Steering control device and steering control method

Abstract

A steering control device according to the present invention executes a target steering torque setting process, a feedback manipulation amount calculation process, and a manipulation process. The target steering torque setting process is for setting a target steering torque, which is a target value for steering torque. The feedback manipulation amount calculation process is for calculating a manipulation amount in feedback control in which a detected value of the steering torque is a control amount. The manipulation process is for manipulating, in accordance with the manipulation amount, the torque of a motor which is mounted on a steering device. The target steering torque setting process is for setting the target steering torque on the basis of a suppression state quantity as an input variable. The suppression state quantity is a state quantity in which an inertial component of a steering state quantity that is used in calculation for manipulation of the torque of the motor is suppressed.

Description

Steering control device and steering control method

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

[0002] Patent Document 1 below describes a device that operates the torque of a motor of a steering device based on an operation amount of feedback control in which a steering torque is a control amount and a target steering torque is a target value of the control amount. In this device, the target steering torque is set based on the sum of the operation amount as an input variable and the steering torque.

[0003] Japanese Unexamined Patent Application Publication No. 2020-179830

[0004] The influence of the inertia component of the steering device is reflected in the operation amount. Therefore, the target steering torque is set to a target value in which the inertia component is reflected. Therefore, in the above device, a driver feels the influence of inertia when operating the steering wheel.

[0005] In one aspect of the present disclosure, a steering control device is provided. The steering control device has a steering device as a control target. The steering control device is configured to execute a target steering torque setting process, a feedback operation amount calculation process, and an operation process. The target steering torque setting process is a process of setting a target steering torque that is a target value of the steering torque. The steering torque is a torque input to an operation unit. The operation unit is a member for a driver to input a torque according to the steering intention. The feedback operation amount calculation process is a process of calculating an operation amount of feedback control in which a detected value of the steering torque is a control amount. The operation process is a process of operating the torque of a motor mounted on the steering device according to the operation amount. The target steering torque setting process is a process of setting the target steering torque based on a suppression state amount as an input variable. The suppression state amount is a state amount in which an inertia component among steering state amounts used for an operation of the torque of the motor is suppressed.

[0006] Another aspect of this disclosure provides a steering control method. The steering control method controls a steering device. The steering control method includes: executing a target steering torque setting process; executing a feedback control amount calculation process; and executing an operation process. The target steering torque setting process is a process of setting a target steering torque, which is a target value of the steering torque. The steering torque is a torque input to an operation unit. The operation unit is a component into which the driver inputs a torque corresponding to their steering intention. The feedback control amount calculation process is a process of calculating a feedback control amount, the detected value of the steering torque being the control amount. The operation process is a process of operating the torque of a motor mounted on the steering device according to the operation amount. The target steering torque setting process is a process of setting the target steering torque based on a suppression state quantity as an input variable. The suppression state quantity is a state quantity in which the inertia component of the steering state quantity used in calculations for operating the motor torque is suppressed.

[0007] This is a diagram showing the configuration of the steering system of a vehicle according to the first embodiment. This is a block diagram showing some of the processes performed by the steering control device according to the first embodiment. This is a diagram showing the Bode plot of a standard model according to the first embodiment. This is a diagram showing the MA-MT characteristics according to a comparative example of the first embodiment. This is a diagram showing the MA-MT characteristics according to the first embodiment. This is a block diagram showing some of the processes performed by the steering control device according to the second embodiment. This is a block diagram showing some of the processes performed by the steering control device according to the third embodiment. This is a diagram showing the configuration of the steering system of a vehicle according to the fourth embodiment. This is a block diagram showing some of the processes performed by the steering control device according to the fourth embodiment.

[0008] <First Embodiment> The first embodiment will be described below with reference to the drawings. "Prerequisite Configuration" As shown in Figure 1, the steering device 10 is equipped with a steering wheel 12. The steering wheel 12 is an operating unit that serves as hardware for the driver to communicate their intention to steer. A transmission shaft 14 is connected to the steering wheel 12. Therefore, when the steering wheel 12 rotates, the transmission shaft 14 rotates together with it. The rotational power of the transmission shaft 14 is transmitted to the steering shaft 16. The steering shaft 16 extends along the vehicle width direction (left and right direction in Figure 1). Steering wheels 20 are connected to both ends of the steering shaft 16 via tie rods 18.

[0009] The transmission shaft 14 is positioned to intersect with the steering shaft 16. Teeth are formed on both the transmission shaft 14 and the steering shaft 16 that mesh with each other. The meshing of these teeth enables the transmission of power from the transmission shaft 14 to the steering shaft 16. In other words, the rotational power of the transmission shaft 14 is converted into axial displacement power of the steering shaft 16. The axial displacement of the steering shaft 16 is transmitted to the steering wheel 20 via the tie rod 18. This changes the steering angle of the steering wheel 20. The steering angle is the angle at which the tire turns.

[0010] Furthermore, the steering system 10 is equipped with an assist motor 30. The assist motor 30 generates an assist force, which is a force to assist the driver in steering. The rotational power of the assist motor 30 is applied to the drive shaft 34. Teeth that mesh with each other are formed on the drive shaft 34 and the steering shaft 16. The meshing of these teeth enables the transmission of power from the drive shaft 34 to the steering shaft 16. In other words, the rotational power of the drive shaft 34 is converted into axial displacement power of the steering shaft 16. Thus, the rotational power of the assist motor 30 is converted into axial displacement power of the steering shaft 16 via the drive shaft 34. Specifically, the assist motor 30 is, as an example, a three-phase brushless motor. In particular, in this embodiment, a surface magnet synchronous motor (hereinafter referred to as SPM) is used as an example. The output voltage of the 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. To control the control amount, the steering control device 40 refers to the steering torque Ts input to the steering wheel 12. The steering torque Ts is detected by the torque sensor 50. The torque sensor 50 is a sensor that detects the steering torque Ts according to the degree of twisting of the 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 the vehicle speed sensor 54. The steering control device 40 also refers to the rotation angle θa of the assist motor 30 detected by the 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. The storage device 44 includes an electrically rewritable non-volatile memory and a storage medium such as a disk medium. The storage device 44 stores a steering control program 44a. The steering control device 40 controls the control amount by having the PU 42 execute the steering control program 44a stored in the storage device 44. "Processing performed by the steering control device 40" Figure 2 shows the processing performed by the steering control device 40. The processing shown in Figure 2 is achieved by having the PU 42 repeatedly execute the steering control program 44a, for example, at a predetermined period.

[0013] The target steering torque setting process M10 is a process that calculates the target steering torque Ts*, which is the target value of the steering torque Ts. The steering operation amount calculation process M12 is a process that calculates the steering operation amount Ms, which is the control operation amount where the steering torque Ts is the control amount and the target steering torque Ts* is the target value of the control amount.

[0014] The steering input calculation process M12 includes the PD input input calculation process M12a. The PD input input calculation process M12a is the control input for PD control where the steering torque Ts is the controlled variable and the target steering torque Ts* is the target value of the controlled variable. Specifically, the PD input input Mpd, which is the output value of the PD input input calculation process M12a, is the sum of the output value of the proportional element and the output value of the differential element. Here, the input variable of the proportional element is the difference between the steering torque Ts and the target steering torque Ts*. The input variable of the differential element is the steering torque Ts. In other words, the PD input input calculation process M12a is, as an example, a leading-derivative type controller. Note that the PD input input Mpd is the value converted to the torque of the transmission shaft 14.

[0015] The steering operation amount calculation process M12 includes the open-loop operation amount calculation process M12b. The open-loop operation amount calculation process M12b is a process that calculates the open-loop operation amount Mff, where the target steering torque Ts* is the target value of the controlled amount, based on the target steering torque Ts* as the input variable.

[0016] The steering operation amount calculation process M12 includes a synthesis process M12c. The synthesis process M12c calculates the steering operation amount Ms, which is the output variable of the steering operation amount calculation process M12, based on the input variables: the open-loop operation amount Mff, the PD operation amount Mpd, and the disturbance torque de. In the synthesis process M12c, the value obtained by subtracting the disturbance torque de from the sum of the open-loop operation amount Mff and the PD operation amount Mpd is substituted into the steering operation amount Ms.

[0017] The steering input calculation process M12 includes a disturbance observer M12d. The disturbance observer M12d calculates a disturbance torque de corresponding to the difference between the steering torque assumed by the nominal model and the actual steering torque Ts. However, the disturbance torque de is converted into the torque of the assist motor 30. The output variable of the open-loop input calculation process M12b is, as an example, a variable that shows the output when the target steering torque Ts* is input to the inverse model of the nominal model.

[0018] The axial force calculation process M14 calculates the axial force Taf by adding the steering torque Ts to the steering operation amount Ms. Since the steering torque Ts is the torque applied to the transmission shaft 14, in this embodiment, the axial force Taf is a value obtained by converting the force applied in the axial direction of the steering shaft 16 into the torque applied to the transmission shaft 14.

[0019] The normative model calculation process M20 calculates the target steering equivalent angle θp*, which is the target value of the steering equivalent angle θp, based on the axial force Taf as an input variable. The steering equivalent angle θp is a variable that indicates the steering angle of the steering wheel 20. The steering equivalent angle θp may, for example, be the rotation angle of the drive shaft 34. More specifically, the normative model calculation process M20 calculates the target steering equivalent angle θp* based on the model equation expressed in the following equation (c1).

[0020] Taf = K・θp* + C・θp*' + J・θp*'' …(c1) The model expressed by the above equation (c1) models the value shown by the steering equivalent angle θp when a torque equal to the axial force Taf is input to the transmission shaft 14. In the above equation (c1), the viscosity coefficient C models the friction of the steering device 10. The inertia constant J models the inertia of the steering device 10. The elastic modulus K models the specifications of the suspension and wheel alignment of the vehicle on which the steering device 10 is mounted. This model is not an accurate representation of the actual steering device 10 or the vehicle on which the steering device 10 is mounted, but rather a normative model designed to make the behavior of the steering angle in response to the input ideal. In other words, in this embodiment, the steering feel can be adjusted through the design of the normative model.

[0021] Specifically, in the inertial torque calculation process M22, the viscous term "C・θp*'" and a composite value including the elastic component are subtracted from the axial force Taf. The target angular acceleration αp* (=θp*'') is calculated by dividing the output of the inertial torque calculation process M22 by the inertial constant J in the inertial constant division process M24. The integration process M26 calculates the target angular velocity ωp* (=θp*') based on the target angular acceleration αp* as an input variable. The integration process M28 calculates the target steering equivalent angle θp* based on the target angular velocity ωp* as an input variable.

[0022] The viscosity coefficient multiplication process M30 calculates the viscosity term "C・θp*'" by multiplying the target angular velocity ωp* by the viscosity coefficient C. The angular axial force calculation process M32 calculates the angular axial force AFa, which corresponds to the spring term "K・θp*" in the above-mentioned normative model, based on the target steering equivalent angle θp* as an input variable. The angular axial force calculation process M32 changes the angular axial force AFa according to the target steering equivalent angle θp*, provided that the absolute value of the angular axial force AFa when the absolute value of the target steering equivalent angle θp* is large is greater than or equal to the absolute value of the angular axial force AFa when the absolute value of the target steering equivalent angle θp* is small. However, the sign of the target steering equivalent angle θp* and the sign of the angular axial force AFa are the same.

[0023] Furthermore, in statements such as "change B according to A while satisfying the condition that B when A is large is greater than or equal to B when A is small," "when A is large" and "when A is small" refer to the relative magnitude relationship when comparing the two. For example, "when A is large" corresponds to "when A is the first value," and "when A is small" corresponds to "when A is the second value which is smaller than the first value." Also, the above statement means that, depending on the settings of the first and second values, B when A is the first value may be larger than B when A is the second value. Also, the above statement means that change B according to A so that A when B is large is larger than A when B is small.

[0024] The current axial force calculation process M34 calculates the current axial force AFc, which has a positive correlation with the current flowing through the assist motor 30, based on the q-axis current iq as an input variable. The q-axis current iq is calculated by PU42 based on the input variables iu, iv, iw and rotation angle θa.

[0025] The current axial force calculation process M34 includes the basic axial force calculation process M34a. The basic axial force calculation process M34a is a process that changes the basic axial force according to the q-axis current iq, under the condition that the absolute value of the basic axial force when the absolute value of the q-axis current iq is large is greater than or equal to the basic axial force when the absolute value of the q-axis current iq is small. The current axial force calculation process M34 includes the filter process M34b. The filter process M34b is a process to attenuate the inertial component of the basic axial force. The inertial component is a component that causes the feeling of resistance at the start of the steering wheel 12 turning operation and the feeling of smoothness at the end of the turning operation. The filter process M34b is a process that attenuates the inertial component that is difficult to remove by the above-mentioned normative model.

[0026] Figure 3 shows the Bode plot of the transfer characteristics of the standard model. The solid line in Figure 3 is the Bode plot for the standard model actually used. As can be seen from this Bode plot, depending on the standard model, the effects of the inertial component cannot be sufficiently eliminated, such as a phase lag occurring near the resonant frequency of the steering device 10. This can be avoided by setting the standard model to realize the Bode plot shown by the dashed line in Figure 3. However, in that case, the stability of the control decreases, so this setting is not adopted in this embodiment.

[0027] Returning to Figure 2, the synthesis process M36 calculates the combined axial force AFs based on the output values ​​of the filtering process M34b, which are the current axial force AFc and the angular axial force AFa, as input variables. As an example, the synthesis process M36 may be a weighted average of the current axial force AFc and the angular axial force AFa.

[0028] The non-inertial state variable calculation process M40 is a process that substitutes the sum of the viscosity term and the combined axial force AFs into the non-inertial axial force AFi. The angle manipulation amount calculation process M50 is a process that calculates the angle manipulation amount Mt, which is the control variable for which the steering equivalent angle θp is the control variable and the target steering equivalent angle θp* is the target value of the control variable. The addition process M52 is a process that substitutes the value obtained by adding the axial force Taf to the angle manipulation amount Mt into the required torque Td. The steering equivalent angle θp is calculated by PU42 based on the rotation angle θa as an input variable.

[0029] The conversion process M54 is a process that converts the requested torque Td into a torque command value Tm, which is the torque command value for the assist motor 30, by dividing the requested torque Td by the reduction ratio Km.

[0030] The operation signal generation process M56 generates and outputs the operation signal MSt for the inverter 32, which controls the torque of the assist motor 30 to the torque command value Tm. In practice, the operation signal MSt becomes the operation signal for each arm of each leg of the inverter 32.

[0031] "Details of Target Steering Torque Setting Process M10" The Target Steering Torque Setting Process M10 is a process that sets the target steering torque Ts* based on the non-inertial axial force AFi and vehicle speed SPD as input variables. More specifically, the Target Steering Torque Setting Process M10 includes a process to calculate the estimated lateral acceleration Lae based on the non-inertial axial force AFi and vehicle speed SPD as input variables. PU42 changes the estimated lateral acceleration Lae according to the non-inertial axial force AFi, provided that the absolute value of the estimated lateral acceleration Lae when the absolute value of the non-inertial axial force AFi is large is greater than or equal to the absolute value of the estimated lateral acceleration Lae when the absolute value of the non-inertial axial force AFi is small. This process may, for example, be a process in which the value obtained by multiplying the non-inertial axial force AFi by a coefficient corresponding to the vehicle speed SPD is substituted into the estimated lateral acceleration Lae.

[0032] The target steering torque setting process M10 includes a process for calculating the target steering torque Ts* based on the estimated lateral acceleration Lae as an input variable. Here, PU42 changes the target steering torque Ts* according to the estimated lateral acceleration Lae, provided that the absolute value of the target steering torque Ts* when the absolute value of the estimated lateral acceleration Lae is large is greater than or equal to the absolute value of the target steering torque Ts* when the absolute value of the estimated lateral acceleration Lae is small. The target steering torque setting process M10 may also include a process for setting the magnitude of the target steering torque Ts* to different values ​​for inward steering and reverse steering operations, depending on the steering angle, etc.

[0033] <Operation and Effects of This Embodiment> The PU 42 controls the torque of the assist motor 30 according to the feedback control operation amount, where the steering torque Ts is the controlled amount and the target steering torque Ts* is the target value of the controlled amount. Here, since the steering device 10 has inertia, the torque required to turn the steering wheel 12 is large at the start of the turning operation of the steering wheel 12. For this reason, at the start of the turning operation of the steering wheel 12, the absolute value of the PD operation amount Mpd etc. tends to be larger compared to during the turning operation. For this reason, when setting the target steering torque Ts* according to the feedback control operation amount including the PD operation amount Mpd and disturbance torque de, the influence of the inertia component is reflected in the target steering torque Ts*. That is, for example, at the start of a turning operation, the absolute value of the target steering torque Ts* tends to be set to a large value due to inertia. This is a factor that causes the driver to feel a sense of resistance at the start of a turning operation.

[0034] Thus, when setting the target steering torque Ts* using a quantity that reflects the influence of the inertia component among the steering state variables used in calculations for controlling the torque of the assist motor 30, the steering feel will be affected by the inertia component.

[0035] Therefore, in this embodiment, the target steering torque Ts* is set based on the non-inertial axial force AFi as an input variable. The non-inertial axial force AFi is the sum of the viscous term "C・θp*'" and the composite axial force AFs. Here, the steering state variable constituting the viscous term is a steering state variable that does not include the inertial component. On the other hand, the composite axial force AFs is the sum of the spring term "K・θp*" and the current axial force AFc. Here, the steering state variable constituting the spring term is a steering state variable that does not include the inertial component. Furthermore, the current axial force AFc is a steering state variable in which the frequency component of the inertial component of the basic axial force is attenuated. Therefore, the non-inertial axial force AFi is a state variable in which the inertial component is suppressed.

[0036] Figure 4 shows the MA-MT characteristics of a comparative example of this embodiment, in which the target steering torque Ts* is set based on the axial force Taf as an input variable. Since the axial force Taf is a quantity that includes the PD manipulated amount Mpd and the disturbance torque de, it is a steering state quantity that includes an inertial component. Specifically, the solid line in Figure 4 shows the MA-MT characteristics when the steering frequency is higher compared to the dashed line.

[0037] As shown in Figure 4, in the comparative example, the MA-MT characteristics rotate when the steering frequency increases. In contrast, Figure 5 shows the MA-MT characteristics of this embodiment. As shown in Figure 5, in this embodiment, the MA-MT characteristics do not change even when the steering frequency increases.

[0038] Furthermore, according to this embodiment, the following effects and advantages can be obtained. (1-1) PU42 calculates the non-inertial axial force AFi based on the steering state variables generated in the normative model calculation process M20 as input variables. The steering state variables generated in the normative model calculation process M20 are clearly distinguished from inertial state variables, which are state variables that represent the inertial component, and other state variables. Therefore, the influence of the inertial component on the non-inertial axial force AFi can be effectively suppressed.

[0039] (1-2) PU42 calculated the non-inertial axial force AFi by taking into account the current axial force AFc. The current axial force AFc is the component obtained by attenuating the inertial component in the high-frequency range that cannot be sufficiently attenuated by the normative model calculation process M20 from the output value of the basic axial force calculation process M34a. Therefore, the influence of the inertial component on the non-inertial axial force AFi can be suitably suppressed. In addition, compared to, for example, the case in which the non-inertial axial force AFi is set as the sum of the viscosity term and the spring term, it is easier to reflect information about the road surface condition in the target steering torque Ts*.

[0040] (1-3) The steering input Ms includes the open-loop input Mff and disturbance torque de, which are calculated using the inverse model of the nominal model in the disturbance observer M12d. This allows for rapid compensation of the error between the actual plant and the nominal model using the disturbance torque de.

[0041] Of the steering operation amount Ms, the component other than the operation amount of the feedback control is limited to the open-loop operation amount Mff using the inverse model of the nominal model in the disturbance observer M12d. As a result, compared with the case where an operation amount other than the open-loop operation amount Mff is added to the operation amount of the feedback control, the controllability of the feedback control can be enhanced.

[0042] <Second Embodiment> Hereinafter, the second embodiment will be described with reference to the drawings, centering on the differences from the first embodiment.

[0043] FIG. 6 shows the processing executed by the steering control device 40 according to this embodiment. The processing shown in FIG. 6 is realized by the PU 42 repeatedly executing a steering control program 44a, for example, at a predetermined cycle. In FIG. 6, for the processing corresponding to the processing shown in FIG. 2, the same reference numerals are given for convenience and the description thereof is omitted.

[0044] The non-inertial state quantity calculation process M40a is a process of substituting, into the non-inertial axial force AFi, the value obtained by subtracting the output value of the inertial torque calculation process M22 from the axial force Taf. Here, the output value of the inertial torque calculation process M22 is the amount obtained by subtracting, from the axial force Taf, the viscous term and the combined axial force AFs. Therefore, the output value of the inertial torque calculation process M22 is an inertial state quantity that represents an inertial component. Therefore, the amount obtained by subtracting the output value of the inertial torque calculation process M22 from the axial force Taf is the amount obtained by subtracting the inertial state quantity from the axial force Taf as a steering state quantity including an inertial component.

[0045] Also in the second embodiment described above, effects similar to the effects illustrated in FIG. 5, effects similar to the effects described in (1-1), and effects described in (1-2), (1-3), and (1-4) can be achieved.

[0046] <Third Embodiment> Hereinafter, the third embodiment will be described with reference to the drawings, centering on the differences from the first embodiment.

[0047] FIG. 7 shows the processing executed by the steering control device 40 according to the present embodiment. The processing shown in FIG. 7 is realized by the PU 42 repeatedly executing the steering control program 44a, for example, at a predetermined period. In FIG. 7, for the processing corresponding to the processing shown in FIG. 2, for convenience, the same reference numerals are given and the description thereof is omitted.

[0048] In the controller shown in FIG. 7, the conversion process M54 is a process of converting the axial force Taf into a torque command value Tm, which is a command for the torque of the assist motor 30, by dividing the axial force Taf by the reduction ratio Km.

[0049] On the other hand, the torque estimation process M60 is a process of calculating an estimated torque Te, which is an estimated value of the torque of the assist motor 30, based on the currents iu, iv, iw and the rotation angle θa as input variables.

[0050] The angular velocity calculation process M62 is a process of calculating the first-order time derivative value of the rotation angle θa as an input variable and substituting it into the angular velocity ω. The angular acceleration calculation process M64 is a process of calculating the first-order time derivative value of the angular velocity ω as an input variable and substituting it into the angular acceleration α. The inertia term multiplication process M66 is a process of calculating the inertia torque Tin by multiplying the angular acceleration α by the inertia constant J.

[0051] The non-inertial state quantity calculation process M40b is a process of substituting the value obtained by subtracting the inertia torque Tin from the sum of the estimated torque Te and the steering torque Ts into the non-inertial axial force AFi. Here, the torque of the assist motor 30 includes an inertial component. Therefore, the estimated torque Te is a steering state quantity including an inertial component. On the other hand, the inertia torque Tin is an inertial state quantity representing the inertial component. Therefore, the amount obtained by subtracting the inertia torque Tin from the sum of the estimated torque Te and the steering torque Ts is the amount obtained by subtracting the inertial state quantity from the steering state quantity including the inertial component.

[0052] Also in the third embodiment described above, the effects according to the effects illustrated in FIG. 5, the effects according to the effects described in (1-1), and the effects described in (1-3) and (1-4) can be achieved.

[0053] <Fourth Embodiment> The fourth embodiment will be described below, focusing on the differences from the third embodiment, with reference to the drawings.

[0054] "Prerequisite Configuration" Figure 8 shows the configuration of the steering control system according to this embodiment. In Figure 8, the same reference numerals are used for members corresponding to those shown in Figure 1 for convenience.

[0055] As shown in Figure 8, 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 that engages with the steering shaft 16. In this embodiment, the output shaft 14b may be omitted.

[0056] A reaction motor 70 is provided on the input shaft 14a. The reaction motor 70 is a motor that applies a reaction force to the steering wheel 12, which is a torque in the opposite direction to the torque input by the driver. The reaction motor 70 is, for example, a three-phase brushless motor. The output voltage of the inverter 72 is applied to the terminals of the reaction motor 70.

[0057] Torque from the steering motor 80 is applied to the steering shaft 16 via the drive shaft 34. The steering motor 80 is, for example, a three-phase brushless motor. The output voltage of the inverter 82 is applied to the terminals of the steering motor 80.

[0058] 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 a control quantity of the controlled object. The steering control device 40 also operates the inverter 82 to control the steering angle of the steering wheels 20, which is a control quantity of the controlled object.

[0059] The steering control device 40 refers to the rotation angle θb of the reaction force motor 70, detected by the rotation angle sensor 90, in order to control the reaction force, which is a control variable. The steering control device 40 also refers to the currents ius, ivs, and iws flowing through the reaction force motor 70 in order to control the reaction force. The steering control device 40 also refers to the rotation angle θc of the steering motor 80, detected by the rotation angle sensor 92, in order to control the steering angle, which is a control variable. The steering control device 40 also refers to the currents iut, ivt, and iwt flowing through the steering motor 80 in order to control the steering angle.

[0060] "Processing performed by the steering control device 40" Figure 9 shows the processing performed by the steering control device 40. In other words, Figure 9 shows the processing performed by the steering control device 40 when the transmission of power from the steering wheel 12 to the steering wheels 20 is interrupted. For convenience, the same reference numerals are used in Figure 9 for the processing corresponding to the processing shown in Figure 7.

[0061] As shown in Figure 9, in this embodiment, the axial force Taf is converted to a reaction torque command value Tr, which is the command value of the torque of the reaction motor 70, in the conversion process M70. The steering-side operation signal generation process M72 is a process that operates the inverter 72 based on the reaction torque command value Tr as an input variable. Specifically, the steering-side operation signal generation process M72 includes a process to calculate a control variable where the torque of the reaction motor 70 is the control variable and the value obtained by converting the reaction torque command value Tr to the torque of the reaction motor 70 is the target value of the control variable. The rotation angle θb and the currents ius, ivs, and iws are referenced in the calculation of the control variable. The steering-side operation signal generation process M72 also includes a process to operate the inverter 72 according to the said control variable. Figure 9 shows the operation signal MSs of the inverter 72. In reality, the operation signal MSs is a separate operation signal for each switching element of the inverter 72.

[0062] The target steering equivalent angle setting process M80 is a process that sets the target steering equivalent angle θp* based on the steering angle θs and vehicle speed SPD as input variables. This process includes, as an example, a process to change the target steering equivalent angle θp* according to the steering angle θs, under the condition that the absolute value of the target steering equivalent angle θp* when the absolute value of the steering angle θs is large is greater than or equal to the absolute value of the target steering equivalent angle θp* when the absolute value of the steering angle θs is small.

[0063] The steering control amount calculation process M82 calculates the steering torque command value Tt as an input variable for feedback control, where the steering equivalent angle θp is the controlled variable and the target steering equivalent angle θp* is the target value of the controlled variable. The steering equivalent angle θp is calculated by PU42 based on the rotation angle θc as an input variable.

[0064] The steering-side operation signal generation process M84 is a process that operates the inverter 82 when a steering torque command value Tt is input. The steering-side operation signal generation process M84 includes a process to calculate a control amount where the torque of the steering motor 80 is the control amount and the value obtained by converting the steering torque command value Tt to the torque of the steering motor 80 is the target value of the control amount. The rotation angle θc and currents iut, ivt, and iwt are referenced in the calculation of the control amount. The steering-side operation signal generation process M84 also includes a process to operate the inverter 82 according to the said control amount. Figure 9 shows the operation signal MSt of the inverter 82. In reality, the operation signal MSt is a separate operation signal for each switching element of the inverter 82.

[0065] The non-inertial state quantity calculation process M40c is a process that substitutes the value obtained by subtracting the inertial torque Tin from the sum of the steering torque command value Tt and the steering torque Ts into the non-inertial axial force AFi. <Operation and Effects of the Fourth Embodiment> For example, at the start of a turning operation of the steering wheel 12, the torque required to steer the steering wheel 20 becomes larger compared to during the turning operation due to the inertia of the steering device 10. This means that at the start of a turning operation, the absolute value of the steering torque command value Tt is larger compared to during the turning operation. In this way, the steering torque command value Tt is a steering state quantity that expresses the inertial component.

[0066] Therefore, PU42 substitutes the amount obtained by subtracting the inertial torque Tin from the sum of the steering torque command value Tt and the steering torque Ts into the non-inertial axial force AFi. This suppresses the reflection of inertia in the target steering torque Ts*.

[0067] <Other Embodiments> This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0068] "Regarding the Feedback Variable Calculation Process" - It is not mandatory for the feedback variable calculation process to consist of the PD variable calculation process M12a and the disturbance observer M12d. The feedback variable calculation process may consist of, for example, only the PD variable calculation process M12a. The classical controllers included in the feedback variable calculation process are not limited to proportional and differential elements. For example, they may include proportional, differential, and integral elements.

[0069] Regarding control where the target steering torque is the controlled variable: It is not mandatory that the input variable for the calculation process of the manipulated variable in open-loop control included in control where the target steering torque is the controlled variable be the target steering torque Ts*. For example, the input variable for the calculation process of the manipulated variable in open-loop control may be the rotation angle, and the calculation process may be the process for calculating the inertia torque Tin mentioned above.

[0070] - It is not mandatory that the control variable whose target steering torque is the controlled variable is the sum of the feedback control variable and the open-loop control variable Mff. The control variable whose target steering torque is the controlled variable may be equal to the feedback control variable.

[0071] "Regarding suppression state variables" (a) Regarding state variables with the inertial component subtracted: Figure 6 shows an example where the input variable of the target steering torque setting process M10 is the amount obtained by subtracting the output value of the inertial torque calculation process M22 from the axial force Taf, which is a steering state variable that includes the inertial component. However, this is not the only steering state variable that includes the inertial component. For example, the steering state variable that includes the inertial component may be the steering operation amount Ms. In other words, the input variable of the target steering torque setting process M10 may be the amount obtained by subtracting the output value of the inertial torque calculation process M22 from the steering operation amount Ms.

[0072] In controllers using a normative model, it is not mandatory to calculate the inertial component to be subtracted using the normative model. The inertial component to be subtracted may be the inertial torque Tin shown in Figure 7. In that case, the "state variable with the inertial component subtracted" may be, for example, the amount obtained by subtracting the inertial torque Tin from the axial force Taf. In other words, the input variable for the target steering torque setting process M10 may be the amount obtained by subtracting the inertial torque Tin from the axial force Taf.

[0073] Figure 7 shows an example where the input variable for the target steering torque setting process M10 is the sum of the estimated torque Te and the steering torque Ts minus the inertial torque Tin, but it is not limited to this. For example, the steering operation amount Ms may be used instead of the estimated torque Te.

[0074] (b) Regarding quantities that include non-inertial state variables and do not include inertial state variables: The quantity that includes non-inertial state variables and does not include inertial state variables, as a suppression state variable, is not limited to the sum of the output value of the viscosity coefficient multiplication process M30 and the output value of the synthesis process M36 as exemplified in Figure 2. The quantity that includes non-inertial state variables and does not include inertial state variables may be, for example, the sum of the output value of the viscosity coefficient multiplication process M30 and the output value of the angular axial force calculation process M32.

[0075] Furthermore, as illustrated in the example "Regarding control where the target steering torque is the controlled variable," if the open-loop manipulated variable Mff includes the inertial torque Tin, the variable that includes non-inertial state variables but does not include inertial state variables may be the manipulated variable for feedback control.

[0076] "Regarding the controller" (a) Regarding the controller of the electric power steering system: In Figure 2 or Figure 6, it is not mandatory to calculate the required torque Td according to the sum of the angle operation amount Mt and the steering operation amount Ms. For example, the angle operation amount Mt may be the required torque Td.

[0077] (b) Controller for steer-by-wire steering system: A controller utilizing a normative model may be applied to the steer-by-wire steering system. In this case, the controller of the steering system 10 should be configured to include processing for feeding back state variables on the steering wheel 20 side to the steering wheel 12. This can be achieved, for example, by setting the reaction torque command value Tr to have a positive correlation with the torque of the steering motor 80. In this case, since inertia is reflected in the torque of the steering motor 80, it is desirable to select a steering state variable in which the influence of the inertial component is suppressed as the input variable for the target steering torque setting process M10. Furthermore, the above-mentioned feedback processing may include processing to superimpose a torque on the reaction torque command value Tr that prevents the absolute value of the difference between the angle obtained by converting the steering angle of the steering wheel 20 to a steering angle and the actual steering angle from becoming even larger when the absolute value of the difference is large. In this case, when the absolute value of the above difference becomes large due to the influence of inertia, a torque that prevents the absolute value from becoming even larger is superimposed on the reaction torque command value Tr. As a result, the reaction torque command value Tr reflects inertia, so it is desirable to select a steering state quantity in which the influence of the inertia component is suppressed as the input variable for the target steering torque setting process M10. The torque corresponding to the absolute value of the difference between the converted angle and the actual steering angle corresponds to the torque that takes into account the torque required to steer the steering wheel 20.

[0078] "Regarding the motor" - In the above embodiment, an example was shown where the assist motor 30 is an SPM, but it is not limited to this. The assist motor 30 may be, for example, an embedded magnet synchronous motor. In that case, the input variables of the current axial force calculation process M34 may be the d-axis current and the q-axis current. Alternatively, the input variables of the current axial force calculation process M34 may be the torque of the assist motor 30 estimated from the d-axis current and the q-axis current.

[0079] "Regarding the steering control device" The steering control device is not limited to one that performs various processes using a PU. For example, it may be equipped with a dedicated hardware circuit such as an ASIC that performs at least a part of the processes performed in the above embodiment. That is, the steering control device may be equipped with any of the following processing circuits (a) to (c): (a) A processing circuit comprising a processing unit that performs 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 unit and a program storage device that perform a part of the above processes according to a program, and a dedicated hardware circuit that performs the remaining processes. (c) A processing circuit equipped with a dedicated hardware circuit that performs all of the above processes. Here, there may be multiple software execution devices equipped with processing units and program storage devices, or multiple dedicated hardware circuits.

[0080] Regarding the entity that executes the processes: It is not required that the entity that executes each of the above processes be a single control device, nor is it required that all of the executing entities be installed in the vehicle.

[0081] <Note> The steering control device wherein the feedback control variable calculation process includes a disturbance observer, the input variable of the control variable calculation process is a control variable whose control variable is the steering torque, and the component other than the feedback control variable included in the control variable whose control variable is the steering torque is limited to the open-loop control variable using the inverse model of the nominal model in the disturbance observer.

Claims

1. A steering control device in which a steering device is the target of control, configured to perform a target steering torque setting process, a feedback control amount calculation process, and an operation process, wherein the target steering torque setting process is a process of setting a target steering torque which is a target value of the steering torque, the steering torque is a torque input to an operation unit, the operation unit is a member in which the driver inputs a torque according to the driver's intention to steer, the feedback control amount calculation process is a process of calculating a feedback control amount whose detected value of the steering torque is the control amount, the operation process is a process of operating the torque of a motor mounted on the steering device according to the operation amount, the target steering torque setting process is a process of setting the target steering torque based on a suppression state amount as an input variable, and the suppression state amount is a state amount in which the inertia component of the steering state amount used for calculations for operating the torque of the motor is suppressed.

2. The steering control device according to claim 1, wherein the steering state quantity includes an inertial state quantity which is a state quantity that represents the inertial component and a non-inertial state quantity which is different from the inertial state quantity, and the suppression state quantity includes the non-inertial state quantity but does not include the inertial state quantity.

3. The steering control device according to claim 2, wherein the operation process includes a target angle calculation process, the target angle calculation process is a process of setting a target angle for the steering device in accordance with a normative model based on the operation amount as an input variable, the operation process is a process of operating the torque of the motor in accordance with the operation amount of feedback control, the target angle being the target value of the controlled amount, the normative model having an inertia term and a non-inertia term, and the suppression state amount includes the steering state amount constituting the non-inertia term without including the steering state amount constituting the inertia term in the normative model.

4. The steering control device according to claim 3, wherein the non-inertial term includes a viscous term which is a quantity proportional to the steering speed and a spring term which depends on the angle of the steering device, and the suppression state quantity is a quantity corresponding to the sum of the steering state quantity which constitutes the viscous term and the steering state quantity which constitutes the spring term.

5. The steering control device according to claim 1, wherein the steering state quantity includes an inertial state quantity which is a state quantity that represents the inertial component, and the suppression state quantity is the amount obtained by subtracting the inertial state quantity from the steering state quantity which includes the inertial component.

6. The steering control device according to claim 5, wherein the operation process includes a target angle calculation process, the target angle calculation process is a process of setting a target angle for the steering device in accordance with a normative model based on the operation amount as an input variable, the operation process is a process of operating the torque of the motor in accordance with the operation amount of feedback control, the normative model has an inertia term and a non-inertia term, and the suppression state amount is an amount obtained by subtracting the steering state amount constituting the inertia term from the steering state amount which includes the inertia component.

7. The steering control device according to claim 5, wherein the suppression state quantity is the value obtained by subtracting the value of the inertia estimation variable from the value of the torque variable, the torque variable is a variable indicating the torque of the motor, and the inertia estimation variable is a variable indicating an estimated value of the inertia torque of the steering device.

8. The steering control device according to claim 1, wherein the motor is configured to steer the steering wheels.

9. The steering control device according to claim 1, wherein the motor is configured to provide a reaction force to the operation of the control unit by the driver, and the target steering torque setting process includes a process of setting the target steering torque taking into account the torque required for steering the steering wheels.

10. A steering control method in which a steering device is the object of control, comprising: execution of a target steering torque setting process; execution of a feedback operation amount calculation process; and execution of an operation process, wherein the target steering torque setting process is a process of setting a target steering torque which is a target value of the steering torque; the steering torque is a torque input to an operation unit; the operation unit is a member in which the driver inputs a torque according to the driver's intention to steer; the feedback operation amount calculation process is a process of calculating an operation amount for feedback control in which the detected value of the steering torque is the control amount; the operation process is a process of operating the torque of a motor mounted on the steering device according to the operation amount; the target steering torque setting process is a process of setting the target steering torque based on a suppression state amount as an input variable; and the suppression state amount is a state amount in which the inertia component of the steering state amount used for calculations for operating the torque of the motor is suppressed.

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