Control device and control method for steering system

Abstract

This control device for a steer-by-wire type steering system executes: first control in which the turning angle is controlled on the basis of the steering angle of a steering wheel operated by a driver, and a reaction torque for the operation of the steering wheel is applied to the steering wheel in accordance with a self-aligning torque that a wheel receives from a road surface; second control in which the steering angle and the turning angle are controlled on the basis of a target steering angle according to predetermined driving assist control, and a steering assist torque according to an angle difference between the target steering angle and the steering angle or the turning angle is applied to the steering wheel; and switching control in which the second control is cancelled and switched to the first control as the angle difference increases during the execution of the second control, wherein the acceleration of a change in the reaction torque that occurs when the second control is switched to the first control is limited.

Description

Steering system control device and control method

[0001] The present disclosure relates to a control device and a control method for a steering system.

[0002] In recent years, in driving assistance controls such as lane keeping control and automatic driving controls that allow a vehicle to travel autonomously, automatic steering controls have been put into practical use, which recognize the road shape and obstacles around the vehicle, set a target driving trajectory, and automatically steer the wheels so that the vehicle travels along the target driving trajectory.In such driving assistance controls and automatic driving controls, there is known a technique configured to accept manual steering operation by the driver even during automatic steering control, so that the driver can correct the driving trajectory, for example, to avoid an unexpected obstacle.

[0003] For example, Patent Document 1 discloses a steering system in which, while lane keeping assistance is being performed to keep the vehicle in the center of the driving lane, the driver's intentional steering operation causes the driver's target steering angle to deviate from the driving assistance target steering angle, and until the magnitude of the steering torque accordingly exceeds an intervention threshold, the driving assistance target steering angle is calculated as the final target steering angle, and once the magnitude of the steering torque exceeds a switching threshold, the driver's target steering angle is calculated as the final target steering angle as is.

[0004] Furthermore, Patent Document 2 discloses a technology in a steer-by-wire steering system that generates a steering reaction torque that urges the steering wheel toward a neutral position in response to a self-aligning torque acting on the steered wheels when the vehicle is turning.

[0005] JP 2022-111970 A JP 2016-107750 A

[0006] In the steering system described in Patent Document 1, a steering assist torque that causes the wheel steering angle to follow the driving assistance target steering angle is applied to the steering wheel until the final target steering angle is switched from the driving assistance target steering angle to the driver's target steering angle. On the other hand, after the final target steering angle is switched to the driver's target steering angle, it is desirable to apply a reaction torque corresponding to the self-aligning torque to the steering wheel, as described in Patent Document 2.

[0007] However, the assist torque curve, which indicates the steering assist torque applied to make the steering angle (steering angle) follow the target steering angle (target steering angle), is different from the reaction torque curve, which indicates the reaction torque corresponding to the self-aligning torque. Therefore, when the applied torque switches from the steering assist torque to the reaction torque, torque fluctuations become large, which may cause the driver to feel uncomfortable or the steering angle to change suddenly.

[0008] The present disclosure has been made in consideration of the above-mentioned problems, and an object of the present disclosure is to provide a control device and control method for a steering system that can suppress torque fluctuations that occur when the torque applied to the steering wheel switches from steering assist torque to reaction torque.

[0009] In order to solve the above-mentioned problems, according to one aspect of the present disclosure, there is provided a control device for a steer-by-wire steering system in which a steering wheel operated by a driver of a vehicle and a wheel steering device that steers the wheels are provided so as to be mechanically separated, and the control device controls the steering angle of the wheels based on the steering angle of the steering wheel, the control device executing: a first control that controls the steering angle based on the steering angle of the steering wheel operated by the driver, and applies to the steering wheel a reaction torque against the operation of the steering wheel in accordance with a self-aligning torque that the wheels receive from a road surface; a second control that controls the steering angle and the steering angle based on a target steering angle by predetermined driving assist control, and applies to the steering wheel a steering assist torque that is a steering assist torque in accordance with an angular difference between the target steering angle and the steering angle or the turning angle; and a switching control that cancels the second control and switches to the first control as the angular difference increases during execution of the second control, and limits the acceleration of a change in the reaction torque that occurs when the second control is switched to the first control.

[0010] Furthermore, in order to solve the above-mentioned problems, according to another aspect of the present disclosure, there is provided a control method for a steer-by-wire steering system in which a steering wheel operated by a driver of a vehicle and a wheel steering device that steers the wheels are provided so as to be mechanically separated, and the steering angle of the wheels is controlled based on a steering angle of the steering wheel, the control method comprising: executing a first control that controls the steering angle based on the steering angle of the steering wheel operated by the driver, and applies to the steering wheel a reaction torque against the operation of the steering wheel in accordance with a self-aligning torque that the wheels receive from a road surface; a second control that controls the steering angle and the steering angle based on a target steering angle by predetermined driving assist control, and applies to the steering wheel a steering assist torque that is a steering assist torque in accordance with an angular difference between the target steering angle and the steering angle or the steering angle; and a switching control that cancels the second control and switches to the first control as the angular difference increases during execution of the second control, and limits the acceleration of change in the reaction torque that occurs when the second control is switched to the first control.

[0011] As described above, according to the present disclosure, it is possible to suppress torque fluctuations that occur when the torque applied to the steering wheel switches from steering assist torque to reaction torque.

[0012] FIG. 1 is a schematic diagram showing an example of the configuration of a vehicle equipped with a steering system according to an embodiment of the present disclosure; FIG. 2 is an explanatory diagram showing an example of the configuration of the steering system according to the embodiment; FIG. 3 is a block diagram showing an example of the configuration of a control device for the steering system according to the embodiment; FIG. 4 is an explanatory diagram showing an example of an aligning torque map (aligning torque information) used in the embodiment; FIG. 5 is an explanatory diagram showing an example of an assist torque map (assist torque information) used in the embodiment; FIG. 6 is an explanatory diagram showing a steering assist torque based on a target steering angle according to the embodiment superimposed on an aligning torque map; FIG. 7 is an explanatory diagram showing a change in reaction torque generated when steering control is switched by the control device of the steering system according to the embodiment; FIG. 8 is a flowchart showing the processing operation of the control device of the steering system according to the embodiment; FIG. 9 is a flowchart showing the processing operation of first control by the control device of the steering system according to the embodiment; FIG. 10 is a flowchart showing the processing operation of second control by the control device of the steering system according to the embodiment; FIG. 11 is a flowchart showing the processing operation of switching control by the control device of the steering system according to the embodiment.

[0013] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0014] 1. Overall Configuration of Vehicle First, an example of the overall configuration of a vehicle equipped with a control device for a steering system according to an embodiment of the present disclosure (hereinafter also referred to as a "steering control device") will be described.

[0015] Fig. 1 is a schematic diagram showing an example configuration of a vehicle 1. The vehicle 1 shown in Fig. 1 is configured as a front-wheel drive four-wheel vehicle in which drive torque output from a drive power source 13 that generates drive torque for the vehicle is transmitted to left and right front wheels 3LF, 3RF. The vehicle 1 may be a vehicle equipped with an internal combustion engine such as a gasoline engine or a diesel engine as the drive power source 13, an electric vehicle equipped with a drive motor as the drive power source 13, or a hybrid electric vehicle equipped with both an internal combustion engine and a drive motor as the drive power source 13.

[0016] The combination of drive wheels and the drive method are not limited. For example, vehicle 1 may be a rear-wheel drive vehicle, a four-wheel drive vehicle, or an electric vehicle equipped with a drive motor for each wheel. Furthermore, if vehicle 1 is an electric vehicle or a hybrid electric vehicle, vehicle 1 is equipped with a secondary battery that stores power supplied to the drive motor, and a motor or a generator such as a fuel cell that generates power to charge the battery.

[0017] The vehicle 1 includes a driving force source 13, an electric steering system 30, and brake devices 7LF, 7RF, 7LR, and 7RR (hereinafter collectively referred to as "brake devices 7" unless a distinction is required) as devices used to control the driving of the vehicle 1. The driving force source 13 outputs a driving torque that is transmitted to a front-wheel drive shaft 5 via a front-wheel differential mechanism (not shown). The driving of the driving force source 13 is controlled by a vehicle control device 11 that includes one or more electronic control units (ECUs). During manual driving, the vehicle control device 11 controls the driving of the driving force source 3 based on the accelerator opening operated by the driver. Furthermore, during execution of driving assistance control or automatic driving control, the vehicle control device 11 controls the driving of the driving force source 3 based on a target driving torque for automatic driving.

[0018] The electric steering system 30 includes an electric motor and a gear mechanism (not shown), and adjusts the steering angle of the left and right front wheels 3LF, 3RF by being controlled by a steering control device 60. During manual driving, the steering control device 60 controls the steering angle of the front wheels 3LF, 3RF based on the steering angle of the steering wheel 31 by the driver. Furthermore, during execution of driving assistance control or automatic driving control, the steering control device 60 controls the steering angle of the front wheels 3LF, 3RF based on a target steering angle set according to a target driving trajectory.

[0019] The brake devices 7LF, 7RF, 7LR, and 7RR apply braking forces to the front, rear, left, and right wheels 3LF, 3RF, 3LR, and 3RR, respectively. The brake devices 7 are configured, for example, as hydraulic friction brake devices, and generate predetermined braking forces by adjusting the hydraulic pressure supplied to each brake device 7. If the vehicle 1 is an electric vehicle or a hybrid electric vehicle, the brake devices 7 are used in combination with regenerative braking using a drive motor. The hydraulic pressure supplied to the brake devices 7 is controlled by a hydraulic pressure control unit (not shown).

[0020] The vehicle 1 also includes a surrounding environment sensor 15 and a driving assistance device 17. The surrounding environment sensor 15 is one or more sensors that detect information about the surrounding environment of the vehicle 1. The surrounding environment sensor 15 detects the positions, distances, speeds, etc. of obstacles such as other vehicles and pedestrians, road shapes, and boundary lines of driving lanes, and outputs information about the detection results to the driving assistance device 17. The surrounding environment sensor 15 includes, for example, one or more sensors selected from a camera, a LiDAR, a radar sensor, and an ultrasonic sensor. In FIG. 1 , the vehicle 1 includes, as the surrounding environment sensor 15, a pair of left and right stereo cameras 15L, 15R that capture images ahead of the vehicle 1.

[0021] The driving assistance device 17 executes driving assistance control or automatic driving control of the vehicle 1 using information on obstacles and other detection results detected by the surrounding environment sensor 15. In this embodiment, the driving assistance device 17 has at least an assistance function for automatically driving the vehicle 1 at a predetermined position in a driving lane. Examples of such assistance functions include lane keeping control and automatic driving control. For example, the driving assistance device 17 sets a target driving trajectory for the vehicle 1, sets target values ​​for the acceleration / deceleration of the vehicle 1 and the steering angle of the steering wheel 31 so that the vehicle 1 drives along the target driving trajectory, and outputs information on the target values ​​to the vehicle control device 11 and the steering control device 60.

[0022] The vehicle 1 also includes tire force sensors 9L, 9R corresponding to the left and right front wheels 3LF, 3RF. The tire force sensors 9L, 9R are provided at the connection between the front wheel drive shaft 5 and the front wheels 3LF, 3RF, respectively. The tire force sensors 9L, 9R are load sensors that detect the loads applied to the left and right front wheels 3LF, 3RF, respectively. For example, the tire force sensors 9L, 9R may be six-component force detectors that detect loads in each of the three axial directions of the vehicle 1, namely the longitudinal direction (x-axis), the transverse direction (y-axis), and the height direction (z-axis), as well as moments generated around each of the three axes.

[0023] 2. Steering System Next, an example of the overall configuration of the electric steering system 30 according to this embodiment will be described.

[0024] 2 is a schematic diagram showing an example of the configuration of the electric steering system 30. The electric steering system 30 is constructed as a steer-by-wire type steering system in which a steering wheel 31 operated by a driver and a wheel steering device 40 that steers the wheels are provided mechanically separated from each other, and the steering angle of the front wheels 3LF, 3RF is controlled based on a detected value of the steering angle (rotation angle) of the steering wheel 31.

[0025] The electric steering system 30 has a steering device 33 and a wheel steering device 40 that steers the front wheels (steerable wheels) 3RFLF, 3RF. The steering device 33 receives steering inputs from a steering wheel 31 operated by the driver. The electric steering system 30 is a steer-by-wire type steering system in which the steering device 33 and the wheel steering device 40 are mechanically separated (linkless) and controlled in conjunction with each other by a steering control device 60.

[0026] The steering device 33 is configured to include a steering wheel 31, a steering shaft 32 connected to the steering wheel 31, and a reaction motor 34 coaxially incorporated at an axially intermediate position of the steering shaft 32. The reaction motor 34 is a means for applying a reaction force (rotational resistance) to the driver operating the steering wheel 31 via the steering shaft 32 and the steering wheel 31. The drive of the reaction motor 34 is controlled by a steering control device 60, and the output torque of the reaction motor 34 is transmitted to the steering wheel 31 via the steering shaft 32.

[0027] The wheel steering device 40 is configured to include a rack shaft 51 extending in the left-right direction of the vehicle body, and knuckle arms 53L, 53R connected via tie rods 52L, 52R to both ends of the rack shaft 51. The left and right front wheels 3LF, 3RF are connected to the knuckle arms 53L, 53R, respectively.

[0028] Rack shaft 51 is supported by housing 49 so as to be movable in the left-right direction of vehicle 1. Rack gear 54 is provided on rack shaft 51. Pinion gear 55 meshes with rack gear 54. Pinion gear 55 is connected to pinion shaft 56. A steering motor 57 is coaxially mounted on pinion shaft 56 at an intermediate position in the axial direction.

[0029] The steering motor 57 is an electric motor that steers the left and right front wheels 3LF, 3RF, and the drive of the steering motor 57 is controlled by a steering control device 60. The output torque of the steering motor 57 is transmitted to the rack shaft 51 via the pinion shaft 56, the pinion gear 55, and the rack gear 54. This causes the left and right front wheels 3LF, 3RF to turn.

[0030] A clutch mechanism 37 is provided between the steering shaft 32 and the pinion shaft 56. The clutch mechanism 37 is engaged by the steering control device 60 in the event of a failure of the reaction motor 34 or the steering motor 57, thereby directly connecting the steering shaft 32 and the pinion shaft 56 and enabling the driver to steer the front wheels 3LF, 3RF.

[0031] Sensor signals output from the steering angle sensor 35, steering torque sensor 36, turning angle sensor 58, and tire force sensors 9L, 9R are input to the steering control device 60. The steering angle sensor 35 detects the steering angle (rotation angle) of the steering wheel 31. The steering torque sensor 36 detects the steering torque, which is the torque input to the steering wheel 31 by the driver. The steering torque corresponds to the reaction torque that the driver receives from the steering wheel 31. The turning angle sensor 58 detects the turning angle (wheel angle) of the left and right front wheels 3LF, 3RF. The tire force sensors 9L, 9R detect the self-aligning torque applied to the left and right front wheels 3LF, 3RF from the road surface.

[0032] In place of the tire force sensors 9L, 9R, for example, a torque sensor that is provided coaxially with the pinion shaft 56 and detects the self-aligning torque may be provided.

[0033] Based on the inputs from these sensors, steering control device 60 controls the drive of reaction force motor 34 and steering motor 57. In other words, steering control device 60 controls linkless steering device 33 and wheel steering device 40 in conjunction with each other (steer-by-wire control) according to a pre-stored program.

[0034] 3. Steering Control Device The steering control device 60 functions as a device that executes processing to control the electric steering system 30 by having one or more processors, such as CPUs (Central Processing Units), execute a computer program. The computer program is a computer program that causes the processor to execute operations, described below, that should be executed by the steering control device 60. The computer program executed by the processor may be recorded on a recording medium that functions as a storage unit (memory) provided in the steering control device 60, or may be recorded on a recording medium built into the steering control device 60 or any recording medium that can be externally attached to the steering control device 60.

[0035] Examples of recording media for recording computer programs include magnetic media such as hard disks, floppy disks, and magnetic tapes; optical recording media such as CD-ROMs (Compact Disc-Read Only Memory), DVDs (Digital Versatile Discs), and Blu-ray (registered trademark); magneto-optical media such as floptical disks; memory elements such as RAMs (Random Access Memory) and ROMs (Read Only Memory); and flash memories such as USB (Universal Serial Bus) memories and SSDs (Solid State Drives), as well as other media capable of storing programs.

[0036] 3 is a block diagram showing an example of the configuration of the steering control device 60. The steering control device 60 includes a processing unit 61 and a storage unit 63. The processing unit 61 is configured to include one or more processors. A part or all of the processing unit 61 may be configured as an updatable unit such as firmware, or may be a program module executed by commands from a CPU or the like. The steering control device 60 may be configured as a stand-alone device, or may be configured as a plurality of devices connected to each other so that they can communicate with each other.

[0037] The storage unit 63 is configured with one or more storage elements (memories), such as RAM or ROM, communicably connected to the processing unit 61. However, the number and type of storage units 63 are not particularly limited. The storage unit 63 stores computer programs executed by the processing unit 61, various parameters used in arithmetic processing, detection data, calculation results, and other data. A part of the storage unit 63 functions as a work area for the processing unit 61.

[0038] The steering control device 60 is communicatively connected to the driving assistance device 17, tire force sensors 9L, 9R, steering angle sensor 35, steering torque sensor 36, turning angle sensor 58, tire force sensors 9L, 9R, reaction force motor 34, and turning motor 57 via a dedicated line or via communication means such as CAN (Controller Area Network) or LIN (Local Internet).

[0039] The processing unit 61 includes a first control unit 71, a second control unit 73, and a switching control unit 75. The first control unit 71, the second control unit 73, and the switching control unit 75 are functions realized by execution of a computer program by one or more processors. Note that part of the first control unit 71, the second control unit 73, and the switching control unit 75 may be configured by hardware such as an analog circuit.

[0040] The function of each part of the processing unit 61 will be briefly explained below, and the specific processing operation of the processing unit 61 will be explained in detail later.

[0041] (First control unit) The first control unit 71 controls the steering angle based on the steering angle of the steering wheel 31 operated by the driver, and also performs a first control that applies a reaction torque to the steering wheel 31 in response to the self-aligning torque that the left and right front wheels 3LF, 3RF receive from the road surface.

[0042] When the driver manually steers vehicle 1, first control unit 71 detects the steering angle of steering wheel 31 based on the sensor signal of steering angle sensor 35, and sets target steering angles for left and right front wheels 3LF, 3RF based on the actual steering angle. Hereinafter, the steering angle detected based on the sensor signal of steering angle sensor 35 will be referred to as the actual steering angle. Steering angle and steering angle can be converted into each other using a predetermined coefficient, and first control unit 71 sets the target steering angle based on the actual steering angle using the coefficient. In addition, first control unit 71 converts the target steering angle into a rotation angle of steering motor 57 and controls the rotation angle of steering motor 57.

[0043] Furthermore, while executing the first control, the first control unit 71 detects the self-aligning torque that the front wheels 3LF, 3RF receive from the road surface based on the sensor signals of the tire force sensors 9L, 9R, and sets the reaction torque to be applied to the steering wheel 31 based on the self-aligning torque. The self-aligning torque is a restoring force that acts to return the orientation of the front wheels 3LF, 3RF to the fore-and-aft direction of the vehicle 1 while the vehicle 1 is turning. The reaction torque is a restoring force that acts in response to the self-aligning torque acting on the front wheels 3LF, 3RF to return the steering wheel 31 to the neutral position (a position where the vehicle 1 is traveling straight).

[0044] The self-aligning torque and the reaction torque can be converted into each other using a predetermined coefficient, and the first control unit 71 sets the reaction torque based on the self-aligning torque using the coefficient. The first control unit 71 also sets a drive command value for the reaction motor 34 that can output the set reaction torque, and controls the drive of the reaction motor 34. For example, the first control unit 71 calculates a command value for the reaction torque by feedback calculation based on the difference between a detection value of the reaction torque detected based on a sensor signal from the steering torque sensor 36 (hereinafter also referred to as the "actual torque value") and a target value of the reaction torque that is set based on the self-aligning torque, and sets the drive command value for the reaction motor 34.

[0045] 4 shows an aligning torque map (aligning torque information) that indicates the reaction torque F_co according to the steering angle θs of the steering wheel 31. The steering angle θs is shown with the neutral position θ0 as the center, with the right turning direction θs_R as a positive value and the left turning direction θs_L as a negative value. Furthermore, the reaction torque F_co is shown with the force pushing the steering wheel 31 in the left turning direction as a positive value and the force pushing the steering wheel 31 in the right turning direction as a negative value.

[0046] 4, the larger the steering angle θs in each of the right turning direction θs_R and the left turning direction θs_L, the larger the absolute value of the reaction torque F_co that acts to return the steering angle θs to the neutral position θ0 is set to. The relationship between the steering angle θs and the reaction torque F_co shown in the aligning torque map can also be seen as the relationship between the steering angle of the front wheels 3LF, 3RF and the self-aligning torque that the front wheels 3LF, 3RF receive from the road surface.

[0047] (Second control unit) The second control unit 73 controls the steering angle and the turning angle based on the target steering angle determined by the driving assist control of the driving assist device 17, and also executes second control to apply a steering assist torque to the steering wheel 31 according to the angular difference between the target steering angle and the steering angle or the turning angle. As described above, the steering angle and the turning angle are convertible to each other, and the target steering angle may be either a target value of the steering angle or a target value of the turning angle. However, in this embodiment, an example will be described in which the target steering angle is a target value of the steering angle (hereinafter referred to as the "target steering angle"). Therefore, in the following description, the angular difference between the target steering angle and the steering angle refers to the value obtained by subtracting the absolute value of the target steering angle from the absolute value of the steering angle.

[0048] Second control unit 73 controls the steering angle of front wheels 3LF, 3RF based on a target steering angle set by an assistance function that causes vehicle 1 to automatically travel in a predetermined position in the driving lane, such as lane keeping control or automatic driving control by driving assistance device 17. Second control unit 73 sets a target steering angle based on the target steering angle using a predetermined coefficient. Second control unit 73 also converts the target steering angle into a rotation angle of steering motor 57 and controls the rotation angle of steering motor 57.

[0049] Furthermore, the second control unit 73 controls the steering angle of the steering wheel 31 based on the target steering angle set by the driving assistance device 17. At this time, the second control unit 73 sets a steering assist torque according to the angular difference between the target steering angle and the actual steering angle. The steering assist torque is an assist force that acts to make the actual steering angle follow the target steering angle. For example, the second control unit 73 sets the steering assist torque using an assist torque map (assist torque information) in which a value of the steering assist torque relative to the angular difference is set in advance. The second control unit 73 sets a drive command value for the reaction force motor 34 that can output the set steering assist torque, and controls the drive of the reaction force motor 34.

[0050] 5 shows an assist torque map in which a steering assist torque F_as to be generated according to the angular difference Δθ between the target steering angle θs_tgt and the steering angle θs is set. As described above, the angular difference Δθ indicates a difference value obtained by subtracting the absolute value of the target steering angle θs_tgt from the absolute value of the steering angle θs, and is shown with the angular difference Δθ=0 as the center, with a positive value indicating that the steering angle θs is larger than the target steering angle θs_tgt and a negative value indicating that the steering angle θs is smaller than the target steering angle θs_tgt. Furthermore, the steering assist torque F_as indicates a force in a direction to reduce the steering angle θs as a positive value and a force in a direction to increase the steering angle θs as a negative value.

[0051] In each of the states where the steering angle θs is larger and smaller than the target steering angle θs_tgt, the larger the angle difference Δθ between the steering angle θs and the target steering angle θs_tgt, the larger the absolute value of the steering assist torque F_as that acts to make the steering angle θs follow the target steering angle θs_tgt is set to. Note that the illustrated switching threshold Δθ_thr_1 is a threshold at which the steering control is switched (overridden) from the second control based on the driving assist control to the first control based on the driver's steering.

[0052] (Switching control unit) The switching control unit 75 executes switching control to cancel the second control and switch the steering control to the first control as the angular difference between the target steering angle and the steering angle increases during execution of the second control. In other words, the switching control unit 75 detects that the driver is intentionally attempting to correct the driving trajectory while the driving assistance function is automatically steering the vehicle 1 so that it travels along the target driving trajectory, and switches (overrides) to the first control that controls the steering angle based on the steering operation by the driver.

[0053] In this embodiment, the switching control unit 75 switches the steering control from the second control to the first control when the angular difference Δθ (absolute value |Δθ|) between the target steering angle θs_tgt and the actual steering angle θs_act increases and exceeds the switching threshold value Δθ_thr_1. The switching control unit 75 also limits the acceleration of the change in the reaction torque F_co that occurs when the steering control is switched from the second control to the first control. This causes the amount of change in the reaction torque F_co after the steering control is switched from the second control to the first control to change continuously, thereby suppressing abrupt torque fluctuations.

[0054] As described above, the first control unit 71 calculates the command value of the reaction torque by feedback calculation based on the difference between the actual torque value detected based on the sensor signal of the steering torque sensor 36 and the target value of the reaction torque set based on the self-aligning torque. After switching the steering control from the second control to the first control, the switching control unit 75 sets the command value of the reaction torque by adding a virtual inertia for suppressing changes in the angular velocity of the steering angle to the calculation of the command value of the reaction torque.

[0055] Alternatively, the switching control unit 75 may set the rate of change of the reaction torque generated after switching the steering control from the second control to the first control to a predetermined reference rate or less, or may set the time rate of change of the rate of change of the reaction torque to a predetermined change rate threshold or less. In this case, the reference rate of the rate of change or the change rate threshold for the time rate of change may be set to any appropriate value. This limits the acceleration of the change in the reaction torque F_co, and the amount of change in the reaction torque F_co after switching the steering control from the second control to the first control changes continuously, thereby suppressing sudden torque fluctuations.

[0056] 6 is a diagram for explaining a reference example in which the steering assist torque F_as is set to gradually increase as the angular difference Δθ between the target steering angle θs_tgt and the steering angle θs increases in the second control, and the steering control is switched from the second control to the first control when the angular difference Δθ exceeds a switching threshold Δθ_thr_1. FIG. 6 is an explanatory diagram of a reference example in which the steering assist torque F_as based on the target steering angle θs_tgt when the vehicle 1 is turning right is superimposed on an aligning torque map.

[0057] 6 , in the reference example, when the steering angle θs is greater than the target steering angle θs_tgt and the angular difference Δθ between the steering angle θs and the target steering angle θs_tgt exceeds the steering angle θs_h at which the switching threshold Δθ_thr_1 is reached, the steering control is switched from the second control to the first control. At this time, if the steering assist torque F_as greatly exceeds the reaction torque F_co at the steering angle θs_h, the torque applied to the steering wheel 31 changes significantly before and after the switching of the steering control from the second control to the first control. As a result, the steering angle θs of the steering wheel 31 changes abruptly, which may cause the behavior of the vehicle 1 to become unstable.

[0058] Furthermore, when the steering angle θs is smaller than the target steering angle θs_tgt and the angular difference Δθ between the steering angle θs and the target steering angle θs_tgt exceeds a steering angle θs_l at which the switching threshold Δθ_thr_1 is reached, the steering control is switched from the second control to the first control. At this steering angle θs_l, the steering assist torque F_as and the reaction torque F_co are torques in opposite directions, and the torque applied to the steering wheel 31 changes suddenly before and after the switching of the steering control from the second control to the first control. For this reason, the steering angle θs of the steering wheel 31 changes suddenly, which may cause the driver to feel uncomfortable and may cause the behavior of the vehicle 1 to become unstable.

[0059] 7 is an explanatory diagram showing a change in reaction torque F_co generated when the steering control is switched by the steering control device 60 according to this embodiment. As shown in Fig. 7, in this embodiment, the switching control unit 75 limits the acceleration of the change in reaction torque F_co generated when the steering control is switched from the second control to the first control, thereby suppressing a sudden fluctuation in reaction torque F_co when the steering control is switched from the second control to the first control.

[0060] 6 and 7, the steering angle θs when the rotation direction of the steering wheel 31 is in the right turning direction is shown as a positive value, the torque pushing the steering wheel 31 in the direction to return to the neutral position is shown as a positive value, and the torque pushing the steering wheel 31 further in the right turning direction is shown as a negative value. The explanation based on these Figures 6 and 7 can also be understood in the same way if the steering angle θs when the rotation direction of the steering wheel 31 is in the left turning direction is shown as a positive value, the torque pushing the steering wheel 31 in the direction to return to the neutral position is shown as a positive value, and the torque pushing the steering wheel 31 further in the left turning direction is shown as a negative value.

[0061] 3. Processing Operation of Steering Control Device Up to this point, an example configuration of the steering control device 60 according to this embodiment has been described. Next, the processing operation of the steering control device 60 will be specifically described. Note that in the following description, the right turning direction and the left turning direction are understood to be positive values ​​with respect to the neutral position (steering angle θs=0) of the steering wheel 31. Therefore, the generated torque or applied torque is also understood to be a positive value.

[0062] 8 shows a flowchart of the processing operation of the steering control device 60. First, when the steering system is started (step S11), the processing unit 61 determines whether or not the driving assistance function is operating (step S13). For example, the processing unit 61 determines that the driving assistance function is operating when it receives a signal indicating that the driving assistance function is operating from the driving assistance device 17. The processing unit 61 may also determine whether or not the driving assistance function is operating based on an on / off signal of an activation switch for the driving assistance function. As described above, the driving assistance function is an assistance function that automatically drives the vehicle 1 in a predetermined position in the driving lane, and may be, for example, lane keeping control or automatic driving control.

[0063] When the processing unit 61 does not determine that the driving assistance function is in operation (S13 / No), the first control unit 71 executes the first control (step S15).

[0064] 9 is a flowchart showing the processing operation of the first control by first control unit 71. First, first control unit 71 detects the actual steering angle θs_act of steering wheel 31 based on the sensor signal of steering angle sensor 35 (step S31). Next, first control unit 71 sets the target steering angle θw_tgt based on the actual steering angle θs_act (step S33). For example, first control unit 71 calculates the target steering angle θw_tgt by multiplying the actual steering angle θs_act by a predetermined coefficient set in advance.

[0065] Next, first control unit 71 drives steering motor 57 to control the steering of front wheels 3LF, 3RF (step S35). For example, first control unit 71 refers to a map that defines the relationship between the steering angle and the drive command value for steering motor 57, obtains the drive command value that corresponds to target steering angle θw_tgt, and drives steering motor 57.

[0066] Next, the first control unit 71 detects the self-aligning torque F_al that the left and right front wheels 3LF, 3RF receive from the road surface based on the sensor signals of the tire force sensors 9L, 9R (step S37), and then multiplies the self-aligning torque F_al by a predetermined coefficient to calculate the reaction torque F_co (step S39).

[0067] Next, the first control unit 71 drives the reaction motor 34 to apply a reaction torque F_co corresponding to the self-aligning torque F_al to the steering wheel 31 (step S41).

[0068] In this way, the first control unit 71 controls the steering angle θw of the left and right front wheels 3LF, 3RF based on the actual steering angle θs_act of the steering wheel 31 operated by the driver. The first control unit 71 also applies to the steering wheel 31 a reaction torque F_co that corresponds to the self-aligning torque F_al that the left and right front wheels 3LF, 3RF receive from the road surface, causing the driver to feel a reaction force that corresponds to the self-aligning torque F_al.

[0069] Returning to Figure 8, on the other hand, in the above step S13, if the processing unit 61 determines that the driving assistance function is operating (S13 / Yes), the second control unit 73 performs steering control using the second control (step S17).

[0070] 10 is a flowchart showing the processing operation of the second control by the second control unit 73. First, the second control unit 73 acquires information on the target steering angle θs_tgt transmitted from the driving assistance device 17 (step S51). Next, the second control unit 73 detects the actual steering angle θs_act of the steering wheel 31 based on the sensor signal of the steering angle sensor 35 (step S53).

[0071] Next, the second control unit 73 calculates the angle difference Δθ by subtracting the target steering angle θs_tgt from the actual steering angle θs_act (step S55). Here, it is determined whether the actual steering angle θs_act is turned too far or too far from the target steering angle θs_tgt.

[0072] Next, the second control unit 73 sets the steering assist torque F_as based on the calculated angular difference Δθ (step S57). For example, the second control unit 73 sets the steering assist torque F_as according to the angular difference Δθ based on a preset assist torque map (see FIG. 5). Next, the second control unit 73 drives the reaction force motor 34 to apply the steering assist torque F_as to the steering wheel 31 (step S59).

[0073] Next, second control unit 73 sets target steering angle θw_tgt based on actual steering angle θs_act (step S61), similar to step S33 described above. Next, second control unit 73 drives steering motor 57 to control the steering of front wheels 3LF, 3RF (step S63), similar to step S35 described above.

[0074] As described above, the second control unit 73 sets the steering assist torque F_as based on the angle difference Δθ between the target steering angle θs_tgt set by the driving support device 17 and the actual steering angle θs, and applies the steering assist torque F_as to the steering wheel 31 so that the actual steering angle θs follows the target steering angle θs_tgt. Then, the second control unit 73 controls the steering angle θw of the left and right front wheels 3LF, 3RF based on the actual steering angle θs_act. Therefore, in the second control, the steering of the vehicle 1 is basically controlled in accordance with the target steering angle θs_tgt set by the driving support device 17, but when the driver intervenes in operating the steering wheel 31, the vehicle 1 is steered in a manner reflecting the driver's intention.

[0075] Returning to FIG. 8, in the execution state of the second control, the switching control unit 75 executes the switching control (step S19).

[0076] 11 is a flowchart showing the processing operation of the switching control by the switching control unit 75. First, the switching control unit 75 determines whether or not the angle difference Δθ obtained by subtracting the target steering angle θs_tgt set by the driving support device 17 from the actual steering angle θs_act detected based on the sensor signal of the steering angle sensor 35 exceeds a predetermined switching threshold Δθ_tgt (step S71). If the switching control unit 75 does not determine that the angle difference Δθ exceeds the predetermined switching threshold Δθ_tgt (S71 / No), it ends the switching control and continues the second control.

[0077] On the other hand, if the switching control unit 75 determines that the angle difference Δθ exceeds the predetermined switching threshold Δθ_tgt (S71 / Yes), it detects the actual steering angle θs_act (step S73) and further detects the actual steering angle θw_act based on the sensor signal of the steering angle sensor 58 (step S75).

[0078] Next, switching control unit 75 determines whether the absolute value |θs_act−θw_act| of the difference between actual steering angle θs_act and actual turning angle θw_act is less than a predetermined angle threshold Δθ_thr_2 (step S77). The predetermined angle threshold Δθ_thr_2 is a threshold set for switching the steering control from the second control to the first control in a state in which the steering angle θS of steering wheel 31 and the turning angle θw of left and right front wheels 3LF, 3RF are considered to be synchronized, and may be set to any appropriate value.

[0079] If the switching control unit 75 determines that the absolute value |θs_act - θw_act| of the difference between the actual steering angle θs_act and the actual turning angle θw_act is not less than the predetermined angle threshold Δθ_thr_2 (S77 / No), the process returns to step S71. On the other hand, if the switching control unit 75 determines that the absolute value |θs_act - θw_act| of the difference between the actual steering angle θs_act and the actual turning angle θw_act is less than the predetermined angle threshold Δθ_thr_2 (S77 / Yes), the switching control unit 75 cancels the second control and switches the steering control to the first control (step S79). In other words, since it is determined that the driver is intentionally attempting to correct the driving trajectory in a direction that turns the steering wheel 31 back relative to the target steering angle θs_tgt, the switching control unit 75 overrides the steering control based on the driving assistance function with the steering control based on the driver's steering operation. As a result, the execution of the first control starts in accordance with the flowchart shown in FIG.

[0080] Next, the switching control unit 75 limits the acceleration of change in the reaction torque F_co applied to the steering wheel 31 in the first control (step S81). For example, the switching control unit 75 sets the reaction torque command value F_co_tgt by adding virtual inertia to the feedback calculation for setting the reaction torque command value F_co_tgt in the first control. Alternatively, the switching control unit 75 may limit the rate of change of the reaction torque F_co applied to the steering wheel 31 to a predetermined reference rate or less, or may set the time rate of change of the rate of change of the reaction torque F_co to a predetermined change rate threshold or less. This suppresses abrupt fluctuations in the reaction torque F_co applied to the steering wheel 31 after switching the steering control from the second control to the first control, thereby suppressing abrupt changes in the steering angle of the steering wheel 31.

[0081] Next, the switching control unit 75 determines whether or not a condition for releasing the limit on the acceleration of the change in the reaction torque F_co is satisfied (step S83). For example, the switching control unit 75 determines that the condition for releasing the limit on the acceleration of the change in the reaction torque F_co is satisfied when the angular velocity of the change in the actual steering angle θs_act becomes equal to or less than a predetermined reference angular velocity. The predetermined reference angular velocity may be set to any appropriate value that can determine that the fluctuation of the steering angle θs of the steering wheel 31 has become gentle. Note that the condition for releasing the limit on the acceleration of the change in the reaction torque F_co is not limited to the angular velocity of the change in the actual steering angle θs_act becoming equal to or less than the predetermined reference angular velocity, and other conditions may be set.

[0082] When the switching control unit 75 does not determine that the condition for releasing the limit on the acceleration of change in the reaction torque F_co is satisfied (S83 / No), the first control is executed with the limit on the acceleration of change in the reaction torque F_co being imposed, and the determination of step S83 is repeated. On the other hand, when the switching control unit 75 determines that the condition for releasing the limit on the acceleration of change in the reaction torque F_co is satisfied (S83 / Yes), the switching control unit 75 releases the limit on the acceleration of change in the reaction torque F_co (step S85).

[0083] 8 , while the first control or the second control is continued, or after the steering control is switched from the second control to the first control during the second control, the processing unit 61 determines whether the activation of the steering system 10 has been stopped (step S21). If the processing unit 61 does not determine that the activation of the steering system 10 has been stopped (S21 / No), the processing unit 61 returns to step S13 and executes the processing of each step described above. On the other hand, if the processing unit 61 determines that the activation of the steering system 10 has been stopped (S21 / Yes), the processing unit 61 ends the steering control.

[0084] 4. Effects As described above, the control device of the steering system according to this embodiment limits the acceleration of the change in reaction torque F_co that occurs when steering control is switched from the second control to the first control. This suppresses abrupt fluctuations in reaction torque F_co that occur when matching reaction torque F_co to command value F_co_tgt due to the difference between steering assist torque F_as and reaction torque F_co, thereby reducing the sense of discomfort experienced by the driver and suppressing abrupt fluctuations in steering angle θs of the steering wheel 31.

[0085] Furthermore, the control device for the steering system according to this embodiment sets a command value for the reaction torque by feedback calculation based on the difference between the actual torque value detected by the steering torque sensor 36 and the target value for the reaction torque set based on the self-aligning torque during the first control, and when the second control is switched to the first control, sets a command value for the reaction torque by adding a virtual inertia that suppresses changes in the angular velocity of the steering angle. This limits the acceleration of changes in the command value for the reaction torque, making it possible to limit the reaction torque applied by the reaction motor 34.

[0086] Furthermore, the control device of the steering system according to this embodiment may limit the rate of change of the reaction torque generated when the steering control is switched from the second control to the first control to a predetermined reference rate or less, or may set the time rate of change of the rate of change of the reaction torque to a predetermined change rate threshold or less. This makes it possible to limit the output of the reaction motor 34 without changing the calculation of the reaction torque command value.

[0087] Furthermore, the control device for the steering system according to this embodiment releases the limit on the acceleration of the change in the reaction torque when the angular velocity of the steering angle becomes equal to or less than a predetermined reference angular velocity after switching from the second control to the first control. Therefore, when the limit is released, it is possible to prevent the steering angle of the steering wheel 31 from fluctuating abruptly.

[0088] Although the preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, the present disclosure is not limited to such examples. It is clear that a person skilled in the art to which the present disclosure pertains can conceive of various modifications or alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure.

[0089] For example, in the above embodiment, an example was described in which the target steering angle was a target value of the steering angle, but the target steering angle may also be a target value of the turning angle. In this case, as already mentioned, since the steering angle and the turning angle can be converted into each other using a predetermined coefficient, the same effect can be obtained by implementing the angle difference between the actual steering angle and the target steering angle in the above embodiment as the angle difference between the actual turning angle and the target turning angle.

[0090] In addition, the technology of the present disclosure can also be realized as a vehicle equipped with the steering control device described in the above embodiment, a steering control method using the steering control device, a computer program that causes a computer to function as the above steering control device, and a non-temporary tangible recording medium on which the computer program is recorded.

[0091] 1: Vehicle 3LF / 3RF: Front wheels 9L: Tire force sensor 9R: Tire force sensor 10: Steering system 17: Driving assistance device 30: Electric steering system 31: Steering wheel 33: Steering device 34: Reaction motor 35: Steering angle sensor 36: Steering torque sensor 40: Wheel steering device 57: Steering motor 58: Steering angle sensor 60: Steering control device 61: Processing unit 63: Memory unit 71: First control unit 73: Second control unit 75: Switching control unit

Claims

1. A control device for a steer-by-wire type steering system in which a steering wheel operated by a driver of a vehicle and a wheel steering device for steering the wheels are provided mechanically separated, and the steering angle of the wheels is controlled based on the steering angle of the steering wheel, the control device executing: a first control that controls the steering angle based on the steering angle of the steering wheel operated by the driver, and applies to the steering wheel a reaction torque against the operation of the steering wheel in accordance with the self-aligning torque that the wheels receive from the road surface; a second control that controls the steering angle and the steering angle based on a target steering angle by a predetermined driving assistance control, and applies to the steering wheel a steering assist torque that is a steering assist torque in accordance with the angular difference between the target steering angle and the steering angle or the steering angle; and a switching control that releases the second control and switches to the first control as the angular difference increases while the second control is being executed, and limits the acceleration of the change in the reaction torque that occurs when the second control is switched to the first control.

2. A control device for a steering system as described in claim 1, wherein the control device, in the first control, sets a command value for the reaction torque by a feedback calculation based on the difference between an actual torque value and a target value for the reaction torque, and when the second control is switched to the first control, sets a command value for the reaction torque by adding a virtual inertia that suppresses changes in the angular velocity of the steering angle.

3. A control device for a steering system as described in claim 1, wherein the control device limits the rate of change of the reaction torque generated when the second control is switched to the first control to a predetermined reference speed or less.

4. A control device for a steering system according to claim 1, wherein the control device sets a time rate of change in the speed of change of the reaction torque to a predetermined change rate threshold or less.

5. A control device for a steering system as described in claim 1, wherein the control device releases the limit on the acceleration of the change in the reaction torque when the angular velocity of the steering angle becomes equal to or lower than a predetermined reference angular velocity after switching from the second control to the first control.

6. A control method for a steer-by-wire type steering system in which a steering wheel operated by a driver of a vehicle and a wheel steering device for steering the wheels are provided mechanically separated and the steering angle of the wheels is controlled based on the steering angle of the steering wheel, the control method comprising the steps of: a first control for controlling the steering angle based on the steering angle of the steering wheel operated by the driver, and applying to the steering wheel a reaction torque against the operation of the steering wheel in accordance with a self-aligning torque that the wheels receive from the road surface; a second control for controlling the steering angle and the steering angle based on a target steering angle by a predetermined driving assist control, and applying to the steering wheel a steering assist torque that is a steering assist torque in accordance with the angular difference between the target steering angle and the steering angle or the steering angle; and a switching control for releasing the second control and switching to the first control as the angular difference increases while the second control is being executed, and limiting the acceleration of the change in the reaction torque that occurs when the second control is switched to the first control.

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