Steering control device and steering control method

Abstract

A steering control device (40) is configured to execute feedback processing, operation processing, and reduction processing. The feedback processing is processing for calculating a feedback operation amount. The feedback operation amount is an operation amount of the feedback control, in which the detection value of a steering torque is a control amount. The steering torque is a torque input by the driver to a steering device. The operation processing is processing for controlling the torque of the motor of the steering device, by using the feedback operation amount as an input. The reduction processing is processing for reducing the absolute value of the feedback operation amount when the magnitude of a target steering torque is equal to or greater than a predetermined value. The target steering torque is a target value of the steering torque.

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, Patent Document 1 listed below describes a steering control device that assists the steering of steered wheels in accordance with the amount of feedback control in which the detected value of steering torque is the control amount.

[0003] Japanese Patent Application Laid-Open No. 2004-203089

[0004] However, there is a limit to the range in which a sensor for detecting steering torque can accurately detect steering torque. Therefore, if the absolute value of the actual steering torque is excessively large, a correct value cannot be obtained as the control variable for the feedback control. As a result, there is a risk that the torque of the motor will be controlled by an inappropriate value as the control variable for the feedback control.

[0005] An aspect of the present disclosure provides a steering control device. The steering control device is configured to execute a feedback process, an operation process, and a decrease process. The feedback process is a process for calculating a feedback operation amount. The feedback operation amount is a feedback control operation amount in which a detected value of steering torque is a control amount. The steering torque is a torque input by a driver to the steering device. The operation process is a process for controlling the torque of a motor of the steering device using the feedback operation amount as an input. The decrease process is a process for decreasing the absolute value of the feedback operation amount when the magnitude of a target steering torque is equal to or greater than a predetermined value. The target steering torque is a target value of the steering torque.

[0006] Another aspect of the present disclosure provides a steering control method. The steering control method includes steps of executing a feedback process, an operation process, and a decrease process. The feedback process is a process of calculating a feedback operation amount. The feedback operation amount is a feedback control operation amount in which a detected value of steering torque is a control amount. The steering torque is a torque input by a driver to a steering device. The operation process is a process of controlling the torque of a motor of the steering device using the feedback operation amount as an input. The decrease process is a process of decreasing the absolute value of the feedback operation amount when the magnitude of a target steering torque is equal to or greater than a predetermined value. The target steering torque is a target value of the steering torque.

[0007] Fig. 4 is a diagram showing the configuration of a steering control device and a steering device according to a first embodiment. Fig. 5 is a block diagram showing processing executed by the steering control device of Fig. 1. Fig. 6 is a diagram showing gains adjusted by the gain adjustment processing in Fig. 2. Fig. 7 is a diagram showing the configuration of a steering control device and a steering device according to a second embodiment. Fig. 8 is a block diagram showing processing executed by the steering control device of Fig. 4.

[0008] <First embodiment> A first embodiment will be described below with reference to the drawings. "Prerequisite configuration" As shown in FIG. 1, a steering device 10 includes a steering wheel 12. The steering wheel 12 is a means for the driver to transmit steering intentions. A transmission shaft 14 is connected to the steering wheel 12. Therefore, when the steering wheel 12 rotates, the transmission shaft 14 rotates integrally. The rotational power of the transmission shaft 14 is transmitted to a turning shaft 16. The turning shaft 16 extends in the vehicle width direction (the left-right direction in FIG. 1). Turnable wheels 20 are connected to both ends of the turning shaft 16 via tie rods 18.

[0009] The transmission shaft 14 is arranged to intersect with the steered shaft 16. The transmission shaft 14 and the steered shaft 16 are formed with teeth that mesh with each other. The meshing of these teeth enables the transmission of power from the transmission shaft 14 to the steered shaft 16. In other words, the rotational power of the transmission shaft 14 is converted into power that displaces the steered shaft 16 in the axial direction. The displacement of the steered shaft 16 in the axial direction is transmitted to the steered wheels 20 via tie rods 18. This changes the steering angle of the steered wheels 20. The steering angle refers to the turning angle of the tires.

[0010] The steering device 10 also includes an assist motor 30. The assist motor 30 generates an assist force that assists the driver in steering. The rotational power of the assist motor 30 is applied to a drive shaft 34. The drive shaft 34 and the steered shaft 16 have meshed teeth formed thereon. The meshing of these teeth enables power transmission from the drive shaft 34 to the steered shaft 16. In other words, the rotational power of the drive shaft 34 is converted into axial displacement power of the steered shaft 16. As a result, the rotational power of the assist motor 30 is converted into axial displacement power of the steered shaft 16 via the drive shaft 34. More specifically, the assist motor 30 is, for example, a three-phase brushless motor. The output voltage of an inverter 32 is applied to the terminals of the assist motor 30.

[0011] The steering control device 40 controls the control amount of the steering device 10, which is the object of control. In order to control the control amount, the steering control device 40 refers to the steering torque Th input to the steering wheel 12. The steering torque Th is detected by a torque sensor 50. The torque sensor 50 is a sensor that detects the steering torque Th according to the degree of torsion of a torsion bar 52, which is part of the transmission shaft 14. The steering control device 40 also refers to the vehicle speed SPD detected by a vehicle speed sensor 54. The steering control device 40 also refers to the rotation angle θa of the assist motor 30 detected by a rotation angle sensor 56. The steering control device 40 also refers to the currents iu, iv, and iw flowing through the assist motor 30.

[0012] The steering control device 40 includes a PU 42 and a storage device 44. The PU 42 is a software processing device such as a CPU, a GPU, and a TPU. The storage device 44 includes a storage medium such as an electrically rewritable nonvolatile memory and a disk medium. A steering control program 44a is stored in the storage device 44. The steering control device 40 controls the control amount by the PU 42 executing the steering control program 44a stored in the storage device 44.

[0013] "Processing Executed by Steering Control Device 40" Fig. 2 shows processing executed by the steering control device 40. The processing shown in Fig. 2 is realized by the PU 42 executing the steering control program 44a, for example, at a predetermined interval.

[0014] The target steering torque calculation 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 Fa. The axial force Fa is a force applied to the steered shaft 16. The axial force Fa is an amount converted into torque of the transmission shaft 14. The target steering torque calculation process M10 includes a process for setting the target steering torque Th* to a different value depending on the vehicle speed SPD, even if the axial force Fa is the same. This setting is intended to allow the driver to experience an optimal steering feel depending on the vehicle speed SPD.

[0015] The open-loop manipulated variable calculation process M12 is a process for calculating the open-loop manipulated variable Mff. The open-loop manipulated variable Mff is a manipulated variable of open-loop control in which the steering torque Th is the controlled variable and the target steering torque Th* is the controlled variable target value. The open-loop manipulated variable calculation process M12 is a process for calculating the open-loop manipulated variable Mff by inputting the target steering torque Th*. The open-loop manipulated variable calculation process M12 calculates the open-loop manipulated variable Mff based on an inverse model of the nominal model Pn. The nominal model Pn is a model in which the input is the assist torque Ta, which is the torque of the assist motor 30, and the output is the estimated steering torque The, which is an estimated value of the steering torque Th. Here, the assist torque Ta is a value converted into the torque of the transmission shaft 14. The inverse model is a model in which the input is the estimated steering torque The, and the output is the assist torque Ta.

[0016] The deviation calculation process M14 calculates a deviation, which is a value obtained by subtracting the target steering torque Th* from the steering torque Th. The PD operation amount calculation process M16 calculates a PD operation amount Mpd0 using the deviation as an input. The PD operation amount Mpd0 is a feedback control operation amount in which the steering torque Th is the control amount and the target steering torque Th* is the target value of the control amount. The PD operation amount Mpd0 is the sum of the output value of a proportional element to which the deviation is input and the output value of a derivative element to which the deviation is input. The PD operation amount Mpd0 is a value converted into the torque of the transmission shaft 14. More specifically, the PD operation amount calculation process M16 includes a process of changing at least one of the gain of the proportional element and the gain of the derivative element in accordance with the vehicle speed SPD.

[0017] The gain adjustment process M18 is a process in which the PD operation amount Mpd0 is multiplied by the gain Kpd and the resulting value is assigned to the PD operation amount Mpd. The torque command value calculation process M20 is a process in which the inputs are the open-loop operation amount Mff, the PD operation amount Mpd, and the estimated second disturbance torque de, and the output is the assist torque Ta. More specifically, the torque command value calculation process M20 is a process in which the value obtained by subtracting the estimated second disturbance torque de from the sum of the open-loop operation amount Mff and the PD operation amount Mpd is assigned to the assist torque Ta.

[0018] The assist torque Ta is input to an axial force calculation process M22. The axial force calculation process M22 is a process for substituting the sum of the assist torque Ta and the steering torque Th for the axial force Fa. The assist torque Ta is input to a disturbance observer M30. The disturbance observer M30 includes a steering torque estimation process M32, a first disturbance calculation process M34, and a second disturbance calculation process M36.

[0019] The steering torque estimation process M32 is a process for inputting the assist torque Ta to the nominal model Pn, thereby outputting the estimated steering torque The. The estimated steering torque The is the steering torque assumed by the nominal model Pn.

[0020] The first disturbance calculation process M34 is a process for calculating an estimated first disturbance torque dhe. The estimated first disturbance torque dhe is a disturbance component of the steering torque Th of the actual control object. The estimated first disturbance torque dhe is the difference between the torque estimated from the nominal model Pn and the actual torque. In other words, the estimated first disturbance torque dhe is the difference between the steering torque assumed by the nominal model Pn and the actual steering torque Th. More specifically, the first disturbance calculation process M34 is a process for substituting the value obtained by subtracting the estimated steering torque The from the steering torque Th for the estimated first disturbance torque dhe.

[0021] The second disturbance calculation process M36 is a process in which the input is the estimated first disturbance torque dhe and the output is the estimated second disturbance torque de0. The estimated second disturbance torque de0 is the disturbance torque converted into the torque of the assist motor 30. The second disturbance calculation process M36 is a process in which the estimated second disturbance torque de0 is calculated using an inverse model of the nominal model Pn and a filter Hd.

[0022] The filter Hd is provided to reduce noise caused by the differential operation included in the nominal model Pn. In this embodiment, the filter Hd is, for example, a third-order low-pass filter.

[0023] The gain adjustment process M24 is a process of multiplying the estimated second disturbance torque de0 by the gain Kimc and assigning the result to the estimated second disturbance torque de. As described above, the assist torque Ta is a value obtained by subtracting the estimated second disturbance torque de from the sum of the open-loop operation amount Mff and the PD operation amount Mpd. On the other hand, the estimated second disturbance torque de is an amount obtained by converting the difference between the steering torque assumed by the nominal model Pn and the actual steering torque Th into torque of the assist motor 30. This means that the estimated second disturbance torque de is an amount corresponding to the difference between the steering torque assumed by the nominal model Pn and the actual steering torque Th. Therefore, the assist torque Ta is an amount obtained by correcting the sum of the open-loop operation amount Mff and the PD operation amount Mpd using a correction amount corresponding to the difference between the steering torque assumed by the nominal model Pn and the actual steering torque Th.

[0024] The operation signal generation process M40 is a process for operating the inverter 32 by inputting the assist torque Ta. Specifically, the operation signal generation process M40 includes a process for calculating a control operation amount in which the torque of the assist motor 30 is the control amount and the assist torque Ta is the target value of the control amount. The operation signal generation process M40 also includes a process for operating the inverter 32 so as to obtain this operation amount. The operation amount may be, for example, the time ratio of the ON operation time to one cycle of the ON / OFF operation of the switching elements of the inverter 32. FIG. 2 shows an operation signal MS for the inverter 32. However, in reality, the operation signal MS is a separate operation signal for each switching element of the inverter 32.

[0025] Regarding the Gain Adjustment Process: FIG. 3 shows the gains Kpd and Kimc adjusted by the gain adjustment processes M18 and M24. As shown in FIG. 3, the gains Kpd and Kimc are set using the absolute value of the target steering torque Th* as an input. Specifically, when the absolute value of the target steering torque Th* is equal to or less than the threshold value Th1, the PU 42 assigns "1" to the gains Kpd and Kimc. On the other hand, when the absolute value of the target steering torque Th* is greater than the threshold value Th1 and equal to or less than the upper limit value Thth, the PU 42 changes the gains Kpd and Kimc in accordance with the absolute value. Specifically, the PU 52 changes the gains Kpd and Kimc in accordance with the absolute value under the condition that the gains Kpd and Kimc when the absolute value is large are equal to or less than the gains Kpd and Kimc when the absolute value is small.

[0026] In the description of this specification, "changing B according to A while satisfying the condition that when A is large, B is equal to or smaller 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." This means that, depending on the settings of the first and second values, B when A is the first value may be smaller than B when A is the second value.

[0027] Specifically, the PU 42 performs map calculations to determine the gains Kpd and Kimc according to the absolute value of the target steering torque Th*, with map data stored in advance in the storage device 44. The map data includes two types of data. One is data in which the input variable is the absolute value of the target steering torque Th* and the output variable is the gain Kpd. The other is data in which the input variable is the absolute value of the target steering torque Th* and the output variable is the gain Kimc.

[0028] The upper limit value Thth is set in accordance with the upper limit value at which the steering torque Th can be detected by the torque sensor 50. Specifically, the upper limit value Thth may be equal to the upper limit value at which the steering torque Th can be detected by the torque sensor 50, or may be a value obtained by subtracting a predetermined margin from the upper limit value.

[0029] <Functions and Effects of the Present Embodiment> The PU 42 determines the assist torque Ta in accordance with the PD manipulation amount Mpd0, which is the manipulation amount of feedback control in which the steering torque Th is the control amount. The torque sensor 50 has a limited detectable range. Therefore, if the absolute value of the steering torque Th becomes excessively large, the steering torque Th detected by the torque sensor 50 may deviate from the actual steering torque. In such a case, the PD manipulation amount Mpd0 is not an appropriate amount for bringing the steering torque Th closer to the target steering torque Th*. Therefore, in the above configuration, the PU 42 sets the PD manipulation amount Mpd to zero when the absolute value of the target steering torque Th* is equal to or greater than the upper limit value Thth. This makes it possible to suppress the influence of the PD manipulation amount Mpd0 on the assist torque Ta when the PD manipulation amount Mpd0 is not an appropriate value for bringing the torque input to the steering wheel 12 closer to the target steering torque Th*.

[0030] Furthermore, the PU 42 calculates the estimated second disturbance torque de0 according to the difference between the output of the nominal model Pn and the steering torque Th. When the absolute value of the target steering torque Th* is equal to or greater than the upper limit value Thth, the PU 42 sets the estimated second disturbance torque de to zero. This makes it possible to suppress the influence of the estimated second disturbance torque de on the assist torque Ta when the estimated second disturbance torque de is not an appropriate value for bringing the torque input to the steering wheel 12 closer to the target steering torque Th*.

[0031] According to the present embodiment described above, the following further actions and effects are obtained. (1-1) When the absolute value of the target steering torque Th* is greater than the threshold value Th1 and equal to or less than the upper limit value Thth, the PU 42 sets the gains Kpd and Kimc to have a negative correlation with the absolute value of the target steering torque Th*. This makes it possible to mitigate changes in the feedback manipulated variable compared to when the gains Kpd and Kimc are set to either "1" or "0" depending on whether the absolute value is equal to or less than the upper limit value Thth or exceeds the upper limit value Thth. Therefore, it is possible to suppress abrupt changes in the assist torque Ta. Incidentally, the deviation calculation process M14, the PD manipulated variable calculation process M16, and the disturbance observer M30 all receive the steering torque Th as an input. In other words, these processes are processes in which the steering torque Th, which is a controlled variable, is fed back.

[0032] (1-2) The PU 42 sets the assist torque Ta according to the open-loop control variable Mff in addition to the PD control variable Mpd and the estimated second disturbance torque de as feedback control variables. Therefore, even if the gains Kpd and Kimc are reduced, the control in which the steering torque Th is the control variable can be continued.

[0033] Second Embodiment A second embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment.

[0034] "Prerequisite Configuration" The configuration of the steering control system according to this embodiment is shown in Fig. 4. In Fig. 4, members corresponding to those shown in Fig. 1 are denoted by the same reference numerals for convenience.

[0035] 4, in the steering device 10, the transmission shaft 14 is separated into an input shaft 14a connected to the steering wheel 12 and an output shaft 14b engaged with the steered shaft 16. Note that in this embodiment, the output shaft 14b is not actually required. However, for convenience of the following explanation, the output shaft 14b is provided.

[0036] A reaction motor 70 is provided on the input shaft 14a. The reaction motor 70 is a motor for applying a reaction force, which is a torque in the opposite direction to the torque input by the driver, to the steering wheel 12. The reaction motor 70 is, for example, a three-phase brushless motor. The output voltage of an inverter 72 is applied to the terminals of the reaction motor 70.

[0037] Torque from a steering motor 80 is applied to steering shaft 16 via drive shaft 34. Steering motor 80 is, for example, a three-phase brushless motor. The output voltage of an inverter 82 is applied to terminals of steering motor 80.

[0038] The steering control device 40 controls the steering device 10. The steering control device 40 operates the inverter 72 to control the reaction force, which is the control variable of the control object. The steering control device 40 also operates the inverter 82 to control the steering angle of the steered wheels 20, which is the control variable of the control object.

[0039] Steering control device 40 refers to rotation angle θs of reaction force motor 70 detected by rotation angle sensor 90 in order to control the reaction force, which is a control variable. Steering control device 40 also refers to currents ius, ivs, iws flowing through reaction force motor 70 in order to control the reaction force. Steering control device 40 also refers to rotation angle θt of steering motor 80 detected by rotation angle sensor 92 in order to control the steering angle, which is a control variable. Steering control device 40 also refers to currents iut, ivt, iwt flowing through steering motor 80 in order to control the steering angle.

[0040] "Processing Executed by Steering Control Device 40" Figure 5 shows processing executed by the steering control device 40. In other words, Figure 5 shows processing executed by the steering control device 40 in a state where the transmission of power from the steering wheel 12 to the steered wheels 20 is interrupted. Note that in Figure 5, processing corresponding to the processing shown in Figure 2 is denoted by the same reference numerals for convenience.

[0041] As shown in Fig. 5, the torque command value calculation process M20 is a process for outputting a reaction force command value Tr*. The torque command value calculation process M20 is a process for substituting a value obtained by subtracting the estimated second disturbance torque de from the sum of the open-loop operation amount Mff and the PD operation amount Mpd into the reaction force command value Tr*. The reaction force command value Tr* is a command value for the reaction torque to be applied to the steering wheel 12. The reaction force command value Tr* is converted into the angle of the transmission shaft 14.

[0042] The steering operation signal generation process M40a is a process for operating the inverter 72 by inputting the reaction force command value Tr*. Specifically, the steering operation signal generation process M40a includes a process for calculating a control operation amount in which the torque of the reaction force motor 70 is the control amount and the reaction force command value Tr* is the target value of the control amount. The calculation of the operation amount is performed by referring to the rotation angle θs and the currents ius, ivs, and iws. The steering operation signal generation process M40a also includes a process for operating the inverter 72 in accordance with the operation amount. FIG. 5 shows an operation signal MSs for the inverter 72. Note that in reality, the operation signal MSs is a separate operation signal for each switching element of the inverter 72.

[0043] The target angle calculation process M50 is a process for calculating a target angle θp*, which is a target value for the rotation angle of the drive shaft 34. The rotation angle of the drive shaft 34 has a one-to-one correspondence with the steering angle. The target angle calculation process M50 may be a process for calculating the target angle θp* from the reaction force command value Tr* using, for example, a model of the steering device 10. In this model, for example, the reaction force command value Tr* may be regarded as a torque applied to the transmission shaft 14 when it is assumed that the input shaft 14a and the output shaft 14b are mechanically coupled.

[0044] The angle control process M52 is a process for calculating a control manipulated variable in which the rotation angle of drive shaft 34 is the controlled variable and target angle θp* is the target value of the controlled variable. This manipulated variable is a steering torque command value Tt*, which is a torque command value for steering motor 80. The rotation angle of drive shaft 34 is calculated by PU 42 using rotation angle θt as an input.

[0045] The steering operation signal generation process M54 is a process for operating inverter 82 in response to input of steering torque command value Tt*. The steering operation signal generation process M54 includes a process for calculating a control operation amount in which the torque of steering motor 80 is the control amount and the value obtained by converting steering torque command value Tt* into the torque of steering motor 80 is the target value of the control amount. The calculation of the operation amount references the rotation angle θt and currents iut, ivt, and iwt. The steering operation signal generation process M54 also includes a process for operating inverter 82 in accordance with the operation amount. FIG. 5 shows an operation signal MSt for inverter 82. Note that in reality, the operation signal MSt is a separate operation signal for each switching element of inverter 82.

[0046] <Other Embodiments> This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0047] "Regarding Feedback Processing" (a) Processing in which the Difference Between Steering Torque Th and Target Steering Torque Th* is Input The processing in which the difference between steering torque Th and target steering torque Th* is input is not limited to the PD manipulation amount calculation processing M16. For example, the manipulation amount of this processing may be the sum of the output value of a proportional element to which the difference is input and the output value of a differential element to which the difference is input and the output value of an integral element corresponding to the difference. Also, for example, the manipulation amount of this processing may be the sum of the output value of a proportional element to which the difference is input and the output value of an integral element corresponding to the difference. Also, for example, the manipulation amount of this processing may be the sum of the output value of a differential element to which the difference is input and the output value of an integral element corresponding to the difference. Also, for example, the manipulation amount of this processing may be any one of the output values ​​of the proportional element to which the difference is input and the output value of a differential element to which the difference is input and the output value of an integral element corresponding to the difference.

[0048] (b) Regarding the operation amount corresponding to the difference between the output of the nominal model Pn and the steering torque Th: The second disturbance calculation process M36 does not necessarily have to be a process for calculating the estimated second disturbance torque de0 using the inverse model of the nominal model Pn and the filter Hd. For example, the second disturbance calculation process M36 may be a process for calculating the estimated second disturbance torque de0 using only the inverse model of the nominal model Pn.

[0049] (c) Others The feedback processing does not necessarily include both a process for inputting the difference between the steering torque Th and the target steering torque Th* and a process for calculating the manipulated variable corresponding to the difference between the output of the nominal model Pn and the steering torque Th. For example, the feedback processing may be configured by only the PD manipulated variable calculation process M16. Also, for example, the feedback processing may be configured by only the disturbance observer M30.

[0050] Regarding the target steering torque calculation process M10: It is not essential that the target steering torque calculation process M10 is a process for calculating the target steering torque Th* based on the axial force Fa. For example, the target steering torque calculation process M10 may be a process for calculating the target steering torque Th* by inputting the steering torque Th and the assist torque Ta.

[0051] The input to the target steering torque calculation process M10 does not necessarily include the vehicle speed SPD. The input to the target steering torque calculation process M10 is not limited to the above. For example, two or more sampled values ​​of the steering angle at different sampling timings may be included in the input to the target steering torque calculation process M10. In this case, a process for distinguishing between when the steering wheel 12 is turned and when it is returned can be realized in accordance with the input. Therefore, for example, the absolute value of the target steering torque Th* may be set to a larger value when the steering wheel 12 is turned compared to when it is returned.

[0052] Regarding the open-loop manipulated variable calculation process: The input to the open-loop manipulated variable calculation process M12 is not limited to the target steering torque Th*. For example, the input to the open-loop manipulated variable calculation process M12 may be the axial force Fa. In this case, the transfer function of the open-loop manipulated variable calculation process M12 may be the product of a transfer function that calculates the target steering torque Th* from the axial force Fa and an inverse model of the nominal model Pn.

[0053] Regarding the Operation Process: In the process shown in FIG. 2 , the operation process is a process in which the torque of the assist motor 30 is the controlled variable and the assist torque Ta is the target value of the controlled variable. However, this is not limited to this. For example, the operation process may include a process of calculating a target value of the rotation angle of the assist motor 30 from the axial force Fa. In this case, the operation process is a process of operating the inverter 32 in accordance with a feedback control operation amount in which the rotation angle of the assist motor 30 is the controlled variable. Note that the axial force Fa is the sum of the steering torque Th and a value obtained by correcting the operation amount determined from the open-loop operation amount Mff and the feedback operation amount Mfb with the estimated second disturbance torque de. Therefore, the operation process is a process of operating the inverter 32 in accordance with a value obtained by correcting the operation amount determined from the open-loop operation amount Mff and the PD operation amount Mpd with the estimated second disturbance torque de. This is a process of controlling the torque of the assist motor 30 so as to generate a torque corresponding to the value obtained by correcting the operation amount determined from the open-loop operation amount Mff and the PD operation amount Mpd according to the estimated second disturbance torque de.

[0054] 5, the operation process is a process in which the torque of the reaction force motor 70 is the controlled variable and the reaction force command value Tr* is the target value of the controlled variable, but this is not limited to this. For example, the operation process may include a process of calculating a target value of the rotation angle of the reaction force motor 70 from the axial force Fa. In this case, the operation process is a process of operating the inverter 72 in accordance with the manipulated variable of feedback control, in which the rotation angle of the reaction force motor 70 is the controlled variable.

[0055] Regarding the Steering Control Device In the configuration illustrated in FIG. 4, the device for operating the reaction force motor 70 and the device for operating the steering motor 80 may be separate devices.

[0056] The steering control device is not limited to a device that includes the PU 42 and the storage device 44 and executes software processing. For example, a dedicated hardware circuit such as an ASIC that executes at least part of the processing executed in the above embodiment may be included. In other words, the steering control device may include a processing circuit that has any one of the following configurations (a) to (c):

[0057] (a) A processing circuit comprising a processing device that executes all of the above processes according to a program and a program storage device such as a memory device that stores the program. (b) A processing circuit comprising a processing device and program storage device that executes part of the above processes according to a program, and a dedicated hardware circuit that executes the remaining processes.

[0058] (c) A processing circuit comprising a dedicated hardware circuit for executing all of the above processes. Here, there may be a plurality of software execution devices each comprising a processing device and a program storage device. Also, there may be a plurality of dedicated hardware circuits.

[0059] Regarding the steering control method: The entity that executes the various controls described above is not limited to a steering control device attached to the vehicle. For example, some of the processes for control to the target steering torque Th*, such as the disturbance observer M30, may be executed by a mobile terminal of the driver.

[0060] Regarding the input unit: The input unit to which the steering torque is input is not limited to the steering wheel 12. Regarding the power transmission cut-off state: The configuration for realizing the power transmission cut-off state between the input unit to which the steering torque is input and the steered wheels 20 is not limited to the configuration illustrated in Fig. 4. For example, a clutch may be provided between the input shaft 14a and the output shaft 14b.

[0061] Regarding the steering device: As the actuator for steering the steered wheels 20, for example, one in which the assist motor 30 or the steering motor 80 is arranged coaxially with the steering shaft 16 may be used. Also, for example, one in which the power of the assist motor 30 or the steering motor 80 is transmitted to the steering shaft 16 via a belt-type reducer using a ball screw mechanism may be used.

[0062] The steering device capable of changing the relationship between the steering angle and the turning angle is not limited to the steering device in which the transmission of power between the steering wheel 12 and the steered wheels 20 is blocked, as shown in Fig. 5. For example, a steering device capable of changing the relationship between the steering angle and the turning angle may be configured by using a variable gear as the gear that enables the transmission of power between the steering wheel 12 and the steered wheels 20.

[0063] Others: In the above embodiment, for convenience of explanation, the assist torque Ta is the command value of the torque of the assist motor 30, but this is not limited to this. The assist torque Ta may be, for example, the command value of the torque of the drive shaft 34. In this case, the operation signal generation process M40 includes a process of converting the assist torque Ta into the torque of the assist motor 30.

[0064] In the above embodiment, for convenience of explanation, the reaction force command value Tr* is a command value for the torque of the reaction force motor 70. However, this is not limited to this. For example, assuming that a speed reduction mechanism is provided between the reaction force motor 70 and the transmission shaft 14, the reaction force command value Tr* may be a command value for the torque of an appropriate rotating body in the speed reduction mechanism. In this case, the steering operation signal generation process M40a includes a process of converting the reaction force command value Tr* into the torque of the reaction force motor 70.

Claims

1. A steering control device configured to execute a feedback processing, an operation processing, and a reduction processing, wherein the feedback processing is a processing for calculating a feedback operation amount, the feedback operation amount is a feedback control operation amount in which the detection value of steering torque is the control amount, the steering torque is a torque input by a driver to a steering device, the operation processing is a processing for controlling the torque of a motor of the steering device using the feedback operation amount as an input, the reduction processing is a processing for reducing the absolute value of the feedback operation amount when the magnitude of a target steering torque is greater than or equal to a predetermined value, and the target steering torque is a target value of the steering torque.

2. A steering control device as described in claim 1, wherein the reduction process includes a process of reducing the feedback operation amount when the magnitude of the target steering torque is greater than an upper limit value of a detectable range of a sensor that detects the steering torque, compared to when the magnitude of the target steering torque is less than the upper limit value.

3. A steering control device as described in claim 1, wherein the reduction process includes a process of reducing the feedback operation amount when the magnitude of the target steering torque is greater than a threshold value, compared to when the magnitude is less than the threshold value, and the threshold value is smaller than the upper limit value of the detectable range of a sensor that detects the steering torque.

4. A steering control device as described in claim 3, wherein the reduction process is a process in which the feedback operation amount output by the feedback process is multiplied by a gain, and the value is used as the feedback operation amount that becomes the input to the operation process, and when the magnitude of the target steering torque is greater than or equal to the threshold value and less than the upper limit value, the gain when the magnitude of the target steering torque is large is less than or equal to the gain when the magnitude of the target steering torque is small.

5. A steering control device as described in claim 1, configured to execute an open-loop operation amount calculation process, the open-loop operation amount calculation process being a process of calculating an open-loop operation amount, which is an operation amount of open-loop control in which the steering torque is a control amount, using the target steering torque as an input, and the operation process being a process of controlling the torque of the motor using the feedback operation amount and the open-loop operation amount as input.

6. A steering control device according to claim 1, wherein the feedback processing includes a process for calculating the feedback operation amount using an output value of at least one of a proportional element and a differential element to which the difference between the detected value of the steering torque and the target steering torque is input.

7. A steering control device as described in claim 1, wherein the feedback processing includes a process of calculating the feedback operation amount according to a difference between the detection value and an output of a nominal model when an input of the operation processing is input to the nominal model, using the detection value as an input.

8. A steering control method having steps of executing a feedback process, an operation process, and a reduction process, wherein the feedback process is a process of calculating a feedback operation amount, the feedback operation amount is a feedback control operation amount in which the detection value of steering torque is a control amount, the steering torque is a torque input by a driver to a steering device, the operation process is a process of controlling the torque of a motor of the steering device using the feedback operation amount as an input, the reduction process is a process of reducing the absolute value of the feedback operation amount when the magnitude of a target steering torque is equal to or greater than a predetermined value, and the target steering torque is a target value of the steering torque.

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