Steering control device

Abstract

To provide a steering control device which can make a preferable compromise between inhibiting variations of steering torque and maintaining high controllability by a value of a control torque variable.SOLUTION: A PU 52 calculates torque set according to a value obtained by multiplying a sum of a detection value Trq detected by a torque sensor 72 and torque of an assist motor 42 by a coefficient which varies depending on a steering angle. The PU 52 controls the torque of the assist motor 42 according to the calculated torque. The PU 52 sets the varying component to zero when determining that vehicle travel control by a host ECU should have priority.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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-205846 Summary of the Invention [Problem to be solved by the invention]

[0004] In the case of a device equipped with a universal joint as described above, the ratio of the torque applied to the steering shaft to the torque applied to the transmission shaft varies depending on the steering angle. The inventors therefore considered applying the torque of the motor to a position closer to the steered wheels than the universal joint. In this case, if the torque at the position closer to the steered wheels is controlled so as not to vary depending on the steering angle, the torque applied to the steering shaft varies depending on the steering angle. If the torque applied to the steering shaft varies depending on the steering angle, the driver may feel uncomfortable. [Means for solving the problem]

[0005] The means for solving the above problems and their effects will be described below. 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 connecting the input shaft and the intermediate shaft, the second Cardan joint is a member connecting 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, and is configured to execute a steering angle variable acquisition process, an assist torque variable calculation process, a control torque acquisition process, an operation process, a variable torque control process, and a limiting process, the steering angle variable acquisition process is a process of acquiring a value of a steering angle variable, the steering angle variable is a variable indicating a steering angle which is the angle of the steering wheel, and the assist torque a steering control device in which the variable calculation process is a process of calculating a value of an assist torque variable, the assist torque variable being a variable indicating a torque for assisting steering by a driver in accordance with operation of the steering wheel; the control torque acquisition process is a process of acquiring a value of a control torque variable, the control torque variable being a variable indicating a torque for controlling a traveling direction of a vehicle independently of operation of the steering wheel; the operation process is a process of operating a drive circuit of the assist motor in accordance with a torque corresponding to at least one of the value of the assist torque variable and the value of the control torque variable; the variable torque control process is a process of varying torque as an input variable of the operation process in accordance with the steering angle based on the value of the steering angle variable as an input variable; and the limiting process is a process of limiting the magnitude of variation of torque as an input variable of the operation process in accordance with the steering angle to a smaller side in accordance with the priority of the value of the control torque variable in the operation process.

[0006] In the above configuration, the ratio of the torque at a position closer to the steered wheels than the second Cardan joint to the steering torque varies depending on the value of the steering angle variable. Therefore, suppressing the fluctuation in the steering torque causes the torque at a position closer to the steered wheels than the second Cardan joint to fluctuate. Therefore, in the above configuration, the torque of the assist motor is varied depending on the steering angle. This makes it possible to suppress the fluctuation in the steering torque.

[0007] However, varying the torque of the assist motor may interfere with the targeted vehicle behavior control based on the value of the control torque variable. Therefore, in the above configuration, the magnitude of the variation is limited to a small value according to the priority of the value of the control torque variable. This makes it possible to achieve a good compromise between suppressing fluctuations in the steering torque and maintaining high controllability based on the value of the control torque variable.

[0008] 2. A steering control device as described in 1 above, configured to execute a steering torque variable acquisition process, wherein the steering torque variable acquisition process is a process for acquiring the value of a steering torque variable that is a variable indicating steering torque, and the limiting process includes a process for determining the priority in accordance with the value of the steering torque variable as an input variable.

[0009] The steering torque is a variable that indicates the driver's steering intention. Therefore, the value of the steering torque variable is a variable that is suitable for determining the priority between the driver's steering and the steering based on the value of the control torque variable. Therefore, the above configuration allows the priority to be set appropriately.

[0010] 3. A steering control device as set forth in 1 or 2 above, wherein the limiting process includes a process of determining the priority based on a signal that determines the priority of the value of the control torque variable in accordance with information external to the vehicle.

[0011] The information outside the vehicle may include information on whether or not the situation is one in which the value of the control torque variable is to be prioritized regardless of the driver's steering intention. Therefore, with the above configuration, the priority can be set appropriately.

[0012] 4. A steering control device as described in any one of 1 to 3 above, wherein the limiting process includes a process of gradually reducing the magnitude of the fluctuation to zero, triggered by the priority of the value of the control torque variable switching from a low state to a high state compared to the priority of the value of the assist torque variable.

[0013] In the above configuration, by switching to a state in which the value of the control torque variable has a high priority, the magnitude of the fluctuation is gradually reduced, thereby making it possible to transition to a state in which the controllability based on the value of the control torque variable is enhanced while avoiding a sudden change in the control state.

[0014] 5. A steering control device as described in any one of 1 to 4 above, wherein the limiting process includes a process of gradually increasing the magnitude of the fluctuation from zero, triggered by the priority of the value of the control torque variable switching from a higher state to a lower state compared to the priority of the value of the assist torque variable.

[0015] In the above configuration, the magnitude of the fluctuation is gradually increased by switching to a state in which the priority of the control torque variable value is low, thereby making it possible to transition to a state in which fluctuations applied to the steering wheel are suppressed while avoiding a sudden change in the control state.

[0016] 6. A steering control device as set forth in any one of 1 to 5 above, wherein the value of the control torque variable is a torque that is superimposed on the value of the assist torque variable in order to correct steering in accordance with operation of the steering wheel.

[0017] When the value of the control torque variable is superimposed on the assist torque, the operation process can be a process of operating the drive circuit taking both torques into account. However, even when both are taken into account, whether to prioritize the steering feel or the controllability based on the value of the control torque variable varies depending on the situation. Therefore, there is a particular advantage to limiting the magnitude of the fluctuation according to the priority. [Brief explanation of the drawings]

[0018] [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] 4 is a flowchart showing a procedure for processing related to setting a gain in the processing of FIG. 3. [Figure 5] 4 is a time chart showing the effect of the embodiment. [Figure 6] 4 is a time chart showing the effect of the embodiment. [Figure 7] FIG. 10 is a block diagram showing a process executed by a control device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] 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."

[0020] 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.

[0021] 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.

[0022] 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, which serves as a drive circuit, is applied to the terminals of assist motor 42.

[0023] 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.

[0024] 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. The host ECU 80 executes processing to control the traveling direction of the vehicle based on image data showing an image of the front of the vehicle taken by the camera 84.

[0025] 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.

[0026] "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.

[0027] 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).

[0028]

number

[0029] 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.

[0030] "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.

[0031] In the following, a description will be given first of the processing when there is no steering intervention by the host ECU 80. In other words, a manual steering processing will be described. "Manual steering processing" 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.

[0032] 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 reality, the motor torque Tm is the torque of the assist motor 42 converted into the torque of the pinion shaft 22.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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).

[0037]

number

[0038] 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).

[0039] θp´ =arctan(tan[arctan{tan(θh)·cos(α1)}+ψ]·cos(α2))…(c5) Therefore, the pinion angle θp is expressed by the following equation (c6).

[0040] θp=θp´-arctan{tan(ψ)·cos(α2)}…(c6) The above equation (c2) is derived by eliminating θp' from equations (c5) and (c6).

[0041] 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 equation (c1) is calculated based on the ratio of the first-order time differential of the steering angle θh to the first-order time differential of the pinion angle θp, and the equation of conservation of energy. The first-order time differential of the steering angle θh can be calculated by the time differential of the above equation (c2).

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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 basic assist torque calculation process M42 is a process for calculating the basic assist torque Tb based on the steering torque Th as an input variable. That is, the basic assist torque calculation process M42 is a process for changing the basic assist torque Tb in accordance with the driver's steering intention indicated by the steering torque Th.

[0047] The torque fluctuation calculation process M44 is a process for calculating the torque fluctuation Tbc by dividing the basic assist torque Tb by the ratio f(θh). The superposition process M46 is a process for calculating the assist torque Ta by adding the fluctuation torque Tbc and the Cardan joint compensation torque Tcjc.

[0048] 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.

[0049] "When there is steering intervention" The process when steering intervention occurs will be described below with reference to FIG. The control torque calculation process M50 is a process for calculating the control torque Tdc based on the target pinion angle θp* and the pinion angle θp as input variables. The target pinion angle θp* is a value calculated by the host ECU 80 to control the running direction of the vehicle. The control torque Tdc is a manipulated variable of feedback control in which the pinion angle θp is a controlled variable and the target pinion angle θp* is a target value of the controlled variable.

[0050] The compensation torque limiting process M60 is a process for limiting the magnitude of the Cardan joint compensation torque Tcjc to a smaller value. More specifically, the compensation torque limiting process M60 is a process for correcting the Cardan joint compensation torque Tcjc by multiplying the output value of the compensation torque calculation process M38 by a gain G.

[0051] The amplitude limiting process M62 is a process for limiting the amplitude of the ratio f to a smaller value. Specifically, the amplitude limiting process M62 is a process for substituting the sum of the ratio f output by the ratio calculation process M32 multiplied by the gain G and "1-G" into the ratio f.

[0052] Fig. 4 shows the procedure for setting the gain G used for limiting in the compensation torque limiting process M60 and the amplitude limiting process M62. The process shown in Fig. 4 is realized by the PU 52 repeatedly executing a program stored in the storage device 54, for example, at a predetermined interval. Note that, below, the step number of each process is represented by a number preceded by "S."

[0053] In the series of processes shown in FIG. 4, the PU 52 first determines whether the control mode is a tracking-priority mode (S10). The tracking-priority mode is a mode in which priority is given to the tracking of the vehicle's driving direction by the host ECU 80 over the steering feel associated with the driver's operation of the steering wheel 12. If the PU 52 determines that the control mode is the tracking-priority mode (S10: YES), the PU 52 determines whether the absolute value of the steering torque Th is equal to or greater than a first threshold value ThthH (S12). If the PU 52 determines that the absolute value of the steering torque Th is equal to or greater than the first threshold value ThthH (S12: YES), the PU 52 switches the control mode to a steering feel priority mode (S14). The steering feel priority mode is a mode in which priority is given to the steering feel associated with the driver's operation of the steering wheel 12 over the tracking of the driving direction control. Then, the PU 52 assigns the value that is not greater than the other of two values, namely, a value obtained by adding a positive predetermined amount Δ to the gain G and 1, to the gain G (S16).

[0054] On the other hand, when the PU 52 determines that the control mode is not the tracking priority mode (S10: NO), it determines whether the logical sum of the following conditions (A) and (B) is true (S18).

[0055] Condition (A): The absolute value of the steering torque Th is equal to or less than a second threshold value ThthL. The second threshold value ThthL is smaller than the first threshold value ThthH. Condition (B): This condition indicates that an emergency avoidance request has been made. An emergency avoidance request is a request to prevent the vehicle from colliding with an object ahead in the traveling direction. The host ECU 80 monitors whether or not there is a situation in which the vehicle is likely to collide with an object ahead in the traveling direction, based on image data of the area ahead in the traveling direction captured by the camera 84. If the host ECU 80 determines that there is a risk of the vehicle colliding with an object ahead in the traveling direction, it determines that there is an emergency avoidance request. The host ECU 80 outputs a signal indicating that there is an emergency avoidance request to the control device 50. If the PU 52 receives this signal from the host ECU 80, it determines that condition (B) is met.

[0056] If the PU 52 determines that the logical sum is false (S18: NO), it proceeds to the process of S16. On the other hand, if the PU 52 determines that the logical sum is true (S18: YES), it sets the control mode to the tracking priority mode (S20). If the PU 52 completes the process of S20 or makes a negative determination in the process of S12, it assigns the greater of the two values, a value obtained by subtracting a predetermined amount Δ from the gain G, or 0, to the gain G (S22).

[0057] When the PU 52 completes the processes of S16 and S22, it temporarily ends the series of processes shown in FIG. "Actions and Effects of the Present Embodiment" The following equation (c5) is the equation of motion for the pinion shaft 22.

[0058] 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.

[0059] 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).

[0060] 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.

[0061] Th=Tp+f(θh)·(Gp-Tbc) …(c9) Substituting "Tbc=Tb / f(θh)" into the above equation (c9), the following equation (c10) is obtained.

[0062] 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.

[0063] 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 fluctuation 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.

[0064] In this way, by setting the assist torque Ta in accordance with the Cardan joint compensation torque Tcjc, etc., it is possible to suppress the steering torque Th from fluctuating periodically in accordance with the steering angle θh, and therefore it is possible to suppress, through control, the deterioration of the steering feel caused by the structure of the steering device.

[0065] Meanwhile, a control torque Tdc is superimposed on the assist torque Ta. The control torque Tdc is a torque required for proper vehicle driving and for avoiding critical situations. For example, if the vehicle is about to deviate from its lane, the control torque Tdc is set to a value that finely corrects the driver's steering to prevent the vehicle from deviating from its lane. However, there is a risk that the control torque Tdc and the Cardan joint compensation torque Tcjc may interfere with each other. In other words, there is a risk that the actual vehicle behavior may deviate from the vehicle behavior intended by the control torque Tdc due to the Cardan joint compensation torque Tcjc.

[0066] Therefore, when the control mode is switched from the steering feel priority mode to the tracking priority mode, the PU 52 sets the gain G to zero. As a result, the Cardan joint compensation torque Tcjc input by the compensation torque limiting process M60 to the superimposing process M46 is set to zero. Therefore, when priority should be given to vehicle driving control by the host ECU 80, it is possible to prevent the Cardan joint compensation torque Tcjc from interfering with the driving intended by the host ECU 80. Furthermore, when the gain G is set to zero, the ratio f input by the amplitude limiting process M62 to the steering torque calculation process M40 and the division process M34 is set to 1. Therefore, the steering torque Th becomes equal to the detection value Trq. In other words, the amplitude that periodically varies the detection value Trq in accordance with the steering angle θh is set to zero.

[0067] FIG. 5 illustrates changes in the steering angle θh, the Cardan joint compensation torque Tcjc, and the pinion angle θp in the steering feel priority mode. As shown in FIG. 5, when the Cardan joint compensation torque Tcjc is varied periodically in accordance with the steering angle θh, the pinion angle θp varies due to the Cardan joint compensation torque Tcjc, as indicated by the solid line.

[0068] Fig. 6 shows an example of a change in the control mode. In the series of processes shown in Fig. 6, at time t1, the absolute value of the steering torque Th becomes equal to or greater than the first threshold value ThthH, causing the gain G to gradually increase to 1. At time t2, the absolute value of the steering torque Th becomes equal to or less than the second threshold value ThthL, causing the gain G to gradually decrease to 0. When the gain G is zero, the Cardan joint compensation torque Tcjc is set to zero, thereby suppressing small fluctuations in the pinion angle θp.

[0069] According to this embodiment, the following further actions and effects can be obtained. (1) The PU 52 grasps the priority between the driver's steering and the steering by the control torque Tdc according to the steering torque Th. The steering torque Th is a variable that indicates the driver's intention to steer, and therefore the steering torque Th is a variable that is suitable for determining the priority between the driver's steering and the steering by the control torque Tdc. Therefore, the priority can be set appropriately.

[0070] (2) The PU 52 grasps the priority between the driver's steering and the steering by the control torque Tdc according to the steering torque Th depending on whether or not an emergency avoidance request is made. When an emergency avoidance request is made, it is considered that the control torque Tdc is given priority regardless of the driver's steering intention. Therefore, the PU 52 can appropriately set the priority by considering whether or not an emergency avoidance request is made.

[0071] (3) When the control mode is switched from the steering feel priority mode to the tracking priority mode, the PU 52 gradually reduces the gain G to zero. This allows the control state to be shifted to a state in which the controllability by the control torque Tdc is enhanced while avoiding a sudden change in the control state.

[0072] (4) When the control mode is switched from the tracking priority mode to the steering feel priority mode, the PU 52 gradually increases the gain G to 1. This allows the control state to be shifted to a state in which fluctuations applied to the steering wheel 12 are suppressed while avoiding a sudden change in the control state.

[0073] <Second embodiment> The second embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment.

[0074] Fig. 7 shows the processing executed by the control device 50 in this embodiment. The processing shown in Fig. 7 is realized by the PU 52 repeatedly executing, for example, at a predetermined interval, an assist control program 54a stored in the storage device 54. For convenience, the same reference numerals are used in Fig. 7 to designate processing corresponding to that shown in Fig. 3.

[0075] As shown in FIG. 7, in this embodiment, amplitude limiting processing M62 is provided, but compensation torque limiting processing M60 is not adopted. In this case, when the gain G is set to zero in the tracking priority mode, the output value of the subtraction process M36 is zero, and therefore the output value of the compensation torque calculation process M38 is zero, and therefore the Cardan joint compensation torque Tcjc is zero.

[0076] <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 steering angle calculation process M30, the stiffness coefficient multiplication process M31, and the steering angle correction process M33. The assist torque variable calculation process corresponds to the basic assist torque calculation process M42. The control torque acquisition process corresponds to the control torque calculation process M50. The operation process corresponds to the operation signal output process M48. The drive circuit corresponds to the inverter 60. The fluctuation torque control process corresponds to the process of calculating the Cardan joint compensation torque Tcjc and the fluctuation torque Tbc. The limiting process corresponds to the compensation torque limiting process M60 and the amplitude limiting process M62. [2] The steering torque variable acquisition process corresponds to the processes of S12 and S18. [3] The signal that determines the priority of the control torque according to information outside the vehicle corresponds to the emergency avoidance request signal. [4] The process of gradually decreasing to zero corresponds to the process of S22. [5] The process of gradually increasing corresponds to the process of S16. [6] In the superposition process M46, it corresponds to adding the control torque Tdc to the fluctuating torque Tbc.

[0077] <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.

[0078] "About Restriction Processing" The limiting process does not necessarily have to be a process of gradually changing the gain G over time. For example, the limiting process may be a process of changing the magnitude of the gain G within a range of 0 to 1 depending on the magnitude of the absolute value of the steering torque Th.

[0079] The limiting process does not necessarily have to change the gain G in stages. The limiting process may be, for example, a process in which the gain G is always set to one of two values, "0" and "1."

[0080] "Control torque acquisition process" The control torque acquisition process does not necessarily have to be the control torque calculation process M50. For example, the host ECU 80 may output the control torque Tdc to the control device 50, and the PU 52 may execute a process of receiving the control torque Tdc.

[0081] "About control torque" The control torque Tdc does not necessarily have to be a torque that is superimposed on the fluctuating torque Tbc. For example, the control torque Tdc may be a torque that causes the vehicle to automatically travel when the driver takes his / her hands off the steering wheel 12.

[0082] "About the steering angle variable acquisition process" In the above embodiment, the steering angle θh is estimated based on the pinion angle θp as an input variable, but this is not limitative. For example, the axial displacement of the rack shaft 30 may be used instead of the pinion angle θp.

[0083] "Basic assist torque calculation process" The basic assist torque calculation process M42 for calculating the basic assist torque Tb that does not depend on the steering angle θh is not essential. For example, the process may be one in which the steering torque Th and the steering angle θh are used as inputs to directly calculate the fluctuating torque Tbc. This process constitutes the assist torque variable calculation process and the fluctuating torque control process.

[0084] "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.

[0085] "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 a processing circuit having any of the following configurations (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.

[0086] "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.

[0087] "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]

[0088] 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 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 steering angle variable acquisition process, the assist torque variable calculation process, the control torque acquisition process, the operation process, the variable torque control process, and the limiting process are executed. the steering angle variable acquisition process is a process for acquiring a value of a steering angle variable, the steering angle variable is a variable indicating a steering angle, which is the angle of the steering wheel, the assist torque variable calculation process is a process of calculating a value of an assist torque variable, the assist torque variable is a variable indicating a torque for assisting the steering of the driver in response to the operation of the steering wheel, the control torque acquisition process is a process for acquiring a value of a control torque variable, the control torque variable is a variable indicating a torque for controlling the traveling direction of the vehicle independently of the operation of the steering wheel, the operation process is a process of operating a drive circuit of the assist motor in accordance with a torque corresponding to at least one of the value of the assist torque variable and the value of the control torque variable, the variable torque control process is a process of varying torque as an input variable of the operation process in accordance with the steering angle, based on a value of the steering angle variable as an input variable, The limiting process is a process of limiting the magnitude of fluctuation in torque as an input variable of the operation process according to the steering angle to a smaller value according to the priority of the value of the control torque variable in the operation process.

2. configured to execute a steering torque variable acquisition process; the steering torque variable acquisition process is a process of acquiring a value of a steering torque variable that is a variable indicating a steering torque, 2. The steering control device according to claim 1, wherein the restriction process includes a process of determining the priority in accordance with the value of the steering torque variable as an input variable.

3. 2. The steering control device according to claim 1, wherein the limiting process includes a process of determining the priority based on a signal that determines the priority of the value of the control torque variable in accordance with information external to the vehicle.

4. 2. The steering control device according to claim 1, wherein the limiting process includes a process of gradually reducing the magnitude of the fluctuation to zero, triggered by a change in priority of the value of the control torque variable from a low state to a high state compared with a priority of the value of the assist torque variable.

5. 2. The steering control device according to claim 1, wherein the limiting process includes a process of gradually increasing the magnitude of the fluctuation from zero, triggered by a change from a state in which the priority of the value of the control torque variable is higher to a state in which the priority of the value of the assist torque variable is lower.

6. 2. A steering control device according to claim 1, wherein the value of the control torque variable is a torque that is superimposed on the value of the assist torque variable in order to correct steering in response to operation of the steering wheel.

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