Vehicle steering system control device

Abstract

To provide a control device of a steering system for a vehicle that can obtain a steering feeling reflecting a situation of a road surface.SOLUTION: The control device of a steering system for a vehicle comprises: a steering torque target value generating part that generates a steering torque target value; a turning angle target value generating part that generates a turning angle target value on the basis of a steering angle; and a turning angle control part that generates a motor current command value It_ref that is supplied to a motor for turning, on the basis of the turning angle target value. The steering torque target value generating part comprises a steering torque compensation value generating part that generates a torque value Tref_c that is a compensation value for the steering torque target value in response to the motor current command value It_ref. The steering torque compensation value generating part calculates road-surface reaction force torque estimate value Tsat_est by filter processing using predetermined transfer function, with respect to the motor current command value It_ref, and generates a torque value Tref_c, on the basis of the road-surface reaction force torque estimate value Tsat_est.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. 2020-185819 Summary of the Invention [Problem to be solved by the invention]

[0004] In SBW systems, where the steering mechanism and the turning mechanism are mechanically separated, oversteer and understeer conditions, such as when driving on a low-μ road where the road surface has significantly reduced friction resistance due to frozen roads or hydroplaning in rainy weather, must be transmitted to a reaction device as a steering reaction force.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide a control device for a vehicle steering system that can provide a steering feel that reflects the road surface conditions. [Means for solving the problem]

[0006] In order to achieve the above object, a control device for a vehicle steering system according to one aspect of the present invention is a control device for a vehicle steering system including a reaction device that applies a steering reaction force to the steering wheel in accordance with the steering angle of the steering wheel, and a steering device that drives a steering motor that steers the 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 angle target value that generates a target value of the steering angle of the steered wheels based on the steering angle. and a steering angle control unit that generates, based on the steering angle target value, a current command value that is a target value of current to be supplied to the steering motor, wherein the steering torque target value generation unit includes a steering torque compensation value generation unit that generates a compensation value for the steering torque target value in accordance with the current command value, and the steering torque compensation value generation unit calculates a road surface reaction force torque estimate value by filtering the current command value using a predetermined transfer function, and generates the compensation value based on the road surface reaction force torque estimate value.

[0007] According to the above configuration, a steering reaction force corresponding to the road surface reaction torque estimate can be applied to the steering wheel, thereby providing a steering feel that reflects the road surface conditions.

[0008] In a preferred embodiment of the control device for a vehicle steering system, the compensation value preferably increases as the road surface reaction torque estimated value increases.

[0009] According to the above configuration, a compensation value according to the road surface reaction torque estimated value is obtained.

[0010] In a preferred embodiment of the control device for a vehicle steering system, the compensation value preferably increases at a rate that decreases as the road surface reaction torque estimated value increases.

[0011] According to the above configuration, it is possible to provide the driver with an appropriate steering feel when turning the steering wheel further.

[0012] In a preferred embodiment of the control device for a vehicle steering system, the steering torque compensation value generating section increases or decreases the compensation value in accordance with the vehicle speed.

[0013] According to the above configuration, a compensation value according to the vehicle speed is obtained.

[0014] In a preferred embodiment of the control device for a vehicle steering system, the compensation value preferably increases as the vehicle speed increases.

[0015] According to the above configuration, a compensation value according to an increase in vehicle speed is obtained.

[0016] In a preferred embodiment of the control device for a vehicle steering system, the steering torque compensation value generating section preferably includes a phase compensation filter that performs phase lag compensation for the compensation value.

[0017] According to the above configuration, the phase delay of the compensation value can be compensated for, thereby improving the steering feel.

[0018] In a preferred embodiment of the control device for a vehicle steering system, the steering torque compensation value generation unit preferably includes a tracking compensation unit that performs tracking compensation for the compensation value.

[0019] According to the above configuration, it is possible to compensate for the phase shift due to the tracking ability between the compensation value and the actual steering torque, thereby applying a steering reaction force with reduced time delay, and enabling control with high tracking ability.

[0020] In a preferred embodiment of the control device for a vehicle steering system, the transfer function is set so that the estimated road surface reaction torque approximates an actual road surface reaction torque obtained while the vehicle is traveling.

[0021] According to the above configuration, a road surface reaction torque estimate value corresponding to the behavior of the actual road surface reaction torque when the vehicle is actually traveling can be obtained, thereby making it possible to apply a steering reaction force appropriate to the behavior of the actual road surface reaction torque.

[0022] In a preferred aspect of the control device for a vehicle steering system, the steering angle control unit includes a friction compensation unit that calculates different current compensation values ​​for when the steered wheels are steered to the right and when they are steered to the left, based on the target steering angle value, and the steering angle control unit generates a motor current command value for driving the steering motor, based on the current command value and the current compensation value.

[0023] According to the above configuration, friction compensation control can be performed effectively regardless of the steering speed of the driver, thereby reducing the sense of discomfort felt by the driver when the steering direction is changed from turning the steering wheel further to turning it back, or from turning it back to turning the steering wheel further.

[0024] As a desirable aspect of the control device for a vehicle steering system, it is preferable that the current command value is a value after PID control in the steering angle control unit, and the steering angle control unit generates the motor current command value by adding the current compensation value to the current command value.

[0025] With the above configuration, the steering torque compensation value generating unit can generate the compensation value for the steering torque target value based on the current command value before adding the current compensation value.

[0026] In a preferred embodiment of the control device for a vehicle steering system, the current compensation value has a hysteresis characteristic according to a change in the target steering angle value.

[0027] According to the above configuration, different current compensation values ​​are calculated when the steered wheels are steered to the right and when the steered wheels are steered to the left.

[0028] In a desirable aspect of the control device for a vehicle steering system, it is preferable that the current compensation value monotonically increases in a region from a first steering angle target value at the start of steering to a second steering angle target value obtained by adding a predetermined steering angle change amount threshold to the first steering angle target value, and becomes a constant value in a region greater than the second steering angle target value.

[0029] With the above configuration, friction compensation control can be performed effectively from a state in which the steered wheels are stationary, regardless of the steering speed of the driver. This reduces the sense of discomfort felt by the driver when the steering direction is changed from further turning to returning, or from returning to further turning, even in situations in which the driver's steering is extremely slow.

[0030] In a preferred embodiment of the control device for a vehicle steering system, the friction compensation unit increases or decreases the current compensation value in accordance with the motor current command value.

[0031] According to the above configuration, it is possible to realize friction compensation control according to the friction force caused by the gear torque.

[0032] In a preferred embodiment of the control device for a vehicle steering system, the current compensation value preferably increases monotonically with an increase in the motor current command value.

[0033] According to the above configuration, it is possible to realize friction compensation control according to the friction force caused by the gear torque, which increases monotonically with an increase in the motor current command value.

[0034] A desirable aspect of the control device for a vehicle steering system includes a current compensation value calculation unit that calculates a first current compensation value, and a current-sensitive gain generation unit that generates a gain that monotonically increases as the motor current command value increases, and it is preferable that the friction compensation unit calculates a second current compensation value by multiplying the first current compensation value by the gain.

[0035] According to the above configuration, it is possible to realize friction compensation control according to the friction force caused by the gear torque, which increases monotonically with an increase in the motor current command value.

[0036] In a preferred embodiment of the control device for a vehicle steering system, the friction compensation unit holds data relating the motor current command value to a gain that monotonically increases as the motor current command value increases, and calculates the current compensation value based on the data.

[0037] According to the above configuration, it is possible to realize friction compensation control according to the friction force caused by the gear torque, which increases monotonically with an increase in the motor current command value. [Effects of the Invention]

[0038] According to the present invention, a control device for a vehicle steering system can be provided that can apply a steering reaction force to the steering wheel in accordance with an estimated road reaction torque value, thereby providing a steering feel that reflects the road surface conditions. [Brief explanation of the drawings]

[0039] [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 a first example of a control block configuration of a control device according to the present disclosure. [Figure 4] FIG. 4 is a block diagram showing an example of the configuration of the steering torque target value generating unit according to the first embodiment. [Figure 5A] FIG. 5A is a diagram showing an example of the characteristics of the basic map. [Figure 5B] FIG. 5B is a diagram showing an example of the characteristics of the torque value Tref_a. [Figure 6A] FIG. 6A is a diagram showing an example of the characteristics of a damper gain map. [Figure 6B] FIG. 6B is a diagram showing an example of the characteristics of the torque value Tref_a+Tref_b. [Figure 7] FIG. 7 is a region diagram for explaining the steering direction in the present disclosure. [Figure 8] FIG. 8 is a block diagram showing an example of the configuration of the steering torque compensation value calculation unit according to the first embodiment. [Figure 9] FIG. 9 is a conceptual diagram for explaining a method for calculating the actual road surface reaction torque acting on the steering mechanism. [Figure 10] FIG. 10 is a conceptual diagram showing a configuration for executing a simulation for deriving the transfer function Gfil. [Figure 11] FIG. 11 is a diagram showing an example of the characteristics of the steering torque compensation value map. [Figure 12] FIG. 12 is a diagram conceptually showing an example of the characteristics of the torque value Tref_c after sign conversion. [Figure 13] FIG. 13 is a block diagram showing a modified example of the steering torque compensation value calculation unit according to the first embodiment. [Figure 14] FIG. 14 is a block diagram showing an example of the configuration of a steering torque target value generating unit according to the second embodiment. [Figure 15] FIG. 15 is a block diagram illustrating the configuration of a phase compensation unit according to the second embodiment. [Figure 16] FIG. 16 is a diagram conceptually showing a specific example of the operation of the steering torque target value generating unit according to the second embodiment. [Figure 17] FIG. 17 is a diagram illustrating a second example of a control block configuration of the control device according to the present disclosure. [Figure 18] FIG. 18 is a block diagram showing an example of the configuration of a steering torque target value generating unit according to the third embodiment. [Figure 19]FIG. 19 is a block diagram showing an example of the configuration of the steering angle control unit according to the third embodiment. [Figure 20] FIG. 20 is a block diagram illustrating an example of the configuration of a friction compensation unit according to the third embodiment. [Figure 21] FIG. 21 is a diagram showing an example of the characteristics of the current compensation value in the current compensation value calculation unit. [Figure 22A] FIG. 22A is a diagram showing a first example of a current-sensitive gain map. [Figure 22B] FIG. 22B is a diagram showing a second example of a current-sensitive gain map. [Figure 23] FIG. 23 is a diagram showing an example of the output characteristics of the friction compensation unit according to the third embodiment. [Figure 24] FIG. 24 is a block diagram showing an example of the configuration of a friction compensation unit according to a modified example of the third embodiment. [Figure 25A] FIG. 25A is a first conceptual diagram illustrating a specific example of friction compensation control by the friction compensation unit according to the third embodiment. [Figure 25B] FIG. 25B is a first conceptual diagram illustrating a specific example of friction compensation control by the friction compensation unit according to the third embodiment. [Figure 26A] FIG. 26A is a second conceptual diagram illustrating a specific example of friction compensation control by the friction compensation unit according to the third embodiment. [Figure 26B] FIG. 26B is a second conceptual diagram illustrating a specific example of friction compensation control by the friction compensation unit according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0040] 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.

[0041] (Embodiment 1) 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.

[0042] 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.

[0043] The reaction force device 30 includes a reaction force motor 31 and a speed 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, which is 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 speed reduction mechanism 32.

[0044] 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."

[0045] 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.

[0046] 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."

[0047] 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.

[0048] 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.

[0049] 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.

[0050] Fig. 3 is a diagram showing a first 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] The steering torque target value generating section 200 generates a steering torque target value Th_ref.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] A steering angle target value generating section 600 generates a steering angle target value θt_ref based on the steering angle θh.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] In this embodiment, 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 may have any configuration that can realize each control in reaction force control system 60 or turning control system 70, and are not limited by the configuration of each control block. The configuration of steering torque target value generation section 200 according to this embodiment will now be described with reference to Figure 4.

[0064] Fig. 4 is a block diagram showing an example of the configuration of the steering torque target value generating unit according to embodiment 1. As shown in Fig. 4, the steering torque target value generating unit 200 according to this embodiment includes, as main components, a basic map unit 210, a damper torque generating unit 220, and a steering torque compensation value generating unit 230.

[0065] In the present disclosure, the sign extraction unit 280 shown in FIG. 4 extracts the sign of the steering angle θh. Specifically, for example, the value of the steering angle θh is divided by the absolute value of the steering angle θh. As a result, the sign extraction unit 280 outputs "1" when the sign of the steering angle θh is "+", and outputs "-1" when the sign of the steering angle θh is "-". Specifically, the sign extraction unit 280 generates, for example, a sign function Sgn(θh) of the steering angle θh.

[0066] Fig. 5A is a diagram showing an example of the characteristics of the basic map. The steering angle |θh| and vehicle speed Vs that have been subjected to absolute value processing in the absolute value calculation unit 260 are input to the basic map unit 210. The basic map unit 210 generates a torque value Tref_basic using the vehicle speed Vs as a parameter, using the basic map shown in Fig. 5A. The torque value Tref_basic is used to generate a basic steering reaction force according to the steering angle |θh| and the vehicle speed Vs.

[0067] The torque value Tref_basic has an angle-sensitive characteristic that increases or decreases according to the steering angle |θh|. More specifically, as shown in FIG. 5A, the torque value Tref_basic increases as the steering angle |θh| increases. Furthermore, the torque value Tref_basic has a vehicle-speed-sensitive characteristic that increases or decreases according to the vehicle speed Vs. More specifically, as shown in FIG. 5A, the torque value Tref_basic increases as the vehicle speed Vs increases. In other words, the reaction force obtained by the torque value Tref_basic derived from the basic map shown in FIG. 5A increases as the amount of operation of the steering wheel 1 by the driver (steering angle θh) increases, and also increases as the vehicle speed (vehicle speed Vs) increases. Note that although the basic map shown in FIG. 5A has a vehicle-speed-sensitive characteristic, the present invention is not limited to this.

[0068] Fig. 5B is a diagram showing an example of the characteristics of the torque value Tref_a. The torque value Tref_a shown in Fig. 5B is obtained by multiplying the torque value Tref_basic output from the basic map unit 210 by the sign function Sgn(θh) output from the sign extraction unit 280 in the multiplication unit 293. Note that a configuration without the sign extraction unit 280 may also be adopted in which the torque value Tref_a is obtained using a basic map corresponding to the positive and negative steering angles θh, as shown in Fig. 5B.

[0069] The damper torque generation unit 220 includes a damper gain map unit 221 and a multiplication unit 222. Fig. 6A is a diagram showing an example of the characteristics of the damper gain map. The vehicle speed Vs is input to the damper gain map unit 221. The damper gain map unit 221 generates the damper gain DG using the damper gain map shown in Fig. 6A.

[0070] 6A, the damper gain DG has a vehicle speed-sensitive characteristic that increases or decreases according to the vehicle speed Vs. The damper torque generation unit 220 multiplies the angular velocity of the steering wheel 1 (hereinafter also referred to as "steering angular velocity ωh") calculated by differentiating the steering angle θh (differentiation unit 270) by the damper gain DG output from the damper gain map unit 221 (multiplication unit 222), and outputs the result as a torque value Tref_b.

[0071] The torque value Tref_b output from the damper torque generation unit 220 is added to the torque value Tref_a output from the basic map unit 210 (addition unit 291). This makes it possible to compensate for the steering reaction force in proportion to the steering angular velocity ωh.

[0072] Fig. 6B is a diagram showing an example of the characteristics of the torque value Tref_a+Tref_b. The torque value Tref_a+Tref_b is obtained by adding the torque value Tref_a to the torque value Tref_b output from the damper torque generation unit 220. In Fig. 6B, the solid line indicates the torque value Tref_a+Tref_b when the steering angular velocity ωh is a positive value (ωh>0), and the dashed line indicates the torque value Tref_a+Tref_b when the steering angular velocity ωh is a negative value (ωh<0). Also in Fig. 6B, the dashed line indicates the torque value Tref_a.

[0073] 7 is a region diagram for explaining the steering direction in the present disclosure, in which the horizontal axis represents the steering angle θh and the vertical axis represents the steering angular velocity ωh.

[0074] Area A ((θh, ωh) = (+, +)) shown in FIG. 7 indicates that the steering wheel 1 is turned to the right (θh > 0) and is being turned further to the right (ωh > 0). Area B ((θh, ωh) = (+, -)) shown in FIG. 7 indicates that the steering wheel 1 is turned to the right (θh > 0) and is being turned back to the left (ωh < 0). Area C ((θh, ωh) = (-, -)) shown in FIG. 7 indicates that the steering wheel 1 is turned to the left (θh < 0) and is being turned further to the left (ωh < 0). Area D ((θh, ωh) = (-, +)) shown in FIG. 7 indicates that the steering wheel 1 is turned to the left (θh < 0) and is being turned back to the right (ωh > 0). Also, in Figure 7, on the steering angle θh axis (ωh=0), it is shown that the steering wheel 1 is neither being turned further nor turned back ((θh, ωh)=(θh,0)), and on the steering angular velocity ωh axis (θh=0), it is shown that the steering wheel 1 is in the center position ((θh, ωh)=(0, ωh)).

[0075] The torque value Tref_b output from the damper torque generation unit 220 is a positive value in regions A and D where the steering angular velocity ωh>0, and a negative value in regions B and C where the steering angular velocity ωh<0. As a result, when the steering angular velocity ωh>0, that is, in region A where the steering wheel 1 is turned to the right (θh>0) and further turned to the right, or in region D where the steering wheel 1 is turned to the left (θh<0) and turned back to the right, the torque value Tref_b is a value obtained by adding |Tref_b| to Tref_a, as shown by the solid line in Fig. 6B. On the other hand, when the steering angular velocity ωh<0, that is, in region B where the steering wheel 1 is turned to the right (θh>0) and turned back to the left, or in region C where the steering wheel 1 is turned to the left (θh<0) and further turned to the left, the torque value Tref_b is a value obtained by subtracting |Tref_b| from Tref_a, as shown by the dashed line in Fig. 6B.

[0076] 6B, the torque value Tref_a+Tref_b increases with increasing steering angle θ as the steering angle θh increases and approaches the steering end point limited by the stopper (rotation limiting mechanism) 35. In other words, the torque value Tref_a+Tref_b has a characteristic that the rate of change gradually decreases as the steering angle θh increases.

[0077] As described above, the SBW system does not have an intermediate shaft mechanically coupled to the column shaft 2. In other words, the steering mechanism and the turning mechanism are mechanically separated. For this reason, it is necessary to transmit to the reaction device 30 the steering reaction force when the vehicle is oversteered or understeered, for example, when traveling on a low-μ road where the frictional resistance of the road surface is significantly reduced due to an icy road surface or hydroplaning during rainy weather.

[0078] In the present disclosure, as shown in Figures 3 and 4, there is provided a steering torque compensation value generation unit 230 that estimates road surface reaction torque according to motor current command value It_ref generated by steering angle control unit 700, and torque value Tref_c generated by steering torque compensation value generation unit 230 is added to torque value Tref_a+Tref_b. This makes it possible to apply a steering reaction force according to the estimated value of road surface reaction torque to steering wheel 1. Below, a detailed description is given of the configuration and operation that can apply a steering reaction force according to the estimated value of road surface reaction torque to steering wheel 1.

[0079] Fig. 8 is a block diagram showing an example of the configuration of a steering torque compensation value calculation unit according to embodiment 1. In the example configuration shown in Fig. 8, a steering torque compensation value calculation unit 240 includes, as main components, a road surface reaction force torque estimation unit 241 and a steering torque compensation value map unit 242.

[0080] First, a method for estimating the road surface reaction torque estimated value Tsat_est in the road surface reaction torque estimating section 241 will be described.

[0081] Motor current command value It_ref generated by steering angle control unit 700 is input to road surface reaction force torque estimator 241. Also, a transfer function Gfil shown in the following equation (1) is set in road surface reaction force torque estimator 241. Transfer function Gfil is stored, for example, in a ROM of an ECU constituting control device 50.

[0082] Gfil=N(s) / D(s)=(Ds+E) / (As 2 +Bs+C)···(1)

[0083] In the above equation (1), the linear function N(s) = Ds + E and the quadratic function D(s) = As 2 A, B, C, D, and E in +Bs+C are coefficients set by the simulation shown below.

[0084] In the present disclosure, the transfer function Gfil is assumed to be a transfer function with a first order numerator and a second order denominator, but the order of the numerator and denominator can be changed as appropriate depending on the allowable error between the actual road surface reaction torque Tsat_act and the road surface reaction torque estimate value Tsat_est, the load on the ECU, etc.

[0085] For example, if the order of the numerator and denominator is increased, the relationship between the motor current command value It_ref and the actual road surface reaction torque Tsat_act determined by an experiment described below can be made to match well with the transfer characteristics of the transfer function Gfil, making it possible to estimate a road surface reaction torque estimated value Tsat_est that is close to the actual measured value.

[0086] On the other hand, if the order of the numerator and denominator is reduced, the load on the ECU can be reduced.

[0087] Assume that the relationship shown in the following equation (2) holds between the road surface reaction torque Tsat and the motor current command value It_ref. The road surface reaction torque Tsat shown in the following equation (2) is defined as the road surface reaction torque estimated value Tsat_est in this disclosure.

[0088] In other words, the transfer function Gfil calculates the road surface reaction torque estimated value Tsat_est from the motor current command value It_ref by simulating the relationship between the motor current command value It_ref and the actual road surface reaction torque Tsat_act obtained through experiments.

[0089] Tsat=Gfil×It_ref=Tsat_est···(2)

[0090] On the other hand, the actual road surface reaction torque Tsat_act acting on the steering mechanism can be calculated from the axial force applied to the tie rod. Fig. 9 is a conceptual diagram for explaining a method for calculating the actual road surface reaction torque acting on the steering mechanism.

[0091] The actual road surface reaction torque Tsat_act can be calculated by the following equation (3) using the axial forces FL and FR applied to the tie rods 3a and 3b and the length L of the arms 6a and 6b determined for each vehicle type.

[0092] Tsat_act = FL × L - FR × L (3)

[0093] In the present disclosure, the actual road surface reaction torque Tsat_act is calculated using the above formula (3) that uses the axial forces FL and FR measured in advance through experiments using an actual vehicle. The axial forces FL and FR can be measured, for example, by attaching force sensors to the tie rods 3 a and 3 b.

[0094] FIG. 10 is a conceptual diagram showing a configuration for executing a simulation for deriving the transfer function Gfil.

[0095] The motor current command value It_ref and axial forces FL and FR are input to the processing device shown in Fig. 10. The processing device derives a transfer function Gfil such that the road surface reaction torque estimated value Tsat_est shown in the above equation (2) approximates the actual road surface reaction torque Tsat_act calculated by the above equation (3). An example of the processing device shown in Fig. 10 is one that includes a frequency characteristic analysis device (servo analyzer).

[0096] Specifically, the processing device performs curve fitting using a sweep method to derive the coefficients A, B, C, D, and E of the transfer function Gfil shown in the above equation (1). An example of the curve fitting method is the least squares approximation method. The curve fitting method is not limited to the least squares approximation method.

[0097] Road surface reaction torque estimating section 241 performs filtering on motor current command value It_ref generated by steering angle control section 700 using transfer function Gfil derived as described above, and calculates road surface reaction torque estimated value Tsat_est shown in equation (2) above. This makes it possible to obtain road surface reaction torque estimated value Tsat_est that corresponds to the behavior of actual road surface reaction torque Tsat_act when the vehicle is actually traveling.

[0098] Returning to FIG. 8 , the sign extraction unit 244 extracts the sign of the road reaction force torque estimated value Tsat_est. Specifically, for example, the value of the road reaction force torque estimated value Tsat_est is divided by the absolute value of the road reaction force torque estimated value Tsat_est. As a result, the sign extraction unit 244 outputs "1" when the sign of the road reaction force torque estimated value Tsat_est is "+", and outputs "-1" when the sign of the road reaction force torque estimated value Tsat_est is "-". Specifically, the sign extraction unit 244 generates, for example, a sign function Sgn(Tsat_est) of the road reaction force torque estimated value Tsat_est.

[0099] Fig. 11 is a diagram showing an example of the characteristics of a steering torque compensation value map. The road surface reaction torque estimated value |Tsat_est| and vehicle speed Vs that have been subjected to absolute value processing in absolute value calculation section 243 are input to steering torque compensation value map section 242. Steering torque compensation value map section 242 generates a torque value Tref_c0 using the steering torque compensation value map shown in Fig. 11 with vehicle speed Vs as a parameter.

[0100] As shown in FIG. 11, the torque value Tref_c0 has a torque-sensitive characteristic that increases or decreases according to the road surface reaction torque estimated value |Tsat_est|.

[0101] More specifically, the torque value Tref_c0 increases as the road surface reaction torque estimated value |Tsat_est| increases, and the rate of increase decreases as the road surface reaction torque estimated value |Tsat_est| increases.

[0102] Furthermore, the torque value Tref_c0 has a vehicle speed-sensitive characteristic that increases and decreases according to the vehicle speed Vs. More specifically, the torque value Tref_c0 increases as the vehicle speed Vs increases, as shown in Fig. 11 .

[0103] That is, the reaction force obtained by the torque value Tref_c0 derived from the steering torque compensation value map shown in Fig. 11 increases as the road surface reaction torque estimated value |Tsat_est| increases and as the vehicle speed (vehicle speed Vs) increases. Note that although the steering torque compensation value map shown in Fig. 11 has a vehicle speed sensitive characteristic, the present invention is not limited to this.

[0104] The steering torque compensation value calculation unit 240 multiplies the torque value Tref_c0, which is the output value of the steering torque compensation value map unit 242, by a sign function Sgn(Tsat_est) of the road surface reaction torque estimated value Tsat_est in a multiplication unit 245, and outputs the sign-converted torque value Tref_c. Fig. 12 is a diagram conceptually showing an example of the characteristics of the torque value Tref_c after sign conversion.

[0105] The steering torque compensation value calculation unit 240 may also be configured as shown in Fig. 13. Fig. 13 is a block diagram showing a modified example of the steering torque compensation value calculation unit according to the first embodiment.

[0106] The steering torque compensation value map section 242a in the modified example of the steering torque compensation value calculation section shown in FIG. 13 may have a steering torque compensation value map with the characteristics shown in FIG. 12 instead of the steering torque compensation value map with the characteristics shown in FIG. 11.

[0107] The torque value Tref_c output from the steering torque compensation value generation unit 230 is added to the torque value Tref_a and the torque value Tref_b in the addition units 291 and 292 shown in Fig. 4. As a result, the steering torque target value generation unit 200 outputs the steering torque target value Th_ref.

[0108] In the present disclosure, as described above, the road reaction torque estimator 241 calculates the road reaction torque estimated value Tsat_est using the transfer function Gfil derived by simulating an actual vehicle, thereby obtaining the road reaction torque estimated value Tsat_est according to the behavior of the actual road reaction torque Tsat_act when the vehicle is actually traveling, and applying a steering reaction force according to the road reaction torque estimated value Tsat_est. This makes it possible to obtain a steering feel that reflects the road surface conditions.

[0109] Furthermore, in the present disclosure, input of the axial force applied to the tie rod or the like is not required, and the road surface reaction torque estimated value Tsat_est is calculated using the motor current command value It_ref used in the internal processing of the control device 50 and a preset transfer function Gfil, thereby reducing costs and simplifying processing.

[0110] The transfer function used when calculating the road surface reaction torque estimated value Tsat_est in the road surface reaction torque estimator 241 is not limited to the above-described (1). Specifically, the present disclosure is not limited by the orders of the functions N(s) and D(s), for example.

[0111] Furthermore, the characteristics of the steering torque compensation value map are not limited to the aspects shown in Fig. 11 or 12. Furthermore, for example, instead of the aspects of the maps shown in Fig. 11 or 12, the characteristics may be defined by a predetermined transfer function.

[0112] (Embodiment 2) FIG. 14 is a block diagram showing an example of the configuration of a steering torque target value generating unit according to the second embodiment.

[0113] In the configuration example shown in FIG. 14, the steering torque compensation value generation unit 230a of the steering torque target value generation unit 200a according to the second embodiment includes a phase compensation unit 250 in addition to the steering torque compensation value calculation unit 240 described in the first embodiment.

[0114] The phase compensation unit 250 performs the following phase compensation on the torque value Tref_c output from the steering torque compensation value calculation unit 240 to calculate a torque value Tref_d.

[0115] 15 is a block diagram showing the configuration of a phase compensation unit according to embodiment 2. In the present disclosure, the phase compensation unit 250 includes a phase compensation filter 251 and a tracking compensation unit 252. Note that, in the following description, a case where a phase lag compensator is used as the phase compensation filter 251 will be described, but a phase lead compensator can also be used as the phase compensation filter 251.

[0116] The phase compensation filter 251 performs phase lag compensation for the torque value Tref_c output from the steering torque compensation value calculation unit 240. The following equation (4) is a phase compensation filter C f It shows the characteristics of

[0117] C f =(T n s+1) / (T d s+1) (4)

[0118] The cutoff frequency f of the numerator in (4) above n is f n =1 / (2π×T n ) and the cutoff frequency f d is f d =1 / (2π×T d )

[0119] The phase compensation filter 251 calculates the torque value Tref_c output from the steering torque compensation value calculation unit 240 using the phase compensation filter C f This compensates for the phase lag of the torque value Tref_c.

[0120] In addition, T in the above equation (4) n , T d , i.e., the cutoff frequency f n , f d By adjusting the coefficient of the phase compensation filter 251, it is possible to improve the steering feel. Furthermore, the configuration of the phase compensation filter 251 is not limited to the above-described embodiment, and it may be realized by, for example, a second-order or higher filter. Furthermore, as described above, it is also possible to adjust the coefficient of the phase compensation filter 251 so that the phase compensation filter 251 functions as a phase lead compensator to compensate for the phase lead of the torque value Tref_c.

[0121] The tracking compensation unit 252 performs tracking compensation on the torque value Tref_c output from the steering torque compensation value calculation unit 240 .

[0122] The relational expression shown in the following equation (5) holds between the steering torque target value Th_ref and the actual steering torque Th_Act.

[0123] Th_act = Gref × Th_ref (5)

[0124] The tracking performance compensation unit 252 performs an inverse calculation (1 / Gref) of the transfer function Gref shown in the above equation (5) on the torque value Tref_c output from the steering torque compensation value calculation unit 240. This makes it possible to compensate for the phase shift due to tracking performance between the torque value Tref_c and the actual steering torque Th_Act.

[0125] The torque value Tref_d output from the steering torque compensation value generation unit 230a is added to the torque values ​​Tref_a and Tref_b in addition units 291 and 292 shown in Fig. 14. As a result, the steering torque target value generation unit 200a outputs the steering torque target value Th_ref.

[0126] Fig. 16 is a diagram conceptually showing a specific example of the operation of the steering torque target value generation unit according to the second embodiment. In Fig. 16, the horizontal axis represents time, and the vertical axis represents the actual steering torque Th_act. The dashed line in Fig. 16 represents an example of operation based on the steering torque target value Th_ref to which the torque value Tref_c, which is the output value of the steering torque compensation value calculation unit 240, is applied, and the solid line represents an example of operation based on the steering torque target value Th_ref to which the torque value Tref_d, which is phase-compensated in the phase compensation unit 250, is applied. The dash-dotted line in Fig. 16 represents the actual steering torque Th_act when the compensation value in the steering torque compensation value generation unit 230 is not applied.

[0127] FIG. 16 shows an example in which the driver turns the steering wheel 1 further to the right, and after time t_low_μ, the vehicle deviates from a curve in which the road reaction torque is not reflected, enters a low μ road, and the tires begin to slip.

[0128] As shown by the dashed line in Fig. 16, when the compensation value in the steering torque compensation value generation unit 230 is not applied, the road surface reaction force is not reflected after time t_low_μ. In contrast, as shown by the dashed line in Fig. 16, when the torque value Tref_c that is the output value of the steering torque compensation value calculation unit 240 is applied, a road surface reaction force that corresponds to the behavior of the actual road surface reaction torque Tsat_act when the vehicle is actually traveling is applied. Furthermore, as shown by the solid line in Fig. 16, when the torque value Tref_d that is the compensation value after phase compensation is applied, a steering reaction force with reduced time delay is applied, enabling control with high follow-up to the behavior of the actual road surface reaction torque Tsat_act.

[0129] (Embodiment 3) Fig. 17 is a diagram showing a second example of a control block configuration of a control device according to the present disclosure. Fig. 18 is a block diagram showing an example configuration of a steering torque target value generation section according to embodiment 3. In the configurations shown in Figs. 17 and 18, current command value Iref_a in steering angle control section 700a is input to steering torque compensation value generation section 230b of steering torque target value generation section 200b, instead of motor current command value It_ref. The main configurations of steering torque target value generation section 200b and steering torque compensation value generation section 230b are the same as those of embodiment 1 or embodiment 2, so detailed description will be omitted here.

[0130] Steering angle control unit 700a 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 700a calculates motor current command value It_ref so that deviation θt_err between steering angle target value θt_ref and actual steering angle θt_act approaches zero. A more specific configuration example of steering angle control unit 700a according to the third embodiment will be described later with reference to FIG. 19. In FIG. 17, some components of the specific configuration shown in FIG. 19 are omitted.

[0131] In the present embodiment, steering torque control section 400, current control section 500, turning angle target value generation section 600 and current control section 800 are not limited by the configuration of each control block as long as they are capable of realizing the respective controls in reaction force control system 60 or turning control system 70. Below, a specific configuration of turning angle control section 700a according to the present embodiment will be described with reference to Fig. 19.

[0132] Fig. 19 is a block diagram showing an example configuration of a steering angle control unit according to embodiment 3. As shown in Fig. 19, steering angle control unit 700a according to the present embodiment includes feedforward compensation unit 710, PID control unit 730, stabilization compensation unit 740, output limiting unit 760, friction compensation unit 770, and addition units 720, 750.

[0133] Feedforward compensation section 710 is configured with a filter (FF filter) for improving the ability of actual turning angle θt_act to follow target turning angle value θt_ref. Feedforward compensation section 710 performs filtering on target turning angle value θt_ref. Specifically, for example, an LPF having a first-order or second-order lag transfer function is used, and the LPF is designed so that the time delay caused by filtering by the LPF is equivalent to the delay in the actual turning angle θt_act following target turning angle value θt_ref.

[0134] PID control section 730 performs PID control so that deviation θt_err between target turning angle value θt_ref, which is the calculation result of addition section 720, and actual turning angle θt_act approaches zero.

[0135] The stabilization compensation unit 740 is configured with a filter (stabilization filter) having transfer characteristics required for stabilizing control. The stabilization compensation unit 740 performs filtering on the output value of the PID control unit 730.

[0136] The output limiting unit 760 performs output limiting processing on the current command value Iref_c, which is the calculation result of the adding unit 750, and outputs the motor current command value It_ref. Upper and lower limit values ​​for the current command value Iref_c are set in advance in the output limiting unit 760. The output limiting unit 760 limits the upper and lower limit values ​​of the current command value Iref_c and outputs the motor current command value It_ref.

[0137] It should be noted that the above-described feedforward compensation section 710 and stabilization compensation section 740 are not necessarily required components, and for example, either one or both of the feedforward compensation section 710 and the stabilization compensation section 740 may be omitted.

[0138] Friction compensation section 770 calculates current compensation value Iref_b (second current compensation value) for compensating for a delay in the response of actual turning angle θt_act to turning angle target value θt_ref, which occurs due to friction in the turning mechanism, based on turning angle target value θt_ref. The specific configuration and operation of friction compensation section 770 according to the present embodiment will be described in detail below.

[0139] Fig. 20 is a block diagram showing an example of the configuration of a friction compensation unit according to embodiment 3. As shown in Fig. 20, a friction compensation unit 770 according to this embodiment includes, as main components, a current compensation value calculation unit 771 and a current sensitive gain generation unit 773.

[0140] Current compensation value calculation section 771 receives as input the steering angle target value θt_ref and the turning speed target value ωt_ref calculated by differentiating the steering angle target value θt_ref by differentiating section 772. Current compensation value calculation section 771 calculates current compensation value Iref_b0 (first current compensation value) based on the steering angle target value θt_ref and the turning speed target value ωt_ref.

[0141] A method for calculating the current compensation value Iref_b0 (first current compensation value) in the current compensation value calculation unit 771 will be described below.

[0142] Fig. 21 is a diagram showing an example of the characteristics of the current compensation value in the current compensation value calculation unit. In Fig. 21, the horizontal axis represents the steering angle target value θt_ref, and the vertical axis represents the current compensation value Iref_b0 (first current compensation value). Also in Fig. 21, the solid line represents the current compensation value Iref_b0 (first current compensation value) when steering to the right, and the dashed line represents the current compensation value Iref_b0 (first current compensation value) when steering to the left. As shown in Fig. 21, the current compensation value Iref_b0 (first current compensation value) calculated in current compensation value calculation unit 771 has hysteresis characteristics that result in different values ​​when steering to the left and when steering to the right. L1 shown in Figure 21 indicates the trajectory when the steered wheels 5L and 5R are steered to the right from their center position (origin (0,0)), L2 indicates the trajectory when a switch from right steering to left steering occurs at coordinate A (x1, y1), and L3 indicates the trajectory when a switch from right steering to left steering occurs at coordinate B (x2, y2).

[0143] Current compensation value calculation unit 771 calculates current compensation value Iref_b0 (first current compensation value) using the following equations (6) and (7) based on the steering angle target value θt_ref and the steering speed target value ωt_ref. Specifically, when the sign ωt_ref(sgn) of the steering speed target value ωt_ref is a positive value ("+"), current compensation value Iref_b0 (first current compensation value) is calculated using the following equation (6), and when the sign ωt_ref(sgn) of the steering speed target value ωt_ref is a negative value ("-"), current compensation value Iref_b0 (first current compensation value) is calculated using the following equation (7). In the following equations (6) and (7), x is the steering speed target value ωt_ref, y is the R is the current compensation value Iref_b0 (first current compensation value) when steering right, y L is the current compensation value Iref_b0 (first current compensation value) when steering left. Furthermore, the coefficient a is greater than 1, and the coefficient c is greater than 0. The coefficient Ahys indicates the output width of the hysteresis characteristic (the width of the current compensation value Iref_b0 (first current compensation value)), and the coefficient c is a coefficient that indicates the roundness of the hysteresis characteristic.

[0144] y R =Ahys{1-a-c(x-b)}···(6)

[0145] y L =-Ahys{1-a c(x-b’)}···(7)

[0146] That is, when steering to the right (ωt_ref(sgn)="+"), the current compensation value calculation unit 771 calculates the current compensation value Iref_b0(y R ) is calculated, and when steering left (ωt_ref(sgn) = "-"), the current compensation value Iref_b0(y L ) is calculated.

[0147] When a switch from right steering to left steering occurs (ωt_ref(sgn) = "+" → "-"), or when a switch from left steering to right steering occurs (ωt_ref(sgn) = "-" → "+"), current compensation value calculation unit 771 takes over the previous values ​​of steering angle target value θt_ref and current compensation value Iref_b0 (first current compensation value), and substitutes coefficient b or b' shown in equation (8) or (9) below into equation (6) or (7) above that is applied after the steering switch. This maintains continuity before and after the steering switch. Specifically, when a switch from right steering to left steering occurs (ωt_ref(sgn)="+" → "-"), current compensation value calculation unit 771 applies the steering angle target value θt_ref and the previous value (coordinate A(x1, y1) shown in FIG. 21) of current compensation value Iref_b0 (first current compensation value) to equation (7) above, and substitutes coefficient b' shown in equation (9) below to calculate current compensation value Iref_b0 (first current compensation value). Furthermore, when a switch from left steering to right steering occurs (ωt_ref(sgn)="-" → "+"), current compensation value calculation unit 771 applies the steering angle target value θt_ref and the previous value (coordinates B(x2, y2) shown in FIG. 21) of current compensation value Iref_b0 (first current compensation value) to equation (6) above, and substitutes coefficient b shown in equation (8) below to calculate current compensation value Iref_b0 (first current compensation value).

[0148] b=x1+(1 / c)log a {1-(y1 / Ahys)} (8)

[0149] b'=x1-(1 / c)log a {1-(y1 / Ahys)}···(9)

[0150] The above formulas (8) and (9) are obtained by substituting x1 for x in the above formulas (6) and (7) and R and y L It can be derived by substituting y1 into

[0151] When Napier's constant e is used as the coefficient a, the above equations (6), (7), (8), and (9) can be expressed as the following equations (10), (11), (12), and (13), respectively.

[0152] y R =Ahys[1-exp{-c(xb)}]···(10)

[0153] y L =-Ahys[{1-exp{c(x-b')}]···(11)

[0154] b=x1+(1 / c)log e {1-(y1 / Ahys)}···(12)

[0155] b'=x1-(1 / c)log e {1-(y1 / Ahys)}···(13)

[0156] Returning to Fig. 20, previous value holding unit 774 holds the previous output value It_ref' of steering angle control unit 700a. Specifically, the previous output value It_ref' is the motor current command value It_ref in the previous process. Previous value holding unit 774 is formed, for example, by a RAM of an ECU constituting control device 50.

[0157] In the present disclosure, absolute value calculation section 775 performs absolute value processing of the previous output value It_ref′ of turning angle control section 700 a output from previous value holding section 774 .

[0158] Current sensitive gain generation section 773 receives as input the previous output value |It_ref'| of turning angle control section 700a that has been subjected to absolute value processing in absolute value calculation section 775. Current sensitive gain generation section 773 generates gain Gi according to the previous output value |It_ref'| of turning angle control section 700a.

[0159] Current sensitive gain generation section 773 has a current sensitive gain map in which gain Gi is set according to previous output value |It_ref'| of steering angle control section 700a. The current sensitive gain map is stored, for example, in the ROM of the ECU that constitutes control device 50. Fig. 22A is a diagram showing a first example of the current sensitive gain map. Fig. 22B is a diagram showing a second example of the current sensitive gain map.

[0160] The first example of the current-sensitive gain map shown in Fig. 22A has a current-value-sensitive characteristic in which gain Gi increases or decreases according to the previous output value |It_ref'| of turning angle control unit 700a. More specifically, as shown in Fig. 22A, gain Gi monotonically increases as the previous output value |It_ref'| of turning angle control unit 700a increases.

[0161] Fig. 23 is a diagram showing an example of the output characteristics of the friction compensation unit according to embodiment 3. In Fig. 23, the horizontal axis represents the target steering angle value θt_ref, and the vertical axis represents the current compensation value Iref_b (second current compensation value).

[0162] The frictional force generated in the steering mechanism includes friction due to gear torque between steering motor 41 and reduction mechanism 42. Gear torque refers to torque resulting from frictional force generated in the mechanical elements of the reduction gear. For example, in the case of a worm reduction gear, the frictional torque caused by frictional force generated at the meshing portion between the worm gear and the worm wheel can be defined as gear torque. The frictional force due to this gear torque increases monotonically with motor current.

[0163] In the present disclosure, the friction compensation unit 770 calculates the current compensation value Iref_b (second current compensation value) by multiplying (by a multiplication unit 776) the current compensation value Iref_b0 (first current compensation value) output from the current compensation value calculation unit 771 by the gain Gi generated by the current sensitive gain generation unit 773. As a result, as shown in Fig. 23, a characteristic is obtained in which the output width of the hysteresis characteristic (the width of the current compensation value Iref_b (second current compensation value)) increases and decreases according to the motor current command value It_ref, and friction compensation control according to the frictional force caused by the gear torque can be realized.

[0164] Specifically, when the motor current command value It_ref is relatively large, the gear torque becomes relatively large, and the frictional force caused by the gear torque acts strongly. Under such circumstances, by multiplying the current compensation value Iref_b0 (first current compensation value) output from the current compensation value calculation unit 771 by a gain Gi_H that is relatively larger than the gain Gi_M, it is possible to increase the output width of the hysteresis characteristic (width of the current compensation value Iref_b (second current compensation value)), as shown by the dashed line.

[0165] Furthermore, when the motor current command value It_ref is relatively small, the gear torque becomes relatively small, and the frictional force caused by the gear torque becomes smaller. Under such circumstances, by multiplying the current compensation value Iref_b0 (first current compensation value) output from the current compensation value calculation unit 771 by a gain Gi_L that is relatively smaller than the gain Gi_M, it is possible to narrow the output width of the hysteresis characteristic (width of the current compensation value Iref_b (second current compensation value)), as shown by the dashed dotted line.

[0166] The mode of the current sensitive gain map is not limited to the mode of the first example shown in Fig. 22A. For example, as in a second example shown in Fig. 22B, a mode may be adopted in which current compensation value Iref_b0 (first current compensation value) output from current compensation value calculation unit 771 is multiplied by a constant gain Gi=k (for example, k=1) to calculate current compensation value Iref_b (second current compensation value), regardless of motor current command value It_ref (previous output value |It_ref'| of steering angle control unit 700a).

[0167] The current compensation value Iref_b (second current compensation value) output from the friction compensation unit 770 is added to the current command value Iref_a output from the stabilization compensation unit 740 by the addition unit 750 shown in Figure 19, and the motor current command value It_ref, which is output by the output limiting unit 760 and limited by the output limiting unit 760 with respect to the current command value Iref_c after the addition, is output.

[0168] In the configuration according to the third embodiment, current command value Iref_a is substantially equivalent to motor current command value It_ref in the first and second embodiments. In other words, current command value Iref_a corresponds to motor current command value It_ref in the first and second embodiments. That is, even in the configuration in which steering angle control unit 700a is provided with friction compensation unit 770, it is possible to obtain a steering feel that reflects the state of the road surface, similar to the configuration in which steering torque target value generation unit 200 according to the first embodiment shown in FIG. 4 is provided and the configuration in which steering torque target value generation unit 200a according to the second embodiment shown in FIG. 14 is provided.

[0169] FIG. 24 is a block diagram showing an example configuration of a friction compensation unit according to a modification of the third embodiment. In the example configuration shown in FIG. 20, current compensation value Iref_b0 (second current compensation value) output from current compensation value calculation unit 771 is multiplied by gain Gi generated by current sensitive gain generation unit 773. However, in the modification shown in FIG. 24, current compensation value calculation unit 771a may be configured to hold a table (data) in which motor current command value It_ref (previous output value |It_ref'| of steering angle control unit 700a) is associated with coefficient Ahys in equations (6) to (13) above, and to obtain a characteristic in which the output width of the hysteresis characteristic (width of current compensation value Iref_b (second current compensation value)) increases or decreases depending on motor current command value It_ref, as shown in FIG. 23. This data, like the current sensitive gain map, can be stored, for example, in the ROM of the ECU constituting control device 50. As a result, friction compensation control according to frictional force caused by gear torque can be realized, similar to the configuration shown in FIG. 20.

[0170] Note that the present invention is not limited to the aspect in which steering speed target value ωt_ref is obtained by differentiating steering angle target value θt_ref, and may alternatively be an aspect in which it is determined that the steering direction has been switched using the motor angular velocity of steering motor 41. Also, a configuration may be adopted in which a filter is provided in a stage preceding current compensation value calculation section 771 and current sensitive gain generation section 773, or a configuration in which a filter is provided in a stage subsequent to current sensitive gain generation section 773. Furthermore, a configuration may be adopted in which a limiter that performs output limiting processing on current compensation value Iref_b (second current compensation value) is provided in a stage subsequent to friction compensation section 770, similar to output limiting section 760 described above.

[0171] Fig. 25A and Fig. 25B are first conceptual diagrams illustrating a specific example of friction compensation control by a friction compensation unit according to embodiment 3. In Fig. 25A and Fig. 25B, the horizontal axis represents time, and the vertical axis represents steering angle. The dashed lines in Fig. 25A and Fig. 25B represent steering angle target value θt_ref, and the solid lines represent actual steering angle θt_act. Fig. 25A illustrates a time response when friction compensation control is not performed by friction compensation unit 770 according to embodiment 3. Fig. 25B illustrates a time response when friction compensation control is performed by friction compensation unit 770 according to embodiment 3.

[0172] The examples shown in Fig. 25A and Fig. 25B show time responses when steered wheels 5L, 5R are steered left and right from the center position at a relatively fast predetermined frequency. When friction compensation control is not performed by friction compensation unit 770 according to the third embodiment, as shown in Fig. 25A, distortion occurs in actual steering angle θt_act when the steering direction is switched, as enclosed by the dashed line. In this case, when the driver switches the steering direction from steering further to steering back, or from steering back to steering further, a discrepancy occurs between the operation (steering) of steering wheel 1 and the steering of steered wheels 5L, 5R, which may cause the driver to feel uncomfortable. In contrast, when friction compensation control is performed by friction compensation unit 770 according to the third embodiment, distortion in actual steering angle θt_act when the steering direction is switched, as enclosed by the dashed line, as shown in Fig. 25B.

[0173] To explain in more detail, when the steering angle target value θt_ref is switched during a change in steering direction, the steering speed target value ωt_ref becomes approximately zero. However, since the current compensation value Iref_b0 (first current compensation value) is determined according to the steering angle target value θt_ref, the friction compensation unit 770 can perform predetermined friction compensation control even when the steering speed target value ωt_ref is approximately zero.

[0174] This reduces the sense of discomfort felt by the driver when the steering direction is switched from further turning to returning, or from returning to further turning.

[0175] 26A and 26B are second conceptual diagrams illustrating a specific example of friction compensation control by a friction compensation unit according to embodiment 3. In FIGS. 26A and 26B, the horizontal axis represents time, and the vertical axis represents steering angle. The dashed lines in FIGS. 26A and 26B represent steering angle target value θt_ref, and the solid lines represent actual steering angle θt_act. FIG. 26A illustrates a time response when friction compensation control is performed in accordance with steering speed target value ωt_ref, as a comparative example of friction compensation control according to embodiment 3. FIG. 26B illustrates a time response when friction compensation control is performed by friction compensation unit 770 according to embodiment 3.

[0176] The examples shown in Figures 26A and 26B show time responses when the steering is performed more slightly to the left or right than in Figures 25A and 25B. When friction compensation control according to steering speed target value ωt_ref according to the comparative example is performed, as shown in Figure 26A, when the steering is performed slightly to the left or right, distortion occurs in actual steering angle θt_act when the steering direction is switched, as surrounded by a dashed line. In contrast, when friction compensation control is performed by friction compensation unit 770 according to embodiment 3, as shown in Figure 26B, distortion of actual steering angle θt_act when the steering direction is switched, as surrounded by a dashed line, is suppressed.

[0177] Explaining in more detail, if the steering wheel is operated slowly, minutely, and slowly, when the steering direction is switched, as in the example of Figures 25A and 25B, when the steering angle target value θt_ref switches, the steering speed target value ωt_ref becomes approximately zero. Here, unlike the example of Figures 25A and 25B, because the steering angle target value θt_ref also takes a value close to zero, a small value is also output as current compensation value Iref_b0 (first current compensation value) output from current compensation value calculation section 771, but by multiplying current compensation value Iref_b0 (first current compensation value) by gain Gi calculated by current sensitive gain generation section 773, it is possible to prevent current compensation value Iref_b from becoming too small.

[0178] This reduces the sense of discomfort felt by the driver when the steering direction of the driver's steering wheel is changed from turning more to turning back, or from turning back to turning more, even in a situation where the driver's steering operation is slight.

[0179] As described above, steering angle control unit 700a according to the third embodiment is provided with friction compensation unit 770 and is configured to calculate, based on steering angle target value θt_ref, current compensation value Iref_b (second current compensation value) for compensating for the delay in the response of actual steering angle θt_act to steering angle target value θt_ref caused by friction in the steering mechanism, thereby enabling effective and appropriate friction compensation control to be performed regardless of the steering wheel operation speed by the driver.

[0180] Furthermore, as described above, by making the current compensation value Iref_b (second current compensation value) have the characteristic of increasing or decreasing according to the motor current command value It_ref, it is possible to realize friction compensation control according to the friction force caused by the gear torque.

[0181] Steering torque target value generation section 200b according to the third embodiment calculates road surface reaction torque estimated value Tsat_est according to current command value Iref_a equivalent to the motor current command value before adding current compensation value Iref_b (second current compensation value) output from friction compensation section 770 in steering angle control section 700a configured as described above, thereby obtaining road surface reaction torque estimated value Tsat_est according to the behavior of actual road surface reaction torque Tsat_act when the vehicle is actually traveling, and can apply a steering reaction force according to road surface reaction torque estimated value Tsat_est. Therefore, even in the configuration according to the third embodiment in which steering angle control section 700a is provided with friction compensation section 770, it is possible to obtain a steering feel that reflects the road surface conditions, similar to the configuration including steering torque target value generation section 200 according to the first embodiment shown in Figure 4 and the configuration including steering torque target value generation section 200a according to the second embodiment shown in Figure 14.

[0182] It should be noted that the figures used in the above-described embodiment are conceptual diagrams for qualitatively explaining the present disclosure, and the present disclosure is not limited to these. Furthermore, while the above-described embodiment is an example of a preferred embodiment of the present disclosure, the present disclosure is not limited to this, and various modifications are possible within the scope of the present disclosure. For example, instead of using the motor current command value It_ref as the signal input to the steering torque compensation value calculation unit 240, the actual current value (motor current value) It_act can be used. [Explanation of symbols]

[0183] 1 handle 2 column axis 3a, 3b tie rod 5L,5R steered wheels 6a,6b Arms 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, 200a, 200b Steering torque target value generation unit 210 Basic Map Section 220 Damper torque generating unit 221 Damper gain map section 222 Multiplication section 230, 230a, 230b Steering torque compensation value generation unit 240 Steering torque compensation value calculation unit 241 Road reaction torque estimation unit 242, 242a Steering torque compensation value map section 243 Absolute value calculation unit 244 Code extraction part 245 Multiplication section 250 Phase compensation section 251 Phase Compensation Filter 252 Tracking Compensation Unit 260 Absolute value calculation unit 270 Differential part 280 Code extraction part 291,292 Addition section 293 Multiplication section 400 Steering torque control unit 500 Current control section 600 steering angle target value generation unit 700,700a Steering angle control unit 710 Feedforward compensation section 720 Addition Section 730 PID control unit 740 Stabilization compensation section 750 Addition Section 760 Output Limiter 770,770a Friction compensation section 771,771a Current compensation value calculation unit 772 Differential part 773 Current Sensitive Gain Generator 774 Previous value storage unit 775 Absolute Value Calculation Unit 776 Multiplication Unit 800 Current control section

Claims

1. A control device for a vehicle steering system including a reaction force device that applies a steering reaction force to a steering wheel in accordance with a steering angle of the steering wheel, and a steering device that drives 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 angle target value generation unit that generates a steering angle target value that is a target value of the steering angle of the steered wheels based on the steering angle; a steering angle control unit that generates a current command value that is a target value of a current to be supplied to the steering motor based on the steering angle target value; Equipped with The steering torque target value generation unit a steering torque compensation value generation unit that generates a compensation value for the steering torque target value in accordance with the current command value, the steering torque compensation value generation unit calculates a road surface reaction torque estimation value by performing a filter process using a predetermined transfer function on the current command value, and generates the compensation value based on the road surface reaction torque estimation value. A control device for a vehicle steering system.

2. The compensation value increases as the road surface reaction torque estimated value increases.

2. The control device for a vehicle steering system according to claim 1.

3. The compensation value increases at a decreasing rate as the road surface reaction torque estimated value increases.

3. The control device for a vehicle steering system according to claim 2.

4. The steering torque compensation value generation unit increases or decreases the compensation value depending on the vehicle speed. The control device for a vehicle steering system according to any one of claims 1 to 3.

5. The compensation value increases as the vehicle speed increases.

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

6. The steering torque compensation value generation unit includes a phase compensation filter that performs phase lag compensation for the compensation value. The control device for a vehicle steering system according to any one of claims 1 to 5.

7. The steering torque compensation value generation unit includes a tracking compensation unit that performs tracking compensation for the compensation value. The control device for a vehicle steering system according to any one of claims 1 to 6.

8. The transfer function is set so that the road surface reaction torque estimate value approximates an actual road surface reaction torque acquired while the vehicle is traveling. The control device for a vehicle steering system according to any one of claims 1 to 7.

9. The steering angle control unit a friction compensation unit that calculates different current compensation values ​​when the steered wheels are steered to the right and when the steered wheels are steered to the left based on the steering angle target value, The steering angle control unit generating a motor current command value for driving the steering motor based on the current command value and the current compensation value; The control device for a vehicle steering system according to any one of claims 1 to 8.

10. the current command value is a value after PID control in the steering angle control unit, the steering angle control unit generates the motor current command value by adding the current compensation value to the current command value. The control device for a vehicle steering system according to claim 9.

11. the current compensation value has a hysteresis characteristic according to a change in the target steering angle value. The control device for a vehicle steering system according to claim 9 or 10.

12. the current compensation value monotonically increases in a region where the current compensation value is equal to or less than a second turning angle target value obtained by adding a predetermined turning angle change amount threshold to a first turning angle target value at the start of steering, and becomes a constant value in a region where the current compensation value is greater than the second turning angle target value. The control device for a vehicle steering system according to any one of claims 9 to 11.

13. the friction compensation unit increases or decreases the current compensation value in accordance with the motor current command value. The control device for a vehicle steering system according to any one of claims 9 to 12.

14. the current compensation value monotonically increases as the motor current command value increases. The control device for a vehicle steering system according to claim 13.

15. a current compensation value calculation unit that calculates a first current compensation value; a current sensitive gain generating unit that generates a gain that monotonically increases as the motor current command value increases; Equipped with the friction compensation unit calculates a second current compensation value by multiplying the first current compensation value by the gain; The control device for a vehicle steering system according to claim 14.

16. the friction compensation unit holds data in which the motor current command value is associated with a gain that monotonically increases as the motor current command value increases, and calculates the current compensation value based on the data; The control device for a vehicle steering system according to claim 14.

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