Vehicle steering system control device

Abstract

To provide a control device of a vehicular steering system that can perform friction compensation control by which proper steering reaction force can be transmitted.SOLUTION: A control device of a vehicular steering system comprises a steering torque control part that generates a current command value (first current command value) on the basis of a steering torque target value. The steering torque control part comprises: a static friction compensation part 450 that derives a static friction compensation value Iref_st, on the basis of actual steering torque Th_act of a steering wheel; and a kinetic friction compensation part 460 that derives a kinetic friction compensation value Iref_dy, on the basis of an actual steering angle speed obtained by differentiating an actual steering angle θh_act of the steering wheel. The steering torque control part generates a motor current command value (second current command value) for driving a motor for reaction force, on the basis of the static friction compensation value Iref_st and the kinetic friction compensation value Iref_dy.SELECTED DRAWING: Figure 8

Description

[Technical Field]

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

[0002] One type of vehicle steering system is the steer-by-wire (SBW) system, in which a steering mechanism (FFA: Force Feedback Actuator) having a steering wheel operated by the driver and a road wheel actuator (RWA: Road Wheel Actuator) that steers the steered wheels are mechanically separated. In the SBW system, the steering mechanism and the road wheel actuator are electrically connected via an electronic control unit (ECU). The steering wheel operation is transmitted to the road wheel actuator via an electrical signal to steer the steered wheels, and the road wheel actuator generates a steering reaction force to give the driver an appropriate steering feel. The steering mechanism generates the steering reaction force using a reaction force actuator equipped with a reaction force motor, and the road wheel actuator steers the steered wheels using a steering actuator equipped with a steering motor. The reaction force actuator and the road wheel are mechanically connected via a column shaft, and the reaction force (torque) generated by the reaction force actuator is transmitted to the driver via the column shaft and the road wheel (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-175770 Summary of the Invention [Problem to be solved by the invention]

[0004] In a SBW system where the steering mechanism and the turning mechanism are mechanically separated, the control device controls the actual steering torque so that it follows the steering torque target value. However, there is a possibility that the steering reaction force will not be transmitted properly due to friction acting on the steering mechanism, such as the reduction gear mechanism and the reaction force motor.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a control device for a vehicle steering system that can perform friction compensation control that can transmit an appropriate steering reaction force. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, a control device for a vehicle steering system according to one embodiment of the present invention is a control device for a vehicle steering system equipped with a reaction force motor that applies a steering reaction force to the steering wheel in accordance with the steering angle of the steering wheel, and a steering motor that steers steered wheels in accordance with the steering angle of the steering wheel, and includes: a steering torque target value generation unit that generates a steering torque target value that is a target value of the steering torque for obtaining the steering reaction force; and a steering torque control unit that generates a first current command value based on the steering torque target value, wherein the steering torque control unit includes: a static friction compensation unit that derives a static friction compensation value based on an actual steering torque that is an actual steering torque of the steering wheel; and a dynamic friction compensation unit that derives a dynamic friction compensation value based on an actual steering angular velocity that is an actual steering angular velocity of the steering wheel, and the steering torque control unit generates a second current command value for driving the reaction force motor based on the static friction compensation value and the dynamic friction compensation value.

[0007] According to the above configuration, it is possible to compensate for the friction component caused by the Coulomb friction of the steering mechanism, and to perform friction compensation control that can transmit an appropriate steering reaction force.

[0008] As a desirable aspect of the control device for a vehicle steering system, it is preferable that the static friction compensation unit derives the static friction compensation value in accordance with the first current command value, and the dynamic friction compensation unit derives the dynamic friction compensation value in accordance with the first current command value.

[0009] According to the above configuration, the static friction compensation value and the dynamic friction compensation value are obtained according to the increase or decrease in the first current command value.

[0010] In a preferred embodiment of the control device for a vehicle steering system, the static friction compensation unit includes a first current sensitive gain generation unit that generates a first gain that monotonically increases as the first current command value increases, and a second current sensitive gain generation unit that generates a second gain that monotonically decreases as the first current command value increases, and it is preferable that the static friction compensation unit derives the static friction compensation value based on the first gain and the second gain.

[0011] According to the above configuration, a static friction compensation value that appropriately compensates for the friction component caused by Coulomb friction of the steering mechanism can be obtained in accordance with the gain that increases or decreases as the first current command value increases.

[0012] In a preferred embodiment of the control device for a vehicle steering system, the static friction compensation unit includes a hysteresis component removal unit that calculates an intermediate value between the actual steering torque when the steering wheel is turned further and the actual steering torque when the steering wheel is turned back, and the hysteresis component removal unit calculates the intermediate value based on a value obtained by multiplying a predetermined value by the first gain, and the static friction compensation unit derives the static friction compensation value by multiplying a value obtained by subtracting the intermediate value from the actual steering torque by the second gain.

[0013] According to the above configuration, it is possible to derive a static friction compensation value that approximates a value that monotonically increases with the magnitude of the friction component caused by Coulomb friction in the steering mechanism.

[0014] In a preferred embodiment of the control device for a vehicle steering system, the dynamic friction compensation unit includes a third current sensitive gain generation unit that generates a third gain that monotonically increases as the first current command value increases, and the dynamic friction compensation unit preferably derives the dynamic friction compensation value based on the third gain.

[0015] According to the above configuration, a dynamic friction compensation value that appropriately compensates for the friction component caused by Coulomb friction of the steering mechanism can be obtained in accordance with the gain that increases or decreases as the first current command value increases.

[0016] As a desirable aspect of the control device for a vehicle steering system, it is preferable that the dynamic friction compensation unit derives the dynamic friction compensation value by multiplying the third gain by a sign function of the actual steering angular velocity when the magnitude of the actual steering angular velocity is equal to or greater than a predetermined steering angular velocity threshold.

[0017] According to the above configuration, it is possible to derive a dynamic friction compensation value that approximates a value that monotonically increases with the magnitude of the friction component caused by Coulomb friction of the steering mechanism.

[0018] As a desirable aspect of the control device for a vehicle steering system, when the magnitude of the actual steering angular velocity is equal to or greater than a predetermined steering angular velocity threshold, it is preferable that the dynamic friction compensation unit derives the dynamic friction compensation value by multiplying the third gain by a sign function of the actual steering angular velocity and a predetermined coefficient.

[0019] According to the above configuration, it is possible to derive a dynamic friction compensation value that approximates a value that monotonically increases with the magnitude of the friction component caused by Coulomb friction of the steering mechanism.

[0020] In a preferred embodiment of the control device for a vehicle steering system, the steering torque control unit preferably includes a ratio control unit that controls the ratio between the static friction compensation value and the dynamic friction compensation value based on the actual steering angular velocity.

[0021] According to the above configuration, the ratio of the static friction compensation value to the static friction compensation value and the ratio of the dynamic friction compensation value to the dynamic friction compensation value can be changed in accordance with a change in the actual steering angular velocity.

[0022] As a desirable aspect of the control device for a vehicle steering system, it is preferable that the ratio control unit makes the ratio of the dynamic friction compensation value larger than the ratio of the static friction compensation value when the magnitude of the actual steering angular velocity is equal to or larger than a predetermined steering angular velocity threshold, and makes the ratio of the static friction compensation value larger than the ratio of the dynamic friction compensation value when the magnitude of the actual steering angular velocity is smaller than the steering angular velocity threshold.

[0023] According to the above configuration, friction compensation control can be performed in accordance with the ratio between the Coulomb static friction and the Coulomb dynamic friction of the steering mechanism, which changes depending on the steering state.

[0024] As a desirable aspect of the control device for a vehicle steering system, it is preferable that the ratio control unit monotonically increases the ratio of the dynamic friction compensation value during the period from when the magnitude of the actual steering angular velocity becomes equal to or greater than the steering angular velocity threshold value until the ratio of the dynamic friction compensation value reaches its maximum value, and monotonically decreases the ratio of the dynamic friction compensation value during the period from when the magnitude of the actual steering angular velocity becomes less than the steering angular velocity threshold value until the ratio of the dynamic friction compensation value reaches its minimum value.

[0025] According to the above configuration, it is possible to suppress fluctuations in the steering reaction force caused by switching between the static friction compensation value and the dynamic friction compensation value.

[0026] In a preferred embodiment of the control device for a vehicle steering system, the ratio control unit monotonically decreases the ratio of the static friction compensation value during the period from when the magnitude of the actual steering angular velocity becomes equal to or greater than the steering angular velocity threshold value until the ratio of the static friction compensation value reaches its minimum value, and monotonically increases the ratio of the static friction compensation value during the period from when the magnitude of the actual steering angular velocity becomes less than the steering angular velocity threshold value until the ratio of the static friction compensation value reaches its maximum value.

[0027] According to the above configuration, it is possible to suppress fluctuations in the steering reaction force caused by switching between the static friction compensation value and the dynamic friction compensation value. [Effects of the Invention]

[0028] According to the present invention, it is possible to provide a control device for a vehicle steering system that can perform friction compensation control that can transmit an appropriate steering reaction force. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a configuration diagram showing an example of an outline of an SBW system including a control device according to the present disclosure. [Figure 2] FIG. 2 is a schematic diagram showing the hardware configuration of the ECU. [Figure 3] FIG. 3 is a diagram illustrating an example of a basic control block configuration of a control device according to the present disclosure. [Figure 4] FIG. 4 is a region diagram for explaining the steering direction in the present disclosure. [Figure 5] FIG. 5 is a conceptual diagram showing the relationship between the actual steering torque and the steering torque target value. [Figure 6] FIG. 6 is a conceptual diagram showing the relationship between the difference between the actual steering torque and the steering torque target value and the motor current value of the reaction force motor. [Figure 7] FIG. 7 is a block diagram showing an example of the configuration of the steering torque control unit according to the embodiment. [Figure 8] FIG. 8 is a block diagram showing an example of the configuration of the friction compensation unit according to the embodiment. [Figure 9] FIG. 9 is a block diagram showing an example of the configuration of a static friction compensation unit according to the embodiment. [Figure 10] FIG. 10 is a diagram showing an example of the first current-sensitive gain map. [Figure 11] FIG. 11 is a conceptual diagram illustrating a specific example of the input / output characteristics of the hysteresis component removing unit. [Figure 12] FIG. 12 is a flowchart showing an example of the hysteresis component removal process. [Figure 13] FIG. 13 is a conceptual diagram illustrating a specific example of the output characteristic of the hysteresis component extraction unit. [Figure 14] FIG. 14 is a diagram showing an example of the second current-sensitive gain map. [Figure 15]FIG. 15 is a conceptual diagram illustrating a specific example of the static friction compensation value. [Figure 16] FIG. 16 is a block diagram illustrating an example of the configuration of a dynamic friction compensation unit according to the embodiment. [Figure 17] FIG. 17 is a flowchart showing an example of the steering state determination process. [Figure 18] FIG. 18 is a conceptual diagram illustrating a specific example of input characteristics of the dynamic friction compensation value code generation unit. [Figure 19] FIG. 19 is a conceptual diagram illustrating a specific example of the output characteristic of the steering state determining unit. [Figure 20] FIG. 20 is a conceptual diagram illustrating a specific example of the output characteristic of the dynamic friction compensation value code generation unit. [Figure 21] FIG. 21 is a diagram showing an example of the third current-sensitive gain map. [Figure 22] FIG. 22 is a conceptual diagram illustrating a specific example of a dynamic friction compensation value using the third current sensitive gain map. [Figure 23] FIG. 23 is a conceptual diagram illustrating a modified example of the dynamic friction compensation value using the third current sensitive gain map. [Figure 24] FIG. 24 is a conceptual diagram showing an example of switching of the steering state determination flag. [Figure 25] FIG. 25 is a conceptual diagram showing an example of the operation of the ratio control unit. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings. Note that the present invention is not limited to the following embodiments. Furthermore, the components in the following embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

[0031] 1 is a block diagram showing an example of an outline of an SBW system equipped with a control device according to the present disclosure, which includes a reaction force device 30 constituting a steering mechanism having a steering wheel operated by a driver, a steering device 40 constituting a steering mechanism for steering steered wheels, and a control device 50 for controlling both devices.

[0032] The SBW system does not have an intermediate shaft that is mechanically connected to the column shaft (steering shaft, handle shaft) 2, which is found in general electric power steering devices, and instead transmits the driver's operation of the steering wheel 1 as an electrical signal, specifically the steering angle θh output from the reaction force device 30, as an electrical signal.

[0033] The reaction force device 30 includes a reaction force motor 31 and a reduction mechanism 32 that reduces the rotational speed of the reaction force motor 31. The reaction force device 30 transmits the vehicle's motion state, transmitted from the steered wheels 5L, 5R, to the driver as a steering reaction force. The reaction force motor 31 applies the steering reaction force to the steering wheel 1 via the reduction mechanism 32, such as a worm reducer or a planetary gear reducer.

[0034] The reaction force device 30 further includes a steering angle sensor 33 and a torque sensor 34. The steering angle sensor 33 detects the steering angle θh of the steering wheel 1. The torque sensor 34 detects the steering torque Th of the steering wheel 1. Hereinafter, the steering angle θh detected by the steering angle sensor 33 will also be referred to as the "actual steering angle θh_act," and the steering torque Th detected by the torque sensor 34 will also be referred to as the "actual steering torque Th_act."

[0035] In the present disclosure, a stopper (rotation limiting mechanism) 35 that physically sets a steering end point, which is the limit of possible steering, is provided on the column shaft 2. That is, the magnitude (absolute value) of the steering angle θh is limited by the stopper 35.

[0036] The steering device 40 includes a steering motor 41, a speed reduction mechanism 42 that reduces the rotational speed of the steering motor 41, and a pinion rack mechanism 44 that converts the rotational motion of the steering motor 41 into linear motion. The steering device 40 drives the steering motor 41 in accordance with the steering angle θh, and the resulting drive force is applied to the pinion rack mechanism 44 via the speed reduction mechanism 42, and the drive force is passed through the tie rods 3a and 3b to steer the steerable wheels 5L and 5R. An angle sensor 43 is disposed near the pinion rack mechanism 44 and detects the steering angle θt of the steerable wheels 5L and 5R. Instead of the steering angle θt of the steerable wheels 5L and 5R, for example, the motor angle of the steering motor 41 or the position of the rack may be detected and the detected value may be used. Hereinafter, the steering angle θt detected by the angle sensor 43 will also be referred to as the "actual steering angle θt_act."

[0037] In order to cooperatively control the reaction force device 30 and the steering device 40, the control device 50 generates a voltage control command value Vref1 for driving and controlling the reaction force motor 31 and a voltage control command value Vref2 for driving and controlling the steering motor 41 based on information such as the steering angle θh and the turning angle θt output from both devices, as well as the vehicle speed Vs detected by the vehicle speed sensor 10.

[0038] The control device 50 is supplied with power from the battery 12 and receives an ignition key signal via the ignition key 11. A CAN (Controller Area Network) 20 that transmits and receives various vehicle information is also connected to the control device 50, and the vehicle speed Vs can also be received from the CAN 20. Furthermore, a non-CAN 21 that transmits and receives communications other than the CAN 20, analog / digital signals, radio waves, etc. can also be connected to the control device 50.

[0039] Specifically, the control device 50 is, for example, an ECU (Electronic Control Unit) mounted on a vehicle. The ECU is mainly composed of a CPU (including an MCU, an MPU, etc.). Fig. 2 is a schematic diagram showing the hardware configuration of the ECU. Cooperative control of the reaction force device 30 and the steering device 40 is mainly executed by a program inside the CPU of the ECU.

[0040] Fig. 3 is a diagram showing an example of a control block configuration of a control device according to the present disclosure. In Fig. 3, reaction force device 30 includes, in addition to reaction force motor 31 and the above-described configuration, a PWM (pulse width modulation) control unit 37, an inverter 38, and a motor current detector 39. Furthermore, turning device 40 includes, in addition to turning motor 41 and the above-described configuration, a PWM control unit 47, an inverter 48, and a motor current detector 49. Control device 50 implements the control blocks of reaction force control system 60, which controls reaction force device 30, and steering control system 70, which controls steering device 40. Reaction force control system 60 and steering control system 70 cooperate to control reaction force device 30 and steering device 40.

[0041] Note that some or all of the components of the control device 50 may be realized by hardware. The control device 50 may include, for example, a RAM (random access memory) or a ROM (read only memory) for storing data, programs, etc., as shown in Fig. 2. The control device 50 may also include a PWM control unit 37, an inverter 38, a motor current detector 39, a PWM control unit 47, an inverter 48, and a motor current detector 49.

[0042] As shown in Fig. 3, control device 50 includes, as control blocks, steering torque target value generation section 200, steering torque control section 400, current control section 500, turning angle target value generation section 600, turning angle control section 700, and current control section 800. Steering torque target value generation section 200, steering torque control section 400, and current control section 500 are control blocks that make up reaction force control system 60. Turning angle target value generation section 600, turning angle control section 700, and current control section 800 are control blocks that make up steering control system 70.

[0043] The reaction force control system 60 performs control such that the actual steering torque Th_act detected by the torque sensor 34 follows the steering torque target value Th_ref, which is the target value of the steering torque of the reaction force device 30.

[0044] The steering torque target value generating section 200 generates a steering torque target value Th_ref.

[0045] The steering torque control unit 400 generates a motor current command value Ih_ref, which is a control target value of the current to be supplied to the reaction force motor 31. The steering torque control unit 400 calculates the motor current command value Ih_ref so that the deviation Th_err between the steering torque target value Th_ref and the actual steering torque Th_act approaches zero.

[0046] The current control unit 500 controls the current of the reaction force motor 31. The current control unit 500 calculates a voltage control command value Vh_ref such that the deviation Ih_err between the motor current command value Ih_ref output from the steering torque control unit 400 and the actual current value (motor current value) Ih_act of the reaction force motor 31 detected by the motor current detector 39 approaches zero.

[0047] In the reaction force device 30, the reaction force motor 31 is controlled and driven via a PWM control unit 37 and an inverter 38 based on the voltage control command value Vh_ref.

[0048] The steering control system 70 performs control such that the actual steering angle θt_act detected by the angle sensor 43 follows the target steering angle value θt_ref.

[0049] A steering angle target value generating section 600 generates a steering angle target value θt_ref based on the steering angle θh.

[0050] Steering angle control unit 700 generates motor current command value It_ref, which is a control target value for the current supplied to steering motor 41. Steering angle control unit 700 calculates motor current command value It_ref such that deviation θt_err between steering angle target value θt_ref and actual steering angle θt_act approaches zero.

[0051] Current control unit 800 controls the current of steering motor 41. Current control unit 800 calculates a voltage control command value Vt_ref such that deviation It_err between motor current command value It_ref output from steering angle control unit 700 and actual current value (motor current value) It_act of steering motor 41 detected by motor current detector 49 approaches zero.

[0052] In the steering device 40, the steering motor 41 is controlled and driven via a PWM control unit 47 and an inverter 48 based on the voltage control command value Vt_ref.

[0053] In this embodiment, steering torque control unit 400, current control unit 500, steering angle target value generation unit 600, steering angle control unit 700, and current control unit 800 may be configured to realize each control in reaction force control system 60 or steering control system 70, and are not limited by the configuration of each of these control blocks.

[0054] Here, the steering direction in the present disclosure will be described. Fig. 4 is a region diagram for explaining the steering direction in the present disclosure. In Fig. 4, the horizontal axis represents the steering angle, and the vertical axis represents the steering angular velocity.

[0055] Area A ((θh, ωh) = (+, +)) shown in FIG. 4 indicates that the steering wheel 1 has been turned to the right (θh>0) and has been turned further to the right (ωh>0) (hereinafter also referred to as "additional right steering"). Area B ((θh, ωh) = (+, -)) shown in FIG. 4 indicates that the steering wheel 1 has been turned to the right (θh>0) and has been turned back to the left (ωh<0) (hereinafter also referred to as "return left steering"). Area C ((θh, ωh) = (-, -)) shown in FIG. 4 indicates that the steering wheel 1 has been turned to the left (θh<0) and has been turned further to the left (ωh<0) (hereinafter also referred to as "additional left steering"). Area D ((θh, ωh) = (-, +)) shown in Figure 4 indicates that the steering wheel 1 is turned to the left (θh < 0) and then turned back to the right (ωh > 0) (hereinafter also referred to as "right return steering"). Also, in Figure 4, on the steering angle θh axis (ωh = 0) it is indicated that the steering wheel 1 is neither turned further nor turned back ((θh, ωh) = (θh, 0)), and on the steering angular velocity ωh axis (θh = 0) it is indicated that the steering wheel 1 is in the center position ((θh, ωh) = (0, ωh)).

[0056] 1, Coulomb friction (static friction and kinetic friction) that monotonically increases with an increase in the normal load occurs on the contact surfaces of gears such as the reduction gear 32 and the reaction force motor 31, and this may prevent the steering reaction force corresponding to the steering torque target value Th_ref from being properly transmitted. This Coulomb friction causes static friction of about 1 Nm and kinetic friction of about 0.5 Nm on the column shaft 2.

[0057] Fig. 5 is a conceptual diagram showing the relationship between the actual steering torque and the steering torque target value. Fig. 6 is a conceptual diagram showing the relationship between the difference between the steering torque target value and the actual steering torque and the motor current value of the reaction force motor.

[0058] In the example shown in Fig. 5, the horizontal axis represents the steering angle, and the vertical axis represents the steering torque. The solid line in Fig. 5 represents the actual steering torque Th_act, and the dashed line represents the steering torque target value Th_ref. In Fig. 5, the steering torque target value Th_ref is set to be proportional to the steering angle θh.

[0059] In the example shown in Fig. 6, the horizontal axis indicates the motor current value of the reaction force motor when the steering shown in Fig. 5 is performed, and the vertical axis indicates the friction component (=Th_act-Th_ref) that appears as the torque difference between the actual steering torque and the steering torque target value. Note that in Fig. 6, the motor current value Ih_act when steering to the right is a positive value and the motor current value Ih_act when steering to the left is a negative value, but it is also possible for the motor current value Ih_act when steering to the right to be a negative value and the motor current value Ih_act when steering to the left to be a positive value.

[0060] As shown in FIGS. 5 and 6, the friction component Th_F caused by the Coulomb friction of the steering mechanism is positive during strong steering to the right as indicated by arrow A in the figures, and increases as the steering angle θh increases to positive values. The friction component Th_F caused by the Coulomb friction of the steering mechanism is negative during strong steering to the left as indicated by arrow B in the figures, and decreases as the steering angle θh decreases to positive values. The friction component Th_F caused by the Coulomb friction of the steering mechanism is negative during strong steering to the left as indicated by arrow C in the figures, and increases as the steering angle θh increases to negative values. The friction component Th_F caused by the Coulomb friction of the steering mechanism is positive during strong steering to the right as indicated by arrow D in the figures, and decreases as the steering angle θh decreases to negative values. In this way, a phenomenon occurs in which the actual steering torque Th_act deviates from the steering torque target value Th_ref generated by the steering torque target value generating section 200 due to Coulomb friction in the steering mechanism.

[0061] As shown in Fig. 5, the torque Th has a characteristic of monotonically increasing as the steering angle θh increases. Also, as shown in Fig. 6, the magnitude of the friction component Th_F caused by the Coulomb friction of the steering mechanism has a characteristic of monotonically increasing as the motor current value Ih_act increases.

[0062] A specific configuration and operation for compensating for the friction component Th_F caused by the Coulomb friction of the steering mechanism will be described below.

[0063] 7 is a block diagram showing an example of the configuration of a steering torque control unit according to this embodiment. As shown in FIG. 7, a steering torque control unit 400 according to this embodiment includes a subtraction unit 410, a PID control unit 420, a subtraction unit 430, and a friction compensation unit 440.

[0064] The steering torque control unit 400 receives the steering torque target value Th_ref output from the steering torque target value generation unit 200, the actual steering torque Th_act detected by the torque sensor 34, and the actual steering angle θh_act detected by the steering angle sensor 33.

[0065] A subtraction unit 410 calculates a deviation Th_err between the steering torque target value Th_ref and the actual steering torque Th_act. A PID control unit 420 performs PID control so that the deviation Th_err between the steering torque target value Th_ref and the actual steering torque Th_act, which is the calculation result of the subtraction unit 410, approaches zero.

[0066] The friction compensation unit 440 receives the actual steering torque Th_act, the actual steering angle θh_act, and the current command value Iref_a output from the PID control unit 420. In the present disclosure, the current command value Iref_a corresponds to the "first current command value."

[0067] The friction compensation unit 440 derives a current compensation value Iref_b for compensating for the friction component Th_F caused by the Coulomb friction of the steering mechanism.

[0068] The subtraction unit 430 calculates the motor current command value Ih_ref by subtracting the current compensation value Iref_b derived by the friction compensation unit 440 from the current command value Iref_a output from the PID control unit 420. This results in the motor current command value Ih_ref in which the influence of Coulomb friction occurring in the steering mechanism is suppressed. In the present disclosure, the motor current command value Ih_ref corresponds to the "second current command value."

[0069] 8 is a block diagram showing an example of the configuration of a friction compensation unit according to the embodiment. The friction compensation unit 440 includes a static friction compensation unit 450, a dynamic friction compensation unit 460, and a ratio control unit 470.

[0070] The static friction compensation unit 450 derives the static friction compensation value Iref_st based on the actual steering torque Th_act and the current command value Iref_a.

[0071] The kinetic friction compensation unit 460 derives a kinetic friction compensation value Iref_dy based on the actual steering angle θh_act and the current command value Iref_a. The kinetic friction compensation unit 460 also derives a steering state determination flag Ls indicating the steering state of the steering wheel 1 based on the actual steering angle θh_act.

[0072] The ratio control unit 470 adds the static friction compensation value Iref_st output from the static friction compensation unit 450 and the dynamic friction compensation value Iref_dy output from the dynamic friction compensation unit 460 at a ratio corresponding to the steering state determination flag Ls output from the dynamic friction compensation unit 460, and calculates the current compensation value Iref_b.

[0073] The static friction compensation unit 450 according to the embodiment will be described in detail below.

[0074] 9 is a block diagram showing an example of the configuration of a static friction compensation unit according to the embodiment. The static friction compensation unit 450 includes, as its main components, a hysteresis component extraction unit 451, a first current sensitive gain generation unit 452, and a second current sensitive gain generation unit 453.

[0075] In the present disclosure, the filter unit 455 is a filter that removes noise components contained in the actual steering torque Th_act. Examples of the filter that constitutes the filter unit 455 include an LPF (Low Pass Filter) and a BPF (Band Pass Filter). The filter unit 455 is expressed by a first-order transfer function shown in the following equation (1), for example. In the following description, "x(z -1 )" indicates the past value of the variable or coefficient x one sample before. The transfer function shown in the following equation (1) is stored, for example, in the ROM of the ECU constituting the control device 50. The past value one sample before is temporarily stored, for example, in the RAM of the ECU constituting the control device 50.

[0076] [b0+b1(z -1 )] / [1+a1(z -1 )]···(1)

[0077] The hysteresis component extraction unit 451 includes a hysteresis component removal unit 456 and a subtraction unit 457. The hysteresis component removal unit 456 receives the actual steering torque Th_act filtered by the filter unit 455 and the first gain Gi1 generated by the first current sensitive gain generation unit 452.

[0078] 10 is a diagram showing an example of a first current sensitive gain map. The first current sensitive gain generator 452 generates the first gain Gi1 using the first current sensitive gain map shown in FIG.

[0079] As shown in FIG. 10, the first gain Gi1 has a characteristic of monotonically increasing as the current command value Iref_a output from the PID control unit 420 increases.

[0080] The first current-sensitive gain map shown in Fig. 10 is stored, for example, in the ROM of the ECU that constitutes the control device 50. Note that the manner in which the first gain Gi1 is generated is not limited to the map shown in Fig. 10, and for example, the first gain Gi1 may be generated using a transfer function having the characteristics shown in Fig. 10. In this case, the transfer function may also be stored, for example, in the ROM of the ECU that constitutes the control device 50.

[0081] As shown in Fig. 5, the steering torque target value Th_ref corresponds to a value approximately midway between the value of the actual steering torque Th_act during further steering and the value of the actual steering torque Th_act during return steering. In other words, the actual steering torque Th_act has a hysteresis characteristic with the steering torque target value Th_ref as a substantially midway value. The hysteresis component removal unit 456 removes the hysteresis component from the actual steering torque Th_act filtered by the filter unit 455, and calculates an intermediate value Th_act_cen (≒Th_ref) equivalent to the steering torque target value Th_ref.

[0082] Fig. 11 is a conceptual diagram illustrating a specific example of the input / output characteristics of the hysteresis component removal unit. In the example shown in Fig. 11, the horizontal axis represents time and the vertical axis represents steering torque. The solid line in Fig. 11 represents the actual steering torque Th_act, and the dashed line represents the intermediate value Th_act_cen (≒Th_ref) of the actual steering torque Th_act, which corresponds to the steering torque target value Th_ref.

[0083] FIG. 11 shows an example in which steering is performed to turn further to the right from time t1 to time t2, steering to turn back to the left from time t2 to time t3, steering to turn further to the left from time t3 to time t4, and steering to turn back to the right from time t4 onwards.

[0084] 5 and 6, during right-increasing steering, the friction component Th_F generated due to Coulomb friction of the steering mechanism increases as the positive steering angle θh increases. Therefore, as shown in Fig. 11, during right-increasing steering from time t1 to time t2, the deviation of actual steering torque Th_act from steering torque target value Th_ref increases as the positive steering torque increases.

[0085] 5 and 6, during left return steering, the friction component Th_F generated due to Coulomb friction of the steering mechanism decreases as the positive steering angle θh decreases. Therefore, as shown in Fig. 11, during left return steering from time t2 to time t3, the deviation of the actual steering torque Th_act from the steering torque target value Th_ref decreases as the positive steering torque decreases.

[0086] 5 and 6, during left-turn steering, the friction component Th_F generated due to Coulomb friction of the steering mechanism increases as the steering angle θh becomes more negative. Therefore, as shown in Fig. 11, during left-turn steering from time t3 to time t4, the deviation of actual steering torque Th_act from steering torque target value Th_ref increases as the steering torque becomes more negative.

[0087] 5 and 6, during right return steering, the friction component Th_F generated due to Coulomb friction of the steering mechanism decreases as the steering angle θh becomes less negative. Therefore, as shown in Fig. 11, during right return steering after time t4, the deviation of the actual steering torque Th_act from the steering torque target value Th_ref becomes smaller as the steering torque becomes less negative.

[0088] The hysteresis component removal unit 456 calculates an intermediate value Th_act_cen (≈Th_ref) of the actual steering torque Th_act, which corresponds to the desired steering torque value Th_ref, by the hysteresis component removal process described below.

[0089] 12 is a flowchart showing an example of the hysteresis component removal process. The hysteresis component removal unit 456 executes the hysteresis component removal process shown in FIG.

[0090] The hysteresis component removal unit 456 acquires the actual steering torque Th_act (step S101), and determines whether the conditional expression shown in the following equation (2) is satisfied (step S102). In the following equation (2), ΔT indicates a predetermined torque width. The following equation (2) and the torque width ΔT are stored, for example, in the ROM of the ECU constituting the control device 50. The previous value Th_act_cen(z) of the intermediate value Th_act_cen of the actual steering torque Th_act one sample before -1 ) is temporarily stored in the RAM of the ECU that constitutes the control device 50, for example.

[0091] Th_act>Th_act_cen(z -1 )+ΔT×Gi1 (2)

[0092] If the conditional expression of the above equation (2) is satisfied (step S102; Yes), the hysteresis component removal unit 456 calculates the intermediate value Th_act_cen of the actual steering torque Th_act using the following equation (3) (step S103), and ends the hysteresis component removal process. The following equation (3) is stored, for example, in the ROM of the ECU that constitutes the control device 50.

[0093] Th_act_cen=Th_act-ΔT×Gi1···(3)

[0094] If the conditional expression (2) above is not satisfied (step S102; No), the hysteresis component removal unit 456 then determines whether the conditional expression shown in the following equation (4) is satisfied (step S104). The following equation (4) is stored, for example, in the ROM of the ECU constituting the control device 50.

[0095] Th_act <Th_act_cen(z -1 )-ΔT×Gi1 (4)

[0096] If the conditional expression of the above equation (4) is satisfied (step S104; Yes), the hysteresis component removal unit 456 calculates the intermediate value Th_act_cen of the actual steering torque Th_act using the following equation (5) (step S105), and ends the hysteresis component removal process. The following equation (5) is stored, for example, in the ROM of the ECU that constitutes the control device 50.

[0097] Th_act_cen=Th_act+ΔT×Gi1···(5)

[0098] If the conditional expression of the above equation (4) is not satisfied (step S104; No), the hysteresis component removal unit 456 calculates the intermediate value Th_act_cen of the actual steering torque Th_act using the following equation (6) (step S106), and ends the hysteresis component removal process. The following equation (6) is stored, for example, in the ROM of the ECU that constitutes the control device 50.

[0099] Th_act_cen=Th_act_cen(z -1 )···(6)

[0100] The above-described hysteresis component removal process provides the input / output characteristics shown in Fig. 11. The difference between the actual steering torque Th_act and its intermediate value Th_act_cen shown in Fig. 11 corresponds to the product (ΔT × Gi1) of a predetermined torque width ΔT and the first gain Gi1.

[0101] More specifically, the difference between the actual steering torque Th_act and its intermediate value Th_act_cen at time t1 corresponds to ΔT×Gi1_BL. Also, the difference between the actual steering torque Th_act and its intermediate value Th_act_cen at time t3 corresponds to −ΔT×Gi1_BL. Gi1_BL corresponds to the first gain when the current command value Iref_a=0 (see FIG. 10).

[0102] As described above, the magnitude of the friction component Th_F caused by the Coulomb friction of the steering mechanism has a characteristic of monotonically increasing with the motor current value. Therefore, by multiplying a predetermined value (torque width ΔT) by the first gain Gi1, which has a characteristic of monotonically increasing with an increase in the current command value Iref_a output from the PID control unit 420 (ΔT×Gi1), it is possible to derive a value that is close to a value that monotonically increases with the magnitude of the friction component Th_F caused by the Coulomb friction of the steering mechanism.

[0103] Fig. 13 is a conceptual diagram illustrating a specific example of the output characteristics of the hysteresis component extraction unit. In the example shown in Fig. 13, the horizontal axis represents time, and the vertical axis represents the difference between the actual steering torque and its intermediate value (=Th_act-Th_act_cen). Times t1, t2, t3, and t4 shown in Fig. 13 correspond to times t1, t2, t3, and t4 shown in Fig. 11.

[0104] A subtraction unit 457 subtracts the intermediate value Th_act_cen of the actual steering torque Th_act derived by the above-described hysteresis component removal process from the actual steering torque Th_act, thereby extracting the hysteresis component of the actual steering torque Th_act shown in Fig. 13 .

[0105] The hysteresis component of the actual steering torque Th_act shown in Figure 13 can be regarded as an approximation of a value that monotonically increases with the magnitude of the friction component Th_F caused by Coulomb friction in the steering mechanism by appropriately adjusting the torque width ΔT and the first gain Gi1 shown in Figure 10.

[0106] 14 is a diagram showing an example of the second current sensitive gain map. The second current sensitive gain generator 453 generates the second gain Gi2 using the second current sensitive gain map shown in FIG.

[0107] As shown in FIG. 14, the second gain Gi2 has a characteristic of monotonically decreasing as the current command value Iref_a output from the PID control unit 420 increases.

[0108] The second current sensitive gain map shown in Fig. 14 is stored, for example, in the ROM of the ECU that constitutes the control device 50. Note that the manner in which the second gain Gi2 is generated is not limited to the map shown in Fig. 14, and, for example, the second gain Gi2 may be generated using a transfer function having the characteristics shown in Fig. 14. In this case, the transfer function may also be stored, for example, in the ROM of the ECU that constitutes the control device 50.

[0109] A multiplication unit 454 multiplies the hysteresis component of the actual steering torque Th_act output from the hysteresis component extraction unit 451 by a second gain Gi2 having the characteristics shown in Fig. 14. As a result, a static friction compensation value Iref_st is obtained.

[0110] Fig. 15 is a conceptual diagram illustrating a specific example of a static friction compensation value. In the example shown in Fig. 15, the horizontal axis represents time, and the vertical axis represents the static friction compensation value. Times t1, t2, t3, and t4 shown in Fig. 15 correspond to times t1, t2, t3, and t4 shown in Fig. 11 and Fig. 13.

[0111] By setting the first gain Gi1 and the second gain Gi2, the static friction compensation value Iref_st shown in Fig. 15 is obtained. As the absolute value of the current command value Iref_a increases, the static friction compensation value Iref_st monotonically increases.

[0112] As described above, the static friction compensation unit 450 according to this embodiment includes a hysteresis component removal unit 456 that calculates an intermediate value Th_act_cen between the actual steering torque Th_act when the steering wheel 1 is turned further and the actual steering torque Th_act when the steering wheel 1 is turned back. The hysteresis component removal unit 456 calculates the intermediate value Th_act_cen based on a value (ΔT×Gi1) obtained by multiplying a predetermined torque width ΔT by the first gain Gi1. The static friction compensation unit 450 derives the static friction compensation value Iref_st by multiplying a value obtained by subtracting the intermediate value Th_act_cen from the actual steering torque Th_act by the second gain Gi2.

[0113] The dynamic friction compensation unit 460 according to the embodiment will be described in detail below.

[0114] 16 is a block diagram showing an example of the configuration of a dynamic friction compensation unit according to the embodiment. The dynamic friction compensation unit 460 includes, as its main components, a dynamic friction compensation value code generation unit 461 and a third current sensitive gain generation unit 462.

[0115] In the present disclosure, the differentiating unit 464 is a component that differentiates the actual steering angle θh_act to calculate the actual steering angular velocity ωh_act of the steering wheel 1.

[0116] The dynamic friction compensation value sign generation unit 461 includes a sign extraction unit 465, an absolute value calculation unit 466, a steering state determination unit 467, and a multiplication unit 468. The actual steering angular velocity |ωh_act| that has been subjected to absolute value processing by the absolute value calculation unit 466 is input to the steering state determination unit 467.

[0117] The steering state determination unit 467 derives the steering state determination flag Ls by the steering state determination process described below.

[0118] 17 is a flowchart showing an example of a steering state determination process. The steering state determination unit 467 executes the steering state determination process shown in FIG.

[0119] The steering state determination unit 467 acquires the actual steering angular velocity |ωh_act| (step S201), and determines whether the conditional expression shown in the following expression (8) is satisfied (step S202). In the following expression (8), ωth represents a predetermined steering angular velocity threshold value. The following expression (8) and the steering angular velocity threshold value ωth are stored in, for example, a ROM of an ECU constituting the control device 50.

[0120] |ωh_act|≧ωth (8)

[0121] If the conditional expression of the above equation (8) is satisfied (step S202; Yes), the steering state determination unit 467 sets the steering state determination flag Ls to "1" (Ls=1) (step S203), and ends the steering state determination process.

[0122] If the conditional expression of the above equation (8) is not satisfied (step S202; No), the steering state determination unit 467 sets the steering state determination flag Ls to "0" (Ls=0) (step S204), and ends the steering state determination process.

[0123] In the above-described steering state determination process, if the conditional expression of the above equation (8) is satisfied (step S202; Yes), the steering state determination flag Ls becomes "1" (Ls=1) (step S203), and it is determined that the steering wheel 1 is being steered. On the other hand, if the conditional expression of the above equation (8) is not satisfied (step S202; No), the steering state determination flag Ls becomes "0" (Ls=0) (step S204), and it is determined that the steering wheel 1 is not being steered.

[0124] Fig. 18 is a conceptual diagram illustrating a specific example of the input characteristics of the dynamic friction compensation value code generation unit. Fig. 19 is a conceptual diagram illustrating a specific example of the output characteristics of the steering state determination unit. In the examples shown in Fig. 18 and Fig. 19, the horizontal axis represents time. In the example shown in Fig. 18, the vertical axis represents the actual steering angular velocity, and in the example shown in Fig. 19, the vertical axis represents the value of the steering state determination flag.

[0125] 18 and 19 show time responses when the steering wheel 1 is steered left or right at a predetermined frequency from the center position of the steering wheel 1. Also, Fig. 18 and 19 show examples in which the actual steering angular velocity |ωh_act| is equal to or greater than the steering angular velocity threshold value ωth (|ωh_act|≧ωth) in the period from time t1 to time t2 and in the period from time t3 to time t4 (step S202 in Fig. 17; Yes), and the steering state determination flag Ls is set to "1" (Ls=1) (step S203 in Fig. 17).

[0126] In the present disclosure, the sign extraction unit 465 of the dynamic friction compensation value sign generation unit 461 extracts the sign of the actual steering angular velocity ωh_act. Specifically, for example, the value of the actual steering angular velocity ωh_act is divided by the absolute value of the actual steering angular velocity ωh_act. As a result, the sign extraction unit 465 outputs "1" when the sign of the actual steering angular velocity ωh_act is "+", and outputs "-1" when the sign of the actual steering angular velocity ωh_act is "-". Specifically, the sign extraction unit 465 generates, for example, a sign function Sgn(ωh_act) of the actual steering angular velocity ωh_act.

[0127] 20 is a conceptual diagram illustrating a specific example of the output characteristics of the dynamic friction compensation value code generator. Times t1, t2, t3, and t4 shown in FIG. 20 correspond to times t1, t2, t3, and t4 shown in FIGS.

[0128] Multiplication unit 468 multiplies steering state determination flag Ls by sign function Sgn(ωh_act) output from sign extraction unit 465 to obtain Ls×Sgn(ωh_act) shown in Fig. 20. Specifically, in the period from time t1 to time t2, Ls×Sgn(ωh_act)=1, and in the period from time t3 to time t4, Ls×Sgn(ωh_act)=-1.

[0129] 21 is a diagram showing an example of the third current sensitive gain map. The third current sensitive gain generator 462 generates the third gain Gi3 using the third current sensitive gain map shown in FIG.

[0130] As shown in FIG. 21, the third gain Gi3 has a characteristic of monotonically increasing as the current command value Iref_a output from the PID control unit 420 increases.

[0131] Fig. 22 is a conceptual diagram illustrating a specific example of a dynamic friction compensation value using the third current sensitive gain map. Times t1, t2, t3, and t4 shown in Fig. 22 correspond to times t1, t2, t3, and t4 shown in Figs. 18, 19, and 20.

[0132] The multiplication unit 463 multiplies the output value Ls×Sgn(ωh_act) of the kinetic friction compensation value code generation unit 461 by a third gain Gi3 having the characteristics shown in Fig. 21 to set the dimension of the kinetic friction compensation value Iref_dy to a current value similar to that of the current command value Iref_a. As a result, the kinetic friction compensation value Iref_dy shown in Fig. 22 is obtained.

[0133] Specifically, in the example shown in Fig. 22, the dynamic friction compensation value Iref_dy is a value corresponding to the current command value Iref_a during the period from time t1 to time t2 when the steering state determination flag Ls is "1" (Ls=1) and during the period from time t3 to time t4 when Ls×Sgn(ωh_act)=-1. Gi3_BL corresponds to the third gain when the current command value Iref_a=0 (see Fig. 21). Note that the dashed line in Fig. 22 indicates an example in which the steering angular velocity threshold ωth in the above-described steering state determination process is approximated to "0."

[0134] As described above, the magnitude of the friction component Th_F caused by the Coulomb friction of the steering mechanism has the characteristic of monotonically increasing with an increase in the motor current value. Therefore, by multiplying the output value Ls×Sgn(ωh_act) of the kinetic friction compensation value code generation unit 461 by the third gain Gi3, which has the characteristic of monotonically increasing with an increase in the current command value Iref_a output from the PID control unit 420 (Ls×Sgn(ωh_act)×Gi3), it is possible to derive a value that is close to a value that monotonically increases with the magnitude of the friction component Th_F caused by the Coulomb friction of the steering mechanism.

[0135] Fig. 23 is a conceptual diagram illustrating a modified example of the dynamic friction compensation value using the third current sensitive gain map. Times t1, t2, t3, and t4 shown in Fig. 23 correspond to times t1, t2, t3, and t4 shown in Figs. 18, 19, 20, and 21.

[0136] In step S204 of the steering state determination processing shown in Figure 17, by setting the steering state determination flag Ls to "|ωh_act| / ωth" (Ls = |ωh_act| / ωth), the dynamic friction compensation value Iref_dy can be smoothly changed in the region -ωth<ωh_act<ωth shown in Figure 18, as shown in Figure 23.

[0137] As described above, when the actual steering angular velocity |ωh_act| is equal to or greater than the predetermined steering angular velocity threshold ωth (|ωh_act|≧ωth) and the actual steering angular velocity ωh_act is a positive value (Sgn(ωh_act)>0), the dynamic friction compensation unit 460 according to the embodiment multiplies the third gain Gi3 by the sign function of the actual steering angular velocity (Sgn(ωh_act)=1) to derive the dynamic friction compensation value Iref_dy, and when the actual steering angular velocity |ωh_act| is equal to or greater than the predetermined steering angular velocity threshold ωth (|ωh_act|≧ωth) and the actual steering angular velocity ωh_act is a negative value, the dynamic friction compensation unit 460 multiplies the third gain Gi3 by the sign function of the actual steering angular velocity (Sgn(ωh_act)=-1) to derive the dynamic friction compensation value Iref_dy.

[0138] Alternatively, the dynamic friction compensation unit 460 may be configured to derive the dynamic friction compensation value Iref_dy by multiplying the third gain Gi3 by a sign function of the actual steering angular velocity (Sgn(ωh_act)=1) and a predetermined coefficient when the actual steering angular velocity |ωh_act| is equal to or greater than a predetermined steering angular velocity threshold ωth (|ωh_act|≧ωth) and the actual steering angular velocity ωh_act is a positive value (Sgn(ωh_act)>0), and to derive the dynamic friction compensation value Iref_dy by multiplying the third gain Gi3 by a sign function of the actual steering angular velocity (Sgn(ωh_act)=-1) and a predetermined coefficient when the actual steering angular velocity |ωh_act| is equal to or greater than the predetermined steering angular velocity threshold ωth (|ωh_act|≧ωth) and the actual steering angular velocity ωh_act is a negative value.

[0139] The ratio control unit 470 according to the embodiment will be described in detail below.

[0140] As described above, the ratio control unit 470 calculates the current compensation value Iref_b by adding the static friction compensation value Iref_st output from the static friction compensation unit 450 and the kinetic friction compensation value Iref_dy output from the kinetic friction compensation unit 460 at a ratio according to the steering state determination flag Ls output from the kinetic friction compensation unit 460. The ratio control unit 470 changes the static friction compensation value ratio r_st to the static friction compensation value Iref_st and the kinetic friction compensation value ratio r_dy to the kinetic friction compensation value Iref_dy according to a change in the steering state determination flag Ls, i.e., a change in the actual steering angular velocity |ωh_act|.

[0141] Specifically, the ratio control unit 470 calculates the current compensation value Iref_b using, for example, the following equation (9): The following equation (9), the static friction compensation value ratio r_st, and the dynamic friction compensation value ratio r_dy are stored, for example, in the ROM of the ECU constituting the control device 50.

[0142] Iref_b=r_st×Iref_st+r_dy×Iref_dy···(9)

[0143] Fig. 24 is a conceptual diagram showing an example of switching of the steering state determination flag. Fig. 25 is a conceptual diagram showing an example of operation of the ratio control unit. In the examples shown in Fig. 24 and Fig. 25, the horizontal axis represents time. In the example shown in Fig. 24, the vertical axis represents the value of the steering state determination flag, and in the example shown in Fig. 25, the vertical axis represents the ratio of the static friction compensation value to the dynamic friction compensation value. In the example shown in Fig. 25, the solid line represents the static friction compensation value ratio, and the dashed line represents the dynamic friction compensation value ratio.

[0144] Figures 24 and 25 show an example in which the steering state determination flag Ls switches from "0" to "1" at time t1, the steering state determination flag Ls switches from "1" to "0" at time t2, and the steering state determination flag Ls switches from "0" to "1" at time t3.

[0145] When the steering state determination flag Ls is "1" (Ls=1), the actual steering angular velocity |ωh_act| is equal to or greater than the steering angular velocity threshold ωth (|ωh_act|≧ωth). When the steering state determination flag Ls is "0" (Ls=0), the actual steering angular velocity |ωh_act| is less than the steering angular velocity threshold ωth (|ωh_act|<ωth).

[0146] In the examples shown in Figures 24 and 25, when the steering state determination flag Ls is "1" (Ls = 1) at time t1 (t3), that is, when the actual steering angular velocity |ωh_act| becomes equal to or greater than the steering angular velocity threshold value ωth (|ωh_act| ≧ ωth), the static friction compensation value ratio r_st monotonically decreases from "1.0" and becomes "0.3" at time t1' (t3').

[0147] In other words, the static friction compensation value ratio r_st monotonically decreases from time t1 (t3) when the actual steering angular velocity |ωh_act| becomes equal to or greater than the steering angular velocity threshold ωth (|ωh_act|≧ωth) to time t1' (t3') when the static friction compensation value ratio r_st becomes its minimum value (0.3 in the example shown in FIG. 25).

[0148] Also, in the examples shown in Figures 24 and 25, when the steering state determination flag Ls is "1" (Ls = 1) at time t1 (t3), that is, when the actual steering angular velocity |ωh_act| becomes equal to or greater than the steering angular velocity threshold value ωth (|ωh_act| ≧ ωth), the dynamic friction compensation value ratio r_dy monotonically increases from "0" and becomes "1.0" at time t1'' (t3'').

[0149] In other words, the dynamic friction compensation value ratio r_dy monotonically increases from time t1 (t3) when the actual steering angular velocity |ωh_act| becomes equal to or greater than the steering angular velocity threshold ωth (|ωh_act|≧ωth) to time t1' (t3') when the dynamic friction compensation value ratio r_dy reaches its maximum value ("1.0" in the example shown in FIG. 25).

[0150] Also, in the examples shown in Figures 24 and 25, when the steering state determination flag Ls is "0" (Ls = 0) at time t2, that is, when the actual steering angular velocity |ωh_act| is less than the steering angular velocity threshold ωth (|ωh_act| < ωth), the static friction compensation value ratio r_st monotonically increases from "0.3" and becomes "1.0" at time t2'.

[0151] In other words, the static friction compensation value ratio r_st monotonically increases from time t2 when the actual steering angular velocity |ωh_act| becomes less than the steering angular velocity threshold ωth (|ωh_act|<ωth) to time t2' when the static friction compensation value ratio r_st reaches its maximum value ("1.0" in the example shown in Figure 25).

[0152] Also, in the examples shown in Figures 24 and 25, when the steering state determination flag Ls is "0" (Ls = 0) at time t2, that is, when the actual steering angular velocity |ωh_act| is less than the steering angular velocity threshold ωth (|ωh_act| < ωth), the dynamic friction compensation value ratio r_dy monotonically decreases from "1.0" and becomes "0" at time t2''.

[0153] In other words, the dynamic friction compensation value ratio r_dy monotonically decreases from time t2 when the actual steering angular velocity |ωh_act| becomes less than the steering angular velocity threshold ωth (|ωh_act|<ωth) to time t2″ when the dynamic friction compensation value ratio r_dy reaches its minimum value (in the example shown in FIG. 25, “0”).

[0154] In this way, by changing the static friction compensation value ratio r_st to the static friction compensation value Iref_st and the dynamic friction compensation value ratio r_dy to the dynamic friction compensation value Iref_dy in accordance with the change in the steering state determination flag Ls, i.e., the change in the actual steering angular velocity |ωh_act|, it becomes possible to perform friction compensation control that follows the ratio of the Coulomb static friction and Coulomb dynamic friction of the steering mechanism, which change in accordance with the steering state.

[0155] In addition, by gradually changing the static friction compensation value ratio r_st and the dynamic friction compensation value ratio r_dy from the time the steering state determination flag Ls is switched, fluctuations in the steering reaction force due to switching between the static friction compensation value Iref_st and the dynamic friction compensation value Iref_dy that occur as the steering state changes can be suppressed.

[0156] As described above, the ratio control unit 470 according to the embodiment makes the dynamic friction compensation value ratio r_dy greater than the static friction compensation value ratio r_st when the actual steering angular velocity |ωh_act| is greater than or equal to the predetermined steering angular velocity threshold ωth (|ωh_act|≧ωth), and makes the static friction compensation value ratio r_st greater than the dynamic friction compensation value ratio r_dy when the actual steering angular velocity |ωh_act| is less than the steering angular velocity threshold ωth (|ωh_act|<ωth).

[0157] Furthermore, ratio control unit 470 monotonically increases the dynamic friction compensation value ratio r_dy during the period from when the actual steering angular velocity |ωh_act| becomes equal to or greater than the steering angular velocity threshold ωth (|ωh_act|≧ωth) to when the dynamic friction compensation value ratio r_dy reaches its maximum value ("1.0" in the example shown in FIG. 25), and monotonically decreases the dynamic friction compensation value ratio r_dy during the period from when the actual steering angular velocity |ωh_act| becomes less than the steering angular velocity threshold (|ωh_act|<ωth) to when the dynamic friction compensation value ratio r_dy reaches its minimum value ("0" in the example shown in FIG. 25).

[0158] In addition, ratio control unit 470 monotonically decreases the static friction compensation value ratio r_st during the period from when the actual steering angular velocity |ωh_act| becomes equal to or greater than the steering angular velocity threshold ωth (|ωh_act|≧ωth) to when the static friction compensation value ratio r_st reaches its minimum value ("0.3" in the example shown in FIG. 25), and monotonically increases the static friction compensation value ratio r_st during the period from when the actual steering angular velocity |ωh_act| becomes less than the steering angular velocity threshold ωth (|ωh_act|<ωth) to when the static friction compensation value ratio r_st reaches its maximum value ("1.0" in the example shown in FIG. 25).

[0159] In the static friction compensation unit 450 configured as described above, the friction component Th_F generated due to Coulomb friction of the steering mechanism can be appropriately compensated for by appropriately adjusting the characteristics of the first gain Gi1 shown in Fig. 10, the second gain Gi2 shown in Fig. 14, the third gain Gi3 shown in Fig. 21, the torque width ΔT, the steering angular velocity threshold ωth, the static friction compensation value ratio r_st, and the dynamic friction compensation value ratio r_dy, etc. This makes it possible to transmit a steering reaction force that is appropriately set by the steering torque target value.

[0160] It should be noted that the drawings used in the above-described embodiments are conceptual diagrams for qualitatively explaining the present disclosure, and are not intended to be limiting. Furthermore, while the above-described embodiment is an example of a preferred embodiment of the present disclosure, the present disclosure is not limited thereto, and various modifications can be made within the scope of the gist of the present disclosure. [Explanation of symbols]

[0161] 1 handle 2 column axis 3a, 3b tie rod 5L,5R steered wheels 10 Vehicle speed sensor 11 Ignition key 12 Battery 30 Reaction Device 31 Reaction motor 32 Reduction mechanism 33 Steering angle sensor 34 Torque sensor 35 Stopper (rotation limiting mechanism) 40 Steering gear 41 Steering motor 42 Reduction mechanism 43 Angle Sensor 44 Pinion rack mechanism 50 Control device 60 Reaction Force Control System 70 Steering control system 200 Steering torque target value generation unit 400 Steering torque control unit 410 Subtraction section 420 PID control unit 430 Subtraction Section 440 Friction compensation section 450 Static friction compensation section 451 Hysteresis component extraction section 452 First current-sensitive gain generating unit 453 Second current sensitive gain generating unit 454 Multiplication Unit 455 Filter section 456 Hysteresis component removal section 457 Subtraction Section 460 Dynamic friction compensation section 461 Dynamic friction compensation value code generation unit 462 Third current-sensitive gain generator 463 Multiplication Unit 464 Differential part 465 Code extraction part 466 Absolute Value Calculation Unit 467 Steering state determination unit 468 Multiplication Unit 470 Ratio Control Unit 500 Current control section 600 steering angle target value generation unit 700 Steering angle control unit 800 Current control section

Claims

1. A control device for a vehicle steering system including a reaction motor that applies a steering reaction force to a steering wheel in accordance with a steering angle of the steering wheel, and a steering motor that steers steered wheels in accordance with the steering angle of the steering wheel, a steering torque target value generating unit that generates a steering torque target value that is a target value of the steering torque for obtaining the steering reaction force; a steering torque control unit that generates a first current command value based on the steering torque target value; Equipped with The steering torque control unit a static friction compensation unit that derives a static friction compensation value based on an actual steering torque that is an actual steering torque of the steering wheel; a dynamic friction compensation unit that derives a dynamic friction compensation value based on an actual steering angular velocity that is an actual steering angular velocity of the steering wheel; Equipped with The steering torque control unit generating a second current command value for driving the reaction force motor based on the static friction compensation value and the kinetic friction compensation value; The static friction compensation unit is deriving the static friction compensation value in accordance with the first current command value; The dynamic friction compensation unit deriving the kinetic friction compensation value in accordance with the first current command value; A control device for a vehicle steering system.

2. The static friction compensation unit is a first current sensitive gain generating unit that generates a first gain that monotonically increases as the first current command value increases; a second current sensitive gain generating unit that generates a second gain that monotonically decreases as the first current command value increases; Equipped with The static friction compensation unit is deriving the static friction compensation value based on the first gain and the second gain; 2. The control device for a vehicle steering system according to claim 1.

3. The static friction compensation unit is a hysteresis component removal unit that calculates an intermediate value between an actual steering torque when the steering wheel is turned further and an actual steering torque when the steering wheel is turned back, The hysteresis component removal unit calculating the intermediate value based on a value obtained by multiplying a predetermined value by the first gain; The static friction compensation unit is deriving the static friction compensation value by multiplying a value obtained by subtracting the intermediate value from the actual steering torque by the second gain; 3. The control device for a vehicle steering system according to claim 2.

4. The dynamic friction compensation unit a third current sensitive gain generating unit that generates a third gain that monotonically increases as the first current command value increases; The dynamic friction compensation unit deriving the dynamic friction compensation value based on the third gain; The control device for a vehicle steering system according to any one of claims 1 to 3.

5. The dynamic friction compensation unit When the magnitude of the actual steering angular velocity is equal to or greater than a predetermined steering angular velocity threshold, the dynamic friction compensation value is derived by multiplying the third gain by a sign function of the actual steering angular velocity.

5. The control device for a vehicle steering system according to claim 4.

6. The dynamic friction compensation unit When the magnitude of the actual steering angular velocity is equal to or greater than a predetermined steering angular velocity threshold, the third gain is multiplied by a sign function of the actual steering angular velocity and a predetermined coefficient to derive a kinetic friction compensation value.

5. The control device for a vehicle steering system according to claim 4.

7. The steering torque control unit a ratio control unit that controls a ratio between the static friction compensation value and the dynamic friction compensation value based on the actual steering angular velocity, The control device for a vehicle steering system according to any one of claims 1 to 6.

8. The ratio control unit When the magnitude of the actual steering angular velocity is equal to or greater than a predetermined steering angular velocity threshold, the ratio of the dynamic friction compensation value is made larger than the ratio of the static friction compensation value; When the magnitude of the actual steering angular velocity is less than the steering angular velocity threshold value, the ratio of the static friction compensation value is made larger than the ratio of the dynamic friction compensation value. The control device for a vehicle steering system according to claim 7.

9. The ratio control unit monotonically increasing the ratio of the kinetic friction compensation value during a period from when the magnitude of the actual steering angular velocity becomes equal to or greater than the steering angular velocity threshold value until when the ratio of the kinetic friction compensation value reaches a maximum value; monotonically decreasing the ratio of the kinetic friction compensation value during a period from when the magnitude of the actual steering angular velocity becomes less than the steering angular velocity threshold value until when the ratio of the kinetic friction compensation value becomes a minimum value; The control device for a vehicle steering system according to claim 8.

10. The ratio control unit monotonically decreasing the ratio of the static friction compensation value during a period from when the magnitude of the actual steering angular velocity becomes equal to or greater than the steering angular velocity threshold value until when the ratio of the static friction compensation value becomes a minimum value; monotonically increasing the ratio of the static friction compensation value during a period from when the magnitude of the actual steering angular velocity becomes less than the steering angular velocity threshold value until when the ratio of the static friction compensation value reaches a maximum value; The control device for a vehicle steering system according to claim 8 or 9.

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