Steering control device

Abstract

To provide a steering control device which enables a value of an adjustment torque variable to a proper value set according to a steering angle or a change speed of the steering angle.SOLUTION: A PU 52 calculates a pinion angle which is an angle of a pinion shaft 22 based on a rotation angle θm of an assist motor 42 detected by a rotation angle sensor 70. The PU 52 estimates a steering angle which is a rotation angle of a steering wheel 12 based on the pinion angle. The PU 52 controls torque of the assist motor 42 based on the estimated steering angle.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] For example, Patent Document 1 listed below describes a device that transmits steering wheel torque to steered wheels via a steering shaft, an intermediate shaft, and a transmission shaft. Here, the steering shaft and the intermediate shaft, and the intermediate shaft and the transmission shaft are connected by universal joints, respectively. This device also includes a motor that applies torque to the intermediate shaft.

[0003] Conventionally, the torque of an assist motor that assists steering wheel operation has been controlled in accordance with a value obtained by adding an adjustment torque to an assist torque that corresponds to the steering torque. The adjustment torque includes a torque that corresponds to the steering angle or its time derivative. For example, an example of the adjustment torque is a torque that is set in accordance with the steering angle so that the steering angle returns to a neutral position when the driver releases his or her hands from the steering wheel. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-205846 Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of a device equipped with a universal joint as described above, the ratio between the steering angle, which is the rotation angle of the steering shaft, and the rotation angle of the transmission shaft varies depending on the steering angle. The inventors therefore considered applying the torque of the assist motor to a position closer to the steered wheels than the universal joint. In this case, if the adjustment torque is set according to the rotation angle of the transmission shaft, which is determined according to the rotation angle of the assist motor, the adjustment torque may unintentionally vary depending on the steering angle. This variation may cause discomfort to the driver. [Means for solving the problem]

[0006] The means for solving the above problems and their effects will be described below. 1. A steering control device for controlling a steering device, the steering device comprising a steering wheel, an input shaft, an intermediate shaft, an output shaft, a first Cardan joint, a second Cardan joint, an assist motor, and steered wheels, the input shaft being connected to the steering wheel, the first Cardan joint being a member connecting the input shaft and the intermediate shaft, the second Cardan joint being a member connecting the intermediate shaft and the output shaft, steering torque input to the steering wheel being transmitted to the steered wheels via the input shaft, the intermediate shaft, and the output shaft, the assist motor being a motor that imparts torque to a position closer to the steered wheels than the second Cardan joint, the steering control device being configured to execute a steering equivalent angle acquisition process, a steering angle variable estimation process, a basic assist torque setting process, an adjustment torque calculation process, and an operation process, the steering equivalent angle acquisition process being in response to a detection value of a sensor as an input variable the steering angle variable estimation process is a process of estimating a value of a steering angle variable based on the steering equivalent angle as an input variable, the steering equivalent angle being a variable indicating the steering angle of the steered wheels, and the detection value of the sensor is a detection value of a physical quantity at a position closer to the steered wheels than the second Cardan joint; the steering angle variable estimation process is a process of estimating a value of a steering angle variable based on the steering equivalent angle as an input variable, and the steering angle variable is a variable indicating a steering angle which is the angle of the steering wheel or a time derivative value of the steering angle; the basic assist torque setting process is a process of setting a value of a basic assist torque variable in accordance with the steering torque; the adjustment torque calculation process is a process of calculating a value of an adjustment torque variable based on the value of the steering angle variable as an input variable; and the operation process includes a process of operating a drive circuit of the assist motor to control the torque of the assist motor to a torque in accordance with the sum of the torque indicated by the value of the basic assist torque variable and the torque indicated by the value of the adjustment torque variable.

[0007] In the above configuration, the ratio of the steering equivalent angle to the steering angle periodically varies depending on the steering angle. Therefore, in the above configuration, the value of the adjustment torque variable is calculated using the value of the steering angle variable estimated by the steering angle variable estimation process. Therefore, the value of the adjustment torque variable can be set to an appropriate value depending on the steering angle or its rate of change.

[0008] 2. A steering control device as described in 1 above, wherein the steering angle variable includes a variable indicating the steering angle, and the operation processing is processing for controlling the torque of the assist motor to a torque corresponding to a value obtained by dividing the sum of the torque indicated by the value of the basic assist torque variable and the torque indicated by the value of the adjustment torque variable by the value of a ratio variable, and the ratio variable is a variable that periodically fluctuates according to the value of the variable indicating the steering angle as an input variable, and is a variable that indicates the ratio of the steering torque to the torque at a position closer to the steered wheel than the second Cardan joint.

[0009] The value of the ratio variable varies depending on the steering angle. Therefore, in the above configuration, the torque of the assist motor is controlled to a torque corresponding to the value obtained by dividing the sum of the torque indicated by the value of the assist torque variable and the torque indicated by the value of the adjustment torque variable by the value of the ratio variable. This makes it possible to suppress fluctuations in the torque applied to the steering wheel when the sum is an amount that does not vary periodically depending on the steering angle.

[0010] 3. A steering control device as described in 1 or 2 above, wherein the steering angle variables include a variable indicating the steering angle and a variable indicating a time derivative of the steering angle, the adjustment torque calculation process includes a target return process, and the target return process includes a process of setting a target value of a variable indicating the time derivative in accordance with the value of the variable indicating the steering angle as an input variable, and a process of setting a value of a target return torque variable in accordance with an operation amount of feedback control in which the variable indicating the time derivative is a controlled amount and the target value is a target value of the controlled amount, and the adjustment torque variable includes the target return torque variable.

[0011] The target value should be set to a value that indicates an appropriate steering angular velocity according to the steering angle. However, if the target value is determined based on the steering equivalent angle, there is a risk that the target value will unintentionally fluctuate according to the steering angle. Therefore, in the above configuration, a variable indicating the steering angle is used as an input variable for the target return process. This allows the target value to be set to an appropriate value according to the steering angle.

[0012] 4. A steering control device according to any one of 1 to 3 above, wherein the steering angle variable includes a variable indicating the steering angle, the adjustment torque calculation process includes active return processing, the active return processing includes processing for calculating the value of a return torque variable for returning the steering angle to a neutral position based on a variable indicating the steering angle as an input variable, and the adjustment torque variable includes the return torque variable.

[0013] The active return process is a process for setting an appropriate torque for returning the steering angle to the neutral position according to the steering angle. However, if the value of the return torque variable is determined based on the steering equivalent angle, there is a risk that the value of the return torque variable will fluctuate unintentionally. Therefore, in the above configuration, a variable indicating the steering angle is used as an input variable for the active return process. This makes it possible to prevent the value of the return torque variable from fluctuating unintentionally.

[0014] 5. A steering control device as set forth in any one of 1 to 4 above, wherein the steering angle variable includes a variable indicating a time derivative of the steering angle, the adjustment torque calculation process includes a damping process, the damping process is a process of calculating a value of a damping torque variable based on the value of a variable indicating the time derivative as an input variable, the damping torque variable being a variable with an opposite sign to the time derivative, and the adjustment torque variable including the damping torque variable.

[0015] The damping process described above is a process for setting an appropriate torque for imparting viscosity to the steering wheel operation in accordance with the steering angular velocity. However, if the value of the damping torque variable is determined based on the time differential of the steering equivalent angle, the value of the damping torque variable may unintentionally fluctuate because the steering angular velocity and the time differential of the steering equivalent angle differ. Therefore, the above configuration employs a variable indicating the time differential of the steering angle as an input variable for the damping process. This makes it possible to suppress unintentional fluctuations in the value of the damping torque variable. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a steering control system according to an embodiment. [Figure 2] 4A and 4B are diagrams showing the configuration of a first Cardan joint according to the embodiment. [Figure 3] FIG. 2 is a block diagram showing a process executed by a control device according to the embodiment. [Figure 4] FIG. 4 is a block diagram showing details of the assist amount setting process of the process shown in FIG. 3. [Figure 5] FIG. 4 is a diagram illustrating an example of the relationship between a pinion angle and a steering wheel angle according to the embodiment. [Figure 6] 4 is a time chart illustrating the effect of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment will be described with reference to the drawings. System Configuration As shown in Figure 1, steering device 10 is a device that steers steered wheels 36 through cooperation of steering torque input to steering wheel 12 by the driver and power of steering actuator 40. Steering device 10 is an electric power steering device. Hereinafter, operation of steering wheel 12 to the right or left will be referred to as "steering."

[0018] The steering wheel 12 is fixed to a column shaft 14. The column shaft 14 is mechanically connected to an intermediate shaft 18 via a first Cardan joint 16. The intermediate shaft 18 has a known contractible structure. Of the two axial ends of the intermediate shaft 18, the end opposite to the end connected to the first Cardan joint 16 is connected to a pinion shaft 22 via a second Cardan joint 20.

[0019] The pinion shaft 22 is disposed at a predetermined intersection angle with the rack shaft 30. Rack teeth 30a formed on the rack shaft 30 mesh with pinion teeth 22a formed on the pinion shaft 22 to form a rack-and-pinion mechanism 32. Tie rods 34 are connected to both ends of the rack shaft 30. The ends of the tie rods 34 are connected to knuckles (not shown) to which steered wheels 36 are attached. The rack-and-pinion mechanism 32 converts the rotation of the steering wheel 12 into axial displacement of the rack shaft 30. This axial displacement is transmitted to the knuckles via the tie rods 34, thereby changing the steering angle of the steered wheels 36. The steering angle refers to the turning angle of the tires, which are the steered wheels 36.

[0020] Steering actuator 40 includes assist motor 42 as a drive source, transmission mechanism 44 that transmits the torque of assist motor 42, and ball screw mechanism 46. Ball screw mechanism 46 converts the torque of assist motor 42 transmitted via transmission mechanism 44 into a force that displaces rack shaft 30 in the axial direction. Assist motor 42 is, for example, a three-phase brushless motor. The output voltage of inverter 60 is applied to the terminals of assist motor 42.

[0021] The control device 50 includes a PU 52 and a storage device 54. The PU 52 is a software processing device including at least one of a CPU, a GPU, and the like. The control device 50 operates the inverter 60 to control the control amount of the steered wheels 36, which are the control target. To control the control amount, the control device 50 references the rotation angle θm of the assist motor 42 detected by the rotation angle sensor 70. The control device 50 also references the currents iu, iv, and iw output by the inverter 60. Note that the currents iu, iv, and iw may be understood as voltage drops across shunt resistors provided in each leg of the inverter 60. The control device 50 also references the detection value Trq of the torque sensor 72. The detection value Trq is the detection value of the torque applied to the pinion shaft 22. The torque sensor 72 is a sensor that detects torque in accordance with the torsion angle of a well-known torsion bar provided on the pinion shaft 22.

[0022] The host ECU 80 is an electronic control device that generates commands related to vehicle control at a higher level than the control device 50. The host ECU 80 refers to the steering angle θh detected by the steering angle sensor 82. The steering angle θh is the rotation angle of the steering wheel 12. In other words, it is the rotation angle of the column shaft 14.

[0023] The control device 50 and the host ECU 80 are capable of communicating with each other. The control device 50 can receive the steering angle θh acquired by the host ECU 80. However, the sampling period for the steering angle θh is longer than the sampling period for the rotation angle θm.

[0024] "About Cardan Joints" FIG. 2 shows the configuration of the first Cardan joint 16. The first Cardan joint 16 includes a first yoke 16a, a second yoke 16b, and a cross shaft 16c. The cross shaft 16c has a cross shape. The cross shaft 16c rotatably connects the first yoke 16a and the second yoke 16b to each other. The first yoke 16a is fastened to the end of the column shaft 14 with a bolt. Alternatively, the first yoke 16a may be welded to the end of the column shaft 14. The second yoke 16b is fixed to the end of the intermediate shaft 18 by welding.

[0025] The configuration of the second Cardan joint 20 is similar to that of the first Cardan joint 16, and therefore a description thereof will be omitted. "Torque Fluctuation Caused by Cardan Joints" The ratio f(θh) (=Th / Trq) between the steering torque Th applied to the steering wheel 12 and the torque applied to the pinion shaft 22 has the relationship expressed by the following equation (c1).

[0026]

number

[0027] According to the above formula (c1), for example, when the torque applied to the pinion shaft 22 is constant regardless of the steering angle θh, the steering torque Th can vary depending on the steering angle θh. When the steering torque Th varies depending on the steering angle θh, the driver may feel uncomfortable operating the steering wheel 12. Control to deal with this will be described below.

[0028] "Torque control of assist motor" Fig. 3 shows the process executed by the control device 50. The process shown in Fig. 3 is realized by the PU 52 repeatedly executing an assist control program 54a stored in the storage device 54, for example, at a predetermined interval.

[0029] The detection value acquisition process M10 is a process for acquiring the detection value Trq by the torque sensor 72 at a predetermined sampling period. The torque calculation process M12 is a process for calculating the motor torque Tm, which is the torque generated in the assist motor 42, based on the currents iu, iv, and iw flowing through the assist motor 42. In practice, the motor torque Tm is the torque of the assist motor 42 converted into the torque of the pinion shaft 22.

[0030] The addition process M14 is a process of adding the detected value Trq and the motor torque Tm. The motor angle acquisition process M16 is a process for calculating the rotation angle θm of the rotary shaft of the assist motor 42 at a predetermined sampling period.

[0031] The pinion angle calculation process M18 is a process for calculating a pinion angle θp, which is the rotation angle of the pinion shaft 22, based on the rotation angle θm as an input variable. The differential operator M20 is a process for calculating the first-order time differential value based on the pinion angle θp as an input variable.

[0032] The differential operator M22 is a process that calculates the first-order time differential value based on the output value of the differential operator M20 as an input variable. The inertia term calculation process M24 is a process for outputting an inertia term Gp, which is a value obtained by multiplying the output value of the differential operator M22 by an inertia coefficient J. Note that since the output value of the differential operator M22 is a second-order time differential value of the pinion angle θp, the output value of the inertia term calculation process M24 corresponds to the inertia torque of the steering device 10.

[0033] The subtraction process M26 is a process for subtracting the output value of the inertia term calculation process M24 from the output value of the addition process M14. The steering angle calculation process M30 is a process for calculating the steering angle θh based on the pinion angle θp as an input variable. The steering angle calculation process M30 is a process for calculating the steering angle θh using a mapping defined by the mapping data 54b stored in the storage device 54 shown in FIG. 1. This mapping is a mapping that takes the pinion angle θp as an input and outputs the steering angle θh. The mapping is defined by the following equation (c2).

[0034]

number

[0035] That is, it is derived using the simultaneous equations (c3) and (c4) below. tanθ2=cosα1·tanθh …(c3) tan(θp´)=cosα2·tan(θ2+ψ) …(c4) Note that "θ2" above is the rotation angle of the intermediate shaft 18. Also, "θp'" indicates the phase difference of the pinion angle θp with respect to "θh." More specifically, the following equation (c5) can be determined from equations (c3) and (c4).

[0036] θp´ =arctan(tan[arctan{tan(θh)·cos(α1)}+ψ]·cos(α2))…(c5) Therefore, the pinion angle θp is expressed by the following equation (c6).

[0037] θp=θp´-arctan{tan(ψ)·cos(α2)}…(c6) The above equation (c2) is derived by eliminating θp' from equations (c5) and (c6).

[0038] The mapping data 54b includes data related to the values ​​of the first bending angle α1, the second bending angle α2, and the phase difference ψ. The above formula (c1) is calculated based on the ratio between the first-order time differential of the steering angle θh and the first-order time differential of the pinion angle θp, and the energy conservation equation. The ratio between the first-order time differential of the steering angle θh and the first-order time differential of the pinion angle θp can be calculated by the time differentiation of the above formula (c2).

[0039] The stiffness coefficient multiplication process M31 is a process for multiplying the detected value Trq by the reciprocal of the stiffness coefficient K. The stiffness coefficient K is a coefficient that indicates the torsional stiffness of the torsion bar. The steering angle correction process M33 is a process for correcting the steering angle θh by multiplying the steering angle θh output by the steering angle calculation process M30 by the output value of the stiffness coefficient multiplication process M31. Note that the steering angle θh determined from the above equation (c2) deviates from the actual steering angle by the amount of torsion of the torsion bar. The amount obtained by multiplying the detected value Trq by the reciprocal of the stiffness coefficient K is an estimated value of the amount of torsion of the torsion bar.

[0040] The ratio calculation process M32 is a process for calculating the ratio f(θh) between the torque of the pinion shaft 22 and the steering torque Th. The ratio f(θh) may be expressed, for example, by the above formula (c1). That is, the ratio f(θh) may be calculated by the PU 52 using the formula (c1) by storing data defining the above formula (c1) in the storage device 54. Alternatively, for example, the ratio f(θh) may be calculated by the PU 52 using a map in a state where map data is stored in advance in the storage device 54. Here, the map data is data in which the steering angle θh is an input variable and the ratio f(θh) is an output variable.

[0041] Here, map data refers to a set of data consisting of discrete values ​​of input variables and values ​​of output variables corresponding to each of the input variable values. Furthermore, map calculation may be a process in which, when the value of an input variable matches one of the input variable values ​​in the map data, the value of the corresponding output variable in the map data is the calculation result. Furthermore, map calculation may be a process in which, when the value of an input variable does not match any of the input variable values ​​in the map data, the calculation result is a value obtained by interpolating the values ​​of multiple output variables included in the map data. Alternatively, map calculation may be a process in which, when the value of an input variable does not match any of the input variable values ​​in the map data, the calculation result is the value of the output variable in the map data that corresponds to the closest value of the multiple input variables included in the map data.

[0042] The division process M34 is a process for calculating the reciprocal of the ratio f(θh). The subtraction process M36 is a process of subtracting the output value of the division process M34 from "1". The compensation torque calculation process M38 is a process for calculating the Cardan joint compensation torque Tcjc by multiplying the output value of the subtraction process M26 by the output value of the subtraction process M36.

[0043] The steering torque calculation process M40 is a process for calculating the steering torque Th by multiplying the detected value Trq by the ratio f(θh). The assist torque calculation process M42 is a process for calculating the assist torque Tb based on the steering torque Th as an input variable. That is, the assist torque calculation process M42 is a process for changing the assist torque Tb in accordance with the driver's steering intention indicated by the steering torque Th.

[0044] The variable assist torque calculation process M44 is a process for calculating the variable assist torque Tbc by dividing the assist torque Tb by the ratio f(θh). The superposition process M46 is a process for calculating the assist torque Ta by adding the variable assist torque Tbc and the Cardan joint compensation torque Tcjc.

[0045] The operation signal output process M48 is a process for generating and outputting an operation signal MS for the inverter 60 to control the torque of the assist motor 42 to the assist torque Ta. Note that the operation signal MS is actually an operation signal for each switching element of the inverter 60.

[0046] "Details of assist torque calculation process M42" FIG. 4 shows the detailed process of the assist torque calculation process M42. The basic assist torque setting process M50 is a process for calculating the basic assist torque Tab based on the steering torque Th as an input variable. The basic assist torque setting process M50 is a process for changing the basic assist torque Tab according to the steering torque Th under the following condition: the absolute value of the basic assist torque Tab when the absolute value of the steering torque Th is large is equal to or greater than the absolute value of the basic assist torque Tab when the absolute value of the steering torque Th is small.

[0047] 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 magnitude when comparing the two. For example, "when A is large" corresponds to the case where "A is a first value," and "when A is small" corresponds to the case where "A is a second value smaller than the first value." The above description also 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. The above description also means that B is changed according to A so that A when B is large is larger than A when B is small.

[0048] The active return process M52 is a process that calculates the active return torque Tar based on the steering angle θh as an input variable. The active return torque Tar is a torque for returning the steering angle θh to the neutral position. Therefore, the sign of the active return torque Tar is opposite to the sign of the steering angle θh. The active return process M52 is a process that changes the active return torque Tar according to the steering angle θh under the following condition: the absolute value of the active return torque Tar when the absolute value of the steering angle θh is large is equal to or greater than the absolute value of the active return torque Tar when the absolute value of the steering angle θh is small.

[0049] The target return process M60 is a process for calculating a target return torque Ttr based on the steering angle and steering angular velocity ωh as input variables. The target return torque Ttr is a manipulated variable for controlling the steering angular velocity ωh when returning the steering angle θh to the neutral position so that it approaches the target steering angular velocity ωh*. The target return process M60 includes a target angular velocity setting process M62, a deviation calculation process M64, and a proportional element M66.

[0050] The target angular velocity setting process M62 is a process for setting a target steering angular velocity ωh* based on the steering angle θh as an input variable. Specifically, the target angular velocity setting process M62 may be a process for performing map calculation of the target steering angular velocity ωh* by the PU 52 with map data stored in the storage device 54. Here, the map data is data in which the steering angle θh is an input variable and the target steering angular velocity ωh* is an output variable. The deviation calculation process M64 is a process for calculating the difference between the target steering angular velocity ωh* and the steering angular velocity ωh. The proportional element M66 is a process for multiplying the output variable of the deviation calculation process M64 by a gain Kp and assigning the result to the target return torque Ttr.

[0051] The damping process M70 is a process for calculating a damping torque Tdamp based on the steering angular velocity ωh as an input variable. The damping torque Tdamp is a torque for damping vibrations in the steering system by imparting viscosity to the operation of the steering wheel 12. The sign of the damping torque Tdamp is opposite to the sign of the steering angular velocity ωh. The damping process M70 is a process for calculating the damping torque Tdamp according to the steering angular velocity ωh under the following condition: the absolute value of the damping torque Tdamp when the absolute value of the steering angular velocity ωh is large is equal to or greater than the absolute value of the damping torque Tdamp when the absolute value of the steering angular velocity ωh is small.

[0052] The synthesis process M80 is a process of substituting the sum of the basic assist torque Tab, the active return torque Tar, the target return torque Ttr, and the damping torque Tdamp into the assist torque Tb.

[0053] "Actions and Effects of the Present Embodiment" The following equation (c5) is the equation of motion for the pinion shaft 22. Trq+Tm=Gp+Tp …(c5) Here, the inertia term Gp is ​​the inertia term of the torque of the pinion shaft 22. Furthermore, the torque Tp is the torque applied to the pinion shaft 22 other than the inertia term Gp.

[0054] The above formula (c5) can be expressed as the following formula (c6). Trq=Gp+Tp-Tm …(c6) Using the ratio f(θh) in the above equation (c1), the steering torque Th can be expressed by the following equation (c7).

[0055] Th=f(θh)·(Gp+Tp-Tm) …(c7) Here, the motor torque Tm, which is the assist torque, is given by equation (c8). Tm=Tbc+{1-(1 / f(θh))}·Tp …(c8) Substituting the above equation (c8) into the above equation (c7), the following equation (c9) is obtained.

[0056] Th=Tp+f(θh)·(Gp-Tbc) …(c9) Substituting "Tbc=Tb / f(θh)" into the above equation (c9), the following equation (c10) is obtained.

[0057] Th=Tp-Tb+f(θh)·Gp …(c10) In the above equation (c10), if the term "f(θh)·Gp" is ignored, the ratio of the steering torque Th to "Tp-Tb" does not depend on the steering angle θh.

[0058] Therefore, if the fluctuation of the torque Tp according to the steering angle θh is small, it is possible to suppress the fluctuation of the steering torque Th according to the steering angle θh. Therefore, in this embodiment, the motor torque Tm is set to the sum of the variable assist torque Tbc and the Cardan joint compensation torque Tcjc. That is, the second term on the right side of the above equation (c8) is the Cardan joint compensation torque Tcjc.

[0059] The active return process M52, the target return process M60, and the damping process M70 all operate on the assist motor 42. Therefore, it is natural to understand that the input variables of the active return process M52, the target return process M60, and the damping process M70 are set to the pinion angle θp or its time derivative. Meanwhile, according to the above formula (c2), the relationship between the steering angle θh and the pinion angle θp is nonlinear. This nonlinear relationship is shown on the left side of FIG. 5. Furthermore, the right side of FIG. 5 shows the difference between the steering angle θh and the pinion angle θp relative to the steering angle θh.

[0060] Here, the active return process M52, the target return process M60, and the damping process M70 are all processes for controlling the behavior of the steering wheel 12. Therefore, if the input variable of each of these processes is the pinion angle θp or its time derivative, there is a risk that the behavior of the steering wheel 12 cannot be controlled appropriately.

[0061] In contrast, in this embodiment, the input variables of the active return process M52, the target return process M60, and the damping process M70 are set to the steering angle θh or the steering angular velocity ωh. This allows the active return torque Tar, the target return torque Ttr, and the damping torque Tdamp, which serve as adjustment torques, to be set to appropriate values ​​according to the steering angle θh or its rate of change.

[0062] Fig. 6 illustrates the behavior of the steering angle θh due to the target return processing according to this embodiment and a comparative example. In Fig. 6, the dashed dotted line indicates the transition of the target steering angular velocity ωh*. In Fig. 6, the solid line indicates the transition of the steering angular velocity ωh according to this embodiment. In Fig. 6, the dashed two-dotted line indicates a comparative example in which the pinion angle θp and its time derivative are used as input variables of the target return processing M60 instead of the steering angle θh and the steering angular velocity ωh.

[0063] As shown in FIG. 6, in this embodiment, the ability of the steering angular velocity ωh to follow the target steering angular velocity ωh* is improved compared to the comparative example. According to the present embodiment described above, the following effects can be further obtained.

[0064] (1) The PU 52 calculates the variable assist torque Tbc by dividing the assist torque Tb by the ratio f(θh). The ratio f varies depending on the steering angle θh. Therefore, in this embodiment, the torque of the assist motor 42 is controlled to a torque corresponding to the value obtained by dividing the assist torque Tb by the ratio f(θh). This makes it possible to suppress fluctuations in the torque applied to the steering wheel when the assist torque Tb is an amount that does not vary periodically depending on the steering angle θh.

[0065] <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 means for solving the problem described in the "Means for Solving the Problem" column. [1] The input shaft corresponds to the column shaft 14. The output shaft corresponds to the pinion shaft 22. The steering angle variable acquisition process corresponds to the motor angle acquisition process M16. The steering equivalent angle corresponds to the pinion angle θp. The basic assist torque setting process corresponds to the basic assist torque setting process M50. The adjustment torque calculation process corresponds to the active return process M52, the target return process M60, and the damping process M70. The operation process corresponds to the operation signal output process M48. The drive circuit corresponds to the inverter 60. [2] The ratio variable corresponds to the ratio f. [3] The variable indicating the time differential value corresponds to the steering angular velocity ωh. The target value corresponds to the target steering angular velocity ωh*. The target return torque variable corresponds to the target return torque Ttr. [4] The return torque variable corresponds to the active return torque Tar. [5] The damping torque variable corresponds to the damping torque Tdamp.

[0066] <Other embodiments> This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0067] "Regarding the process of obtaining the steering angle equivalent" In the above embodiment, the steering equivalent angle acquisition process is a process of acquiring the pinion angle θp as a variable indicating the steering angle, but this is not limitative. For example, the steering equivalent angle acquisition process may be a process of acquiring the amount of axial displacement of the rack shaft 30.

[0068] "Basic assist torque setting process" The assist torque calculation process M42 for calculating the assist torque Tb that does not depend on the steering angle θh is not essential. For example, a process for directly calculating the variable assist torque Tbc using the steering torque Th and the steering angle θh as inputs may be employed.

[0069] "About the target return torque variable" The target return variable, which is the output variable of the target return process, does not necessarily have to be the target return torque Ttr. The target return variable may be, for example, a command value for the current flowing through the assist motor 42. Specifically, for example, if the assist motor 42 is an SPM, the target return variable may be the q-axis current.

[0070] "About return torque variables" The return torque variable, which is the output variable of the active return process, does not necessarily have to be the active return torque Tar. The return torque variable may be, for example, a command value for the current flowing through the assist motor 42. Specifically, for example, if the assist motor 42 is an SPM, the return torque variable may be the q-axis current.

[0071] "About damping variables" The damping torque variable as the output variable of the damping process does not necessarily have to be the damping torque Tdamp. The damping torque variable may be, for example, a command value for the current flowing through the assist motor 42. Specifically, for example, if the assist motor 42 is an SPM, the damping torque variable may be the q-axis current.

[0072] "Regarding the adjustment torque calculation process" The adjustment torque calculation process that calculates the value of the adjustment torque variable based on the steering angle θh or the steering angular velocity ωh as an input variable does not necessarily include the target return process, the active return process, and the damping process. For example, the adjustment torque calculation process may include only two of these three processes. Also, for example, the adjustment torque calculation process may include only one of these three processes.

[0073] The adjustment torque calculation process may include processes other than the above three processes. For example, the adjustment torque calculation process may include a process of calculating the value of a hysteresis torque variable that has different values ​​for steering and steering back.

[0074] "About operation processing" The input variables for the operation process are not limited to the two variables of the adjustment torque variable and the assist torque variable. The input variables for the operation process may include, for example, a torque for suppressing torque ripple that periodically occurs depending on the rotation angle due to the structure of the mechanism that transmits the torque of the assist motor 42 to the steered wheels 36.

[0075] "About the first bending angle α1 and the second bending angle α2" In the above embodiment, the first bending angle α1 and the second bending angle α2 are set to predetermined fixed values, but this is not limitative. For example, as shown by the two-dot chain line in FIG. 1, if the height of the steering wheel 12 can be adjusted by rotating the column shaft 14 around the rotation center OT, the first bending angle α1 and the second bending angle α2 may be set according to the amount of rotation of the column shaft 14. Note that the factors that cause the bending angles α1 and α2 to change are not limited to changes in the tilt angle. For example, the bending angles α1 and α2 may change when the telescopic function is used.

[0076] "About steering control devices" The control device 50 is not limited to one that includes the PU 52 and the storage device 54 and executes software processing. For example, it may include a dedicated hardware circuit (such as an ASIC) that executes at least part of the processing executed in the above embodiment. That is, the steering control device may include any of the following processing circuits (a) to (c): (a) a processing circuit that includes a processing device that executes all of the above processing in accordance with a program and a program storage device such as a ROM that stores the program; (b) a processing circuit that includes a processing device and a program storage device that executes part of the above processing in accordance with a program, and a dedicated hardware circuit that executes the remaining processing; (c) a processing circuit that includes a dedicated hardware circuit that executes all of the above processing. Here, there may be multiple software processing circuits that include a processing device and a program storage device, and multiple dedicated hardware circuits. That is, the above processing may be executed by a processing circuit that includes at least one of one or more software processing circuits and one or more dedicated hardware circuits.

[0077] "About the steering device" The configuration is not limited to one in which the rotation shaft of the assist motor 42 and the rack shaft 30 are arranged parallel to each other. For example, a second rack and pinion mechanism may be provided in addition to the rack and pinion mechanism 32, and the torque of the assist motor 42 may be applied via the second rack and pinion mechanism.

[0078] "others" The steering angle θh input to the ratio calculation process M32 does not necessarily have to be the output value of the steering angle correction process M33. For example, the steering angle θh output by the steering angle calculation process M30 may be input to the ratio calculation process M32. [Explanation of symbols]

[0079] 10...Steering device 12...Steering wheel 14...Column axis 16...First cardan joint 16a...1st York 16b...Second York 16c…Cross axis 18...Intermediate shaft 20...Second cardan joint 22...Pinion shaft 22a...Pinion teeth 30...Rack shaft 30a...rack teeth 32...Rack and pinion mechanism 34...Tie rod 36...Steering wheel 40...Steering actuator 42...Assist motor 44...Transmission mechanism 46...Ball screw mechanism 50...Control device

Claims

1. A steering control device that controls a steering device, the steering device includes a steering wheel, an input shaft, an intermediate shaft, an output shaft, a first Cardan joint, a second Cardan joint, an assist motor, and steered wheels; The input shaft is connected to the steering wheel, the first Cardan joint is a member that connects the input shaft and the intermediate shaft, the second Cardan joint is a member that connects the intermediate shaft and the output shaft, A steering torque input to the steering wheel is transmitted to the steered wheels via the input shaft, the intermediate shaft, and the output shaft, the assist motor is a motor that applies torque to a position closer to the steered wheels than the second Cardan joint, The control unit is configured to execute a steering equivalent angle acquisition process, a steering angle variable estimation process, a basic assist torque setting process, an adjustment torque calculation process, and an operation process, The steering equivalent angle acquisition process is a process for acquiring a steering equivalent angle according to a detection value of a sensor as an input variable, The steering equivalent angle is a variable indicating the steering angle of the steered wheels, the detection value of the sensor is a detection value of a physical quantity at a position closer to the steered wheels than the second Cardan joint, the steering angle variable estimation process is a process of estimating a value of a steering angle variable based on the steering equivalent angle as an input variable, the steering angle variable is a variable indicating a steering angle, which is the angle of the steering wheel, or a time differential value of the steering angle, the basic assist torque setting process is a process of setting a value of a basic assist torque variable in accordance with the steering torque, the adjustment torque calculation process is a process of calculating a value of an adjustment torque variable based on a value of the steering angle variable as an input variable, The steering control device, wherein the operation processing includes processing for operating a drive circuit of the assist motor so as to control the torque of the assist motor to a torque corresponding to the sum of the torque indicated by the value of the basic assist torque variable and the torque indicated by the value of the adjustment torque variable.

2. the steering angle variable includes a variable indicating the steering angle, the operation processing is processing for controlling the torque of the assist motor to a torque corresponding to a value obtained by dividing the sum of the torque indicated by the value of the basic assist torque variable and the torque indicated by the value of the adjustment torque variable by the value of a ratio variable, 2. A steering control device according to claim 1, wherein the ratio variable is a variable that periodically varies depending on the value of a variable indicating the steering angle as an input variable, and is a variable that indicates a ratio of the steering torque to a torque at a position closer to the steered wheel than the second Cardan joint.

3. the steering angle variables include a variable indicating the steering angle and a variable indicating a time differential value of the steering angle, the adjustment torque calculation process includes a target return process, the target return processing includes a processing for setting a target value of a variable indicating the time differential value in accordance with a value of a variable indicating the steering angle as an input variable, and a processing for setting a value of a target return torque variable in accordance with an operation amount of feedback control in which the variable indicating the time differential value is a controlled variable and the target value is a controlled variable target value, 2. The steering control device according to claim 1, wherein the adjustment torque variable includes the target return torque variable.

4. the steering angle variable includes a variable indicating the steering angle, the adjustment torque calculation process includes an active return process, the active return process includes a process of calculating a value of a return torque variable for returning the steering angle to a neutral position based on a variable indicating the steering angle as an input variable, The steering control device according to claim 1 , wherein the adjustment torque variable includes the return torque variable.

5. the steering angle variable includes a variable indicating a time differential value of the steering angle, the adjustment torque calculation process includes a damping process, the damping process is a process of calculating a value of a damping torque variable based on a value of a variable indicating the time differential value as an input variable, the damping torque variable is a variable having an opposite sign to the time differential value, 2. The steering control device according to claim 1, wherein the adjustment torque variable includes the damping torque variable.

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