Vehicular steering system

Abstract

To improve the practicability of a vehicular steering system mounted on a plural wheel independent steering vehicle.SOLUTION: A steering system is configured in such a manner that, in one wheel improper steering state where one of steerable plural wheels 10F is an improper steering wheel 10FD improper in steering, for securing a total lateral force FCFREF of the lateral forces to be generated by each of the plural wheels in accordance with a steering request, at least one of the one or more wheels other than the improper steering wheel in the plural wheels is determined to be a steering compensation wheel 10FC, and a target steering amount δC* about the steering compensation wheel is changed.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a steering system mounted on a vehicle. [Background technology]

[0002] Regarding the control of a vehicle having multiple actuators, for example, there is a technology described in the following Patent Document. In this technology, the three tire components are calculated by a quadratic programming method using an effective constraint method based on the six center of gravity forces, and the vehicle is controlled by the multiple actuators based on the three tire components. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-165535 Summary of the Invention [Problem to be solved by the invention]

[0004] Recently, for example, vehicles in which a plurality of wheels are steered independently by a plurality of actuators are being developed. The technology described in the above patent document can be applied to this vehicle. On the other hand, for example, a situation in which one of the plurality of wheels cannot be steered properly due to a failure of one of the plurality of actuators is expected. However, it is difficult to deal with such a situation with the above technology. Therefore, if it is possible to deal with such a situation, it is possible to improve the practicality of a vehicle steering system mounted on a vehicle in which a plurality of wheels can be steered independently (hereinafter, sometimes referred to as a "multiple-wheel independently steered vehicle"). The present invention has been made in view of such a situation, and an object of the present invention is to provide a vehicle steering system with high practicality. [Means for solving the problem]

[0005] In order to solve the above problems, the vehicle steering system of the present invention comprises: A vehicle steering system mounted on a vehicle having a plurality of steerable wheels, A wheel steering device that steers the plurality of wheels independently of one another; a controller that controls the wheel steering device so that the steering amount of each of the plurality of wheels becomes a target steering amount determined for each of the plurality of wheels in response to a steering request; Equipped with The controller: In a one-wheel improperly steering state in which one of the plurality of wheels is an improperly steered wheel that is improperly steered in steering, in order to ensure a total lateral force, which is the sum of the lateral forces that each of the plurality of wheels should generate, in response to the steering request, at least one of the plurality of wheels, excluding the improperly steered wheel, is designated as a steering compensation wheel, and a target steering amount for the steering compensation wheel is changed. Effect of the Invention

[0006] According to the vehicle steering system of the present invention, in the above-mentioned one-wheel improper steering state, the target steering amount for the steering compensation wheel is changed, thereby ensuring a total lateral force according to the steering request. As a result, even in the above-mentioned one-wheel improper steering state, the vehicle can be properly steered and turned.

[0007] The "steering amount" in the vehicle steering system of the present invention (hereinafter sometimes simply referred to as the "steering system") means the steering angle of the wheels (turning angle, toe angle), the amount of operation of a steering member that operates in response to the steering of the wheels, etc. The "wheel steering device" may be, for example, a device equipped with a steering actuator for each wheel. Also, the steering system of the present invention may be a so-called steer-by-wheel type steering system. The "steering request" is a concept of how much turning the vehicle is to be performed, regardless of whether the vehicle is automatically driven or driven by a driver, and in a vehicle driven by a driver, it can be considered to be indicated, for example, by the amount of operation of a steering operation member (for example, the operation angle of the steering wheel).

[0008] The "controller" of this steering system may be configured to include a computer, a drive circuit (driver) for the drive source of the wheel turning device, etc. The controller controls the wheel turning device so that the steering amount of each of the multiple wheels becomes the target steering amount determined for each of the multiple wheels in response to a steering request. In other words, the controller executes steering control. Specifically, this steering control determines, for example, a target steering amount for each wheel based on the steering request, determines a steering force (e.g., steering torque) to be applied to the wheels based on the deviation of the actual steering amount of each wheel from the target steering amount, and, if the wheel turning device includes an electric motor as a drive source, supplies a current corresponding to the steering force to the electric motor.

[0009] An improperly steered wheel that is improperly steered means, for example, a wheel with an excessive difference between a target steering amount and an actual steering amount, a wheel to which steering force cannot be applied, a wheel to which insufficient or excessive steering force is applied, etc. When the wheel steering device has an electric motor as a drive source, a state in which no current is supplied to the electric motor or the actual current supplied deviates from the current that should be supplied due to a malfunction or failure of the drive circuit corresponds to a one-wheel improper steering state.

[0010] The process for dealing with the one-wheel improper steering state can be called one-wheel improper steering state dealing process (hereinafter, sometimes simply referred to as "dealing process"). The dealing process in this steering system is a process for changing the target steering amount of the wheels that are not improperly steered wheels in order to ensure the total lateral force according to the steering request in accordance with the steering request. Specifically, for example, in a case where the lateral force that the improperly steered wheels should generate is insufficient, the target steering amount of the steering compensation wheel is changed in order to make up for the shortage by generating an extra force in the steering compensation wheel. If the total lateral force can be properly ensured, it is possible to properly turn or rotate the vehicle. Note that the "sideways force" referred to here means a general lateral force generated by the wheels, and is a concept including a cornering force, a lateral force, and the like. In this steering system, either a cornering force or a lateral force may be adopted as the lateral force.

[0011] The number of steerable wheels and the number of steering compensation wheels in a vehicle equipped with this steering system are not particularly limited. More specifically, the number of steerable wheels may be two or more, and the number of steering compensation wheels may be one or more. For example, in a vehicle having four wheels, front, rear, left and right, where the four wheels are steerable wheels, two or more wheels can be steering compensation wheels. In that case, compensation for the total lateral force may be appropriately distributed to two or more steering compensation wheels. To illustrate a specific embodiment, in a case where the vehicle has four wheels, front, rear, left and right, and the wheels that can be steered are the left and right front wheels, the controller may be configured to change the target steering amount for the other of the left and right front wheels as the steering compensation wheel when one of the left and right front wheels is an improperly steered wheel in a one-wheel improper steering state.

[0012] Regarding a specific processing mode of the response processing, the controller can be configured to estimate an improper lateral force, which is a lateral force generated by the improperly steered wheel in a one-wheel improperly steered state, and change a target steering amount of the steering compensation wheel based on the estimated improper lateral force. The improper lateral force may be estimated based on an actual steering amount of the improperly steered wheel, or based on a steering force applied to the improperly steered wheel. In the former case, there is a possibility that the improper lateral force cannot be accurately estimated due to a delay in steering the improperly steered wheel. In contrast, in the latter case, it is possible to estimate the improper lateral force taking into account a delay in steering the improperly steered wheel. When the driving source for steering the wheel is an electric motor, the steering force applied to the improperly steered wheel may be estimated from a supply current supplied to the electric motor. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagram conceptually showing an overall configuration of a vehicle steering system according to an embodiment of the present invention; [Diagram 2] 1 is a perspective view showing a wheel arrangement module provided in a vehicle equipped with a vehicle steering system according to an embodiment of the present invention; [Diagram 3] 5 is a flowchart of a target steering angle determination processing program and a single wheel steering processing program executed in the vehicle steering system of the embodiment. [Figure 4] FIG. 4 is a schematic diagram showing a target steering angle determination map, a two-wheel model, and a wheel turning motion model of a steering system, which are referred to in the target steering angle determination process; [Diagram 5] 10 is a flowchart of a one-wheel improper steering state response process subroutine that constitutes the target steering angle determination process program. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a vehicle steering system according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition to the following embodiment, the present invention can be embodied in various forms including those described in the above section on "Modes of the Invention" and various modifications and improvements based on the knowledge of those skilled in the art. EXAMPLES

[0015] [A] Configuration of vehicle steering system The vehicle steering system of the embodiment (hereinafter, sometimes simply referred to as the "steering system") is a so-called steer-by-wire type steering system. As shown in FIG. 1, the steering system is mounted on a vehicle having left and right front wheels 10FL, 10FR and left and right rear wheels 10RL, 10RR. The left and right front wheels 10FL, 10FR are steerable wheels, and the left and right rear wheels 10RL, 10RR are non-steerable wheels. The wheel turning device 12 that steers the left and right front wheels 10FL, 10FR includes a left wheel turning device 12L that steers the left front wheel 10FL and a right wheel turning device 12R that steers the right front wheel 10FR. Furthermore, the steering system includes an operating device 14 for receiving operations from the driver, a pair of steering electronic control units (hereinafter sometimes abbreviated as "steering ECUs") 16L, 16R for controlling the left wheel steering device 12L and the right wheel steering device 12R, respectively, and an operation electronic control unit (hereinafter sometimes abbreviated as "operation ECU") 18 for controlling the operating device 14 and overseeing the pair of steering ECUs 16.

[0016] In the following description, when it is not necessary to distinguish between the left and right front wheels 10FL, 10FR, each of them will be collectively referred to as the front wheel 10F, when it is not necessary to distinguish between the left and right rear wheels 10RL, 10RR, each of them will be collectively referred to as the rear wheel 10R, and when it is not necessary to distinguish between the front wheels 10F and the rear wheels 10R, each of them will be collectively referred to as the wheel 10. As mentioned above, the wheel turning device 12 includes the left wheel turning device 12L and the right wheel turning device 12R, and when it is not necessary to distinguish between the left wheel turning device 12L and the right wheel turning device 12R, each of them will be collectively referred to simply as the wheel turning device 12. Similarly, when it is not necessary to distinguish between the pair of steering ECUs 16L, 16R, each of them will be collectively referred to as the steering ECU 16. Furthermore, various parameters for the left and right front wheels 10FL, 10FR, which will be described later, may be referred to collectively by omitting the L and R in the reference characters when there is no need to distinguish between left and right.

[0017] Each wheel turning device 12 is incorporated in a wheel installation module 20, which will be described in detail later. The pair of steering ECUs 16 and operation ECUs 18 are each connected to a CAN (car area network or controllable area network) 22 and are capable of communicating with each other via the CAN 22. In this steering system, the pair of steering ECUs 16, operation ECUs 18 and CAN 22 can be considered to constitute a controller that controls one wheel turning device 12 including the left wheel turning device 12L and the right wheel turning device 12R.

[0018] As shown in FIG. 2, the wheel installation module (hereinafter sometimes simply referred to as "module") 20 is configured to include a MacPherson suspension device, and is a module for installing the front wheel 10F on the vehicle body. Incidentally, FIG. 2 shows the module 20 for the left front wheel 10FL. The module 20 has a wheel drive unit 24 (also called an "in-wheel motor") as a wheel rotation drive device, and its housing 24a holds the front wheel 10F rotatably about the wheel axis WL, and also functions as a steering knuckle in the wheel turning device 12. Hereinafter, this housing 24a may be referred to as the knuckle 24a.

[0019] This module 20 has the above-mentioned wheel turning device 12 (either the left wheel turning device 12L or the right wheel turning device 12R). The wheel turning device 12 is a single-wheel independent steering device for steering one of the left and right front wheels 10F independently of the other. The wheel turning device 12 is generally configured to include the knuckle 24a described above, a steering actuator 46 disposed on the lower arm 26 at a position close to the base end of the lower arm 26, and a tie rod 48 connecting the steering actuator 46 and the knuckle 24a.

[0020] The steering actuator 46 includes a steering motor 46a, which is an electric motor serving as a drive source, a reduction gear 46b that reduces the speed of rotation of the steering motor 46a, and an actuator arm 46c that is rotated by the rotation of the steering motor 46a via the reduction gear 46b and functions as a pitman arm. A base end of a tie rod 48 is connected to the actuator arm 46c, and a tip end of the tie rod 48 is connected to the knuckle arm 24b.

[0021] In this wheel steering device 12, by operating the steering motor 46a, the actuator arm 46c of the steering actuator 46 rotates about the actuator axis AL, as shown by the thick arrow in the figure. The rotation is transmitted by the tie rod 48, and the knuckle 24a is rotated about the kingpin axis KP.

[0022] The operation device 14 has a general structure in a steer-by-wire type steering system. To put it simply, as shown in Fig. 1, the operation device 14 includes a steering wheel 56 as a steering operation member steered by a driver, and a reaction force imparting device 60 that imparts an operation reaction force to the steering wheel 56. The reaction force imparting device 60 includes a reaction force motor 62 that is an electric motor as a power source, and a reducer 64 for transmitting the force of the reaction force motor 62 to the steering wheel 56.

[0023] Each steering ECU 16 is configured to include a computer having a CPU, ROM, RAM, etc., and a driver (drive circuit) for steering motor 46a, and operation ECU 18 is configured to include a computer having a CPU, ROM, RAM, etc., and a driver (drive circuit) for reaction motor 62. Both steering motor 46a and reaction motor 62 are three-phase brushless DC motors, and the respective drivers of steering ECU 16 and operation ECU 18 are inverters.

[0024] The motor rotation angle (rotation phase) of the steering motor 46a is the steering motor rotation angle δ M and the steering angle δ, which is the amount of steering from the neutral position of the wheel 10 (the position where the wheel 10 should be when the vehicle is traveling straight), have a specific reduction ratio relationship. MR , δ ML Based on this, the steering angle δ of the left front wheel 10L and the right front wheel 10R is L , δ R Similarly, the reaction motor rotation angle θ M and the operation angle θ, which is the amount of operation from the neutral position of the steering wheel 56 (the position where the steering wheel 56 should be located when the vehicle is moving straight ahead), have a specific reduction ratio relationship. M Based on this, the control unit 54 has a function of detecting the operation angle θ of the steering wheel 56.

[0025] [B] Wheel steering control in vehicle steering systems In this steering system, in order to steer the left and right front wheels 10FL, 10FR, the operation ECU 18 and the pair of steering ECUs 16 execute a target steering angle determination process and a single wheel steering process, respectively. L , δ R The target steering angle δ L * , δ R * In the single wheel steering process, the steering angle δ of one front wheel 10F is set to the target steering angle δ * This is a process for operating the steering motor 46a so that the steering angle becomes equal to the target steering angle. The target steering angle determination process and the single wheel steering process will be described in detail below, along with a process for dealing with the case where the left and right front wheels 10FL, 10FR become inappropriate. Note that in order to give the driver an appropriate steering feel, the operation ECU 18 executes an operation reaction force control in which the reaction force application device 60 applies an operation reaction force to the steering wheel 56, but a description of this control will be omitted.

[0026] (a) Target steering angle determination process The target steering angle determination process is performed by the operation ECU 18 repeatedly executing a target steering angle determination program, the flowchart of which is shown in Fig. 3, at short time intervals (for example, several to several tens of µsec). Explaining according to this flowchart, in the target steering angle determination process, first, in step 1 (hereinafter abbreviated as "S1", the same applies to the other steps), the vehicle's running speed (hereinafter sometimes referred to as "vehicle speed") V is acquired via the CAN 22 from the vehicle's brake system (not shown). Incidentally, the vehicle speed V is calculated by multiplying the rotation speed V of each wheel 10 by the following formula: W Next, in S2, the motor rotation angle θ of the reaction force motor 62 is detected based on M The operation angle θ of the steering wheel 56 is detected based on the above.

[0027] In the next step S3, the target steering angles δ of the left and right front wheels 10FL, 10FR are calculated based on the steering angle θ. L * , δ R * To explain in detail, this steering system is a vehicle speed-sensitive steering system, and the higher the vehicle speed V, the larger the target steering angle δ becomes even if the operation angle θ is the same. L * , δ R * Specifically, a target steering angle determination map as shown in FIG. 4(a) is referenced, and the target steering angle δ L * , δ R * is determined.

[0028] Then, in S4, it is determined whether or not one of the left and right front wheels 10FL, 10FR is in an improperly steered state, i.e., a one-wheel improperly steered state. In other words, it is determined whether or not one of the left and right front wheels 10FL, 10FR is an improperly steered wheel that is improperly steered. If it is in a one-wheel improperly steered state, a one-wheel improperly steered state response process is executed in S5. The one-wheel improperly steered state and the one-wheel improperly steered state response process will be described in detail later.

[0029] The target steering angle δ determined in S3 or changed in S5 L * , δ R * In S6, this is transmitted to the steering ECUs 16L, 16R via the CAN 22. After this transmission, one execution of this program is terminated.

[0030] (b) Single wheel steering process The single wheel steering process is performed by each of the steering ECUs 16L, 16R corresponding to the left and right front wheels 10FL, 10FR repeatedly executing a single wheel steering process program shown in the flowchart in Fig. 3 at short intervals (for example, several to several tens of μsec). Explaining according to this flowchart, in the single wheel steering process performed by each steering ECU 16, first, in S11, the operation ECU 18 transmits the target steering angle δ * In the next step S12, the actual steering angle δ of the front wheels 10F is detected, and in step S13, the target steering angle δ is obtained. * The deviation of the steering angle δ with respect to the * -δ) is specified.

[0031] Next, in S14, a target steering torque T, which is a steering torque T required to steer the front wheels 10F, is calculated according to the following formula: * The steering torque T is a type of steering force, and is a torque around the kingpin axis KP. In the following formula, the target steering torque T is determined according to the PID control law based on the steering angle deviation Δδ. * By the way, G in the following equation is determined. P ,G I ,G D are the proportional gain, integral gain, and differential gain, respectively.

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[0032] The turning torque T can be considered to be approximately proportional to the turning current I, which is the current supplied to the turning motor 46a. Accordingly, the target turning torque T determined in S15 is * The steering current determination coefficient K I By multiplying this, the target steering current I is obtained. * Then, in S16, the target steering current I * Based on this, current is supplied to the steering motor 46a, and one execution of this program is terminated.

[0033] (c) Dealing with one wheel improper steering condition It should be assumed that one of the pair of front wheels 10F may be unable to be properly steered due to some cause, such as a failure in the drive circuit of the steering motor 46a. In this steering system, in a one-wheel improper steering state in which one of the pair of front wheels 10F is an improperly steered wheel, the other front wheel 10F is used as a steering compensation wheel, and the target steering angle δ of that front wheel 10F is set to 1 / 100. * The system is designed to address this situation by modifying the

[0034] As described above, whether or not one wheel is in an improperly steered state is determined in S4 of the target steering angle determination process. As a prerequisite, when the front wheel 10F becomes an improperly steered wheel, the steering ECU 16 corresponding to that front wheel 10F determines that the front wheel 10F is in an improperly steered state. In short, the target steering angle δ of the corresponding front wheel 10 is * and the actually detected steering angle δ are greater than the threshold difference for a certain period of time, or when the target steering current I * and the current I actually being supplied is greater than the threshold difference and continues for a certain period of time, the front wheel 10F is determined to be an improperly steered wheel. When a wheel is determined to be an improperly steered wheel, the steering ECU 16 that determined it transmits a notice to the operation ECU 18. Based on the result of the determination, the operation ECU 18 determines that the steering system is in a one-wheel improperly steered state.

[0035] As described above, when one wheel is in an improperly steered state, one wheel improperly steered state response process (hereinafter sometimes referred to as "response process") is performed in S5 of the target steering angle determination process. This response process is performed by the operation ECU 18 executing a response process subroutine whose flowchart is shown in Fig. 5. Before describing the process according to this subroutine, a general theory regarding steering of the wheels 10 will be described.

[0036] With reference to the two-wheel model shown in FIG. 4(b), in a vehicle in which only the front wheels 10F can be steered, a front wheel cornering force F as shown in the following formula is generated for each of the front wheels 10F and the rear wheels 10R in response to the steering of the front wheels 10F: CF ,Rear wheel cornering force F CR In the following equation, β is the vehicle slip angle, γ is the vehicle yaw rate, and l F is the distance in the front-rear direction between the axle line of the front wheel 10F and the center of gravity of the vehicle (hereinafter, sometimes simply referred to as the "distance between the front wheel centers of gravity"); R is the distance in the front-rear direction between the axle line of the rear wheel 10R and the center of gravity of the vehicle (hereinafter, sometimes simply referred to as the "distance between the rear wheel centers of gravity"); K F is the front wheel cornering stiffness, K R is the rear wheel cornering stiffness. The front wheel cornering force F CF ,Rear wheel cornering force F CR are types of lateral forces generated by one front wheel 10F and one rear wheel 10R, respectively.

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[0037] If we consider the vehicle as a whole, the following formula holds: m is the weight of the vehicle (hereinafter sometimes referred to as "vehicle weight").

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[0038] On the other hand, for the turning of a four-wheeled vehicle in which only the front wheels 10F are steered, the following two fundamental equations also hold: J is the moment of inertia of the vehicle around the vertical axis.

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[0039] In the process according to the corresponding process subroutine, first, in S21, it is determined whether or not one of the left and right front wheels 10FL, 10FR is the improperly steered wheel, and the other wheel that is not the improperly steered wheel is determined as the steering compensation wheel. In the following description, the improperly steered wheel may be referred to as 10FD, and the steering compensation wheel may be referred to as 10FC. The steering angle and target steering angle of the improperly steered wheel 10FD may be respectively designated as δ D , δ D * The steering angle and the target steering angle of the steering compensation wheel 10FC are respectively δ C , δ C * It may be written as follows.

[0040] Next, in S22, the target steering angles δ of the left and right front wheels 10FL, 10FR determined in S3 are L * , δ R * are specified, and the target steering angle δ of 1 is calculated by, for example, calculating the average, assuming that they are equal. * Then, in S23, the above two equations (6) and (7) are regarded as simultaneous equations, and the target steering angle δ * By solving these based on the above, the standard yaw rate γ REF , Standard vehicle slip angle β REF Next, in S24, the standard yaw rate γ REF , Standard vehicle slip angle β REF and the target steering angle δ *Based on this, the cornering forces F that should be generated by the left and right front wheels 10FL, 10FR are calculated according to the above formula (2). CF Standard front wheel cornering force F CFREF The standard front wheel cornering force F CFREF Multiplying this by two is the cornering force that should be generated by the entire front wheel 10F, that is, the total standard front wheel cornering force as the total lateral force.

[0041] In the next step S25, the cornering force actually generated by the improperly steered wheel 10FD, that is, the improperly steered wheel cornering force F CFD is estimated. There are two possible methods for this estimation, and either method may be adopted in S25. The two methods are described below.

[0042] The first method is to calculate the actual yaw rate γ, the actual vehicle slip angle β, and the actual steering angle δ of the improperly steered wheel 10FD. D Based on this, the improper turning wheel cornering force F CFD Specifically, this is a method according to the above formula (2). D is the steering motor rotation angle δ M As shown in FIG. 1, the vehicle is provided with a yaw rate sensor 66 and a lateral acceleration sensor 68, and the actual yaw rate γ is detected based on the detection value of the yaw rate sensor 66. The rate of change of the vehicle body slip angle β is calculated according to the above formula (5) based on the actual yaw rate γ and the actual lateral acceleration G detected based on the detection value of the lateral acceleration sensor 68. Y Therefore, the actual vehicle body slip angle β can be estimated based on the rate of change of the estimated vehicle body slip angle β.

[0043] The second method is a method of estimation according to the following equation (8). Incidentally, the following equation (8) is a state equation based on the wheel turning motion model of FIG. 4(c). In the following equation, J Sis the moment of inertia of the wheel 10 about the kingpin axis, and C S represents the damping coefficient in the steering operation, and ξ represents the pneumatic trail.

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[0044] The steering torque T, which is the steering force, can be determined from the steering current I actually supplied to the steering motor 46a. D From the change in and the actual steering current I, the improper steering wheel cornering force F CFD The second method is a method for estimating the improperly steered wheel cornering force F by predicting the change in the steering angle δ of the improperly steered wheel 10FD in the near future. CFD This method allows for estimation without delay, in other words, estimation that takes into account the steering delay.

[0045] Improper steering wheel cornering force F CFD After estimating the above, in S26, the steering compensation wheel cornering force F CFC Specifically, the cornering force to be generated by the entire front wheel 10F, that is, the standard front wheel cornering force F CFREF That is, the total standard front wheel cornering force minus the improper steering wheel cornering force F CFD By reducing the steering compensation wheel cornering force F CFC Determine.

[0046] In the following S27, the steering compensation wheel cornering force F CFC Based on this, the target steering angle δ of the steering compensation wheel 10FC is calculated according to the above formula (2). C *At this time, the actual yaw rate γ and the actual vehicle body slip angle β are used. Then, in S28, the target steering angle δ of one of the left front wheel 10FL and the right front wheel 10FR, which are the steering compensation wheels 10FC, is determined. * From the value determined in S3, the target steering angle δ of the steering compensation wheel 10FC is calculated. C * is replaced by the value determined as

[0047] By the above-described response process, in the one-wheel improper steering state, the target steering amount δ * By changing the steering angle, the cornering force that the front wheels 10F should generate as a whole in response to the steering request is ensured. As a result, the vehicle can be properly steered and turned even when one wheel is in an improper steering state. [Explanation of symbols]

[0048] 10: Wheel 10F: Front wheel 10FD: Improperly steered wheel 10FC: Steering compensation wheel 10R: Rear wheel 12: Wheel steering device 14: Operation device 16: Steering electronic control unit (steering ECU) [controller] 18: Operation electronic control unit (operation ECU) [controller] 20: Wheel arrangement module 22: CAN 24: Wheel drive unit 24a: Housing [steering knuckle] 24b: Knuckle arm 46: Steering actuator 46a: Steering motor [electric motor] [drive source] 48: Tie rod 56: Steering wheel [steering operation member] 66: Yaw rate sensor 68: Lateral acceleration sensor KP: Kingpin axis V: Vehicle travel speed (vehicle speed) G Y : Lateral acceleration γ: Yaw rate β: Vehicle slip angle F CF : Front wheel cornering force (lateral force) F CFREF :Standard front wheel cornering force (total lateral force) F CFD : Improper steering wheel cornering force (improper lateral force) F CFC : Steering compensation wheel cornering force θ: Operation angle [Steering operation amount] [Steering request] δ: Steering angle [Steering amount] δ *: Target steering angle T: Steering torque I: Steering current

Claims

1. A vehicle steering system mounted on a vehicle having a plurality of steerable wheels, A wheel steering device that steers the plurality of wheels independently of one another; a controller that controls the wheel steering device so that the steering amount of each of the plurality of wheels becomes a target steering amount determined for each of the plurality of wheels in response to a steering request; Equipped with The controller: In a one-wheel improperly steering state in which one of the plurality of wheels is an improperly steered wheel that is improperly steered in steering, in order to ensure a total lateral force, which is the sum of the lateral forces that each of the plurality of wheels should generate, in response to the steering request, at least one of the plurality of wheels, excluding the improperly steered wheel, is set as a steering compensation wheel, and a target steering amount for the steering compensation wheel is changed.

2. The controller:

2. The vehicle steering system according to claim 1, further comprising: a steering wheel steering system for steering a vehicle in a one-wheel improperly steered state, the steering wheel steering system being configured to estimate an improper lateral force that is a lateral force generated by the improperly steered wheel, and to change a target steering amount of the steering compensation wheel based on the estimated improper lateral force.

3. The controller:

3. The vehicle steering system according to claim 2, wherein the improper lateral force is estimated based on an actual steering amount of the improperly steered wheel in the one-wheel improperly steered state.

4. The controller:

3. The vehicle steering system according to claim 2, wherein the improper lateral force is estimated based on a steering force applied to the improperly steered wheel in the one-wheel improperly steered state.

5. The vehicle has four wheels, front, rear, left and right, and the plurality of wheels that can be steered are the left and right front wheels, 5. A vehicle steering system as described in any one of claims 1 to 4, wherein the controller is configured to change the target steering amount for the other of the left and right front wheels as the steering compensation wheel when one of the left and right front wheels is the improperly steered wheel in the one-wheel improper steering state.

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