Steering system

Abstract

To provide a steering system capable of suppressing the decline in driving performance even when an abnormality occurs in one of the left and right steering devices.SOLUTION: A steering system of the invention comprises a left steering device 2A steering a left steering wheel 11, a right steering device 2B steering a right steering wheel 12 independently of the left steering device 2A, a left steering controller 3A controlling the left steering device 2A and a right steering controller 3B controlling the right steering device 2B. The left steering controller 3A can detect an abnormality of the right steering controller 3B and when it detects the abnormality of the right steering controller 3B, it executes the right shutdown control to shut off the supply of control current to the right steering device 2B. The right steering controller 3B can detect an abnormality of the left steering controller 3A and when it detects the abnormality of the left steering controller 3A, it executes the left shutdown control to shut off the supply of control current to the left steering device 2A.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a single-wheel independent steering type steering system. [Background technology]

[0002] A single-wheel independent steering type steering system is a system in which left and right wheels are steered independently. In this steering system, a left steering device that steers the left steered wheels and a right steering device that steers the right steered wheels are controlled based on the amount of operation of an operating member in manual driving or a command value in autonomous driving. A single-wheel independent steering type steering system is a steer-by-wire system in which the operating member and the steering device are not mechanically connected. For example, Japanese Patent Application Laid-Open No. 2018-58512 discloses a vehicle steering device that, when a communication abnormality occurs between a host control device and one of the left and right steering control devices, controls the steering angle of the steered wheel corresponding to the steering control device with the communication abnormality to a neutral position. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-58512 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the above device, one of the wheels is held in a neutral position, which increases turning resistance during turning and increases the minimum turning radius, leaving room for improvement in terms of maintaining driving performance, including straight-line performance and cornering performance. An object of the present invention is to provide a steering system that can suppress a decrease in driving performance even if an abnormality occurs in one of the left and right steering devices. [Means for solving the problem]

[0005] The steering system of the present invention is a single-wheel independent steering type steering system comprising a left steering device that steers left steered wheels, a right steering device that steers right steered wheels independently of the left steering device, a left steering controller that controls the left steering device, and a right steering controller that controls the right steering device, wherein the left steering controller is configured to be able to detect an abnormality in the right steering controller, and if an abnormality in the right steering controller is detected, executes right cut-off control to cut off the supply of control current to the right steering device, and the right steering controller is configured to be able to detect an abnormality in the left steering controller, and if an abnormality in the left steering controller is detected, executes left cut-off control to cut off the supply of control current to the left steering device. [Effects of the Invention]

[0006] According to the present invention, if an abnormality occurs in one controller, the other controller cuts off the supply of control current to the steering device controlled by the other controller. As a result, control current is not supplied to the steered wheels corresponding to the abnormal controller, and the steered wheels are placed in a free state similar to driven wheels. After an abnormality is detected, the steered wheels that are placed in a free state follow the traveling direction secured by the normal steered wheels, i.e., the controlled steered wheels, due to self-aligning torque. This minimizes running resistance and prevents a decrease in running performance (straight-line running / turning performance). [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a configuration diagram of a steering system according to an embodiment of the present invention; [Figure 2] FIG. 2 is a perspective view showing the configuration of the right steering device of the present embodiment. [Figure 3] FIG. 2 is a configuration diagram of a steering controller according to the present embodiment. [Figure 4] 4 is a flowchart illustrating an example of a control flow according to the present embodiment. [Figure 5] FIG. 10 is a conceptual diagram for explaining kingpin offset. [Figure 6]FIG. 1 is a conceptual diagram for explaining a caster trail. DETAILED DESCRIPTION OF THE INVENTION

[0008] A steering system 1 according to one embodiment of the present invention will be described in detail below with reference to the drawings. In addition to the following examples, the present invention can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art.

[0009] The steering system 1 of this embodiment is a single-wheel independent steering type (left and right independent steering type) steer-by-wire type steering system. As shown in Fig. 1, the steering system 1 includes a left steering device 2A, a right steering device 2B, a left steering controller 3A, a right steering controller 3B, an operation device 4, and a reaction force controller 5. The steering system 1 is a steer-by-wire type steering system in which the left steering device 2A and the right steering device 2B are not mechanically connected to the operation device 4.

[0010] Communication within the vehicle is carried out using a CAN (car area network or controllable area network) 100. In the drawings, some communication lines are not shown. In this embodiment, the steered wheels are front wheels 11, 12, the left steered wheel is the left front wheel 11, and the right steered wheel is the right front wheel 12. The left steering device 2A is a device that steers the left front wheel 11. The right steering device 2B is a device that steers the right front wheel 12 independently of the left steering device 2A. Because the left steering device 2A and the right steering device 2B have the same configuration, the configuration of the right steering device 2B will be described and a description of the configuration of the left steering device 2A will be omitted.

[0011] (Steering device) As shown in Fig. 2, the right steering device 2B includes a steering knuckle 21, a steering actuator 22, and a tie rod 23. The steering knuckle 21 is a member that rotatably holds the right front wheel 12. The steering knuckle 21 is a housing for an in-wheel motor unit 7, which will be described later.

[0012] Steering actuator 22 is installed at a location on the base end side of lower arm 91. Steering actuator 22 includes a steering motor 221, a reducer 222, an actuator arm 223, and a rotation angle sensor 224. Steering motor 221 is an electric motor serving as a drive source. Steering motor 221 is, for example, a brushless DC motor.

[0013] Reducer 222 is a gear device that reduces the rotation of steering motor 221. Actuator arm 223 is an arm member that rotates by the rotation of steering motor 221 via reducer 222. Actuator arm 223 functions as a pitman arm. Tie rod 23 is a member that connects knuckle arm 211 provided on steering knuckle 21 and actuator arm 223 of steering actuator 22. One end of tie rod 23 is connected to actuator arm 223 via ball joint 231, and the other end of tie rod 23 is connected to knuckle arm 211 via ball joint 232.

[0014] Rotation angle sensor 224 detects the rotation angle of steering motor 221. There is a specific relationship between the rotation angle of steering motor 221 and the steering angle of right front wheel 12. Therefore, each controller can calculate the steering angle of the wheel corresponding to steering motor 221 based on the rotation angle of steering motor 221. When the steering angle of a steered wheel changes due to a road disturbance, the detection result of corresponding rotation angle sensor 224 also changes accordingly. Road disturbance is an external force that wheels 11-14 receive from the road surface, and is generated, for example, when a tire hits a pothole in the road, steps on a stone, or travels on an uneven road.

[0015] The rotation angle sensor 224 of the left steering device 2A corresponds to a left steering angle sensor that detects the steering angle of the left front wheel 11, and the rotation angle sensor 224 of the right steering device 2B corresponds to a right steering angle sensor that detects the steering angle of the right front wheel 12. Hereinafter, the rotation angle sensor 224 of the left steering device 2A will also be referred to as the "left steering angle sensor 224," and the rotation angle sensor 224 of the right steering device 2B will also be referred to as the "right steering angle sensor 224."

[0016] Each suspension device 9 for the front wheels 11, 12 includes a lower arm 91, a steering knuckle 21, a shock absorber 92, and a suspension spring 93. The suspension device 9 is, for example, a MacPherson strut type suspension device. The lower arm 91 is an L-arm, and its two divided base ends are rotatably supported by side members (not shown) of the vehicle body via bushings. The steering knuckle 21 is rotatably connected to the tip end of the lower arm 91 via a ball joint 911. The shock absorber 92 is a member whose lower end is fixedly supported by the steering knuckle 21 and whose upper end is rotatably supported by the vehicle body via an upper support 94. The suspension spring 93 is a member whose upper end is rotatably supported by the vehicle body via the upper support 94 and whose lower end is supported by a lower support 95 provided on the shock absorber 92.

[0017] The vehicle is equipped with various sensors, such as a yaw rate sensor 61 that detects the yaw rate of the vehicle, a wheel speed sensor 62 that detects the wheel speed of each of the wheels 11, 12, 13, and 14, and a lateral acceleration sensor 63 that detects lateral acceleration. Since the vehicle speed is calculated based on the wheel speed of each of the wheels 11 to 14, it can be said that the vehicle is equipped with a vehicle speed sensor that detects the vehicle speed. The vehicle is also equipped with a plurality of other sensors (not shown), such as a longitudinal acceleration sensor.

[0018] In this embodiment, the vehicle is equipped with in-wheel motor units 7 as drive devices on the front wheels 11, 12, which are steered wheels. The in-wheel motor units 7 include a steering knuckle 21 that functions as a housing, a drive motor 71, a reduction gear 72, and an axle hub (not shown). The drive motor 71 is an electric motor built into the steering knuckle 21. The reduction gear 72 is a gear device that reduces the rotation of the drive motor 71. The axle hub is attached to the wheel of the vehicle. The in-wheel motor units 7 are arranged inside the rim of the wheel. Each in-wheel motor unit 7 is controlled by a drive ECU (not shown).

[0019] (operating device) The operation device 4 has a general structure in a steer-by-wire steering system. As shown in Fig. 1, the operation device 4 includes a steering wheel 41, a steering sensor 42, and a reaction force applying device 43. The steering wheel 41 is an operation member that is operated by the driver to steer the vehicle.

[0020] The steering sensor 42 is a sensor that detects the operation angle, which is the rotation angle of the steering wheel 41, as the operation position or operation amount of the steering wheel 41. For example, if the position of the steering wheel 41 when the vehicle is traveling straight is set to a neutral position, the rotation angle in each of the left and right directions from the neutral position is the operation angle of the steering wheel 41.

[0021] The reaction force application device 43 is a device that applies a reaction force (a reaction force against an operation) to the steering wheel 41. The reaction force application device 43 includes a reaction force motor 431, which is an electric motor serving as a power source, a reducer 432 for transmitting the force of the reaction force motor 431 to the steering wheel 41, and an operation torque sensor 433. The operation torque sensor 433 detects an operation torque as an operation force applied to the steering wheel 41 by the driver based on the amount of twist of a torsion bar (not shown) incorporated in the steering shaft. The steering sensor 42 and / or the operation torque sensor 433 can be considered operation amount sensors that detect the amount of operation of the steering wheel 41 (a value related to the operation). In this embodiment, for the sake of explanation, the detection result of the steering sensor 42 is taken as the amount of operation of the steering wheel 41.

[0022] The reaction force controller 5 is an electronic control unit (ECU) equipped with one or more processors 51 and one or more memories 52. The reaction force controller 5 has a configuration similar to that of the left steering controller 3A and the right steering controller 3B described below. The reaction force controller 5 calculates a target reaction force based on the detection result of the steering sensor 42 and the vehicle speed. The reaction force controller 5 controls the reaction force motor 431 based on the target reaction force. In other words, the reaction force controller 5 supplies a control current to the reaction force motor 431 based on the target reaction force.

[0023] (Steering controller) The left steering controller 3A and the right steering controller 3B (hereinafter also referred to as "steering controllers 3A, 3B") are each an electronic control unit (ECU) equipped with one or more processors 31a and one or more memories 31b. The left steering controller 3A, the right steering controller 3B, and the reaction force controller 5 (hereinafter also referred to as "controllers 3A, 3B, 5") are connected to each other so as to be able to communicate with each other via a CAN 100. Each of the controllers 3A, 3B, 5 acquires detection results from various sensors 61, 62, 63, 224, 42.

[0024] As shown in Figure 3, each of the steering controllers 3A, 3B mainly comprises a power supply circuit 30, an MCU 31, a motor drive circuit 32, an input / output protection circuit 33, an input conversion circuit 34, and an inspection circuit 35. The power supply circuit 30 is connected to a power supply 8 that is made redundant, for example, by a main power supply (for example, a battery) and a backup power supply. The power supply 8 comprises, for example, a drive system power supply, a DC-DC converter, a battery, a backup power supply, etc. It should be noted that the power supply 8 may be configured to include a battery.

[0025] The power supply 8 is configured to supply power individually to, for example, each of the controllers 3A, 3B, and 5. The power supply 8 and each of the power supply circuits 30 are connected when the ignition (key switch) is turned on, and disconnected when the ignition (key switch) is turned off, for example, by operation of a system switch 81. The system switch 81 is an example of a switch means that can be switched on and off (connected / disconnected).

[0026] MCU 31 is a microcontroller unit that executes various calculations using processor 31a. MCU 31 controls motor drive circuit 32 based on various sensor or command values. Motor drive circuit 32 supplies a control current to steering motor 221, which is the control target, in accordance with the control of MCU 31. The rotation angle and rotation speed of steering motor 221 are controlled by MCU 31 and motor drive circuit 32. Input / output protection circuit 33 is a circuit that protects MCU 31 mainly in communication between MCU 31 and CAN 100. Input conversion circuit 34 is a circuit that converts input signals from various sensors into signals suitable for the MCU.

[0027] The inspection circuit 35 is a circuit connected to the power supply 8, and is, for example, a circuit for checking whether a specified voltage is applied to the controller when the ignition is turned on. The inspection circuit 35 includes, for example, a relay switch that turns on when the ignition is turned on and off when the ignition is turned off, and a voltmeter that detects the voltage applied to the controller when the relay switch is on. The relay switch is an example of a switch means that can be switched on and off (connected / disconnected). The MCU 31 determines whether the ignition is on and the controller is connected to the power supply 8 based on the detection result (voltage value) of the inspection circuit 35. For example, the MCU 31 is configured not to start or operate when the detection result of the inspection circuit 35 is below a threshold voltage (including an undetected state due to the relay switch being off).

[0028] Left steering controller 3A controls left steering device 2A based on the detection results of steering sensor 42. Right steering controller 3B controls right steering device 2B based on the detection results of steering sensor 42. Each steering controller 3A, 3B calculates a target steering angle based on the detection results of steering sensor 42, and calculates a target control current based on the target steering angle. Each steering controller 3A, 3B supplies a control current to steering motor 221 of the corresponding steering device (left steering device 2A or right steering device 2B) based on the target control current.

[0029] More specifically, each steering controller 3A, 3B calculates a target yaw rate for the vehicle based on vehicle speed information, steering angle information, and steering operation amount information acquired from various sensors. Each steering controller 3A, 3B calculates a target steering angle so that the detection result of yaw rate sensor 61 approaches the target yaw rate. Note that the detection result of lateral acceleration sensor 63 may also be used in calculating the target steering angle.

[0030] The left steering controller 3A is configured to be able to detect abnormalities in the right steering controller 3B and the reaction force controller 5. The right steering controller 3B is configured to be able to detect abnormalities in the left steering controller 3A and the reaction force controller 5. The reaction force controller 5 is configured to be able to detect abnormalities in the left steering controller 3A and the right steering controller 3B. In this way, each of the controllers 3A, 3B, 5 is configured to be able to detect abnormalities in the controllers other than itself.

[0031] Specifically, each of the controllers 3A, 3B, and 5 calculates the target steering angles of both steered wheels, i.e., the target steering angle of the left front wheel 11 and the target steering angle of the right front wheel 12, based on the detection result of the steering sensor 42. Each of the controllers 3A, 3B, and 5 compares the calculation results with each other and determines whether or not there is an abnormality in the other controllers based on the comparison result.

[0032] For example, each of the controllers 3A, 3B, 5 may be configured to determine that one controller is abnormal if the calculation result of only one controller is significantly different from the calculation results of the other controllers (if the difference is greater than a predetermined threshold X). In this case, for example, if the target steering angle of left front wheel 11 calculated by the first controller is 0 degrees and the target steering angle of left front wheel 11 calculated by the second and third controllers is 10 degrees, the second and third controllers will determine that the first controller is abnormal (0 degrees < threshold X < 10 degrees).

[0033] Furthermore, each of the controllers 3A, 3B, and 5 may be configured to determine an expected calculation range of the target steering angle relative to the operation amount based on, for example, a preset relationship between the "operation amount of the steering wheel 41" and the "expected calculation range of the target steering angle," and to determine that a controller that produces a calculation result outside the expected calculation range is abnormal. Furthermore, each of the controllers 3A, 3B, and 5 may be configured to periodically output signals to each other, and a controller that does not output a signal for a certain period of time may be determined to be abnormal. In this way, each of the controllers 3A, 3B, and 5 performs the same calculation and monitors each other's calculation results and signals to determine whether or not a controller is abnormal.

[0034] Controller abnormalities occur due to, for example, an abnormality in the power supply system, an abnormality in the communication system (such as the CAN 100), a disconnection inside the controller, or a calculation error, etc. For example, an abnormality in one controller can be detected by other controllers when the calculation result is abnormal, the calculation result does not reach the other controller, or the calculation itself is not performed.

[0035] (Shut-off control) When the left steering controller 3A detects an abnormality in the right steering controller 3B, it executes right cut-off control to cut off the supply of control current to the right steering device 2B. The right cut-off control is control to cut off the supply of power to the steering motor 221 of the right steering device 2B. The right cut-off control may be, for example, control to forcibly turn off the system switch 81 between the right steering controller 3B and the power supply 8. The right cut-off control may also be control to forcibly turn off the relay switch of the inspection circuit 35 of the right steering controller 3B. Because the voltage applied to the relay switch of the inspection circuit 35 is smaller than the voltage applied to the system switch 81, it is relatively easy to execute on / off control for the inspection circuit 35.

[0036] The right cutoff control can be said to be control that cuts off the power supply to the right steering controller 3B and the right steering device 2B even when the ignition is on. In this way, when the left steering controller 3A detects an abnormality in the right steering controller 3B, it executes the right cutoff control to put the steering motor 221 of the right steering device 2B into a non-energized state (uncontrolled state) and put the right front wheel 12 into a free state. The right cutoff control can also be said to be control that prohibits (stops) the operation of the left steering controller 3A (control of the left steering device 2A by the left steering controller 3A).

[0037] Similarly, when the right steering controller 3B detects an abnormality in the left steering controller 3A, it executes left cutoff control to cut off the supply of control current to the left steering device 2A. The left cutoff control is control to cut off the power supply to the steering motor 221 of the left steering device 2A. The left cutoff control may be, for example, control to forcibly turn off the system switch 81 between the left steering controller 3A and the power source 8, or control to forcibly turn off the relay switch of the inspection circuit 35 of the left steering controller 3A. The left cutoff control can be said to be control to cut off the power supply to the left steering controller 3A even when the ignition is on. In this way, when the right steering controller 3B detects an abnormality in the left steering controller 3A, it executes left cutoff control to put the steering motor 221 of the left steering device 2A into a non-energized state (uncontrolled state) and put the left front wheel 11 into a free state. The left cutoff control can also be said to be control that prohibits (stops) the operation of the right steering controller 3B (control of the right steering device 2B by the right steering controller 3B).

[0038] When the reaction force controller 5 detects an abnormality in one of the left steering controller 3A and the right steering controller 3B, it executes target cut-off control to cut off the supply of control current to the steering device (left steering device 2A or right steering device 2B) that is the control target of that controller. The target cut-off control is the same as the left cut-off control when the left steering controller 3A is abnormal, and is the same as the right cut-off control when the right steering controller 3B is abnormal. Hereinafter, the right cut-off control, left cut-off control, and target cut-off control may be simply referred to as "cut-off control." The cut-off control is control performed by a normal controller, and can be said to be control that puts the steered wheels that are the control target of the controller that is determined to be abnormal into a free state.

[0039] If one of the steering controllers 3A, 3B is abnormal, the reaction force controller 5 and the other of the steering controllers 3A, 3B will execute the same shutoff control, but the shutoff control that was executed first will function effectively. Even if shutoff controls are executed simultaneously by two controllers, the shutoff control will function effectively. Even if a communication line is broken somewhere, the shutoff control of at least one of the controllers will function effectively, so that the abnormal controller can be put into a power-off state.

[0040] According to this embodiment, if an abnormality occurs in one controller, the other controller cuts off the supply of control current to the steering device controlled by that controller. As a result, no control current is supplied to the steered wheels corresponding to the abnormal controller, and those steered wheels are placed in a free state similar to driven wheels. After an abnormality is detected, the steered wheels that are placed in a free state follow the traveling direction secured by the normal steered wheels, i.e., the controlled steered wheels, due to self-aligning torque. This minimizes running resistance and prevents a decrease in running performance (straight-line running / turning performance).

[0041] (Steering control after cutoff control) In a state where right cut-off control is being executed, left steering controller 3A controls left steering device 2A based on the steering operation amount in manual driving or the command value in automatic driving (hereinafter also referred to as the "steering request value"), the detection result of left steering angle sensor 224, and the detection result of right steering angle sensor 224. In a state where left cut-off control is being executed, right steering controller 3B controls right steering device 2B based on the steering request value, the detection result of left steering angle sensor 224, and the detection result of right steering angle sensor 224. As both steering controllers 3A, 3B execute similar control, the control of left steering controller 3A will be described as an example.

[0042] Under normal circumstances, that is, when right cut-off control is not being executed, left steering controller 3A controls left steering device 2A based on the steering request value and the detection result of left steering angle sensor 224. In other words, under normal circumstances, left steering controller 3A controls left steering device 2A so that the actual steering angle of left front wheel 11 (hereinafter also referred to as "actual steering angle") calculated based on the detection result of left steering angle sensor 224 approaches the target steering angle of left front wheel 11 based on the steering request value.

[0043] With right cut-off control being executed, right front wheel 12 is in a free state and there is a possibility that a road surface disturbance will cause the right front wheel 12 to change its steering angle from the state in which it is driven by left front wheel 11. Left steering controller 3A acquires not only the detection result of left steering angle sensor 224 but also the detection result of right steering angle sensor 224, and calculates a target steering angle for left front wheel 11 taking into account changes in the steering angle of right front wheel 12.

[0044] For example, if a change occurs in the steering angle of right front wheel 12 in a free state due to a road disturbance while the vehicle is traveling straight with right cut-off control being executed, left steering controller 3A changes the target steering angle of left front wheel 11 in a controlled state so as to cancel out the change, that is, so that the actual yaw rate (hereinafter also referred to as "actual yaw rate") is maintained at the target yaw rate (0 in the case of traveling straight). Hereinafter, control that calculates the target steering angle of the normal steered wheels based on such a change in the steering angle of the steered wheels in a free state is also referred to as "steering angle correction control."

[0045] In the steering angle correction control, for example, when traveling straight, if the steering angle of right front wheel 12 changes from 0 degrees to 5 degrees to the right due to a road disturbance, left steering controller 3A detects the change and changes the target steering angle of left front wheel 11 from 0 degrees to the left, for example, 5 degrees, so that the actual yaw rate is maintained at the target yaw rate. This makes it possible to respond to unintended steering of right front wheel 12 (steering that does not conform to the steering request value due to a road disturbance) at an early stage, for example, before the actual yaw rate changes.

[0046] Like left steering controller 3A, right steering controller 3B acquires not only the detection result of right steering angle sensor 224 but also the detection result of left steering angle sensor 224 and calculates the target steering angle of right front wheel 12 taking into account changes in the steering angle of left front wheel 11. In this way, each of steering controllers 3A, 3B is configured to be able to execute steering angle correction control.

[0047] The amount of correction of the target steering angle performed by the steering angle correction control can be set, for example, based on the "amount of change in steering angle" of the steered wheels in a free state and the "vehicle speed." Each steering controller 3A may store a map showing the relationship between the amount of change in steering angle and the amount of correction for each vehicle speed (for example, a low speed range map, a medium speed range map, a high speed range map, etc.).

[0048] Even with correction control that is normally performed, i.e., control that corrects the target steering angle based on changes in the actual yaw rate (hereinafter also referred to as "yaw rate correction control"), it is possible to compensate for changes in the steering angle of the steered wheels in a free state due to road disturbances. With yaw rate correction control, it is possible to change the target steering angle of the normally steered wheels in response to changes in the actual yaw rate so that the actual yaw rate is maintained at the target yaw rate, thereby maintaining the direction of travel. Furthermore, as correction control, control that corrects the target steering angle based on changes in actual lateral acceleration detected by lateral acceleration sensor 63 (hereinafter also referred to as "lateral acceleration correction control") may be performed.

[0049] However, yaw rate correction control and lateral acceleration correction control are only executed after the yaw rate or lateral acceleration actually changes, i.e., after the vehicle behavior state changes, and unintended changes in the steering angle can easily cause the vehicle to stagger in its traveling direction. In this embodiment, before yaw rate correction control and lateral acceleration correction control are executed, steering angle correction control is executed for the normal steered wheels based on the detected steering angle of the steered wheels in the free state. This allows compensation for unintended changes in the steering angle to be made relatively quickly. Therefore, it is possible to suppress stagger in the traveling direction of the vehicle due to unintended changes in the steering angle of the steered wheels in the free state. Note that because each steering controller 3A, 3B is configured to execute steering angle correction control, it is also possible to configure it not to execute yaw rate correction control and lateral acceleration correction control. However, by configuring each steering controller 3A, 3B to be able to execute steering angle correction control, yaw rate correction control and / or lateral acceleration correction control, more precise steering control is possible.

[0050] To explain one example of the control flow, as shown in Figure 4, controllers 3A, 3B, 5 monitor each other's status and determine whether or not there is an abnormality in the controller (S1). If one of steering controllers 3A, 3B is abnormal (S1: Yes), the other of steering controllers 3A, 3B and / or reaction force controller 5 executes cut-off control (S2). Hereinafter, one of steering controllers 3A, 3B in which an abnormality has been detected will be referred to as the "abnormal controller," the steered wheel controlled by the abnormal controller will be referred to as the "abnormal wheel," the other of steering controllers 3A, 3B which is normal will be referred to as the "normal controller," and the steered wheel controlled by the normal controller will be referred to as the "normal wheel." The cut-off control cuts off power to steering motor 221 which steers the abnormal wheel, and the abnormal wheel becomes free.

[0051] With the cut-off control being executed, the normal controller acquires the detection results of each steering angle sensor 224, and acquires not only information on the steering angles of normal wheels but also information on the steering angles of abnormal wheels (S3). The normal controller also acquires the detection results of steering sensor 42 and the detection results of the vehicle speed sensor (wheel speed sensor 62) (S4). The normal controller calculates a target yaw rate and a target steering angle for normal wheels based on the information on the steering angle of the abnormal wheel, information on the steering operation amount, and information on the vehicle speed (S5). The normal controller controls steering motor 221, which steers the normal wheels, based on the target steering angle (S6). In this embodiment, the controller executes feedback control based on the target value and the detected value of the sensor. In this way, by executing control that takes into account the steering angle of the abnormal wheel that has become free, control delay is reduced, disturbance in the vehicle's traveling direction is suppressed, and driving performance during abnormal conditions is further improved.

[0052] (Kingpin offset and caster trail) The steering system 1 of this embodiment is mounted on a vehicle configured so that the kingpin offset δ1 and caster trail δ2 are 0. In this embodiment, the suspension device 9 is designed so that the kingpin offset δ1 and caster trail δ2 are substantially 0.

[0053] As shown in FIG. 2, the kingpin axis KP is a straight line passing through the center of the upper support 94 and the center of the ball joint 911. If the longitudinal direction of the vehicle is defined as the X direction, the lateral direction of the vehicle is defined as the Y direction, and the vertical direction of the vehicle is defined as the Z direction, the kingpin offset δ1 is the distance between the intersection of the kingpin axis KP and the ground contact patch and the ground contact patch center SC in the YZ plane as shown in FIG. 5. The ground contact patch is the tire's contact surface with the road surface. The caster trail δ2 is the distance between the intersection of the kingpin axis KP and the ground (road surface) and the ground contact patch center SC in the XZ plane as shown in FIG. 6. Such a configuration is described, for example, in JP 2022-11895 A.

[0054] When the vehicle is stopped (when the vehicle is not bouncing or rebounding), if kingpin offset δ1 and caster trail δ2 are 0, no moment is generated around kingpin axis KP due to the vehicle weight. In this case, even if no control current is supplied to each steering motor 221, the steering angle will be 0 degrees (neutral position, straight-ahead position). In other words, in this case, there is no need to supply power to each steering motor 221 when the vehicle is traveling straight. This configuration is preferable from the perspective of energy conservation, and is an easy-to-control configuration because the abnormal wheel functions as a simple driven wheel even when cut-off control is executed.

[0055] When caster trail δ2 is 0, the self-aligning torque is smaller than when caster trail δ2 is not 0. However, because self-aligning torque is generated in the tires due to the pneumatic trail, the abnormal wheel that has become free can follow the direction of travel of the normal wheel. In this way, steering system 1 is preferably installed in a vehicle configured so that kingpin offset δ1 and caster trail δ2 are 0 when the vehicle is stopped, for example, in a vehicle that does not need to supply control current to left and right steering motors 221 when the vehicle is traveling straight.

[0056] On the other hand, when kingpin offset δ1 and caster trail δ2 are not zero when the vehicle is stopped, as in a typical vehicle, in a single-wheel independent steering configuration, each steering angle will be in a toe-in state (angled toward the inside of the vehicle from 0 degrees) due to the vehicle weight. According to this, in order to maintain each steering angle at 0 degrees when traveling straight, each steering controller 3A, 3B needs to continue supplying control current to the corresponding steering motor 221. In this configuration, when cut-off control is executed, a force that tries to toe-in is constantly applied to the abnormal wheel that has become free. Therefore, the normal controller needs to calculate a target steering angle for the normal wheel that takes into account the force in the toe-in direction of the abnormal wheel.

[0057] For example, if the vertical relative position of the vehicle body with respect to the wheels when the vehicle is stopped and neither bouncing nor rebounding is defined as the standard position, the suspension device 9 may be configured so that the kingpin offset δ1 and caster trail δ2 are 0 in a range from 1 / 2 the position in a full bound state to 1 / 2 the position in a full rebound state, sandwiching the standard position.

[0058] Furthermore, since the wheel drive device of this embodiment is an in-wheel motor unit 7, the drive force is input to the ground contact point. As a result, no moment around the kingpin axis KP is generated by the drive force, and deviation in the traveling direction caused by the drive force applied to the wheel is prevented. The steering system 1 of this embodiment can also be applied to vehicles that employ an on-board drive system in which the drive source is located on the vehicle body rather than on the wheels, and the drive force is transmitted to the wheels via a drive shaft or the like. However, with an on-board drive system, the drive force is applied to the wheel center, so a moment around the kingpin axis KP is generated depending on the offset amount and speed. Therefore, with this configuration, steering control that takes this moment into consideration is required. When applying the steering system 1 to an on-board drive system, a configuration with a small wheel center kingpin offset is preferable.

[0059] (others) The present invention is not limited to the above embodiment. For example, monitoring and detection of controller abnormalities may be performed between two steering controllers 3A, 3B without reaction force controller 5. Furthermore, when autonomous driving is performed in a vehicle, each steering controller 3A, 3B controls the corresponding steering device based on command values ​​(e.g., target steering angle and target yaw rate) transmitted from an autonomous driving ECU instead of the detection result (steering operation amount) of steering wheel 41. Furthermore, in an autonomous driving vehicle, operation device 4 can be omitted. Furthermore, in-wheel motor unit 7 may be provided on all wheels 11 to 14 or rear wheels 13, 14. [Explanation of symbols]

[0060] 1...Steering system, 2A...Left steering device, 2B...Right steering device, 224...Rotation angle sensor (left steering angle sensor, right steering angle sensor), 3A...Left steering controller, 3B...Right steering controller, 4...Operation device, 41...Steering wheel (operation member), 42...Steering sensor (operation amount sensor), 43...Reaction force imparting device, 5...Reaction force controller, 7...In-wheel motor unit, 9...Suspension device

Claims

1. a left steering device that steers the left steering wheel; a right steering device that steers right steered wheels independently of the left steering device; a left steering controller that controls the left steering device; a right steering controller that controls the right steering device; a left steering angle sensor for detecting the steering angle of the left steered wheel; a right steering angle sensor for detecting the steering angle of the right steered wheel; A single-wheel independent steering type steering system comprising: the left steering controller is configured to be able to detect an abnormality in the right steering controller, and when an abnormality in the right steering controller is detected, executes right cut-off control to cut off the supply of control current to the right steering device; the right steering controller is configured to be able to detect an abnormality in the left steering controller, and when an abnormality in the left steering controller is detected, executes left cut-off control to cut off the supply of control current to the left steering device; the left steering controller controls the left steering device based on a steering request value that is an operation amount of an operation member in manual driving or a command value in automatic driving, a detection result of the left steering angle sensor, and a detection result of the right steering angle sensor in a state where the right cutoff control is executed, the right steering controller controls the right steering device based on the steering request value, the detection result of the left steering angle sensor, and the detection result of the right steering angle sensor in a state in which the left cut-off control is executed. Steering system.

2. The operating member is operated by a driver for steering; an operation amount sensor that detects an operation amount of the operation member; a reaction force applying device that applies a reaction force to the operating member; a reaction force controller that controls the reaction force application device based on a detection result of the operation amount sensor; Equipped with the left steering controller controls the left steering device based on the detection result of the operation amount sensor, the right steering controller controls the right steering device based on the detection result of the operation amount sensor, the reaction force controller is configured to be able to detect an abnormality in the left steering controller and an abnormality in the right steering controller, and when an abnormality is detected in one of the left steering controller and the right steering controller, executes target cut-off control to cut off the supply of control current to a steering device that is a control target of the one controller, that is, the abnormal controller; The supply of control current to the steering device that is the control target of the abnormal controller is cut off by one of the left steering controller and the right steering controller that is not the abnormal controller, and / or by the reaction force controller. The steering system of claim 1 .

3. the right cutoff control is control that prohibits operation of the right steering controller, The left cutoff control is a control that prohibits operation of the left steering controller. The steering system of claim 1 .

4. The vehicle is mounted on a vehicle configured so that the kingpin offset and caster trail are zero. A steering system according to any one of claims 1 to 3.

Images