Steering system

Abstract

A steering system (10) includes: a steering wheel (22); a steering actuator (30) including a motor (32) and steering a steering wheel (12); and a control device (40). The control device (40) is configured to perform the following processing: a steering operation amount calculation processing for calculating a steering operation amount; an angle command value calculation processing for calculating an angle command value; an angle operation amount calculation processing for calculating an angle operation amount; an operation processing for operating a drive circuit of the motor (32); and a correction processing for correcting a parameter from an upstream of the angle operation amount calculation processing so that a traction resistance is applied to resist an operation of the steering wheel (22) for increasing the magnitude of the steering angle when the magnitude of the steering angle is equal to or greater than a steering angle threshold.

Description

Technical Field

[0001] The present invention relates to a steering system that operates a steering actuator that includes a motor and turns a steering wheel. Background Art

[0002] For example, Japanese Patent Application Publication No. 2006-175940 (JP 2006-175940A) discloses a device for operating a motor included in a steering actuator, which steers a steering wheel according to an operation amount in feedback control based on a difference between a target steering torque and an actual steering torque and an operation amount in feedback control based on a difference between a target steering angle and a steering angle.

[0003] In an electric power steering system (steering assist system), it is known that steering is prohibited at a tire angle of a predetermined amount or more. Specifically, for example, in a rack and pinion type, it is known that so-called end contact occurs in which the end of the rack shaft contacts the rack housing, and therefore steering is prohibited at a larger tire angle. In this regard, Japanese Patent Application Publication No. 2007-045394 (JP 2007-045394A) discloses a device that makes a restriction to slowly reduce the current command value of the motor when the end of the rack shaft approaches the rack housing. Summary of the invention

[0004] In the device described in JP 2006-175940A, in the control for slowly reducing the current command value of the motor when the end of the rack shaft approaches the rack housing, there is a problem that the driver may not perceive that the magnitude of the steering angle approaches the maximum value before the end of the rack shaft contacts the rack housing. When the driver fails to perceive, there is a problem that a state in which the torque input to the steering wheel by the driver is large may be maintained, and thus the end of the rack shaft may contact the rack housing with a large force.

[0005] One aspect of the present invention is a steering system including a steering wheel, a steering actuator including a motor and configured to steer a steering wheel, and a control device. The control device is configured to perform the following processing: a steering operation amount calculation process of calculating a steering operation amount as an operation amount of the motor for steering the steering wheel to control the steering torque to a target steering torque by feedback control, which is an operation amount that can be converted into a torque required for the motor, the steering torque being input by a driver; an angle command value calculation process of calculating an angle command value, which is a command value of a convertible angle that can be converted into a steering angle of the steering wheel based on the steering operation amount; an angle operation amount calculation process of calculating an angle operation amount as an operation amount for controlling the convertible angle to an angle command value by feedback control, which is an operation amount that can be converted into a torque required for the motor; an operation process of operating a drive circuit of the motor based on the angle operation amount to control the torque of the motor; and a correction process of correcting a parameter from an upstream of the angle operation amount calculation process so that when the magnitude of the steering angle is equal to or greater than a steering angle threshold, a traction resistance is applied to resist the operation of the steering wheel for increasing the magnitude of the steering angle.

[0006] With this configuration, by applying a traction resistance against the operation of the steering wheel for increasing the magnitude of the steering angle when the magnitude of the steering angle is equal to or greater than the steering angle threshold, even when the driver performs an operation to increase a large force for increasing the magnitude of the steering angle, the magnitude of the force for increasing the magnitude of the steering angle can be restricted to be reduced. In order to apply the resistance against the operation of the steering wheel, the parameter from the upstream of the angle operation amount calculation process is corrected. Therefore, compared with the case where the output of the angle operation amount calculation process is corrected, the deterioration of the controllability of the feedback control of the steering angle to the target steering angle can be suppressed.

[0007] In the steering system, the angle command value calculation process may include the following processes: a process of subtracting an elastic force from a steering operation amount as an input of the angle command value calculation process, wherein the elastic force is set to be larger when the magnitude of the steering angle is large than when the magnitude of the steering angle is small; and a process of calculating the angle command value based on the subtracted value. The correction process may include a process of increasing an increase amount of the elastic force as the magnitude of the steering angle increases when the magnitude of the steering angle is equal to or greater than a steering angle threshold.

[0008] With this configuration, since the elastic force set to be larger when the magnitude of the steering angle is large than when the magnitude of the steering angle is small is subtracted from the steering operation amount as the input of the angle command value calculation process, and the angle command value is calculated based on the subtracted value, it can be expressed that the torque required to steer the steering wheel becomes larger when the magnitude of the steering angle is large than when the magnitude of the steering angle is small. By setting the increase amount of the elastic force to increase when the magnitude of the steering angle is equal to or greater than the steering angle threshold, it is possible to apply a traction resistance against the operation of the steering wheel for increasing the magnitude of the steering angle when the steering angle is equal to or greater than the steering angle threshold.

[0009] In the steering system, the angle command value calculation process may include the following processes: a process of subtracting a viscosity force from a steering operation amount as an input of the angle command value calculation process, wherein the viscosity force is set to be larger when the magnitude of the steering angular velocity is large than when the magnitude of the steering angular velocity is small; and a process of calculating the angle command value based on the subtracted value. The steering angular velocity is a rate of change of the steering angle. The control device may be configured to perform a viscosity adjustment process that sets the viscosity force to be larger when the magnitude of the steering angle is equal to or smaller than a steering angle threshold and the magnitude of the steering angle is closer to the steering angle threshold than when the magnitude of the steering angle is farther from the steering angle threshold.

[0010] When a traction resistance is applied to resist the operation of the steering wheel for increasing the magnitude of the steering angle when the steering angle is equal to or greater than the steering angle threshold, there is a problem that when the steering angle reaches the steering angle threshold and the rate of change of the steering angle is large, the impact caused by the conflict between the traction resistance and the force in the opposite direction (e.g., the force for increasing the magnitude of the steering angle) may increase. Therefore, in this configuration, by setting the viscous force to be greater when the magnitude of the steering angle approaches the steering angle threshold than when the magnitude of the steering angle is away from the steering angle threshold, the viscous force may increase in the vicinity of the steering angle threshold, and thus the increase in the rate of change of the steering angle may be suppressed. Therefore, the excessive increase in the rate of change of the magnitude of the steering angle may be suppressed when the steering angle reaches the steering angle threshold, and the impact may be suppressed.

[0011] In the steering system, the correction process may include a process of reducing the magnitude of the steering operation amount input to the angle command value calculation process when the magnitude of the steering angle is equal to or greater than a steering angle threshold value.

[0012] With this configuration, since the magnitude of the steering operation amount is reduced when the magnitude of the steering angle is equal to or greater than the steering angle threshold value, the magnitude of the input to the angle command value calculation process can be reduced when the magnitude of the steering angle is equal to or greater than the steering angle threshold value. Therefore, since the magnitude of the angle command value is calculated to be smaller than the magnitude of the steering torque in the angle command value calculation process, the magnitude of the convertible angle may be larger than the magnitude of the angle command value. In this case, since the angle operation amount calculated in the angle operation amount calculation process is an amount for reducing the magnitude of the steering angle, a traction resistance against the operation of the steering wheel for further increasing the magnitude of the steering angle can be applied.

[0013] In the steering system, the steering wheel may be attached to a traction resistance actuator. The traction resistance actuator may be configured to apply traction resistance as a force resisting the operation of the steering wheel to the steering wheel in a state where power transmission between the steering wheel and the steering wheel is cut off. The control device may be configured to perform a traction resistance operation process of operating the traction resistance actuator according to the angle command value. The correction process may be a process that corrects a parameter from an upstream of the angle operation amount calculation process so that the traction resistance resisting the operation of the steering wheel for increasing the magnitude of the steering angle is applied by the traction resistance actuator when at least one of the following conditions is satisfied: a condition that the magnitude of the steering angle as the rotation angle of the steering wheel is equal to or greater than a steering angle threshold; and a condition that the steering angle is equal to or greater than a steering angle threshold.

[0014] With this configuration, when the logical sum of the steering angle reaching the steering angle threshold value and the steering angle reaching the steering angle threshold value is true, a traction resistance is applied to resist the operation of the steering wheel for increasing the magnitude of the steering angle. Therefore, it is possible to prevent the occurrence of a phenomenon in which a steering operation that causes the magnitude of the steering angle to exceed the upper limit and a steering operation that causes the magnitude of the steering angle to exceed the upper limit are performed.

[0015] In the steering system, the operation process may be a process of operating the drive circuit based on the angle operation amount so that the torque of the motor is controlled regardless of the steering operation amount.

[0016] In the steering system, the control device may be configured to execute a target steering torque calculation process that calculates the target steering torque based on a sum of quantities obtained by converting the steering operation amount and the steering torque into forces acting on the same object.

[0017] Since the steering operation amount can be converted into the torque required by the motor, the force applied from the vehicle side to steer the steering wheel is determined based on the steering operation amount and the steering torque, and the force can be converted into a lateral force. On the other hand, it is possible to determine the target steering torque required to improve the steering feeling of the driver based on the lateral force. Therefore, with the above configuration, by determining the target steering torque based on the sum of the steering operation amount and the steering torque, the target steering torque calculation process can be easily designed. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals denote like elements, and in which:

[0019] Figure 1 is a diagram showing an electric power steering system according to a first embodiment;

[0020] Figure 2 is a block diagram showing a process performed by a steering control system according to a first embodiment;

[0021] Figure 3 is a flowchart showing the flow of reaction force calculation processing according to the first embodiment;

[0022] Figure 4 is a block diagram showing a process performed by a steering control system according to a second embodiment;

[0023] Figure 5 is a flowchart showing the flow of reaction force calculation processing according to the second embodiment;

[0024] Figure 6 is a diagram showing an electric power steering system according to a third embodiment;

[0025] Figure 7 is a block diagram showing a process performed by a steering control system according to a third embodiment; and

[0026] Figure 8 : is a flowchart showing the flow of reaction force calculation processing according to the third embodiment. DETAILED DESCRIPTION

[0027] Hereinafter, a steering control system according to a first embodiment will be described with reference to the accompanying drawings. Figure 1 As shown, the electric power steering system 10 includes a steering mechanism 20 that steers a steering wheel 12 based on an operation of a steering wheel 22 by a driver, and a steering actuator 30 that electrically steers the steering wheel 12 .

[0028] The steering mechanism 20 includes a steering wheel 22, a steering shaft 24 fixed to the steering wheel 22, and a rack and pinion mechanism 27. The steering shaft 24 includes a column shaft 24a connected to the steering wheel 22, an intermediate shaft 24b connected to the lower end of the column shaft 24a, and a pinion shaft 24c connected to the lower end of the intermediate shaft 24b. The lower end of the pinion shaft 24c is connected to the rack shaft 26 via the rack and pinion mechanism 27. The left and right steering wheels 12 are connected to both ends of the rack shaft 26 via a tie rod 28. Therefore, the rotational motion of the steering wheel 22 (i.e., the rotational motion of the steering shaft 24) is converted into the rotational motion of the rack shaft 26 in the axial direction ( Figure 1 The rack and pinion mechanism 27 includes a pinion shaft 24c and a rack shaft 26. The rack and pinion mechanism 27 transmits the translational motion to the steering wheel 12 via the tie rods 28 connected to both ends of the rack shaft 26, thereby changing the steering angle of the steering wheel 12. The maximum value of the displacement of the rack shaft 26 in the axial direction is limited by the rack housing 16.

[0029] On the other hand, the steering actuator 30 shares the rack shaft 26 with the steering mechanism 20, and includes a motor 32, an inverter 33, a ball screw mechanism 34, and a belt reduction gear mechanism 36. The motor 32 is a power source for steering the steering wheel 12, and in this embodiment, for example, a three-phase surface permanent magnet synchronous motor (SPMSM) can be used as the motor 32. The ball screw mechanism 34 is integrally attached to the periphery of the rack shaft 26, and the belt reduction gear mechanism 36 transmits the rotational force of the output shaft 32a of the motor 32 to the ball screw mechanism 34. The rotational force of the output shaft 32a of the motor 32 is converted into a force for translating the rack shaft 26 in the axial direction via the belt reduction gear mechanism 36 and the ball screw mechanism 34. The steering wheel 12 can be steered by the force in the axial direction applied to the rack shaft 26.

[0030] The steering control system 40 controls the steering wheel 12 and operates the steering actuator 30 to control the steering angle as its control parameter. The steering control system 40 controls the control parameter with reference to the steering torque Th, which is the torque input by the driver via the steering wheel 22 and detected by the torque sensor 50, or the vehicle speed V, which is detected by the vehicle speed sensor 52. The steering control system 40 also refers to the rotation angle θm of the output shaft 32a detected by the rotation angle sensor 54 or the currents iu, iv, and iw flowing in the motor 32. The currents iu, iv, and iw can be detected as a voltage drop provided in a shunt resistor provided in each branch of the inverter 33.

[0031] The steering control system 40 includes a central processing unit (CPU) 42, a read only memory (ROM) 44, and a peripheral circuit 46 connected to each other via a communication line 48. The peripheral circuit 46 includes a circuit generating a clock signal for defining internal operations, a power supply circuit, and a reset circuit.

[0032] Figure 2 Some of the processing performed by the steering control system 40 is shown. This is achieved by causing the CPU 42 to execute a program stored in the ROM 44. Figure 2 The processing shown. The basic target torque calculation processing M10 is a processing for calculating the basic target torque Thb* as the base value of the target steering torque Th* based on the axial force Taf to be described later, wherein the target steering torque Th* is to be input by the driver to the steering shaft 24 via the steering wheel 22. Here, the axial force Taf is a force applied to the rack shaft 26 in the axial direction. Since the axial force Taf is a quantity corresponding to the lateral force acting on the steering wheel 12, the lateral force can be determined based on the axial force Taf. On the other hand, it is preferable to determine the torque to be input by the driver to the steering shaft 24 via the steering wheel 22 based on the lateral force. Therefore, the basic target torque calculation processing M10 is a processing for calculating the basic target torque Thb* based on the lateral force determined based on the axial force Taf.

[0033] Specifically, the basic target torque calculation process M10 is a process that calculates the magnitude of the basic target torque Thb* to be lower than when the vehicle speed V is high when the magnitude (absolute value) of the axial force Taf is the same and the vehicle speed V is low. This can be achieved, for example, by causing the CPU 42 to perform mapping calculation on the basic target torque Thb* in a state where mapping data is pre-stored in the ROM 44, wherein the mapping data takes the axial force Taf or the lateral acceleration determined according to the axial force Taf and the vehicle speed V as an input variable and takes the basic target torque Thb* as an output variable. Here, the mapping data is paired data of a discrete value of the input variable and a value of an output variable corresponding to the value of the input variable. For example, the mapping calculation is a process that outputs the value of the corresponding output variable of the mapping data as a calculation result when the value of one input variable matches one of the values ​​of the input variables of the mapping data, and outputs a value obtained by interpolating the values ​​of a plurality of output variables included in the mapping data as a calculation result when the value of one input variable matches any of the values ​​of the input variables.

[0034] The hysteresis processing M14 is a processing for calculating and outputting a hysteresis correction amount Thys for correcting the basic target torque Thb* based on the rotation angle (pinion angle θp) of the pinion shaft 24c, which is a convertible angle that can be converted into the steering angle of the steering wheel 12. Specifically, the hysteresis processing M14 includes the following processing: recognizing the forward switching and the backward switching of the steering wheel 22 based on the change of the pinion angle θp, etc., and calculating the hysteresis correction amount Thys so that the magnitude of the target steering torque Th* is larger when switching forward than when switching backward. Specifically, the hysteresis processing M14 includes a processing for setting the hysteresis correction amount Thys to be variable based on the vehicle speed V.

[0035] The addition process M12 is a process for calculating the target steering torque Th* by adding the hysteresis correction amount Thys to the basic target torque Thb*. The steering operation amount calculation process M16 is a process for calculating the steering operation amount Ts*, which is an operation amount for controlling the steering torque Th to the target steering torque Th* by feedback control. The steering operation amount Ts* is an amount including the operation amount for controlling the steering torque Th to the target steering torque Th* by feedback control, and the steering operation amount Ts* may include a feedforward term. The operation amount for feedback control is an amount for increasing the magnitude (absolute value) of the torque required for the motor 32, for example, when the signs of both the steering torque Th and the target steering torque Th* are positive and the steering torque Th is greater than the target steering torque Th*. In the present embodiment, the steering operation amount Ts* is an amount corresponding to the torque Td required by the motor 32 in the feedback control of the steering torque Th to the target steering torque Th*, and is an amount that has been converted into a torque applied to the steering shaft 24 .

[0036] The axial force calculation process M18 is a process for calculating the axial force Taf by adding the steering torque Th to the steering operation amount Ts*. Since the steering torque Th is a torque applied to the steering shaft 24, the axial force Taf in this embodiment has a value obtained by converting the force applied to the rack shaft 26 in the axial direction into a torque applied to the steering shaft 24.

[0037] The canonical model calculation process M20 is a process of calculating a pinion angle command value θp* as a command value of the pinion angle θp based on the axial force Taf. Specifically, the canonical model calculation process M20 is a process of calculating the pinion angle command value θp* using a model formula represented by expression (c1).

[0038] Taf=K·θp*+C·θp*'+J·θp*” (c1)

[0039] The model represented by the expression (c1) is a model of the value indicated by the pinion angle θp when the same torque amount as the axial force Taf is input to the steering shaft 24. In the expression (c1), the viscosity coefficient C is a model of the friction force of the electric power steering system 10, etc., the inertia coefficient J is a model of the inertia of the electric power steering system 10, and the elastic coefficient K is a model of the specifications of the vehicle in which the electric power steering system 10 is installed, such as the suspension and wheel alignment. This model is not a model that accurately represents the actual electric power steering system 10 or the vehicle in which the electric power steering system 10 is installed, but is a standard model designed to change the steering angle behavior with input to an ideal behavior. In the present embodiment, the steering feel can be adjusted by designing a standard model.

[0040] Specifically, in the subtraction process M21, the viscosity term "C·θp*'", the spring term "K·θp*" and the reaction force Trv are subtracted from the axial force Taf. In the inertia coefficient division process M22, the output of the subtraction process M21 is divided by the inertia coefficient J to calculate the pinion angular acceleration command value αp* (=θp*"). Then, in the integration process M23 with the pinion angular acceleration command value αp* as input, the pinion angular velocity command value ωp* (=θp*') is calculated. In the integration process M24 with the pinion angular velocity command value ωp* as input, the pinion angle command value θp* is calculated.

[0041] The viscosity coefficient multiplication process M25 is a process for calculating a viscosity term “C·θp*′” by multiplying the pinion angular velocity command value ωp* by the viscosity coefficient C. The elastic coefficient multiplication process M26 is a process for calculating a spring term “K·θp*” by multiplying the pinion angle command value θp* by the elastic coefficient K.

[0042] The reaction force calculation processing M30 is a processing for calculating the reaction force Trv based on the pinion angle command value θp* or the pinion angular velocity command value ωp*. The integration processing M40 is a processing for calculating the integral value Inθ of the rotation angle θm of the motor 32. In the present embodiment, the steering angle of the steering wheel 12 when the vehicle is traveling in a straight line is set to "0", and the integral value Inθ when the steering angle is "0" is set to "0". The conversion processing M42 is a processing for calculating the pinion angle θp by dividing the integral value Inθ by the reduction ratio Km from the steering shaft 24 to the motor 32. The pinion angle θp indicates the straight-line travel direction when it is 0, and indicates the right steering angle or the left steering angle depending on whether it is positive or negative.

[0043] The angle operation amount calculation processing M50 is a processing for calculating the angle operation amount Tt*, which is the operation amount for controlling the pinion angle θp to the pinion angle command value θp* by feedback control. The angle operation amount Tt* is an amount corresponding to the torque Td required by the motor 32 in the feedback control of the pinion angle θp to the pinion angle command value θp*, and in the present embodiment, is an amount converted into a torque applied to the steering shaft 24.

[0044] The angle operation amount calculation process M50 includes a disturbance observer M52, which estimates the torque affecting the pinion angle θp as a disturbance torque in addition to the angle operation amount Tt* and the steering torque Th, and sets the disturbance torque as the estimated disturbance torque Tlde. In the present embodiment, the estimated disturbance torque Tlde is converted into a torque applied to the steering shaft 24.

[0045] The disturbance observer M52 calculates the estimated disturbance torque Tlde or the estimated value θpe by expression (c2) using the inertia coefficient Jp, the estimated value θpe of the pinion angle θp, the angle operation amount Tt0*, and the three-row and one-column matrix L for defining the observer gains l1, l2, and l3. The inertia coefficient Jp is a model of the inertia of the electric power steering system 10, and represents the actual inertia of the electric power steering system 10 with higher accuracy than the inertia coefficient J.

[0046]

[0047]

[0048] The differential calculation process M54 is a process of calculating a pinion angular velocity command value by differential calculation of the pinion angle command value θp*.

[0049] Feedback term calculation processing M56 is a processing for calculating the feedback operation amount Ttfb, which is the sum of a proportional term based on the difference between the pinion angle command value θp* and the estimated value θpe and a differential term based on the difference between the differential value of the pinion angle command value θp* and the differential value of the estimated value θpe.

[0050] The second-order differential processing M58 is a processing for calculating the second-order time differential value of the pinion angle command value θp*. The feedforward term calculation processing M60 is a processing for calculating the feedforward operation amount Ttff by multiplying the output value of the second-order differential processing M58 by the inertia coefficient Jp. The two-degree-of-freedom operation amount calculation processing M62 is a processing for calculating the angle operation amount Tt0* by subtracting the estimated disturbance torque Tlde from the sum of the feedback operation amount Ttfb and the feedforward operation amount Ttff.

[0051] The steering torque compensation process M72 is a process for calculating the angle operation amount Tt*, which is the output of the angle operation amount calculation process M50, by subtracting the steering torque Th from the angle operation amount Tt0*. The addition process M74 is a process for calculating the torque Td required by the motor 32 by adding the angle operation amount Tt* to the steering operation amount Ts*.

[0052] The conversion process M76 is a process of converting the required torque Td into a torque command value Tm*, which is a command value of the torque for the motor 32, by dividing the required torque Td by the reduction ratio Km.

[0053] The operation signal generation process M78 is a process of generating and outputting an operation signal MSt for controlling the torque for the motor 32 to the torque command value Tm* of the inverter 33. Actually, the operation signal MSt is an operation signal for each arm of each branch of the inverter 33.

[0054] Figure 3 The flow of the reaction force calculation process M30 is shown. This is achieved by causing the CPU 42 to repeatedly execute a program stored in the ROM 44 (for example, at intervals of a predetermined period of time). Figure 3 In the following description, reference numerals prefixed with "S" represent step numbers of each process.

[0055] exist Figure 3 In the series of processes shown, the CPU 42 first calculates the virtual reaction force Tief (S10). The virtual reaction force Tief has a value greater than "0" before the magnitude of the displacement in the axial direction of the rack shaft 26 reaches the maximum value determined by the rack housing 16, and is used to adjust the displacement to the maximum value.

[0056] Specifically, the CPU 42 sets the virtual reaction force Tief to "0" when the magnitude of the pinion angle command value θp* is less than the threshold value θpth, and when the magnitude of the pinion angle command value θp* is equal to or greater than the threshold value θpth and the magnitude of the pinion angle command value θp* is large, the CPU 42 sets the magnitude (absolute value) of the virtual reaction force Tief to a larger value than when the magnitude of the pinion angle command value θp* is small. Before the magnitude of the displacement in the axial direction immediately adjacent to the rack shaft 26 reaches the maximum value determined by the rack housing 16, the threshold value θpth is set to the pinion angle θp. Specifically, in the process of S10, the CPU 42 performs mapping calculation of the virtual reaction force Tief based on the pinion angle command value θp* in a state where mapping data having the pinion angle θp as an input variable and the virtual reaction force Tief as an output variable is pre-stored in the ROM 44.

[0057] Then, the CPU 42 calculates the offset Δωp* (S12). The CPU 42 sets the size (absolute value) of the offset Δωp* to a larger value when the size of the pinion angle command value θp* is large compared to the case when the size of the pinion angle command value θp* is small, and sets the offset Δωp* to the maximum value Δ0 before the pinion angle command value θp* reaches the threshold value θpth. The offset Δωp* has the same sign as the pinion angle command value θp*. Specifically, the CPU 42 performs mapping calculation on the offset Δωp* in a state where mapping data with the pinion angle θp as an input variable and the offset Δωp* as an output variable is pre-stored in the ROM 44.

[0058] Then, the CPU 42 substitutes a value obtained by adding the offset amount Δωp* to the pinion angular velocity command value ωp*, which is an input parameter in the process of S16 to be described later, into the pinion angular velocity command value ωp* (S14).

[0059] Then, the CPU 42 calculates the viscous reaction force Tωp* based on the pinion angular velocity command value ωp* calculated in the process of S14 (S16). Specifically, when the magnitude of the pinion angular velocity command value ωp* is less than the speed threshold value ωpth, the CPU 42 sets the viscous reaction force Tωp* to "0", and when the magnitude of the pinion angular velocity command value ωp* is equal to or greater than the speed threshold value ωpth and the magnitude of the pinion angular velocity command value ωp* is large, the CPU 42 calculates the viscous reaction force Tωp* to be larger than the case where the magnitude of the pinion angular velocity command value ωp* is small. Specifically, the CPU 42 performs mapping calculation of the viscous reaction force Tωp* in a state where mapping data with the angular velocity as an input variable and with the viscous reaction force Tωp* as an output variable is pre-stored in the ROM 44.

[0060] Then, the CPU 42 substitutes the value obtained by multiplying the viscous reaction force Tωp* by the gain G into the viscous reaction force Tωp* (S18). When the magnitude of the pinion angle command value θp* is small, the CPU 42 sets the gain G to "0", and when the pinion angle command value θp* is close to the threshold value θpth and the magnitude of the pinion angle command value θp* is large, the CPU 42 sets the gain G to be larger than when the magnitude of the pinion angle command value θp* is small. Here, the CPU 42 sets the gain G to the maximum value before the pinion angle command value θp* reaches the threshold value θpth. Specifically, the CPU 42 performs mapping calculation on the gain G in a state where mapping data with the pinion angle θp as an input variable and the gain G as an output variable is pre-stored in the ROM 44.

[0061] Then, the CPU 42 substitutes the sum of the virtual reaction force Tief and the viscous reaction force Tωp* into the reaction force Trv (S20). When the processing of S20 is completed, the CPU 42 temporarily ends the process. Figure 3 The processing flow shown.

[0062] The operation and advantages of this embodiment will be described below. When the driver operates the steering wheel 22, the CPU 42 calculates the target steering torque Th* in response, and controls the steering torque Th to the target steering torque Th* through feedback control. The CPU 42 calculates the pinion angle command value θp* based on the sum of the steering torque Th and the steering operation amount Ts* as the operation amount for feedback control. Then, the CPU 42 calculates the angle operation amount Tt*, which is the operation amount for feedback control of the estimated value θpe of the pinion angle θp to the pinion angle command value θp*. Then, the CPU 42 determines the torque command value Tm* based on the sum of the steering operation amount Ts* and the angle operation amount Tt*, and controls the torque for the motor 32 to the torque command value Tm*.

[0063] Here, when the magnitude of the pinion angle command value θp* is equal to or greater than the threshold value θpth, the CPU 42 calculates the magnitude of the virtual reaction force Tief to be greater than "0". Therefore, when the axial force Taf is the same and the magnitude of the pinion angle command value θp* is equal to or greater than the threshold value θpth, the magnitude of the pinion angle command value θp* is less likely to increase than when the magnitude of the pinion angle command value θp* is less than the threshold value θpth. Therefore, the magnitude of the estimated value θpe is likely to be smaller than the magnitude of the pinion angle command value θp*. When the magnitude of the estimated value θpe is smaller than the magnitude of the pinion angle command value θp*, the torque for the motor 32 is generated as a torque for reducing the magnitude of the pinion angle θp, and thus a traction resistance is applied to the steering wheel 22 against the driver's operation for increasing the magnitude of the pinion angle θp. Therefore, the operation of the steering wheel 22 for increasing the magnitude of the pinion angle θp to be excessively greater than the threshold value θpth is suppressed.

[0064] In the present embodiment, the process of applying the traction resistance to the steering wheel 22 is realized by the process of calculating the reaction force Trv in the specification model calculation process M20. The specification model calculation process M20 is a process of calculating the pinion angle command value θp* based on the specification model designed to adjust the steering feel. Therefore, when the magnitude of the pinion angle θp reaches the vicinity of the threshold value θpth, the increase in the reaction force Trv corresponds to the change of the specification model. Since the angle operation amount calculation process M50 controls the pinion angle θp to the pinion angle command value θp*, the controllability of the angle operation amount calculation process M50 is maintained even when the specification model changes.

[0065] On the other hand, for example, when processing the angle operation amount Tt* based on the reaction force Trv correction, the value of the estimated disturbance torque Tlde is affected, and therefore the estimated disturbance torque Tlde becomes an inappropriate value at the time point when the correction based on the reaction force Trv is not performed, and the controllability of the pinion angle θp deteriorates.

[0066] According to the above-mentioned embodiment, the following operations and advantages are also achieved. The reaction force Trv includes a viscous reaction force Tωp*. Here, the viscous reaction force Tωp* is a parameter that is larger when the size of the pinion angle command value θp* is large compared to when the size of the pinion angle command value θp* is small, and is likely to increase when the size of the pinion angle command value θp* is large compared to the viscosity term "C·ωp*". Therefore, when the pinion angular velocity command value ωp* has a larger value as the pinion angle command value θp* approaches the threshold value θpth, the viscous reaction force Tωp* has a large value, which is used to reduce the size of the pinion angular velocity command value ωp*. Therefore, when the pinion angle command value θp* approaches the threshold value θpth, the excessive increase in the size of the pinion angular velocity command value ωp* can be suppressed. On the other hand, when the magnitude of the rate of change of the pinion angle command value θp* when the pinion angle command value θp* is greater than the threshold value θpth is large, the impact caused by the conflict between the traction resistance applied to the steering wheel 22 based on the virtual reaction force Tief and the force used to increase the magnitude of the pinion angle command value θp* may increase.

[0067] Through the norm model calculation process M20, the pinion angle command value θp* is calculated based on the expression (c1) representing the norm model, and the pinion angle θp is controlled to the pinion angle command value θp*. Therefore, the steering characteristics can be adjusted using the norm model.

[0068] The target steering torque Th* is set based on the sum of the steering operation amount Ts* and the steering torque Th. Here, it is possible to determine the target torque required for improving the steering feeling of the driver based on the lateral force. On the other hand, since the sum of the steering operation amount Ts* and the steering torque Th can be converted into the lateral force of the vehicle, it is easy to design a process that calculates the target steering torque Th* by determining the target steering torque Th* based on the sum.

[0069] Hereinafter, the second embodiment will be described with reference to the drawings, focusing on the differences from the first embodiment.

[0070] Figure 4 Some of the processes performed by the steering control system 40 according to this embodiment are shown. This is achieved by causing the CPU 42 to execute a program stored in the ROM 44. Figure 4 For convenience, the same step numbers are used to refer to Figure 4 in Figure 2 The processing shown corresponds to the processing.

[0071] In the present embodiment, the steering operation amount Ts* output from the steering operation amount calculation process M16 is input to the reaction force application process M80. The steering operation amount Ts* that has been corrected in the reaction force application process M80 is input to the axial force calculation process M18, and is also input to the addition process M74. In this embodiment, the specification model calculation process M20 does not include the reaction force calculation process M30.

[0072] Figure 5 The flow of the reaction force application process M80 is shown. This is achieved by causing the CPU 42 to repeatedly execute a program stored in the ROM 44 (for example, at intervals of a predetermined period of time). Figure 5 The processing flow shown.

[0073] exist Figure 5 In the series of processing shown, first, the CPU 42 acquires the pinion angle θp (S30). Then, the CPU 42 substitutes the value obtained by multiplying the steering operation amount Ts* output from the steering operation amount calculation processing M16 by the gain Gief into the steering operation amount Ts* (S32). Here, when the magnitude of the pinion angle θp is small, the CPU 42 fixes the gain Gief to "1", and when the pinion angle θp is close to the threshold value θpth and the magnitude of the pinion angle θp is large, the CPU 42 sets the gain Gief to a smaller value than when the magnitude of the pinion angle θp is small. The gain Gief has a value from "0" to "1".

[0074] When the processing of S32 is completed, the CPU 42 temporarily terminates Figure 5 The operation and advantages of this embodiment will be described below.

[0075] By setting the gain Gief to a value less than "1" when the magnitude of the pinion angle θp approaches the threshold value θpth, the CPU 42 corrects the magnitude of the steering operation amount Ts* for the process of calculating the axial force Taf to decrease. Therefore, even in the case where the steering operation amount Ts* calculated in the steering operation amount calculation process M16 is the same, when the pinion angle command value θp* is equal to or greater than the threshold value θpth, the magnitude of the pinion angle command value θp* is less likely to increase than when the pinion angle command value θp* is less than the threshold value θpth. Therefore, the magnitude of the pinion angle command value θp* is likely to be smaller than the magnitude of the estimated value θpe. When the magnitude of the pinion angle command value θp* is smaller than the magnitude of the estimated value θpe, a torque for reducing the magnitude of the pinion angle θp is generated for the torque of the motor 32, and thus a force in the direction opposite to the driver's operation is applied to the steering wheel 22. Therefore, the operation of the steering wheel 22 for increasing the magnitude of the pinion angle θp to be excessively greater than the threshold value θpth is suppressed.

[0076] Hereinafter, the third embodiment will be described with reference to the drawings, focusing on differences from the first embodiment.

[0077] Figure 6 FIG. 1 shows the configuration of the electric power steering system 10 according to this embodiment. Figure 6 in Figure 1 The components shown correspond to the components.

[0078] In the present embodiment, a clutch 60 is provided in the pinion shaft 24c, which is capable of cutting off the transmission of power to and from the steering wheel 22. That is, the pinion shaft 24c is connected to one end of the clutch 60, and the input shaft 24d connected to the steering wheel 22 is connected to the other end of the clutch 60. In this embodiment, the input shaft 24d and the pinion shaft 24c are referred to as the steering shaft 24.

[0079] The power of the motor 72 is applied to the input shaft 24d via the reduction gear 70. The voltage of the inverter 74 is applied to the terminals of the motor 72. The traction resistance actuator 80 is composed of the input shaft 24d, the reduction gear 70, the motor 72 and the inverter 74. In this embodiment, the steering control system 40 refers to the rotation angle (steering angle θh) of the steering wheel 22 detected by the steering angle sensor 82.

[0080] Figure 7 Some of the processes performed by the steering control system 40 according to this embodiment are shown. This is achieved by causing the CPU 42 to execute a program stored in the ROM 44. Figure 7 For convenience, the same step numbers are used to refer to Figure 7 in Figure 2 The processing shown corresponds to the processing.

[0081] like Figure 7 As shown, in this embodiment, the command value of the steering angle (steering angle command value θh*), the steering angular velocity command value ωh*, and the steering angular acceleration command value αh* are calculated in the specification model calculation processing M20, instead of calculating the pinion angle command value θp*, the pinion angular velocity command value ωp*, and the pinion angular acceleration command value αp*. On the other hand, the steering angle ratio change processing M82 is a processing that sets the adjustment amount Δa to be variable based on the vehicle speed V, wherein the adjustment amount Δa is used to change the steering angle ratio that is the ratio of the target value of the steering angle (pinion angle command value θp*) to the steering angle command value θh*. Specifically, the adjustment amount Δa is set so that: the change in the steering angle with the change in the steering angle is greater when the vehicle speed V is low than when the vehicle speed V is high. The addition processing M84 sets the pinion angle command value θp* by adding the adjustment amount Δa to the steering angle command value θh*.

[0082] The traction resistance calculation process M86 is a process of calculating a torque command value Tr* for the motor 72, which is an operation amount for feedback control of the steering angle θh to the steering angle command value θh*. The operation signal generation process M88 is a process of operating the inverter 74 by outputting an operation signal MS for controlling the torque for the motor 72 to the torque command value Tr* to the inverter 74.

[0083] In the present embodiment, the steering torque compensation process M72 is not provided, and the output of the angle operation amount calculation process M50 is the angle operation amount Tt0*. In the present embodiment, the angle operation amount Tt0* output in the angle operation amount calculation process M50 is the required torque Td. That is, in the present embodiment, the torque command value Tm* is calculated only based on the angle operation amount Tt0*.

[0084] Figure 8 FIG. 4 shows a flow of the reaction force calculation process M30 according to this embodiment. This is achieved by causing the CPU 42 to repeatedly execute a program stored in the ROM 44 (for example, at intervals of a predetermined period of time). Figure 8 The processing flow shown.

[0085] exist Figure 8In the series of processes shown, first, the CPU 42 calculates the steering side virtual reaction force Tiefs (S40). Here, when the magnitude of the steering angle θh is less than the threshold value θhth, the CPU 42 sets the steering side virtual reaction force Tiefs to "0", and when the magnitude of the steering angle θh is equal to or greater than the threshold value θhth and the magnitude of the steering angle θh is large, the CPU 42 calculates the magnitude of the steering side virtual reaction force Tiefs to be larger than when the magnitude of the steering angle θh is small. Specifically, in a state where mapping data having the steering angle θh as an input variable and the steering side virtual reaction force Tiefs as an output variable is pre-stored in the ROM 44, the CPU 42 performs mapping calculation on the steering side virtual reaction force Tiefs.

[0086] Then, the CPU 42 calculates the angle side virtual reaction force Tieft (S42). Specifically, when the magnitude of the pinion angle command value θp* is less than the threshold value θpth, the CPU 42 sets the angle side virtual reaction force Tieft to "0", and when the magnitude of the pinion angle command value θp* is equal to or greater than the threshold value θpth and the magnitude of the pinion angle command value θp* is large, the CPU 42 calculates the magnitude of the angle side virtual reaction force Tieft to be larger than when the magnitude of the pinion angle command value θp* is small. The threshold value θpth is set to the pinion angle θp before the magnitude of the displacement in the axial direction immediately adjacent to the rack shaft 26 becomes the maximum value determined by the rack housing 16. Specifically, in a state in which mapping data with the pinion angle θp as an input variable and the angle side virtual reaction force Tieft as an output variable is pre-stored in the ROM 44, the CPU 42 performs mapping calculation of the angle side virtual reaction force Tieft based on the pinion angle command value θp*.

[0087] Then, the CPU 42 determines whether the magnitude of the steering side virtual reaction force Tiefs is greater than the magnitude of the angle side virtual reaction force Tieft (S44). Then, when it is determined that the magnitude of the steering side virtual reaction force Tiefs is greater (S44: Yes), the CPU 42 substitutes the steering side virtual reaction force Tiefs into the reaction force Trv (S46). On the other hand, when it is determined that the magnitude of the steering side virtual reaction force Tiefs is equal to or less than the magnitude of the angle side virtual reaction force Tieft (S44: No), the CPU 42 substitutes the angle side virtual reaction force Tieft into the reaction force Trv (S48).

[0088] In addition, when the processing of S46 and S48 is completed, the CPU 42 temporarily ends the Figure 8According to the above-described embodiment, in addition to the advantages corresponding to those in the first embodiment, the present embodiment achieves the following operations and advantages.

[0089] The reaction force Trv includes the steering-side virtual reaction force Tiefs. Therefore, when the magnitude of the steering angle θh is greater than the threshold value θhth, the steering wheel 22 can be prevented from being operated so that the magnitude of the steering angle θh becomes larger. Therefore, when the maximum value of the steering angle θh is determined based on its structure, etc., an excessive increase in the magnitude of the steering torque Th or the steering angular velocity can be suppressed at the maximum value. An example of a factor for defining the maximum value is a factor determined by a spiral cable in a structure in which an electronic device is provided in the steering wheel 22 and power is supplied to the electronic device via the spiral cable. That is, since an excessive force may be applied to the spiral cable when the magnitude of the steering angle is about to be greater than the maximum value, the maximum value of the magnitude of the steering angle θh is specified from the viewpoint of protecting the spiral cable.

[0090] The correspondence between the elements in the above-mentioned embodiment and the elements described in the “Summary of the Invention” is as follows. In the following description, the correspondence will be described for each number in the configuration described in the “Summary of the Invention”. [1] Angle command value calculation processing corresponds to Figure 2 and Figure 4 The canonical model calculation process in M20, or Figure 7 The standard model calculation process M20, the steering angle ratio change process M82 and the addition process M84 in the embodiment. The convertible angle corresponds to the pinion angle θp. The operation process corresponds to the addition process M74, the conversion process M76 and the operation signal generation process M78. The correction process corresponds to the following processes: the process of subtracting the reaction force Trv in the process of S10 from the axial force Taf in the subtraction process M21; the process of S32; or Figure 7 The subtraction process M21 in the subtraction process of the axial force Taf is a process of subtracting the reaction force Trv from the axial force Taf. The drive circuit corresponds to the inverter 33. [2] The elastic force corresponds to the sum of the elastic term "K·θp*" and the virtual reaction force Tief. [3] The viscous force corresponds to the sum of the viscous term "C·θp*'" and the viscous reaction force Tωp*. The viscosity adjustment process corresponds to the processes of S12 to S18. [4] This process corresponds to the process of S32. [5] This process corresponds to Figure 7 and Figure 8 [6] This process corresponds to Figure 7 [7] The target steering torque calculation process corresponds to the basic target torque calculation process M10, the addition process M12 and the hysteresis process M14.

[0091] These embodiments may be modified as follows. The embodiments described above and the modified examples described below may be combined with each other as long as no technical contradiction is caused.

[0092] Correction Processing

[0093] For example, in the process of S10, instead of the pinion angle command value θp*, the virtual reaction force Tief may be calculated based on the pinion angle θp, or the virtual reaction force Tief may be calculated based on the estimated value θpe. For example, in the process of S32, instead of the pinion angle θp, the gain Gief may be calculated based on the estimated value θpe, or the gain Gief may be calculated based on the pinion angle command value θp*.

[0094] For example, in the processing of S42, the angle side virtual reaction force Tieft may be calculated based on the pinion angle θp instead of the pinion angle command value θp*, or the angle side virtual reaction force Tieft may be calculated based on the estimated value θpe. For example, in the processing of S40, the steering side virtual reaction force Tiefs may be calculated based on the steering angle θh instead of the steering angle command value θh*.

[0095] For example, by replacing the threshold value θhth with the smaller value of the threshold value θhth and the steering angle command value θh* in the process of S40 when the pinion angle command value θp* reaches the threshold value θpth, only the process of S40 can be executed, and the process of S42 can be deleted. In this case, the logic that the magnitude of the virtual reaction force Tief is set to be greater than "0" when the steering angle command value θh* is equal to or greater than the threshold value θhth holds, but a process similar to the process of S42 can be adopted in which the magnitude of the virtual reaction force Tief is set to be greater than "0" even when the pinion angle command value θp* is equal to or greater than the threshold value θpth. In this process, it is preferable to set the threshold value θhth to be variable according to the steering angle ratio. Here, the setting to be variable is not necessary. For example, by replacing the threshold value θpth with the smaller value of the threshold value θpth and the pinion angle command value θp* in the process of S42 when the steering angle command value θh* reaches the threshold value θhth, only the process of S42 can be executed, and the process of S40 can be deleted. In this case, it is preferable to set the threshold value θpth to be variable according to the steering angle ratio. Here, setting to be variable is not essential.

[0096] exist Figure 4In the processing flow shown, the reaction force application processing M80 corrects the magnitude of the steering operation amount Ts* to be reduced, but the present invention is not limited to this. For example, in the steering operation amount calculation processing M16, a correction processing for reducing the magnitude of the steering operation amount Ts* may be performed. Therefore, for example, when the steering operation amount calculation processing M16 uses an integral element to calculate the steering operation amount Ts*, the controllability of the torque feedback control can be prevented from being deteriorated. The present invention is not limited to this, and for example, when the steering operation amount Ts* is calculated using an integral element, the value held by the integral element may be corrected to be reduced based on the correction amount by which the steering operation amount Ts* is corrected to be reduced in the reaction force application processing M80.

[0097] Viscosity adjustment process

[0098] For example, you can delete Figure 3 In the process flow shown in FIG. 1 , the process of S18 is performed, and in the process of S20 , the viscous reaction force Tωp* calculated in the process of S16 can be added to the virtual reaction force Tief. Figure 3 In the illustrated processing flow, the processes of S12 and S14 may be deleted.

[0099] exist Figure 4 In the processing flow shown, the viscous reaction force Tωp* is not used in the process of calculating the pinion angle command value θp*, but can be used. Figure 8 In the illustrated processing flow, the viscous reaction force Tωp* is not used in the process of calculating the pinion angle command value θp*, but can be used. Here, the viscous reaction force can be calculated based on, for example, only the time differential value of the pinion angle command value θp*, or can be calculated based on, for example, only the time differential value of the steering angle command value θh*. For example, the viscous reaction force can be calculated based on both the time differential value of the pinion angle command value θp* and the time differential value of the steering angle command value θh*. This can be achieved, for example, by calculating the viscous reaction force based on the smaller value of the time differential value of the pinion angle command value θp* and the time differential value of the steering angle command value θh*.

[0100] The physical quantity indicating the angular velocity of the steering angle (which is the angular velocity used to calculate the viscous reaction force) is not limited to the command value and may be, for example, the time differential value of the pinion angle θp, the time differential value of the estimated value θpe, or the time differential value of the steering angle θh.

[0101] Required torque Td

[0102] exist Figure 2 and Figure 4In the embodiment, the sum of the angle operation amount Tt* and the steering operation amount Ts* is used as the required torque Td, but the present invention is not limited thereto. For example, the angle operation amount Tt* may be used as the required torque.

[0103] exist Figure 7 In the processing flow shown, the angle operation amount Tt* is used as the required torque Td, but the present invention is not limited to this. For example, the sum of the angle operation amount Tt* and the steering operation amount Ts* may be used as the required torque Td.

[0104] Angle command value calculation processing

[0105] In the above embodiment, the pinion angle command value θp* or the steering angle command value θh* is calculated using the axial force Taf as an input, but the present invention is not limited to this, and for example, the steering operation amount Ts* may be used as an input. In the above embodiment, the pinion angle command value θp* or the steering angle command value θh* is calculated based on the expression (c1) or the like using the axial force Taf as an input, but the logic (model) for calculating the pinion angle command value θp* or the steering angle command value θh* is not limited to this.

[0106] For example, in Figure 7 In the illustrated processing flow, the steering angle rate changing process M82 and the adding process M84 may be deleted, and the output of the specification model calculation process M20 may be used as the steering angle command value θh* and the pinion angle command value θp*.

[0107] Interference Observer

[0108] In the above-mentioned embodiment, the disturbance observer is constituted by a simple model in which the torque acting on the steering wheel 12 is balanced with the torque proportional to the angular acceleration of the steering angle, but the present invention is not limited thereto. For example, the disturbance observer may be constituted by a model in which the torque acting on the steering wheel 12 is balanced with the sum of the torque proportional to the angular acceleration of the steering angle and the torque proportional to the angular velocity of the steering angle.

[0109] The method of calculating the estimated disturbance torque Tlde is not limited to the example described in the embodiment. Figure 2 In the processing flow shown, the estimated disturbance torque Tlde can be calculated by subtracting the angle operation amount Tt*, the steering operation amount Ts* and the steering torque Th from the following values: the value is obtained by multiplying the second-order time differential value of the pinion angle command value θp* or the second-order time differential value of the pinion angle θp by the inertia coefficient Jp.

[0110] Angle operation amount calculation processing

[0111] In the above embodiment, the feedforward operation amount Ttff is calculated based on the second-order time differential value of the pinion angle command value θp*, but the present invention is not limited to this, and for example, the feedforward operation amount Ttff can be calculated based on the second-order time differential value of the pinion angle θp or the second-order time differential value of the estimated value θpe.

[0112] In the above-described embodiment, the feedforward term is calculated by modeling the electric power steering system 10 using a simple model in which the torque acting on the steering wheel 12 is balanced with the torque proportional to the angular acceleration of the steering wheel, but the present invention is not limited thereto. For example, a feedforward term may be calculated using a model in which the torque acting on the steering wheel 12 is balanced with the sum of the torque proportional to the angular acceleration of the steering wheel and the torque proportional to the angular velocity of the steering wheel. This can be achieved, for example, by using the sum of the following values ​​as the feedforward operation amount Ttff: a value obtained by multiplying the second-order time differential value of the pinion angle command value θp* by the inertia coefficient Jp; and a value obtained by multiplying the first-order time differential value of the pinion angle command value θp* by the viscosity coefficient Cp. Here, the viscosity coefficient Cp as a proportional coefficient of the angular velocity is different from the viscosity coefficient C used for its purpose in the canonical model calculation process M20, and the viscosity coefficient Cp is preferably obtained by modeling the actual behavior of the electric power steering system 10 with maximum accuracy.

[0113] The feedback control amount other than the input of the feedback term calculation process M56 is not limited to the estimated value θpe or the first time differential value of the estimated value θpe. For example, the pinion angle θp or its time differential value may be used instead of the estimated value θpe or the first time differential value of the estimated value θpe.

[0114] The feedback term calculation process M56 is not limited to the process of outputting the sum of the output value of the proportional element and the differential factor. For example, the output value of the proportional factor may be output, or, for example, the output value of the differential factor may be output. For example, the process of outputting the sum of at least one of the output value of the proportional factor and the output value of the differential factor and the output value of the integral factor may be adopted. When the output value of the integral factor is used, the disturbance observer is preferably deleted. Most importantly, when the output value of the integral factor is not used, the disturbance observer is not necessarily used.

[0115] Adjustable angle

[0116] In the above embodiment, the pinion angle θp is used as the convertible angle, but the present invention is not limited thereto. For example, the steering angle of the steering wheel may be used.

[0117] Steering operation amount

[0118] In the above-mentioned embodiment, the steering operation amount Ts* is converted into a torque for the steering shaft 24, but the present invention is not limited thereto. For example, the steering operation amount Ts* may be converted into a torque for the motor 32. In this case, for example, the sum of a value obtained by dividing the steering torque Th by the reduction ratio Km and the steering operation amount Ts* may be used as the axial force Taf, or the sum of a value obtained by multiplying the steering operation amount Ts* by the reduction ratio Km and the steering torque Th may be used as the axial force Taf.

[0119] Angle operation amount

[0120] In the above embodiment, the angle operation amount Tt* is converted into the torque for the steering shaft 24, but the present invention is not limited thereto. For example, the angle operation amount Tt* may be converted into the torque for the motor 32. Here, for example, when the steering operation amount Ts* is converted into the torque for the steering shaft 24, the sum of the value obtained by multiplying the angle operation amount Tt* by the reduction ratio Km and the steering operation amount Ts* may be used as the required torque Td.

[0121] The basic target torque calculation process is not limited to the process of calculating the basic target torque Thb* based on the axial force Taf and the vehicle speed V. For example, a process of calculating the basic target torque Thb* based only on the axial force Taf may be employed.

[0122] The process of correcting the basic target torque Thb* using the hysteresis correction amount Thys is not necessary. The steering control system is not limited to a system including a CPU 42 and a ROM 44 and performing software processing. For example, a dedicated hardware circuit (e.g., an application-specific integrated circuit (ASIC)) may be provided to perform at least a portion of the software processing performed in the above-described embodiment in hardware. That is, the steering control system may have at least one of the following configurations (a) to (c): (a) a processor that performs all processing according to a program and a program storage device (e.g., a ROM) that stores the program are provided; (b) a processor that performs some processing according to a program, a program storage device, and a dedicated hardware circuit that performs other processing are provided; (c) a dedicated hardware circuit that performs all processing is provided. Here, the number of software processing circuits including a processor and a program storage device or the number of dedicated hardware circuits may be two or more. That is, these processes are performed only by a processing circuit that includes at least one of one or more software processing circuits and one or more dedicated hardware circuits.

[0123] The motor is not limited to a surface permanent magnet synchronous motor (SPMSM), but may be an interior permanent magnet synchronous motor (IPMSM) or the like. The motor is not limited to a synchronous motor, but may be an induction motor. In addition, for example, the motor may be a DC motor with a brush. In this case, an H-bridge circuit may be used as a drive circuit.

[0124] The steering actuator is not limited to the example described in the embodiment. For example, a so-called double pinion type including a second pinion shaft that transmits the power of the motor 32 to the rack shaft 26 separately from the pinion shaft 24c may be adopted. For example, a configuration in which the output shaft 32a of the motor 32 is mechanically connected to the steering shaft 24 may be adopted. In this case, the steering actuator shares the steering shaft 24 or the rack and pinion mechanism 27 with the steering mechanism.

[0125] For example, in Figure 6 In the embodiment, the input shaft 24d may be mechanically connected to the pinion shaft 24c via a gear ratio changing mechanism that changes the gear ratio, instead of the clutch 60. In this case, the same processing as that described for the steer-by-wire type can also be achieved.

Claims

1. A steering system (10), characterized in that include: Steering wheel (22); a steering actuator (30) including a motor (32) and configured to steer the steering wheel (12); as well as A control device (40), wherein: The control device (40) is configured to perform the following processing: a steering operation amount calculation process for calculating a steering operation amount, the steering operation amount being an operation amount of the motor for steering the steering wheel (12) so as to control the steering torque to a target steering torque by feedback control, and being an operation amount convertible into a torque required by the motor (32), the steering torque being input by a driver, the target steering torque being determined based on an axial force corresponding to a lateral force acting on the steering wheel and being input by the driver; An angle command value calculation process of calculating an angle command value, the angle command value being a command value of a convertible angle that can be converted into a steering angle of the steering wheel (12) based on the steering operation amount; Angle operation amount calculation processing for calculating an angle operation amount, the angle operation amount being an operation amount for controlling the convertible angle to the angle command value by feedback control and being an operation amount that can be converted into a torque required by the motor (32); an operation process for operating a drive circuit of the motor (32) based on the angle operation amount to control the torque of the motor (32); and A correction process is provided for correcting parameters from upstream of the angle operation amount calculation process so that when the magnitude of the steering angle is equal to or greater than a steering angle threshold, a traction resistance is applied to resist the operation of the steering wheel (22) for increasing the magnitude of the steering angle.

2. The steering system (10) according to claim 1, characterized in that: The angle command value calculation process includes the following processes: a process of subtracting an elastic force from the steering operation amount as an input of the angle command value calculation process, wherein the elastic force is set to be larger when the magnitude of the steering angle is large than when the magnitude of the steering angle is small; and a process of calculating the angle command value based on the subtracted value; and The correction process includes a process of increasing the amount of increase of the elastic force as the magnitude of the steering angle increases when the magnitude of the steering angle is equal to or greater than the steering angle threshold.

3. The steering system (10) according to claim 1 or 2, characterized in that: The angle command value calculation processing includes the following processing: a processing of subtracting a viscous force from the steering operation amount as an input of the angle command value calculation processing, wherein the viscous force is set to be larger when the magnitude of the steering angular velocity is large compared to when the magnitude of the steering angular velocity is small; and a processing of calculating the angle command value based on the subtracted value, the steering angular velocity being a rate of change of the steering angle; and The control device is configured to perform a viscosity adjustment process, wherein when the steering angle is below the steering angle threshold, the viscosity adjustment process makes the viscosity force when the steering angle is closer to the steering angle threshold greater than the viscosity force when the steering angle is further away from the steering angle threshold.

4. The steering system (10) according to claim 1 or 2, characterized in that: The correction process includes a process of reducing the magnitude of the steering operation amount input to the angle command value calculation process when the magnitude of the steering angle is equal to or greater than the steering angle threshold value.

5. The steering system (10) according to claim 1 or 2, characterized in that: The steering wheel is attached to a traction resistance actuator (80), and the traction resistance actuator (80) is configured to apply traction resistance as a force resisting the operation of the steering wheel (22) to the steering wheel (22) in a state where power transmission between the steering wheel (12) and the steering wheel (22) is cut off; The control device (40) is configured to execute a traction resistance operation process of operating the traction resistance actuator (80) according to the angle command value; and The correction process is a process that corrects the parameters from the upstream of the angle operation amount calculation process so that the traction resistance against the operation of the steering wheel (22) for increasing the magnitude of the steering angle is applied by the traction resistance actuator (80) when at least one of the following conditions is satisfied: a condition that the magnitude of the steering angle as the rotation angle of the steering wheel (22) is equal to or greater than a steering angle threshold; And the condition that the steering angle is equal to or greater than the steering angle threshold.

6. The steering system (10) according to claim 1 or 2, characterized in that: The operation process is a process of operating the drive circuit based on the angle operation amount without considering the steering operation amount so that the torque of the motor (32) is controlled.

7. The steering system (10) according to claim 1 or 2, characterized in that: The control device is configured to execute a target steering torque calculation process of calculating the target steering torque based on a sum of amounts obtained by converting the steering operation amount and the steering torque into forces acting on the same object.

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