between the target steering equivalent angle and the actual steering equivalent angle by an offset correction amount corresponding to the offset amount, the offset cancellation process is a process of reducing the magnitude of the offset correction amount, The situation where the magnitude of the change in the torque of the reaction force motor with respect to the steering request can become excessively large is the situation in which the offset cancellation process is executed. The steering control device according to Claim 1.

3. The reaction force operation process includes an assist amount setting process, an axial force setting process, and a target reaction force setting process, and is a process of controlling the torque of the reaction force motor according to a target reaction force torque, wherein the axial force setting process is a process of setting an axial force that is a force resisting the rotational operation of the steering shaft by the driver, the assist amount setting process is a process of setting an assist amount with the steering torque as an input. The assist amount is the amount that assists the driver in rotating the steering shaft. The target reaction force setting process is a process of setting the target reaction force torque according to a value obtained by subtracting the assist amount from the axial force. The adjustment process is a process of adjusting the axial force set by the axial force setting process. The steering control device according to claim 1.

4. The axial force setting process includes a process of setting a current axial force based on the current of the steering motor as an input variable. The axial force includes the current axial force. The adjustment process includes a process of adjusting the current axial force. The steering control device according to claim 3.

5. The adjustment process includes a process of adjusting the torque of the reaction force motor based on the decreasing speed of the offset amount as an input variable. The steering control device according to claim 2.

6. The adjustment process includes a process of adjusting the torque of the reaction force motor based on the offset amount as an input variable. The steering control device according to claim 2.

7. The adjustment process includes a process of adjusting the magnitude of the torque of the reaction force motor by adjusting the magnitude of the decreasing speed of the offset correction amount according to the steering angular velocity under the condition that the magnitude of the decreasing speed of the offset correction amount when the magnitude of the steering angular velocity is large is less than or equal to the magnitude of the decreasing speed of the offset correction amount when the magnitude of the steering angular velocity is small. The steering control device according to claim 2.

8. It is configured to execute torque specifying processing. The torque specifying process is a process of specifying the torque to be applied to the steering shaft based on the value of the steering angle variable as an input. The adjustment process includes a process of adjusting the change in the torque of the reaction force motor so as to approach the change in the torque specified by the torque specifying process. The steering control device according to claim 1.

9. It is configured to execute predetermined component reflecting processing. The predetermined component reflecting process is a process of reflecting a predetermined component of the frequency signal applied to the steered wheels in the torque of the reaction force motor according to the value of the torque variable of the steering motor as an input. A situation where the magnitude of the change in the torque of the reaction force motor with respect to the steering request can become excessively large includes a situation where the predetermined component is reflected in the torque of the reaction force motor. The adjustment process includes a process of adjusting the degree of reflecting the predetermined component in the torque of the reaction force motor. The steering control device according to claim 1.

10. The offset cancellation process includes a process of setting a decrease rate of the offset correction amount according to a change rate of a target equivalent steering angle set by the target equivalent steering angle setting process. The adjustment process includes a process of adjusting the magnitude of the torque of the reaction force motor by changing a steering angle ratio between the target equivalent steering angle and the steering angle as an input variable of the offset cancellation process when the offset correction process is being executed. The steering control device according to claim 2. **Claim 11** The reaction force operation process includes an assist amount setting process, an axial force setting process, and a target reaction force setting process, and is a process of controlling the torque of the reaction force motor according to the target reaction force torque. The axial force setting process is a process of setting an axial force, which is a force resisting a rotation operation of the steering shaft by a driver. The assist amount setting process is a process of setting an assist amount using the steering torque as an input. The assist amount is an amount for assisting a driver in rotating the steering shaft. The target reaction force setting process is a process of setting the target reaction force torque according to a value obtained by subtracting the assist amount from the axial force. The adjustment process includes a process of restricting the magnitude of a change in the axial force set by the axial force setting process to the smaller side. The steering control device according to claim 1.

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