Steering control device

Abstract

To provide a steering control device that can prevent a steering system from being unstable.SOLUTION: PU assigns a value obtained by subtracting axial force F from an assist amount Ta to target reaction force torque Ts. PU controls torque of a reaction force motor in accordance with the target reaction force torque Ts. PU calculates the assist amount Ta by using a first damping correction amount negatively correlated with steering angular speed. PU calculates the axial force F by using a second damping correction amount negatively correlated with the steering angular speed.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] For example, the following Patent Document 1 describes a steering control device installed in a steer-by-wire system. This control device sets a steering force, which is a force in the direction in which the driver steers the steering wheel, and an axial force. The device then controls the torque of a motor that applies a reaction force to the steering wheel according to a value obtained by subtracting the axial force from the steering force. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-160308 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the inventors have found that in situations where the torque of the motor is large, the steering system becomes unstable, for example, causing the steering wheel to vibrate. [Means for solving the problem]

[0005] Means for solving the above problems and their effects will be described below. 1. A steering control device which has a steering system to be controlled, the steering system including a reaction motor which applies a steering reaction force to a steering shaft, and a steering motor which steers the steered wheels with power transmission from the steering shaft cut off, and is configured to execute an assist amount setting process, an axial force setting process, and a reaction force applying process, wherein the assist amount setting process is a process which sets an assist amount which is an amount which assists a driver in rotating the steering shaft while using an output value of a first damping process, the axial force setting process is a process which sets an axial force which is a force which resists the rotation operation of the steering shaft by the driver while using an output value of a second damping process, the reaction force applying process is a process which operates the reaction force motor using an input value obtained by subtracting the axial force from the assist amount, the first damping process is a process which outputs a first damping correction amount which is correlated with a steering angular velocity, and the second damping process is a process which outputs a second damping correction amount which is positively correlated with the steering angular velocity.

[0006] In the above configuration, since the second damping process is newly provided, it is possible to suppress the steering system from becoming unstable by using the second damping correction amount. 2. A steering control device as described in 1 above, configured to execute a second gain adjustment process that adjusts a second gain, which is the gain of the second damping process, depending on the value of a torque correlation variable, and the torque correlation variable is a variable that has a correlation with the torque of the reaction motor.

[0007] The torque correlation coefficient has a positive correlation with the torque of the reaction motor and the steering torque, which is the torque input by the driver to the steering shaft. The situation in which the steering system becomes unstable is likely to occur when the absolute value of the torque of the reaction motor is large or the absolute value of the steering torque is excessively large. Therefore, in the above configuration, the gain of the second damping process can be adjusted according to the situation by grasping the situation in which the steering system is likely to become unstable using the torque correlation coefficient. Therefore, an appropriate gain can be set to suppress the steering system from becoming unstable.

[0008] 3. The steering control device according to claim 2, wherein the second gain adjustment process adjusts the second gain in accordance with the vehicle speed in addition to the value of the torque correlation variable. In the above configuration, the second gain is set according to the vehicle speed, which makes it possible to set a more appropriate second gain according to a situation in which a decrease in stability is a concern, compared to a case in which the second gain is set without reference to the vehicle speed.

[0009] 4. A steering control device described in any one of 1 to 3 above, wherein the assist amount setting process is a process for setting the assist amount using output values ​​of a plurality of compensation processes including the first damping process, and is configured to execute a compensation gain adjustment process for adjusting a compensation gain, which is the gain of at least one of the plurality of compensation processes, depending on the value of a torque correlation variable, and the torque correlation variable is a variable that is correlated with the torque of the reaction force motor.

[0010] The torque correlation coefficient has a positive correlation with the torque of the reaction motor and the steering torque, which is the torque input by the driver to the steering shaft. The situation in which the steering system becomes unstable is likely to occur when the absolute value of the torque of the reaction motor is large or the absolute value of the steering torque is excessively large. Therefore, in the above configuration, the torque correlation coefficient is used to grasp the situation in which the steering system is likely to become unstable, and the gain of the compensation process can be adjusted according to the situation. Therefore, the output of the compensation process can be adjusted to an appropriate value according to the situation in which a decrease in stability is concerned.

[0011] 5. The steering control device according to claim 4, wherein the compensation gain adjustment process adjusts the compensation gain in response to the vehicle speed in addition to the value of the torque correlation variable. In the above configuration, the compensation gain is set according to the vehicle speed, which makes it possible to set a more appropriate compensation gain according to a situation in which a decrease in stability is a concern, compared to a case in which the compensation gain is set without reference to the vehicle speed.

[0012] 6. The steering control device according to any one of 2 to 5 above, wherein the torque correlation variable is a steering torque. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing a configuration of a steering system according to an embodiment. [Diagram 2] 2 is a block diagram showing a process executed by a control device shown in FIG. 1. [Diagram 3] 2 is a block diagram showing a process executed by a control device shown in FIG. 1. [Figure 4] 2 is a block diagram showing a process executed by a control device shown in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment will be described with reference to the drawings. "Prerequisite configuration" A vehicle steering device 10 shown in FIG. 1 is a steer-by-wire type device. The steering device 10 includes a steering wheel 12, a steering shaft 14, a reaction force actuator 20, and a turning actuator 30. The steering shaft 14 is connected to the steering wheel 12. The reaction force actuator 20 is an actuator that applies a force that resists the force with which the driver operates the steering wheel 12. The reaction force actuator 20 includes a reaction force motor 22, a reaction force inverter 24, and a reaction force reduction mechanism 26. The reaction force motor 22 applies a steering reaction force, which is a force that resists steering, to the steering wheel 12 via the steering shaft 14. The reaction force motor 22 is connected to the steering shaft 14 via the reaction force reduction mechanism 26. As an example, a three-phase synchronous motor is used for the reaction force motor 22. The reaction force reduction mechanism 26 is, for example, a worm and wheel.

[0015] The steering actuator 30 is an actuator used to steer the steered wheels 34 in accordance with the driver's steering intention indicated by the driver's operation of the steering wheel 12. The steering actuator 30 comprises a rack shaft 32, a steering motor 42, a steering inverter 44, a steering transmission mechanism 46, and a conversion mechanism 48. As an example, a three-phase surface permanent magnet synchronous motor (SPM) is adopted for the steering motor 42. The steering transmission mechanism 46 is composed of a belt transmission mechanism. The steering transmission mechanism 46 transmits the rotational power of the steering motor 42 to the conversion mechanism 48. The conversion mechanism 48 converts the transmitted rotational power into displacement power in the axial direction of the rack shaft 32. The axial displacement of the rack shaft 32 causes the steered wheels 34 to be turned.

[0016] The steering control device 50 includes a PU 52 and a storage device 54. The PU 52 is a software processing device such as a CPU, a GPU, or a TPU. The storage device 54 may be an electrically non-rewritable non-volatile memory. The storage device 54 may also be an electrically rewritable non-volatile memory or a storage medium such as a disk medium. The steering control device 50 controls a control target by the PU 52 executing a program stored in the storage device 54.

[0017] The control objects of the steering control device 50 are the steering wheel 12 and the steered wheels 34. That is, the steering control device 50 controls the steering reaction force that resists the steering by the driver, which is the control amount of the steering wheel 12 as the control object. The steering control device 50 also controls the steering angle, which is the control amount of the steered wheels 34 as the control object. The steering angle is the turning angle of the tires as the steered wheels 34.

[0018] The steering control device 50 refers to the steering torque Th detected by the torque sensor 60 in order to control the control amount. The steering torque Th is the torque applied to the steering shaft 14 by the driver through the operation of the steering wheel 12. The steering control device 50 refers to the rotation angle θa, which is the angle of the rotation shaft of the reaction force motor 22, detected by the steering side rotation angle sensor 62 in order to control the control amount. The steering control device 50 also refers to the currents ius, ivs, iws flowing through the reaction force motor 22 in order to control the control amount. The currents ius, ivs, iws may be detected as the voltage drop amount of a shunt resistor provided in each leg of the reaction force inverter 24, for example. The steering control device 50 refers to the rotation angle θb, which is the angle of the rotation shaft of the steering motor 42, detected by the steering side rotation angle sensor 64 in order to control the control amount. The steering control device 50 also refers to the currents iut, ivt, iwt flowing through the steering motor 42 in order to control the control amount. The currents iut, ivt, iwt may be detected, for example, as voltage drop amounts of shunt resistors provided in the respective legs of the steering inverter 44. The steering control device 50 refers to the vehicle speed V detected by the vehicle speed sensor 66.

[0019] "Control Overview" Fig. 2 shows the process executed by the steering control device 50. The process shown in Fig. 2 is realized by the PU 52 repeatedly executing a program stored in the storage device 54, for example, at a predetermined interval.

[0020] The steering angle calculation process M10 includes a process of converting the rotation angle θa into an integrated angle including a range exceeding 360 degrees, for example, by counting the number of rotations of the reaction force motor 22 from a steering neutral position, which is the position of the steering wheel 12 when the vehicle is moving straight. The steering angle calculation process M10 includes a process of multiplying the integrated angle obtained by conversion by a conversion coefficient based on the rotation speed ratio of the reaction force reduction mechanism 26 to calculate the steering angle θs.

[0021] The turning equivalent angle calculation process M12 includes a process of converting the rotation angle θb into an integrated angle including a range exceeding 360 degrees, for example, by counting the number of rotations of the steering motor 42 from the rack neutral position, which is the position of the rack shaft 32 when the vehicle is traveling straight. The turning equivalent angle calculation process M12 includes a process of multiplying the integrated angle obtained by conversion by a conversion coefficient according to the reduction ratio of the turning transmission mechanism 46 and the lead of the conversion mechanism 48, etc., to calculate the turning equivalent angle θp according to the turning angle of the steered wheels 34. The turning equivalent angle θp is an amount proportional to the turning angle. Note that, as an example, the turning equivalent angle θp is positive when it is an angle to the right of the rack neutral position, and negative when it is an angle to the left of the rack neutral position.

[0022] The target steering equivalent angle calculation process M18 is a process in which the steering angle θs and the vehicle speed V are input and the target steering equivalent angle θp* is output. The target steering equivalent angle calculation process M18 may be, for example, a process that calculates the target steering equivalent angle θp* to a value with the same sign as the steering angle θs. The target steering equivalent angle calculation process M18 may be a process that changes the target steering equivalent angle θp* according to the steering angle θs under the condition that the target steering equivalent angle θp* when the absolute value of the steering angle θs is large is equal to or larger than the target steering equivalent angle θp* when the absolute value of the steering angle θs is small.

[0023] In the description "changing B according to A under the condition that when A is large, B is equal to or larger than B when A is small," the case where A is large and the case where A is small refer to the relative relationship of size when comparing the two. For example, "when A is large" corresponds to the case where "A is a first value," and "when A is small" corresponds to the case where "A is a second value smaller than the first value." And according to the above description, depending on the settings of the first value and the second value, B when A is the first value may be larger than B when A is the second value.

[0024] The assist amount setting process M20 is a process in which the steering torque Th and the vehicle speed V are input and the assist amount Ta is output. The assist amount Ta is an amount in the same direction as the steering direction of the driver. The magnitude of the assist amount Ta is set to a large value when the force assisting the steering by the driver is to be increased.

[0025] The axial force setting process M22 is a process in which the vehicle speed V, the q-axis current iqt of the steering motor 42, and the target steering equivalent angle θp* are input, and the axial force F is output. The axial force F is a value that expresses the force acting on the rack shaft 32 through the steering wheels 34 by control. However, the axial force F does not necessarily have to be intended to estimate the force acting on the rack shaft 32 with high accuracy. The axial force F may be, for example, a virtually determined force acting on the rack shaft 32. The axial force F is converted into a torque applied to the steering shaft 14. That is, the axial force F is converted into a torque applied to the steering shaft 14 when it is assumed that the power transmission between the steering wheels 34 and the steering shaft 14 is possible. The axial force F is an amount that acts in the opposite direction to the steering direction of the driver. The q-axis current iqt is calculated by the PU 52 according to the steering equivalent angle θp and the currents iut, ivt, and iwt.

[0026] The subtraction process M24 is a process of substituting a value obtained by subtracting the axial force F from the assist amount Ta into the target reaction torque Ts. The target reaction torque Ts is a target value of the torque that the reaction motor 22 applies to the steering shaft 14.

[0027] The reaction force operation signal generation process M26 is a process for generating an operation signal MSs for the reaction force inverter 24 in order to control the torque of the reaction force motor 22 so that the torque applied to the steering shaft 14 becomes the target reaction force torque Ts. More specifically, the reaction force operation signal generation process M26 includes a process for converting the target reaction force torque Ts into a target torque of the reaction force motor 22. The reaction force operation signal generation process M26 also includes a process for calculating an operation signal MSs for the reaction force inverter 24 in order to make the current flowing through the reaction force motor 22 approach a current determined from the target torque by current feedback control. Note that the operation signal MSs is actually an operation signal for each of the six switching elements of the reaction force inverter 24. The target reaction force torque Ts is usually an amount with an opposite sign to the assist amount Ta. This is because the absolute value of the axial force F is usually greater than the absolute value of the assist amount Ta.

[0028] The steering feedback process M30 is a process for substituting the operation amount of feedback control, in which the steering equivalent angle θp is the control amount and the target steering equivalent angle θp* is the target value of the control amount, into the target steering torque Tt*. The target steering torque Tt* has a constant ratio with the torque of the steering motor 42.

[0029] The steering operation signal generation process M32 is a process for generating an operation signal MSt for the steering inverter 44 in order to control the torque of the steering motor 42 so that the torque of the steering motor 42 becomes a value having a constant ratio with respect to the target steering torque Tt*. In particular, the steering operation signal generation process M32 includes a process for converting the target steering torque Tt* into a target torque of the steering motor 42. The steering operation signal generation process M32 also includes a process for calculating an operation signal MSt for the steering inverter 44 in order to bring the current flowing through the steering motor 42 close to a current determined from the target torque by current feedback control. Note that the operation signal MSt is actually an operation signal for each of the six switching elements of the steering inverter 44.

[0030] "Assist amount setting process" FIG. 3 shows details of the assist amount setting process M20. The phase lag compensation process M40 is a process for delaying the phase of the steering torque Th. This may be a process for the purpose of performing phase compensation on the steering torque Th in order to adjust the frequency characteristic of the phase difference between both sides of a torsion bar provided in the torque sensor 60, for example. The phase-compensated steering torque Th, which is the output value of the phase lag compensation process M40, is the steering torque Thr. The phase lag compensation process M40 includes a filter process M42 and a filter coefficient setting process M44.

[0031] The filter processing M42 includes a phase lag filter and a low-pass filter. The transfer function of the phase lag filter is "(1+α·T1·s) / (1+T1·s)". The transfer function of the low-pass filter is "1 / (1+T2·s)". The steering torque Thr is the value obtained by processing the steering torque Th through the phase lag filter and the low-pass filter.

[0032] The filter coefficient setting process M44 is a process for setting the filter coefficients α and T1 of the phase lag filter and the filter coefficient T2 of the low-pass filter. The filter coefficient setting process M44 is a process in which the assist gradient R and the vehicle speed V described below are input and the filter coefficients α, T1, and T2 are output.

[0033] The basic assist amount setting process M46 is a process in which the steering torque Thr and the vehicle speed V are input and the basic assist amount Tab is output. The basic assist amount setting process M46 is a process in which the basic assist amount Tab is set to a value having a positive correlation with the steering torque Thr. This process may be, for example, a process in which the PU 52 calculates the basic assist amount Tab from a map in a state in which map data is pre-stored in the storage device 54. The map data is data in which the steering torque Thr and the vehicle speed V are input variables and the basic assist amount Tab is an output variable.

[0034] The map data is a set of data consisting of discrete values ​​of input variables and values ​​of output variables corresponding to each of the input variable values. The map calculation may be a process in which, when the value of an input variable matches any of the values ​​of the input variables in the map data, the value of the output variable in the corresponding map data is used as the calculation result. The map calculation may be a process in which, when the value of an input variable does not match any of the values ​​of the input variables in the map data, the value obtained by interpolating the values ​​of multiple output variables included in the map data is used as the calculation result. Alternatively, the map calculation may be a process in which, when the value of an input variable does not match any of the values ​​of the input variables in the map data, the value of the output variable in the map data that corresponds to the closest value among the values ​​of multiple input variables included in the map data is used as the calculation result.

[0035] The basic assist amount setting process M46 includes a process of calculating and outputting an assist gradient R. The assist gradient R indicates the ratio of the change in the basic assist amount Tab to the change in the steering torque Thr.

[0036] The phase lead compensation process M50 is a process for leading the phase of the assist amount Ta. For example, the purpose of this may be to perform phase compensation on the assist amount Ta in order to adjust the response delay of the change in the steering wheel 12 in response to the change in the steering torque Th. The phase lead compensation process M50 includes a differential calculation M52, a gain setting process M54, and a multiplication process M56.

[0037] The differential calculation M52 is a process for calculating a first-order time differential value dTh of the steering torque Th. The gain setting process M54 is a process in which the assist gradient R and the vehicle speed V are input and the gain Gad is output. The gain setting process M54 may be a process for map-calculating the gain Gad in a state in which map data is pre-stored in the storage device 54. This map data is data in which the assist gradient R and the vehicle speed V are input variables and the gain Gad is an output variable.

[0038] The multiplication process M56 is a process of multiplying the time differential value dTh by a gain Gad. The product of the time differential value dTh and the gain Gad is the lead compensation amount Tad as the output of the phase lead compensation process M50.

[0039] The hysteresis processing M60 is a processing for calculating a hysteresis correction amount Thys. The hysteresis correction amount Thys is an amount for making the assist amount Ta different between turning back and turning the steering wheel 12. The hysteresis processing M60 is a processing in which the steering angle θs and the vehicle speed V are input and the hysteresis correction amount Thys is output. As an example, the hysteresis processing M60 is a processing in which the PU 52 performs map calculation of the hysteresis correction amount Thys in a state in which map data is stored in the storage device 54 in advance. This map data is data in which the steering angle θs and the vehicle speed are input variables and the hysteresis correction amount Thys is an output variable.

[0040] The first damping process M70 is a process for calculating a first damping correction amount Tdampa0 that has a negative correlation with the rotation speed of the steering wheel 12. The first damping correction amount Tdampa0 is a correction amount for applying viscous resistance to the operation of the steering wheel 12 through control. The first damping process M70 includes a differential calculation M72 and a first correction amount setting process M74.

[0041] The differential calculation M72 is a process for calculating a first-order time differential value of the steering angle θs. The time differential value is the steering speed ωs. The first correction amount setting process M74 is a process for calculating a first damping correction amount Tdampa0 having a negative correlation with the steering speed ωs. The first damping correction amount Tdampa0 has a dimension of torque. The first correction amount setting process M74 may be a process for map-calculating the first damping correction amount Tdampa0 by the PU 52 in a state in which map data is stored in advance in the storage device 54. The map data is data in which the steering speed ωs is an input variable and the first damping correction amount Tdampa0 is an output variable.

[0042] The first gain adjustment process M76 is a process in which the steering torque Th and the vehicle speed V are input and the first gain G1 is output. As an example, the first gain adjustment process M76 is a process in which the PU 52 performs map calculation of the first gain G1 in a state in which map data is pre-stored in the storage device 54. Here, the map data is data in which the steering torque Th and the vehicle speed V are input variables and the first gain G1 is an output variable.

[0043] The multiplication process M78 is a process of multiplying the first damping correction amount Tdampa0 by the first gain G1 and substituting the resulting value for the first damping correction amount Tdampa. The steering return process M80 is a process for calculating a return correction amount Trv. The return correction amount Trv is a correction amount for returning the steering wheel 12 to the neutral position. The return correction amount Trv has a torque dimension. The steering return process M80 includes a differential calculation M81, a target steering speed setting process M82, a deviation calculation process M83, a base compensation amount calculation process M84, a speed gain setting process M85, a torque gain setting process M86, and a multiplication process M87.

[0044] The differential calculation M81 is a process in which the steering angle θs is input and the steering speed ωs, which is the first-order time differential value, is output. The target steering speed setting process M82 is a process in which the steering angle θs and the vehicle speed V are input and the target steering speed ωs* is output. The target steering speed setting process M82 may be a process in which the PU 52 performs map calculation of the target steering speed ωs* in a state in which map data is stored in advance in the storage device 54. The map data is data in which the steering angle θs and the vehicle speed V are input variables and the target steering speed ωs* is an output variable. The deviation calculation process M83 is a process in which the deviation Δω between the target steering speed ωs* and the steering speed ωs is calculated. The base compensation amount calculation process M84 is a process in which the deviation Δω is input and the base compensation amount Trvb is calculated. The speed gain setting process M85 is a process in which the vehicle speed V is input and the speed gain Gv is output. The speed gain setting process M85 may be a process in which the PU 52 performs map calculation of the speed gain Gv in a state where map data is stored in advance in the storage device 54. The map data is data in which the vehicle speed V is an input variable and the speed gain Gv is an output variable. The torque gain setting process M86 is a process in which the steering torque Th is an input variable and the torque gain Gt is an output variable. The torque gain setting process M86 may be a process in which the PU 52 performs map calculation of the torque gain Gt in a state where map data is stored in advance in the storage device 54. The map data is data in which the steering torque Th is an input variable and the torque gain Gt is an output variable. The multiplication process M87 is a process in which a value obtained by multiplying the base compensation amount Trvb by the speed gain Gv and the torque gain Gt is assigned to the return correction amount Trv.

[0045] The road information processing M90 is a processing for superimposing information on the road surface reaction force, which is a force applied from the road surface to the steered wheels 34, on the steering wheel 12. The road information processing M90 includes a band pass filter M92, a gain multiplication processing M94, and a filter coefficient setting processing M96. The q-axis current iqt is input to the band pass filter M92. The q-axis current iqt is input to the band pass filter M92 as a variable including a vibration component of the steered wheels 34 caused by the road surface reaction force. The band pass filter M92 is a processing for selectively extracting a signal in a vibration frequency band caused by unevenness of the road surface. The gain multiplication processing M94 is a processing for multiplying the output value of the band pass filter M92 by a gain G and substituting the resultant value into the road surface information torque Ti. The filter coefficient setting processing M96 is a processing in which the vehicle speed V is input and the filter coefficient τi of the band pass filter M92 is output. The filter coefficient τi may be a variable for defining a frequency band that the bandpass filter M92 transmits, or may be an attenuation coefficient. The variable for defining the frequency band may be, for example, a center frequency. Here, the filter coefficient τi is described as one variable, but in reality, there may be multiple variables.

[0046] The synthesis process M100 is a process of adding the lead compensation amount Tad, the hysteresis correction amount Thys, the first damping correction amount Tdampa, and the return correction amount Trv to the basic assist amount Tab, and subtracting the road surface information torque Ti from the basic assist amount Tab. The value calculated in this way is the assist amount Ta.

[0047] "Axial force setting process" FIG. 4 shows details of the axial force setting process M22. The angular axial force setting process M110 is a process in which the target steering equivalent angle θp* and the vehicle speed V are input and the angular axial force Fr is output. The angular axial force Fr is an estimated value of the axial force defined by an arbitrarily set vehicle model or the like. The angular axial force Fr is calculated as an axial force that does not reflect road surface information. The road surface information is information such as minute irregularities that do not affect the lateral behavior of the vehicle and steps that affect the lateral behavior of the vehicle. The angular axial force setting process M110 may be a process that calculates the target steering equivalent angle θp* to a value with the same sign as the angular axial force Fr. The angular axial force setting process M110 may be a process that changes the angular axial force Fr under the condition that the absolute value of the angular axial force Fr when the absolute value of the target steering equivalent angle θp* is large is equal to or greater than the absolute value of the angular axial force Fr when the absolute value of the target steering equivalent angle θp* is small. Also, for example, the angular axial force setting process M110 may be a process for changing the angular axial force Fr according to the vehicle speed V under the condition that the absolute value of the angular axial force Fr when the vehicle speed V is high is equal to or greater than the absolute value of the angular axial force Fr when the vehicle speed V is low. As an example, the angular axial force setting process M110 is a process for map-calculating the angular axial force Fr by the PU 52 in a state where map data is prestored in the storage device 54. This map data is data in which the target steering equivalent angle θp* and the vehicle speed V are input variables and the angular axial force Fr is an output variable.

[0048] The current axial force setting process M112 is a process in which the q-axis current iqt of the steering motor 42 is an input and the current axial force Fi is an output. The current axial force Fi is an estimated value of the axial force that actually acts on the rack shaft 32 that operates to steer the steered wheels 34, i.e., the axial force that is actually transmitted to the rack shaft 32. The current axial force Fi is calculated as an axial force that reflects the above-mentioned road surface information. For example, the current axial force setting process M112 is a process that calculates the current axial force Fi on the assumption that the torque applied to the rack shaft 32 by the steering motor 42 is balanced with the torque according to the force applied to the rack shaft 32 through the steered wheels 34. The current axial force setting process M112 is a process that changes the current axial force Fi under the condition that the absolute value of the current axial force Fi when the absolute value of the q-axis current iqt is large is equal to or greater than the absolute value of the current axial force Fi when the absolute value of the q-axis current iqt is small.

[0049] In detail, the current axial force setting process M112 is a process in which the PU 52 performs map calculation of the current axial force Fi in a state in which map data is prestored in the storage device 54. The map data is data in which the q-axis current iqt is an input variable and the current axial force Fi is an output variable.

[0050] The distribution ratio calculation process M114 is a process in which the vehicle speed V and the target turning equivalent angle θp* are input and the ratio Di is output. The ratio Di is the ratio of the current axial force Fi to the sum of the angle axial force Fr and the current axial force Fi. The ratio Di has a value between zero and one. The distribution ratio calculation process M114 may be, for example, a process in which the PU 52 calculates the ratio Di from a map in a state in which map data is stored in advance in the storage device 54. Here, the map data is data in which the vehicle speed V and the target turning equivalent angle θp* are input variables and the ratio Di is an output variable.

[0051] The second distribution ratio calculation process M116 is a process for calculating a second ratio "1-Di" by subtracting the ratio Di from "1." The second ratio is the ratio of the angular axial force Fr to the sum of the angular axial force Fr and the current axial force Fi.

[0052] The first rate multiplication process M118 is a process for multiplying the current axial force Fi by the rate Di. The second rate multiplication process M120 is a process for multiplying the angular axial force Fr by a second rate. The addition process M122 is a process for substituting the sum of the output value of the first rate multiplication process M118 and the output value of the second rate multiplication process M120 into the axial force F0. In other words, the axial force F0 is a weighted average value of the angular axial force Fr and the current axial force Fi.

[0053] The second damping process M130 is a process for calculating a second damping correction amount Tdampb0 having a positive correlation with the rotation speed of the steering wheel 12. The second damping correction amount Tdampb0 is a correction amount for compensating for a phase delay of the axial force F0 by control. The second damping correction amount Tdampb0 may be a correction amount for reducing a damping component caused by the current axial force Fi or the like. The second damping process M130 includes a differential calculation M132 and a second correction amount setting process M134.

[0054] The differential calculation M132 is a process for calculating a first-order time differential value of the steering angle θs. The time differential value is the steering speed ωs. The second correction amount setting process M134 is a process for calculating a second damping correction amount Tdampb0 having a positive correlation with the steering speed ωs. The second damping correction amount Tdampb0 has a dimension of torque. The second correction amount setting process M134 may be a process for map-calculating the second damping correction amount Tdampb0 by the PU 52 in a state in which map data is stored in advance in the storage device 54. The map data is data in which the steering speed ωs is an input variable and the second damping correction amount Tdampb0 is an output variable.

[0055] The second gain adjustment process M136 is a process in which the steering torque Th and the vehicle speed V are input and the second gain G2 is output. As an example, the second gain adjustment process M136 is a process in which the PU 52 performs map calculation of the second gain G2 in a state in which map data is pre-stored in the storage device 54. Here, the map data is data in which the steering torque Th and the vehicle speed V are input variables and the second gain G2 is an output variable.

[0056] The multiplication process M138 is a process of multiplying the second damping correction amount Tdampb0 by the second gain G2 and substituting the resultant value for the second damping correction amount Tdampb. The addition process M139 is a process of adding the second damping correction amount Tdampb to the axial force F0 and substituting the resultant value for the axial force F.

[0057] "Actions and Effects of the Present Embodiment" The PU 52 sets a target reaction torque Ts by subtracting the axial force F from the assist amount Ta, and controls the torque of the reaction motor 22 in accordance with the target reaction torque Ts.

[0058] Here, in a situation where the compensation correction amount such as the first damping correction amount Tdampa and the advance compensation amount Tad, which are variables used to calculate the assist amount Ta, is not reflected, the stability decreases. Such a situation occurs, for example, when the torque input to the steering wheel 12 is excessively large. That is, for example, when the torque exceeds the range detectable by the torque sensor 60, the time differential value dTh becomes zero. Therefore, the advance compensation amount Tad cannot be set to an appropriate value. Also, for example, when the basic assist amount Tab is excessively large, the magnitude of the axial force F becomes relatively small, and the steering of the steering wheel 12 may become unstable. In particular, when a lower limit guard process is applied to the magnitude of the reaction force against the driver's operation of the steering wheel 12, the compensation correction amount may not be reflected due to the lower limit guard value being exceeded.

[0059] Therefore, the PU 52 adds the second damping correction amount Tdampb to the axial force F0. As a result, for example, when the assist amount Ta is excessively large, the axial force F is increased and corrected, and the magnitude of the reaction force against the driver's operation of the steering wheel 12 is prevented from becoming excessively small. Therefore, the deterioration of the stability of the steering device 10 can be suppressed.

[0060] According to the present embodiment described above, the following actions and effects can be obtained. (1) The second damping process M130 has been added to the axial force setting process M22. This makes it possible to realize a process for advancing the phase.

[0061] (2) In addition to the first damping process M70 provided in the assist amount setting process M20, the second damping process M130 is provided in the axial force setting process M22. This makes it possible to set the first damping correction amount Tdampa and the second damping correction amount Tdampb according to the differences in the respective aims, making adaptation easier.

[0062] (3) The PU 52 sets the second gain G2 in accordance with the steering torque Th. First, the steering torque Th is a variable indicating whether or not the object to be detected by the torque sensor 60 is within a range that can be detected. Second, the steering torque Th is a torque-correlated variable that has a positive correlation with the torque of the reaction force motor 22. Therefore, the magnitude of the second damping correction amount Tdampb can be adjusted in accordance with whether or not the object to be detected by the torque sensor 60 is within a range that can be detected and in accordance with whether or not the target reaction force torque Ts is a magnitude that can be realized by the reaction force motor 22.

[0063] (4) The PU 52 sets the second gain G2 in accordance with the vehicle speed V. This makes it possible to set a more appropriate second gain G2 in accordance with a situation in which a decrease in stability is a concern, compared to a case in which the second gain G2 is set without reference to the vehicle speed V.

[0064] (5) The degree to which the first damping correction amount Tdampa0 output by the first damping process M70 included in the assist amount setting process M20 is reflected in the assist amount Ta is adjusted by the first gain G1. This makes it possible to set the first damping correction amount Tdampa obtained by multiplying the first damping correction amount Tdampa0 by the first gain G1 to a value appropriate for suppressing a decrease in the stability of the steering device 10.

[0065] (6) The PU 52 sets the first gain G1 in accordance with the vehicle speed V. This makes it possible to set a more appropriate first gain G1 in accordance with a situation in which a decrease in stability is a concern, compared to a case in which the first gain G1 is set without reference to the vehicle speed V.

[0066] <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the "Means for solving the problem" column is as follows. Below, the correspondence is shown for each number of the solving means described in the "Means for solving the problem" column. [1-3] The reaction force application process corresponds to the subtraction process M24 and the reaction force operation signal generation process M26. The torque correlation coefficient corresponds to the steering torque Th. [4-5] The compensation process corresponds to the phase lag compensation process M40, the phase lead compensation process M50, and the first damping process M70. The compensation gain adjustment process corresponds to the second gain adjustment process M136.

[0067] <Other embodiments> This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0068] "About torque correlation coefficient" The torque correlation coefficient does not necessarily have to be the steering torque Th. For example, the torque correlation coefficient may be the torque of the reaction motor 22 calculated from the current flowing through the reaction motor 22. For example, in the case where a process is executed to feedback control the steering torque Th to its target value, the torque correlation coefficient may be the target value. For example, the torque correlation coefficient may be the target reaction torque Ts.

[0069] "About the second gain adjustment process" The inputs to the second gain adjustment process do not necessarily have to be the torque correlation coefficient and the vehicle speed V. The input to the second gain adjustment process may be, for example, only the torque correlation coefficient.

[0070] "Compensation gain adjustment process" The target of gain adjustment by the compensation gain adjustment process is not limited to the second damping correction amount Tdampb0. The target of gain adjustment by the compensation gain adjustment process may be, for example, the lead compensation amount Tad. Furthermore, for example, the target of gain adjustment by the compensation gain adjustment process may be both the second damping correction amount Tdampb0 and the lead compensation amount Tad.

[0071] The inputs to the compensation gain adjustment process do not necessarily have to be the torque correlation coefficient and the vehicle speed V. The input to the compensation gain adjustment process may be, for example, only the torque correlation coefficient. "About phase lead compensation processing" In FIG. 3, the inputs to the gain setting process M54 are the vehicle speed V and the assist gradient R, but this is not limited thereto. For example, the input to the gain setting process M54 may be only the assist gradient R. Also, for example, the input to the gain setting process M54 may be only the vehicle speed V.

[0072] A low-pass filter may be provided between the differential calculation M52 and the multiplication process M56. Instead of multiplying the time differential value dTh by the gain Gad in the multiplication process M56, map data may be provided in which the time differential value dTh is an input variable and the lead compensation amount Tad is an output variable.

[0073] The phase lead compensation process does not necessarily have to include a process of calculating the time differential value dTh. For example, instead of calculating the time differential value dTh, the phase lead compensation process may include a process in which the input of the phase lead compensation filter is the steering torque Th.

[0074] "Regarding the first dumping process" The first correction amount setting process M74 is not limited to a process of calculating the first damping correction amount Tdampa0 that has a negative correlation with the steering speed ωs. The first correction amount setting process M74 may be a process of setting the first damping correction amount Tdampa0 to a value that has a positive correlation with the steering speed ωs, depending on the value of a predetermined variable such as the target reaction torque Ts.

[0075] "About axial force setting process" The angular axial force setting process M110 does not necessarily have to be a process of calculating the angular axial force Fr from a map. For example, the angular axial force setting process M110 may be a process of multiplying the target steering equivalent angle θp* by a gain and substituting the value for the angular axial force Fr. Here, the gain may be variable according to the vehicle speed V.

[0076] The inputs of the angle axial force setting process M110 do not necessarily have to be the target steering equivalent angle θp* and the vehicle speed V. For example, the inputs of the angle axial force setting process M110 do not have to include the vehicle speed V. Also, for example, the angle variable of the steering system as an input variable of the angle axial force setting process M110 is not limited to the target steering equivalent angle θp*. For example, the angle variable of the steering system may be the steering equivalent angle θp. Also, for example, the angle variable of the steering system may be the steering angle θs.

[0077] The current axial force setting process M112 is not limited to a process of calculating the current axial force Fi using a map. For example, the current axial force setting process M112 may be a process of multiplying the q-axis current iqt by a gain and substituting the value for the current axial force Fi.

[0078] The input of the current axial force setting process M112 is not limited to the q-axis current iqt. For example, the input of the current axial force setting process M112 may be the q-axis current iqt and the vehicle speed V. Also, for example, the input of the current axial force setting process M112 may include angle variables of the steering system, such as the target turning equivalent angle θp*, the turning equivalent angle θp, and the steering angle θs.

[0079] The inputs to the allocation ratio calculation process M114 do not necessarily have to be the target steering equivalent angle θp* and the vehicle speed V. For example, the inputs to the allocation ratio calculation process M114 do not have to include the vehicle speed V. Also, for example, the angle variable of the steering system as an input variable of the allocation ratio calculation process M114 is not limited to the target steering equivalent angle θp*. For example, the angle variable of the steering system may be the steering equivalent angle θp. Also, for example, the angle variable of the steering system may be the steering angle θs.

[0080] The axial force setting process does not necessarily include both the angle axial force setting process M110 and the current axial force setting process M112. For example, the angle axial force setting process M110 and the current axial force setting process M112 may include only one of them.

[0081] "About steering control devices" The steering control device is not limited to one that executes software processing. For example, it may be equipped with a dedicated hardware circuit such as an ASIC that executes at least a part of the processing executed in the above embodiment. That is, the steering control device may include a processing circuit having any of the following configurations (a) to (c). (a) A processing circuit equipped with a processing device that executes all of the above processing according to a program, and a program storage device such as a memory device that stores the program. (b) A processing circuit equipped with a processing device and a program storage device that executes part of the above processing according to a program, and a dedicated hardware circuit that executes the remaining processing. (c) A processing circuit equipped with a dedicated hardware circuit that executes all of the above processing. Here, there may be multiple software execution devices equipped with a processing device and a program storage device. Also, there may be multiple dedicated hardware circuits.

[0082] "Others" The steering motor 42 does not necessarily have to be a synchronous motor. For example, it may be an induction motor.

[0083] In each of the above embodiments, the steering device 10 has a linkless structure in which the steering wheel 12 and the steered wheels 34 are mechanically separated at all times. However, the present invention is not limited to this structure, and the steering device 10 may have a structure in which the steering wheel 12 and the steered wheels 34 can be mechanically separated by a clutch. [Explanation of symbols]

[0084] 10...Steering gear 12…Steering wheel 14…Steering shaft 20…Reaction actuator 22…Reaction motor 24…Reaction force inverter 30...Steering actuator 32…Rack shaft 34…Steering wheel 42...Steering motor 44…Steering inverter 50...Steering control device

Claims

1. A steering system is controlled, the steering system including a reaction motor that applies a steering reaction force to a steering shaft, and a steering motor that steers steered wheels in a state where power transmission from the steering shaft is interrupted, The assist amount setting process, the axial force setting process, and the reaction force applying process are executed. the assist amount setting process is a process for setting an assist amount that is an amount of assisting a driver in rotating the steering shaft while using an output value of a first damping process, the axial force setting process is a process for setting an axial force that is a force resisting a rotation operation of the steering shaft by a driver, while using an output value of a second damping process; the reaction force application process is a process in which a value obtained by subtracting the axial force from the assist amount is input and the reaction force motor is operated; the first damping process is a process of outputting a first damping correction amount having a correlation with a steering angular velocity, A steering control device, wherein the second damping process is a process for outputting a second damping correction amount having a positive correlation with the steering angular velocity.

2. a second gain adjustment process is executed to adjust a second gain, which is a gain of the second damping process, in accordance with a value of a torque correlation variable; 2. The steering control device according to claim 1, wherein the torque correlation variable is a variable that has a correlation with the torque of the reaction motor.

3. 3. The steering control device according to claim 2, wherein the second gain adjustment process adjusts the second gain in accordance with a vehicle speed in addition to the value of the torque correlation variable.

4. the assist amount setting process is a process for setting the assist amount while using output values ​​of a plurality of compensation processes including the first damping process, A compensation gain adjustment process is configured to adjust a compensation gain, which is at least one gain of the plurality of compensation processes, in accordance with a value of a torque correlation variable; 2. The steering control device according to claim 1, wherein the torque correlation variable is a variable that has a correlation with the torque of the reaction motor.

5. 5. The steering control device according to claim 4, wherein the compensation gain adjustment process adjusts the compensation gain in response to a vehicle speed in addition to the value of the torque correlation variable.

6. 3. The steering control device according to claim 2, wherein the torque-correlated variable is steering torque.

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