Steering control device

Abstract

To provide a steering control device that can prevent deterioration in performance in recognizing a lane departure warning during steering angle control performed by lane keeping assist control.SOLUTION: An assist control part 20 calculates an assist torque command Ta* on the basis of steering torque Ts. A steering angle control part 30 makes a servo controller 34 calculate a steering angle control torque command Tθ* so that a steering angle θ is made to follow a target steering angle θ* commanded from an LKA-ECU (a lane keeping assist device) 16. A vibration application control part 50 calculates an LDW control torque command Tv* so that vibrations are applied to assist torque, when receiving a notice of an LDW operation request from an LDW-ECU (a lane departure warning device) 17. A motor driving control part 65 controls driving of the motor 80 on the basis of additional values Tm* of the torque commands Ta*, Tθ* and Tv*. The steering angle control part 30 has a servo response correcting part 38 that corrects steering angle control gain so that responsiveness of the servo controller 34 is reduced during operation of the LDW compared to during non-operation of the LDW.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] 2. Description of the Related Art Conventionally, a steering control device is known for a vehicle equipped with a lane keeping assist device, which assists the driver's steering by using an assist torque output by a motor.

[0003] For example, a vehicle steering device disclosed in Patent Document 1 superimposes a vibration torque for a lane departure warning on an assist torque, and changes the magnitude of the vibration torque according to the steering state of the driver.

[0004] In the motor control device disclosed in Patent Document 2, a target tracking control calculation unit calculates a steering angle steering torque command by tracking control that causes the steering angle to follow a target steering angle commanded by a lane keeping assist device, i.e., automatic steering. The motor control device drives the motor according to the sum of an assist torque command that reduces the steering load and a steering angle steering torque command of the automatic steering, and reduces the responsiveness of the automatic steering when it detects intervention by the driver. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-65587 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-33942 Summary of the Invention [Problem to be solved by the invention]

[0006] During operation of steering angle control by automatic steering, the steering angle based on the motor angle generated when the motor is driven by applying vibration torque of the lane departure warning is corrected to the target steering angle. Because the vibration of the steering angle control cancels out the vibration of the lane departure warning, the vibration that appears in the steering wheel when the lane departure warning is activated is smaller than during normal assistance, making it difficult for the driver to notice the warning.

[0007] The present invention was created in consideration of these points, and its purpose is to provide a steering control device that prevents a decrease in the recognizability of lane departure warnings while steering angle control is being performed by lane keeping assist control. [Means for solving the problem]

[0008] The present invention provides a steering control device for assisting a driver's steering with an assist torque output by a motor 80 in a vehicle equipped with a lane keeping assist system 16 and a lane departure warning system 17. The steering control device includes an assist control unit 20, a steering angle control unit 30, a vibration application control unit 50, and a motor drive control unit 65.

[0009] The assist control section outputs an assist torque command (Ta * The steering angle control unit calculates the steering angle (θ) determined according to the motor output, and the target steering angle (θ) commanded by the lane keeping assist device. * ) by the servo controller (34). * ) is calculated.

[0010] The vibration application control unit applies a lane departure warning control torque command (Tv) to the assist torque when a lane departure warning activation request is notified from the lane departure warning device. * ) is calculated.

[0011] The motor drive control unit calculates the sum (Tm * ) to control the motor drive.

[0012] The servo controller is configured to receive the steering angle deviation (Δθ) between the target steering angle and the actual steering angle, and to adjust the ratio of the output to the input by means of a steering angle control gain. The steering angle control unit has a servo response correction unit (38) that corrects the steering angle control gain so as to reduce the responsiveness of the servo controller when the lane departure warning is activated compared to when the lane departure warning is not activated, except in cases where specified exemption requirements are met.

[0013] In the present invention, the responsiveness of the steering angle control torque command is reduced when the steering angle control by the lane keeping assist control is operating, making it difficult to cancel out the vibration of the lane departure warning, thereby enabling the driver to perceive the warning even while the lane keeping assist control is operating. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram of an electric power steering system. [Figure 2] 1 is a schematic configuration diagram of an EPS-ECU (steering control device) according to a first embodiment. [Figure 3] 4 is a flowchart of a servo response correction process according to the first embodiment. [Figure 4] Steering angle-steering torque vibration amplitude characteristic diagram. [Figure 5] 6 is a time chart illustrating the influence of steering angle control on LDW amplitude in a comparative example. [Figure 6] 4 is a time chart showing a servo response correction process according to the first embodiment. [Figure 7] FIG. 10 is a schematic configuration diagram of an EPS-ECU according to a second embodiment. [Figure 8] 10 is a flowchart of a servo response correction process according to a second embodiment. [Figure 9] 5 is a time chart showing the servo response correction process according to the first embodiment when the target steering angle changes. [Figure 10] 6 is a time chart showing the servo response correction process according to the second embodiment when the target steering angle changes. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, several embodiments of the steering control device will be described with reference to the drawings. In several embodiments, substantially the same configurations are assigned the same reference numerals and descriptions thereof will be omitted. The first and second embodiments will be collectively referred to as "the present embodiment." The steering control device of the present embodiment is applied to an electric power steering system of a vehicle equipped with a lane keeping assist device and a lane departure warning device. In each embodiment, the EPS-ECU corresponds to the "steering control device." Furthermore, the LKA (Lane Keep Assist)-ECU corresponds to the "lane keeping assist device," and the LDW (Lane Departure Warning)-ECU corresponds to the "lane departure warning device." LKA stands for lane keeping assist, and LDW stands for lane departure warning.

[0016] The LKA-ECU commands a target steering angle to maintain the vehicle in the lane it is traveling in during automatic steering. The LDW-ECU issues a warning to the driver when the vehicle is about to depart from its lane during driver steering or automatic steering. In this embodiment, the LDW-ECU works with the EPS-ECU to vibrate the steering wheel instead of or in addition to an audible warning or a display message. The EPS-ECU assists the driver in steering by using the assist torque output by the motor.

[0017] [Electric power steering system configuration] As shown in Fig. 1, the electric power steering system 1 is basically a system that assists the driver in operating a steering wheel 91 by using the driving torque of a motor 80. The steering wheel 91 is fixed to one end of a steering shaft 92, and an intermediate shaft 93 is provided on the other end of the steering shaft 92. The steering shaft 92 and the intermediate shaft 93 are connected by a torsion bar of a torque sensor 94, and these constitute a steering axis 95. The torque sensor 94 detects the steering torque Ts based on the torsion angle of the torsion bar.

[0018] A gear box 96 including a pinion gear 961 and a rack 962 is provided at the end of the intermediate shaft 93 opposite the torque sensor 94. When the driver turns the steering wheel 91, the pinion gear 961 rotates together with the intermediate shaft 93, and the rack 962 moves left and right in response to the rotation of the pinion gear 961. Tie rods 97 provided at both ends of the rack 962 are connected to tires 99 via knuckle arms 98. The tie rods 97 reciprocate left and right, pulling and pushing the knuckle arms 98, thereby changing the orientation of the tires 99.

[0019] The motor 80 is, for example, a three-phase AC brushless motor, and outputs a driving torque in accordance with a driving voltage Vd output from the EPS-ECU 15. In the case of a three-phase AC motor, the driving voltage Vd refers to the voltage of each of the U, V, and W phases. The rotation of the motor 80 is transmitted to an intermediate shaft 93 via a speed reduction mechanism 85 constituted by a worm gear 86, a worm wheel 87, etc. Furthermore, the rotation of the intermediate shaft 93 caused by steering of the steering wheel 91 or reaction force from the road surface is transmitted to the motor 80 via the speed reduction mechanism 85.

[0020] 1 is a column-assist type in which the rotation of the motor 80 is transmitted to the steering shaft 95, but the EPS-ECU 15 of this embodiment is also applicable to a rack-assist type electric power steering system or a steer-by-wire system in which the steering wheel and the steered wheels are mechanically separated. In other embodiments, a polyphase AC motor other than a three-phase motor or a brushed DC motor may be used as the motor.

[0021] Here, the entire mechanism through which the steering force of the steering wheel 91 is transmitted, from the steering wheel 91 to the tires 99, is referred to as the "steering system mechanism 100." The EPS-ECU 15 controls the driving torque output from the motor 80 to the steering system mechanism 100, thereby controlling the steering torque Ts generated by the steering system mechanism 100. The EPS-ECU 15 acquires the steering torque Ts and the steering angle θ from the steering system mechanism 100. The EPS-ECU 15 also acquires the vehicle speed V detected by a vehicle speed sensor 11 provided at a predetermined location on the vehicle.

[0022] In addition, the EPS-ECU 15 receives the target steering angle θ from the LKA-ECU 16. * and a steering angle control request flag F1 from the LDW-ECU 17, and obtains an LDW operation request flag F2 from the LDW-ECU 17. During automatic steering, the LKA-ECU 16 outputs the steering angle control request flag F1 to the EPS-ECU 15. As referred to in Patent Document 2 (JP 2015-33942 A) and the like, the LKA-ECU 16 sets a target course based on the driving lane and the position of the host vehicle detected from the image of the in-vehicle camera, and determines a target steering angle θ for traveling along the target course. * is output to EPS-ECU15.

[0023] As described in Patent Document 1 (JP 2017-65587 A) and the like, the LDW-ECU 17 determines whether there is a possibility of lane departure or collision with an obstacle based on the steering angle, vehicle speed, video from an onboard camera, yaw rate, lateral acceleration, etc. When it determines that there is a possibility of lane departure or collision with an obstacle, the LDW-ECU 17 outputs an LDW operation request flag F2 to the EPS-ECU 15.

[0024] The EPS-ECU 15 operates using power from an on-board battery (not shown) and calculates various torque commands (described later) based on the acquired information. The EPS-ECU 15 drives the motor 80 by applying a drive voltage Vd to the motor 80 in accordance with the sum of the calculated torque commands. Note that the various calculation processes in the EPS-ECU 15 may be software processes in which a CPU executes a program stored in advance in a physical memory device such as a ROM, or may be hardware processes in which a dedicated electronic circuit is used.

[0025] [EPS-ECU configuration] Next, the configuration of the EPS-ECU 15 of each embodiment will be described in order. The reference numeral of the EPS-ECU of each embodiment has the embodiment number added as the third digit following "15".

[0026] (First embodiment) The first embodiment will be described with reference to Figures 2 to 6. As shown in Figure 2, the EPS-ECU 151 of the first embodiment includes an assist control unit 20, a vibration application control unit 50, a steering angle control unit 30, and a motor drive control unit 65. For convenience of explanation, the vibration application control unit 50 will be described before the steering angle control unit 30.

[0027] The assist control unit 20 outputs an assist torque command Ta in response to the steering torque Ts of the driver. * Specifically, the assist control unit 20 calculates the assist torque command Ta based on the steering torque Ts and the vehicle speed V so as to realize a transmission feeling according to the road reaction force (or road load) and a feel according to the steering state. * When the LDW-ECU 17 notifies the driver of a LDW operation request by using the flag F2, the vibration application control unit 50 applies vibration to the assist torque to make the driver aware of the vibration. * Calculate the following.

[0028] The steering angle control unit 30 includes a steering angle deviation calculator 33, a servo controller 34, and a servo response correction unit 38. The steering angle deviation calculator 33 calculates a target steering angle θ *and the steering angle θ, the steering angle deviation Δθ (= θ * The servo controller 34 calculates the target steering angle θ * In order to make the steering angle θ follow the steering angle deviation Δθ, that is, to make the steering angle deviation Δθ approach 0, the steering angle control torque command Tθ is calculated by PID control. * Calculate the following.

[0029] When the LDW-ECU 17 notifies the servo response correction unit 38 of a request to operate the LDW by using the flag F2, i.e., when the LDW is operating, the servo response correction unit 38 corrects the steering angle control gain so as to reduce the responsiveness of the servo controller 34 as a general rule compared to when the LDW is not operating. Here, "as a general rule" means that cases where certain exemption requirements are met are excluded as exceptions. Cases where certain exemption requirements are met will be described later in the second embodiment. This processing by the servo response correction unit 38 is called "servo response correction processing."

[0030] Each torque command Ta * , Tθ * , TV * , Tm * The positive and negative signs of the torque are defined according to the rotation direction in which the torque is applied. For example, a torque applied in the left rotation direction is defined as positive, and a torque applied in the right rotation direction is defined as negative. The positive and negative signs of the steering angle θ are defined, for example, as an angle to the left of the neutral position as positive, and an angle to the right of the neutral position as negative.

[0031] The command adder 60 calculates the assist torque command Ta * , steering angle control torque command Tθ * , and LDW control torque command Tv * The final assist torque command Tm * and outputs it to the motor drive control unit 65. The motor drive control unit 65 calculates the final assist torque command Tm * The motor 80 is driven by applying a drive voltage Vd to the motor 80 in accordance with the final assist torque command Tm * The steering angle θ, which is determined in accordance with the output of the motor, is fed back to the steering angle control unit 30.

[0032] The servo response correction process according to the first embodiment will be described with reference to the flowchart in Figure 3. In the following description of the flowchart, the symbol "S" denotes a step. In S1, it is determined based on the flag F2 from the LDW-ECU 17 whether the LDW is in operation.

[0033] When LDW is operating, the determination in S1 is YES, and in S3 the steering angle control gain is corrected to a smaller value to reduce the responsiveness of the servo control. For example, K is set to 0.3. When LDW is not operating, the determination in S1 is NO, and in S4 the steering angle control gain is set to the reference value K=1. This routine is executed repeatedly at a predetermined calculation cycle.

[0034] Figure 4 shows the relationship between steering angle θ and steering torque vibration amplitude for each steering angle control gain. Here, 0≦θ≦25[deg]. When the steering angle control gain is K=1 while the LKA is operating, as shown by the two-dot chain line, the steering torque vibration amplitude decreases as the steering angle θ increases from the neutral position (θ=0). When the LKA is not operating, that is, when the driver is steering, the steering angle control gain corresponds to K=0. In this case, as shown by the dashed line, the characteristic line of the steering torque vibration amplitude is larger overall compared to the characteristic line for K=1. The difference is larger in areas where the steering angle θ is smaller.

[0035] When the steering angle control gain is corrected from K=1 to K=0.3 by the servo response correction process, the characteristic line of the steering torque vibration amplitude approaches the characteristic line of K=0, as shown by the solid line. In other words, the influence of the steering angle control on the LDW amplitude is suppressed. Note that if the steering angle control gain is set to a value between K=0.3 and K=1 (for example, K=0.5), it is estimated that a characteristic between these characteristic lines will be obtained.

[0036] 5 and 6, the influence of the steering angle control on the LDW amplitude in the comparative example and the first embodiment will be described. * and steering angle θ, steering angle control gain K, steering angle control torque command Tθ * , LDW operation, LDW control torque command Tv *, final assist torque command Tm * , indicates the steering torque vibration amplitude. The dimension of the steering angle is angle ([deg]), and the dimension of each torque command is torque ([Nm]).

[0037] In this time chart, the LDW operates twice. The LDW control torque command Tv * Since the LKA is not operating during the first LDW operation period W1, the LDW control torque command Tv * is not affected by the steering angle control and is directly proportional to the final assist torque command Tm * This becomes a vibration component and is reflected in the steering torque vibration amplitude.

[0038] After the first LDW operation period W1, the operation of the LKA starts at time t1. At time t2, the target steering angle θ * When changes, the steering angle θ changes to the target steering angle θ * At time t3, the target steering angle θ * After that, the LDW operation period W2 occurs during the operation of the LKA. At this time, the steering angle θ that has been vibrated by the LDW vibration is set to the target steering angle θ * The steering angle control torque command Tθ * A vibration component in the opposite direction to the vibration of the steering angle θ is applied to the steering wheel.

[0039] In the comparative example shown in Fig. 5, regardless of the operation of the LKA, the steering angle control gain is K = 1. Therefore, as shown by (*Z1), the steering angle control torque command Tθ * The amplitude of the steering angle control torque command Tθ is large, as shown by (*Z2). * The vibration of the LDW control torque command Tv * Therefore, the vibrations that appear in the steering wheel when LDW is activated are smaller than when LKA is not activated and normal assist is in effect, making it difficult for the driver to perceive the warning.

[0040] In the first embodiment shown in FIG. 6, during the LDW operation periods W1 and W2, the servo response corrector 38 corrects the steering angle control gain from K=1 to K=0.3, and the steering angle control torque command Tθ * Therefore, as shown by (*A1), the steering angle control torque command Tθ * The amplitude of the steering angle control torque command Tθ becomes smaller than that of Fig. 5. Then, as shown by (*A2), * The vibration of the LDW control torque command Tv * This makes it difficult for the vibration components of the vehicle to be canceled out. This means that the driver can still perceive the warning even when LKA is operating.

[0041] (Second embodiment) Next, a second embodiment will be described with reference to Figures 7 to 10. As shown in Figure 7, in an EPS-ECU 152 of the second embodiment, the steering angle deviation Δθ calculated by the steering angle deviation calculator 33 is output to a servo response correction unit 38 in addition to the servo controller 34. Other configurations are the same as those of the EPS-ECU 151 of the first embodiment, and therefore description thereof will be omitted.

[0042] In principle, when LDW is activated, the servo response correction unit 38 executes the servo response correction process in the same manner as in the first embodiment. However, when the absolute value of the steering angle deviation Δθ is greater than a predetermined steering angle deviation threshold Δθth, the servo response correction unit 38 does not execute the servo response correction process, assuming that the case satisfies a "predetermined exemption requirement."

[0043] Fig. 8 shows a flowchart of the servo response correction process according to the second embodiment. Steps that are substantially the same as those in Fig. 3 of the first embodiment are assigned the same step numbers, and their explanations will be omitted. If the determination in S1 is YES while the LDW is operating, in S2, the absolute value of the steering angle deviation Δθ is compared with the steering angle deviation threshold value Δθth.

[0044] When the absolute value of the steering angle deviation Δθ is equal to or smaller than the steering angle deviation threshold Δθth, a YES determination is made in S2. In this case, as in the first embodiment, the steering angle control gain is corrected to a smaller value in S3 so as to reduce the responsiveness of the servo control. For example, K is set to 0.3. When the absolute value of the steering angle deviation Δθ is larger than the steering angle deviation threshold Δθth, a NO determination is made in S2. In this case, the steering angle control gain is set to K=1 in S4. In other words, the same steering angle control gain as when the LDW is not operating is used.

[0045] 9 and 10, the difference between the servo response correction process according to the first and second embodiments when the target steering angle changes will be described. * and steering angle θ, steering angle deviation Δθ, steering angle control gain K, steering angle control torque command Tθ * , indicates the operation of LDW.

[0046] As in Figures 5 and 6, the operation of the LKA starts at time t1. At time t2, the target steering angle θ * When the target steering angle θ changes, the absolute value of the steering angle deviation Δθ increases. * As the steering angle θ follows the target, the steering angle deviation Δθ gradually decreases and converges to 0 at time t3.

[0047] The first embodiment shown in Figure 9 corresponds to a comparative example of the second embodiment. In the first embodiment, the steering angle control gain is always corrected to a small value during LDW operation. During the first LDW operation period W1 before time t1, LKA is not operating and does not affect steering angle control.

[0048] On the other hand, during the second LDW operation period W2, the steering angle control gain is corrected to a smaller value while the LKA is operating. As described with reference to FIG. 6, as shown by (*A1), the steering angle control torque command Tθ * However, as shown in (*A3), the reduction in the response of the steering angle control is countered by the reduction in the target steering angle θ of the steering angle θ. *In other words, the change gradient of the steering angle θ during the LDW operation period W2 becomes smaller, and the response time Tres from time t2 to t3 becomes longer.

[0049] In the second embodiment shown in Fig. 10, when the steering angle θ changes and the absolute value of the steering angle deviation Δθ becomes larger than the steering angle deviation threshold Δθth, priority is given to the tracking of the steering angle control over preventing a decrease in the noticeability of the warning. In other words, the case satisfies the exemption requirements, and processing to reduce the responsiveness of the servo controller 34 is not executed. During the LDW operation period W2, because the absolute value of the steering angle deviation Δθ is larger than the steering angle deviation threshold Δθth, the servo controller 34 uses the same steering angle control gain (i.e., K = 1) as when the LDW is not operating.

[0050] As a result, as shown by (*B1), the target steering angle θ * The tracking ability of the steering angle θ to the steering angle θ does not decrease. When the absolute value of the steering angle deviation Δθ becomes smaller than the steering angle deviation threshold Δθth, the exemption requirement is lifted. When the LDW is activated after time t3, if the absolute value of the steering angle deviation Δθ is equal to or smaller than the steering angle deviation threshold Δθth, the servo response correction unit 38 reduces the responsiveness of the servo controller 34 as a rule. In this way, in the second embodiment, the priority between warning noticeability and tracking ability of steering angle control can be switched according to changes in the steering angle θ.

[0051] (Other embodiments) The exemption requirement for the servo response correction process may be set as a parameter such as the "acceleration of steering angle change" which corresponds to the second derivative of the steering angle θ, in addition to the steering angle deviation Δθ, i.e., the first derivative of the steering angle θ.

[0052] The present invention is not limited to such an embodiment, and can be implemented in various forms without departing from the spirit of the present invention.

[0053] The control unit and the method described herein may be implemented by a special-purpose computer configured by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. Alternatively, the control unit and the method described herein may be implemented by a special-purpose computer configured by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described herein may be implemented by one or more special-purpose computers configured by combining a processor and memory programmed to perform one or more functions with a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by a computer on a computer-readable non-transitory tangible storage medium. [Explanation of symbols]

[0054] 15···EPS-ECU (Steering Control Unit), 16···LKA-ECU (Lane Keeping Assist Device), 17···LDW-ECU (Lane Departure Warning System), 20. Assist control unit, 34... Servo controller, 38...Servo response correction unit, 50... Vibration application control unit, 65 Motor drive control unit, 80···Motor.

Claims

1. A steering control device for a vehicle equipped with a lane keeping assist device (16) and a lane departure warning device (17), which assists a driver's steering with an assist torque output by a motor (80), Based on the steering torque (Ts), an assist torque command (Ta ＊ an assist control unit (20) that calculates The steering angle (θ) determined according to the output of the motor is set to the target steering angle (θ ＊ ) by the servo controller (34). ＊ a steering angle control unit (30) for calculating When a request for activation of the lane departure warning is notified from the lane departure warning device, a lane departure warning control torque command (Tv ＊ a vibration applying control unit (50) that calculates The sum of the assist torque command, the steering angle control torque command, and the lane departure warning control torque command (Tm ＊ a motor drive control unit (65) for controlling the drive of the motor based on the Equipped with the servo controller is configured to receive a steering angle deviation (Δθ) between the target steering angle and the actual steering angle, and to adjust the ratio of the output to the input by a steering angle control gain; The steering control device has a servo response correction unit (38) that corrects the steering angle control gain so as to reduce the responsiveness of the servo controller when the lane departure warning is activated compared to when the lane departure warning is not activated, except in cases where specified exemption requirements are met.

2. When the absolute value of the steering angle deviation (Δθ), which is the difference between the steering angle and the target steering angle, is greater than a predetermined steering angle deviation threshold, the following applies:

2. The steering control device according to claim 1, wherein the servo controller uses the same steering angle control gain when the lane departure warning is activated as when the lane departure warning is deactivated.

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