Vehicle steering system control device

Abstract

To provide a control device of a vehicle steering system that can effectively perform friction compensation control regardless of a handle operation speed by a driver.SOLUTION: A control device of a vehicle steering system includes a turning angle control unit 700 configured to generate, based on a turning angle target value θt_ref, a motor current command value It_ref for driving a turning motor. The turning angle control unit 700 includes a friction compensation unit 770 configured to calculate, based on the turning angle target value θt_ref, different current compensation values Iref_b depending on when turning wheels are turned right and when the turning wheels are turned left. The turning angle control unit 700 generates the motor current command value It_ref based on the current compensation value Iref_b.SELECTED DRAWING: Figure 4

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, which mechanically separates a steering mechanism (Force Feedback Actuator: FFA) with a steering wheel operated by the driver from a road wheel actuator (Road Wheel Actuator: RWA) that steers the steered wheels. In an SBW system, the steering mechanism and the road wheel actuator are electrically connected via an electronic control unit (ECU). 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 a steering reaction force using a reaction actuator equipped with a reaction motor, and the road wheel actuator steers the steered wheels using a steering actuator equipped with a steering motor. The reaction actuator and the road wheel are mechanically connected via a column shaft, and the reaction force (torque) generated by the reaction actuator is transmitted to the driver via the column shaft and the road wheel.

[0003] In a SBW system, it is necessary for the driver's steering operation to be accurately transmitted to the steering mechanism, which then steers the steered wheels appropriately. However, when the target steering angle, which is a target value for the steering angle, changes slightly, such as when the driver turns the steering wheel slightly, friction generated in the steering mechanism can cause a delay in the steering angle's tracking of the target steering angle, preventing the vehicle from moving appropriately in the steering direction, which can cause inconvenience. Patent Document 1 listed below discloses a control device for a vehicle steering system equipped with a friction compensation unit that calculates a compensation motor current command value that compensates for the tracking delay of the steering angle caused by friction in the steering mechanism, based on a target steering angular velocity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-175770 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above Patent Document, the compensation motor current command value is calculated according to the target steering angular velocity. Therefore, in a situation where the driver operates the steering wheel extremely slowly, that is, in a situation where the target steering angular velocity is approximately zero, the compensation motor current command value is not calculated, and appropriate friction compensation control may not be possible.

[0006] Friction compensation unit 230 of the vehicle traveling system described in Patent Document 1 corrects the current command value using a friction compensation value corresponding to the target steering angular velocity ωtref, and therefore friction compensation is not performed when the target steering angular velocity ωtref is approximately zero. The target steering angular velocity ωtref becomes zero when the steering direction is changed. In other words, in the vehicle traveling system described in Patent Document 1, when the steering wheel is turned left or right, a discrepancy is likely to occur between the driver's steering wheel operation and the vehicle's steering angle when the steering direction is changed.

[0007] 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 effectively perform friction compensation control regardless of the driver's steering wheel operation speed. [Means for solving the problem]

[0008] In order to achieve the above-mentioned 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 equipped with a reaction 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 the steered wheels in accordance with the steering angle of the steering wheel, and comprises: a steering angle target value generation unit that generates a steering angle target value that is a target value for the steering angle of the steered wheels, based on the steering angle; and a steering angle control unit that generates a motor current command value for driving the steering motor, based on the steering angle target value, wherein the steering angle control unit comprises a friction compensation unit that calculates different current compensation values ​​depending on whether the steered wheels are steered to the right or left, based on the steering angle target value, and the steering angle control unit generates the motor current command value based on the current compensation value.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] According to the above configuration, it is possible to realize friction compensation control according to the friction force caused by the gear torque.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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]

[0022] According to the present invention, it is possible to provide a control device for a vehicle steering system that can effectively perform friction compensation control regardless of the steering wheel operation speed by the driver. [Brief explanation of the drawings]

[0023] [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 block diagram showing an example of the configuration of the steering angle control unit according to the embodiment. [Figure 5] FIG. 5 is a block diagram showing an example of the configuration of the friction compensation unit according to the embodiment. [Figure 6] FIG. 6 is a region diagram for explaining the steering direction in the present disclosure. [Figure 7] FIG. 7 is a diagram showing an example of the characteristics of the current compensation value in the current compensation value calculation unit. [Figure 8A] FIG. 8A is a diagram showing a first example of a current-sensitive gain map. [Figure 8B] FIG. 8B is a diagram showing a second example of a current-sensitive gain map. [Figure 9]FIG. 9 is a diagram showing an example of the output characteristics of the friction compensation unit according to the embodiment. [Figure 10] FIG. 10 is a block diagram showing an example of the configuration of a friction compensation unit according to a modified example of the embodiment. [Figure 11A] FIG. 11A is a first conceptual diagram illustrating a specific example of friction compensation control by the friction compensation unit according to the embodiment. [Figure 11B] FIG. 11B is a first conceptual diagram illustrating a specific example of friction compensation control by the friction compensation unit according to the embodiment. [Figure 12A] FIG. 12A is a second conceptual diagram illustrating a specific example of friction compensation control by the friction compensation unit according to the embodiment. [Figure 12B] FIG. 12B is a second conceptual diagram illustrating a specific example of friction compensation control by the friction compensation unit according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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."

[0029] 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.

[0030] 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."

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Fig. 3 is a diagram showing an example of a basic 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] The steering torque target value generating section 200 generates a steering torque target value Th_ref.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] A steering angle target value generating section 600 generates a steering angle target value θt_ref based on the steering angle θh.

[0044] 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 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 the steering angle control unit according to the embodiment will be described later with reference to FIG. 4. In FIG. 3, some components of the specific configuration shown in FIG. 4 are omitted.

[0045] 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.

[0046] 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.

[0047] 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 be configured in any way as long as they are able to realize the respective controls in reaction force control system 60 or turning control system 70, and are not limited by the configuration of each of these control blocks. Below, a specific configuration of turning angle control section 700 according to this embodiment will be described with reference to Fig. 4.

[0048] Fig. 4 is a block diagram showing an example of the configuration of the steering angle control unit according to the embodiment. As shown in Fig. 4, steering angle control unit 700 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 and 750.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Fig. 5 is a block diagram showing an example of the configuration of a friction compensation unit according to this embodiment. As shown in Fig. 5, a friction compensation unit 770 according to this embodiment includes, as its main components, a current compensation value calculation unit 771 and a current sensitive gain generation unit 773.

[0056] 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.

[0057] Here, the steering direction in the present disclosure will be described. Fig. 6 is a region diagram for explaining the steering direction in the present disclosure. In Fig. 6, the horizontal axis represents the steering angle θt, and the vertical axis represents the steering speed ωt.

[0058] Area A ((θt, ωt) = (+, +)) shown in FIG. 6 indicates that the steerable wheels 5L, 5R are steered to the right (θt > 0) and are being steered further to the right (ωt > 0). Area B ((θt, ωt) = (+, -)) shown in FIG. 6 indicates that the steerable wheels 5L, 5R are steered to the right (θt > 0) and are being steered to the left (ωt < 0). Area C ((θt, ωt) = (-, -)) shown in FIG. 6 indicates that the steerable wheels 5L, 5R are steered to the left (θt < 0) and are being steered further to the left (ωt < 0). Area D ((θt, ωt) = (-, +)) shown in FIG. 6 indicates that the steerable wheels 5L, 5R are steered to the left (θt < 0) and are being steered further to the right (ωt > 0). Also, in Figure 6, on the steering angle θt axis (ωt = 0), it is shown that the steered wheels 5L, 5R are not steered ((θt, ωt) = (θt, 0)), and on the steering speed ωt axis (θt = 0), it is shown that the steered wheels 5L, 5R are in the center position ((θt, ωt) = (0, ωt)).

[0059] That is, current compensation value calculation unit 771 can determine that the steering direction has changed because the sign of the steering speed target value ωt_ref has reversed (ωt_ref(sgn) = "+" → "-" or "-" → "+").

[0060] 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.

[0061] Fig. 7 is a diagram showing an example of the characteristics of the current compensation value in the current compensation value calculation unit. In Fig. 7, 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. 7, 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. 7, the current compensation value Iref_b0 (first current compensation value) calculated in the current compensation value calculation unit 771 has a hysteresis characteristic in which it is a different value when steering to the left and when steering to the right. L1 shown in FIG. 7 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).

[0062] Current compensation value calculation unit 771 calculates current compensation value Iref_b0 (first current compensation value) using the following equations (1) and (2) 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 (1), 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 (2). In the following equations (1) and (2), 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.

[0063] y R =Ahys{1-a -c(x-b)}···(1)

[0064] y L =-Ahys{1-a c(x-b’)}···(2)

[0065] 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.

[0066] 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 (3) or (4) below into equation (1) or (2) 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 previous values ​​(coordinates A(x1, y1) shown in FIG. 7) of the steering angle target value θt_ref and the current compensation value Iref_b0 (first current compensation value) to the above equation (2), and substitutes coefficient b' shown in the following equation (4) to calculate current compensation value Iref_b0 (first current compensation value). Also, when a switch from left steering to right steering occurs (ωt_ref(sgn)="-"→"+"), current compensation value calculation unit 771 applies the previous values ​​(coordinates B(x2, y2) shown in FIG. 7) of the steering angle target value θt_ref and the current compensation value Iref_b0 (first current compensation value) to the above equation (1), and substitutes coefficient b shown in the following equation (3) to calculate current compensation value Iref_b0 (first current compensation value).

[0067] b=x1+(1 / c)log a {1-(y1 / Ahys)} (3)

[0068] b'=x1-(1 / c)log a {1-(y1 / Ahys)} (4)

[0069] The above formulas (3) and (4) are obtained by substituting x1 for x in the above formulas (1) and (2) and R and y L It can be derived by substituting y1 into

[0070] When Napier's constant e is used as the coefficient a, the above equations (1), (2), (3), and (4) can be expressed as the following equations (5), (6), (7), and (8), respectively.

[0071] y R =Ahys[1-exp{-c(xb)}] (5)

[0072] y L =-Ahys[{1-exp{c(x-b')}]···(6)

[0073] b=x1+(1 / c)log e {1-(y1 / Ahys)}···(7)

[0074] b'=x1-(1 / c)log e {1-(y1 / Ahys)} (8)

[0075] Returning to Fig. 5, previous value holding unit 774 holds the previous output value It_ref' of steering angle control unit 700. Specifically, the previous output value It_ref' is the motor current command value It_ref in the previous processing. Previous value holding unit 774 is formed, for example, by a RAM of an ECU constituting control device 50.

[0076] 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 output from previous value holding section 774 .

[0077] Current sensitive gain generation section 773 receives as input the previous output value |It_ref'| of turning angle control section 700 which 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 700.

[0078] 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 700. The current sensitive gain map is stored, for example, in the ROM of the ECU that constitutes control device 50. Fig. 8A is a diagram showing a first example of the current sensitive gain map. Fig. 8B is a diagram showing a second example of the current sensitive gain map.

[0079] The first example of the current-sensitive gain map shown in Fig. 8A 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 700. More specifically, as shown in Fig. 8A, gain Gi monotonically increases as the previous output value |It_ref'| of turning angle control unit 700 increases.

[0080] 9 is a diagram showing an example of the output characteristics of the friction compensation unit according to the embodiment, in which 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).

[0081] 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.

[0082] 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. 9, 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.

[0083] 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.

[0084] 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.

[0085] The mode of the current sensitive gain map is not limited to the mode of the first example shown in Fig. 8A. For example, as in a second example shown in Fig. 8B, a mode may be adopted in which current compensation value Iref_b0 (first current compensation value) output from current compensation value calculation section 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 section 700).

[0086] The current compensation value Iref_b (second current compensation value) output from the friction compensation unit 770 is added to the current compensation value Iref_a output from the stabilization compensation unit 740 by the addition unit 750 shown in Figure 4, 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.

[0087] FIG. 10 is a block diagram showing an example of the configuration of a friction compensation unit according to a modified example of the embodiment. In the example configuration shown in FIG. 5, 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 modified example shown in FIG. 10, 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 700) is associated with coefficient Ahys in equations (1) to (8) 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. 9. 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. 5.

[0088] 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.

[0089] 11A and 11B are first conceptual diagrams illustrating a specific example of friction compensation control by the friction compensation unit according to the embodiment. In FIGS. 11A and 11B, the horizontal axis represents time, and the vertical axis represents the steering angle. The dashed lines in FIGS. 11A and 11B represent the target steering angle value θt_ref, and the solid lines represent the actual steering angle θt_act. FIG. 11A illustrates a time response when friction compensation control is not performed by friction compensation unit 770 according to the embodiment. FIG. 11B illustrates a time response when friction compensation control is performed by friction compensation unit 770 according to the embodiment.

[0090] The examples shown in FIGS. 11A and 11B 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 embodiment, as shown in FIG. 11A, 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 turning the steering wheel further to steering back, or from steering back to turning 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 embodiment, distortion in actual steering angle θt_act when the steering direction is switched, as enclosed by the dashed line, as shown in FIG. 11B.

[0091] 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.

[0092] 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.

[0093] 12A and 12B are second conceptual diagrams illustrating a specific example of friction compensation control by the friction compensation unit according to the embodiment. In FIGS. 12A and 12B, the horizontal axis represents time, and the vertical axis represents the steering angle. The dashed lines in FIGS. 12A and 12B represent the target steering angle value θt_ref, and the solid lines represent the actual steering angle θt_act. FIG. 12A illustrates a time response when friction compensation control is performed in accordance with the target steering speed value ωt_ref, as a comparative example of friction compensation control according to the embodiment. FIG. 12B illustrates a time response when friction compensation control is performed by friction compensation unit 770 according to the embodiment.

[0094] The examples shown in Figures 12A and 12B show time responses when the steering is performed more slightly to the left or right than in Figures 11A and 11B. When friction compensation control according to steering speed target value ωt_ref according to the comparative example is performed, as shown in Figure 12A, 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 the embodiment, as shown in Figure 12B, distortion of actual steering angle θt_act when the steering direction is switched, as surrounded by a dashed line, is suppressed, even when the steering is performed slightly to the left or right.

[0095] To explain in more detail, if the steering wheel is operated slowly, minutely and slowly, when the steering direction is switched, the steering speed target value ωt_ref becomes approximately zero when the steering angle target value θt_ref switches, as in the example of Figure 11. Here, unlike the example of Figure 11, the steering angle target value θt_ref also takes a value close to zero, and so the current compensation value Iref_b0 (first current compensation value) output from current compensation value calculation section 771 also becomes a small value, 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.

[0096] 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.

[0097] As described above, by providing friction compensation unit 770 according to the embodiment and calculating current compensation value Iref_b (second current compensation value) based on steering angle target value θt_ref to compensate 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, friction compensation control can be performed effectively and appropriately regardless of the steering wheel operation speed of the driver.

[0098] 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.

[0099] 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]

[0100] 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 500 Current control section 600 steering angle target value generation unit 700 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 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 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 motor current command value for driving the steering motor based on the steering angle target value; Equipped with 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 the motor current command value based on the current compensation value; the current compensation value has a hysteresis characteristic according to a change in the target steering angle value, 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 friction compensation unit increases or decreases the current compensation value in accordance with the motor current command value. A control device for a vehicle steering system.

2. the current compensation value monotonically increases as the motor current command value increases.

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

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

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

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