Vehicle steering system

Abstract

The purpose of the present invention is to improve the utility of a vehicle steering system mounted on a multi-wheel independent steering vehicle. In a one-wheel inappropriate steering state in which one of a plurality of steerable wheels (10F) becomes an inappropriate steered wheel (10FD) that is inappropriate during steering, the steering system is configured so as to secure, in accordance with a steering request, a total lateral force (FCFREF), which is the sum of lateral forces that should be generated by the plurality of wheels, and to provide a one-wheel inappropriate steering state in which one of the plurality of steerable wheels (10F) becomes an inappropriate steered wheel (10FD) that is inappropriate during steering. At least one of one or more wheels other than the improperly steered wheel among the plurality of wheels is used as a steering compensation wheel (10FC), and a target steering amount ([delta] C *) for the steering compensation wheel is changed.

Description

Technical Field

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

[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, based on the six-component force of the center of gravity, the three-component force of the tire is calculated by a calculation using a quadratic programming method using an effective constraint method, and based on the three-component force of the tire, the vehicle is controlled by multiple actuators.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2022-165535

[0004] Recently, for example, development of a vehicle that can steer multiple wheels independently of each other by means of multiple actuators has been carried out. The technology described in the above patent document can also be applied to this vehicle. On the other hand, for example, it is also expected that one of the multiple actuators fails and one of the multiple wheels cannot be properly steered. However, it is difficult to deal with such a situation in the above technology. Therefore, if such a situation can be dealt with, the practicality of a vehicle steering system installed in a vehicle that can steer multiple wheels independently of each other (hereinafter referred to as a "multi-wheel independent steering vehicle") can be improved. The present invention was completed in view of such actual conditions, and its subject is to provide a vehicle steering system with higher practicality. Summary of the invention

[0005] In order to solve the above-mentioned problems, a vehicle steering system of the present invention is a vehicle steering system mounted on a vehicle having a plurality of wheels capable of steering, wherein the vehicle steering system comprises: a wheel steering device for steering the plurality of wheels independently of each other; and a controller for controlling the wheel steering device in such a manner that the steering amount of each of the plurality of wheels becomes a target steering amount determined for the plurality of wheels respectively according to a steering request, wherein the controller is configured as follows:

[0006] In an inappropriate steering state in which one of the multiple wheels becomes an inappropriate steering wheel during steering, in order to ensure the sum of the lateral forces that the multiple wheels should generate respectively according to the above-mentioned steering requirement, that is, the total lateral force, at least one or more wheels among the multiple wheels except the above-mentioned inappropriate steering wheel is used as a steering compensation wheel, and the target steering amount of the steering compensation wheel is changed.

[0007] 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 the total lateral force corresponding 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.

[0008] The "steering amount" in the vehicle steering system of the present invention (hereinafter referred to as "steering system") refers to the steering angle (turning angle, front angle) of the wheel, the movement amount of the steering component that moves in accordance with the steering of the wheel, etc. The "wheel steering device" may also be, for example, a device with a steering actuator for each wheel. In addition. The steering system of the present invention may be a so-called steer-by-wire steering system. The "steering request" is a concept of how much the vehicle should turn regardless of whether the vehicle is automatically driven or driven by the driver. In a vehicle driven by a driver, for example, it can be considered to be expressed by the operation amount of the steering operating component (for example, the operating angle of the steering wheel).

[0009] The "controller" of the present steering system can be constructed to include a computer, a driving circuit (driver) of a driving source of a wheel steering device, and the like. The controller controls the wheel steering device in such a way that the steering amount of each of the multiple wheels becomes a target steering amount determined for each of the multiple wheels according to the steering requirement. That is, steering control is performed. Specifically, the steering control is, for example, the following control: the target steering amount of each wheel is determined based on the steering requirement, the steering force (for example, steering torque) to be applied to the wheel is determined based on the deviation of the actual steering amount of each wheel relative to the target steering amount, and when the wheel steering device includes an electric motor as a driving source, the electric motor is supplied with a current corresponding to its steering force.

[0010] An improperly steered wheel that is improper in steering is, for example, a wheel where the difference between the target steering amount and the actual steering amount is too large, a wheel where no steering force can be applied, a wheel where insufficient or excessive steering force is applied, etc. In the case where the wheel steering device has an electric motor as a driving source, a state where no current is supplied to the electric motor due to a malfunction or failure of its driving circuit, or an actual supplied current deviates from the current that should be supplied, is equivalent to a one-wheel improper steering state.

[0011] The process for coping with the inappropriate steering state of one wheel may be referred to as the inappropriate steering state coping process of one wheel (hereinafter, there is a case where it is simply referred to as "coping process"). The coping process in the present steering system is a process for changing the target steering amount of the wheel that is not the inappropriate steering wheel in order to ensure the above-mentioned total lateral force corresponding to the steering request according to the steering request. Specifically, for example, in a case where the lateral force that the inappropriate steering wheel should generate is insufficient, the process is to make the steering compensation wheel additionally generate the insufficient amount to compensate for it and then change the target steering amount of the steering compensation wheel. If the total lateral force can be properly ensured, the vehicle can be properly steered or turned. In addition, the "sideways force" mentioned here refers to all lateral forces generated by the wheels, and is a concept that includes turning force, lateral force, etc. In the present steering system, as the lateral force, either turning force or lateral force can also be used.

[0012] In a vehicle equipped with the present steering system, the number of wheels that can be steered and the number of steering compensation wheels are not particularly limited. Specifically, the number of wheels that can be steered can be two or more, and the number of steering compensation wheels can be one or more. For example, in a vehicle having four wheels on the front, rear, left and right sides, when the four wheels are wheels that can be steered, two or more wheels can be steering compensation wheels. In this case, the compensation for the total lateral force can be appropriately distributed to two or more steering compensation wheels. If a specific embodiment is illustrated, in a case where the vehicle has four wheels on the front, rear, left and right sides, and the plurality of wheels that can be steered are left and right front wheels, the controller is configured to change the target steering amount for the other left and right front wheels that are steering compensation wheels when one of the left and right front wheels becomes an inappropriate steering wheel in the case of one wheel inappropriate steering state.

[0013] As for the specific processing method of the response treatment, the controller can be configured as follows: in the case of one wheel inappropriate steering state, the lateral force generated by the inappropriate steering wheel, that is, the inappropriate lateral force, is inferred, and the target steering amount of the steering compensation wheel is changed based on the inferred inappropriate lateral force. The inference of the inappropriate lateral force can be based on the actual steering amount of the inappropriate steering wheel, and can also be based on the steering force given to the inappropriate steering wheel. In the former case, it may be impossible to accurately infer the inappropriate lateral force due to the delay in the steering of the inappropriate steering wheel. In contrast, in the latter case, the delay in the steering of the inappropriate steering wheel can be taken into consideration for inference. In the case where the driving source for steering the wheel is an electric motor, the steering force given to the inappropriate steering wheel can be inferred based on the supply current supplied to the electric motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a diagram schematically showing the overall structure of the vehicle steering system according to the embodiment.

[0015] Figure 2 It is a perspective view showing a wheel arrangement module provided in a vehicle equipped with the vehicle steering system according to the embodiment.

[0016] Figure 3 This is a flowchart of a target steering angle determination processing routine and a one-wheel steering processing routine executed by the vehicle steering system of the embodiment.

[0017] Figure 4 It is a schematic diagram showing a target steering angle determination map, a two-wheel model of a steering system, and a wheel steering motion model that are referred to in the target steering angle determination process.

[0018] Figure 5 This is a flowchart of a subroutine for coping with a one-wheel improper steering state that constitutes a target steering angle determination processing program.

[0019] Description of Reference Numerals

[0020] 10…wheel; 10F…front wheel; 10FD…improperly steered wheel; 10FC…steering compensation wheel; 10R…rear wheel; 12…wheel steering device; 14…operating device; 16…steering electronic control unit (steering ECU) [controller]; 18…operating electronic control unit (operating ECU) [controller]; 20…wheel configuration module; 22…CAN; 24…wheel drive unit; 24a…housing [steering knuckle]; 24b…steering knuckle arm; 46…steering actuator; 46a…steering motor [electric motor] [drive source]; 48…tie rod; 56…steering wheel [steering operating member]; 66…yaw rate sensor; 68…lateral acceleration sensor; KP…king pin axis; V…vehicle running speed (vehicle speed); G Y ...lateral acceleration; γ...yaw rate; β...body slip angle; F CF ...front wheel turning force (lateral force); F CFREF ...standard front wheel turning force (total lateral force); F CFD ...inappropriate steering wheel turning force (inappropriate lateral force); F CFC …steering compensation wheel turning force; θ…operating angle [steering operation amount] [steering requirement]; δ…steering angle [steering amount]; δ ＊ …target steering angle; T…steering torque; I…steering current. DETAILED DESCRIPTION

[0021] Hereinafter, as a mode for implementing the present invention, a vehicle steering system as an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In addition, the present invention can be implemented in various ways by adding various changes and improvements based on the mode described in the above [Implementation Mode of the Invention] by those skilled in the art, in addition to the following embodiments.

[0022] [Example]

[0023] [A] Structure of vehicle steering system

[0024] The vehicle steering system of the embodiment (hereinafter, sometimes simply referred to as "steering system") is a so-called steer-by-wire steering system. Figure 1 As shown schematically, the present 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 wheels that can be steered, and the left and right rear wheels 10RL, 10RR are wheels that cannot be steered. The wheel steering device 12 for steering the left and right front wheels 10FL, 10FR is configured to include a left wheel steering device 12L for steering the left front wheel 10FL, and a right wheel steering device 12R for steering the right front wheel 10FR. In addition, the present steering system is configured to include an operating device 14 for receiving an operation of the driver, a pair of steering electronic control units (hereinafter, sometimes referred to as "steering ECUs") 16L, 16R for respectively controlling the left wheel steering device 12L and the right wheel steering device 12R, and an operating electronic control unit (hereinafter, sometimes referred to as "operating ECUs") 18 for controlling the operating device 14 and comprehensively managing the pair of steering ECUs 16.

[0025] In the following description, when there is no need to distinguish between the left and right front wheels 10FL and 10FR, they are sometimes collectively referred to as the front wheels 10F, when there is no need to distinguish between the left and right rear wheels 10RL and 10RR, they are sometimes collectively referred to as the rear wheels 10R, and when there is no need to distinguish between the front wheels 10F and the rear wheels 10R, they are sometimes collectively referred to as the wheels 10. In addition, although the description is repeated, the wheel steering device 12 is configured to include a left wheel steering device 12L and a right wheel steering device 12R, but when there is no need to distinguish between these left wheel steering device 12L and right wheel steering device 12R, they are sometimes simply collectively referred to as the wheel steering device 12. Similarly, when there is no need to distinguish between the pair of steering ECUs 16L and 16R, they are sometimes collectively referred to as the steering ECU 16. Moreover, when there is no need to distinguish between the left and right, various parameters for the left and right front wheels 10FL and 10FR described later are sometimes collectively referred to by omitting L and R in the reference numerals.

[0026] Each wheel steering device 12 is assembled in a wheel configuration module 20 which will be described in detail later. A pair of steering ECUs 16 and an operation ECU 18 are connected to CAN (car area network or controllable area network) 22, respectively, and can communicate with each other via CAN 22. In the steering system, it can be considered that the pair of steering ECUs 16, the operation ECU 18, and the CAN 22 constitute a controller for controlling a wheel steering device 12 which is composed of a left wheel steering device 12L and a right wheel steering device 12R.

[0027] like Figure 2 As shown, the wheel arrangement module (hereinafter, sometimes simply referred to as a "module") 20 is a module configured to include a MacPherson suspension device and to arrange the front wheel 10F on the vehicle body. Figure 2 Module 20 for the left front wheel 10FL is shown in FIG. Module 20 has a wheel drive unit 24 (referred to as a so-called "in-wheel motor") as a wheel rotation drive device, and its housing 24a holds the front wheel 10F so that it can rotate around the wheel axis WL, and also functions as a steering knuckle in the wheel steering device 12. Hereinafter, there is a case where the housing 24a is referred to as a steering knuckle 24a.

[0028] This module 20 has the above-mentioned wheel steering device 12 (either the left wheel steering device 12L or the right wheel steering device 12R). The wheel steering device 12 is a single-wheel independent steering device for independently steering one of the left and right front wheels 10F and the other. The wheel steering device 12 is generally configured to include the steering 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 steering knuckle 24a.

[0029] The steering actuator 46 is configured to include a steering motor 46a which is an electric motor as a driving source, a speed reducer 46b which speeds down the rotation of the steering motor 46a, and an actuator arm 46c which rotates by the rotation of the steering motor 46a via the speed reducer 46b and functions as a steering arm. The base end of the tie rod 48 is connected to the actuator arm 46c, and the front end of the tie rod 48 is connected to the knuckle arm 24b.

[0030] In the present wheel steering device 12, by operating the steering motor 46a, the actuator arm 46c of the steering actuator 46 rotates around the actuator axis AL as indicated by the thick arrow in the drawing. The rotation is transmitted through the tie rod 48, so that the steering knuckle 24a rotates around the kingpin axis KP.

[0031] The operating device 14 has a general structure in a steer-by-wire type steering system. Figure 1 As shown, the operating device 14 is configured to include a steering wheel 56 as a steering operating member operated by the driver, and a reaction force applying device 60 that applies an operation reaction force to the steering wheel 56. The reaction force applying device 60 is configured to include an electric motor, that is, a reaction force motor 62 as a force source, and a speed reducer 64 for transmitting the force of the reaction force motor 62 to the steering wheel 56.

[0032] Each steering ECU 16 is configured to include a computer having a CPU, ROM, RAM, etc., and a driver (drive circuit) for the steering motor 46a, and the operation ECU 18 is configured to include a computer having a CPU, ROM, RAM, etc., and a driver (drive circuit) for the reaction force motor 62. The steering motor 46a and the reaction force motor 62 are both three-phase brushless DC motors, and the drivers of the steering ECU 16 and the operation ECU 18 are both inverters.

[0033] The motor rotation angle (rotation phase) of the steering motor 46a, that is, the steering motor rotation angle δ M , and the steering amount of the wheel 10 from the neutral position (the position to be located in the forward state of the vehicle), that is, the steering angle δ, are in a specific reduction ratio relationship, and the steering ECUs 16L and 16R respectively have motor rotation angles δ based on the corresponding steering motors 46a. MR , δ ML To detect the steering angle δ of the left front wheel 10FL and the right front wheel 10FR L , δ R Similarly, the motor rotation angle (rotation phase) of the reaction force motor 62, that is, the reaction force motor rotation angle θ M , and the operation amount of the steering wheel 56 from the neutral position (the position to be located in the forward state of the vehicle), that is, the operation angle θ, is in a specific reduction ratio relationship, and the operation ECU 18 has a motor rotation angle θ based on the reaction force motor 62 M The function of detecting the operation angle θ of the steering wheel 56 is provided.

[0034] [B] Wheel steering control in vehicle steering systems

[0035] In the present 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 respectively execute the target steering angle determination process and the single-wheel steering process. In short, the target steering angle determination process is to determine the steering angles δ of the left and right front wheels 10FL, 10FR according to the steering request of the driver. L , δ R The target steering angle δ of the target L＊ , δ R ＊ The single-wheel steering process is to use the steering angle δ of one front wheel 10F as the target steering angle δ ＊ The processing of operating the steering motor 46a in a manner. The target steering angle determination processing and the single-wheel steering processing are described in detail below, and the processing for dealing with a case where the left and right front wheels 10FL and 10FR become inappropriate is described. In addition, the operation ECU 18 performs operation reaction force control to make the operation reaction force act on the steering wheel 56 through the reaction force applying device 60 in order to give the driver a suitable steering operation feeling, but the description of this control is omitted.

[0036] (a) Target steering angle determination process

[0037] By operating the ECU 18 to repeatedly execute the Figure 3 The target steering angle determination process is performed according to the target steering angle determination process shown in the flowchart. As described in the flowchart, in the target steering angle determination process, first, in step 1 (hereinafter referred to as "S1". The other steps are the same.), the vehicle's running speed (hereinafter referred to as "vehicle speed") V is obtained from the vehicle's brake system (not shown) via CAN 22. The vehicle speed V is based on the rotation speed V of each wheel 10. W Next, in S2, based on the motor rotation angle θ of the reaction force motor 62 M The operation angle θ of the steering wheel 56 is detected.

[0038] In the next S3, the target steering angle δ of each of the left and right front wheels 10FL and 10FR is determined based on the operating angle θ. L ＊ , δ R ＊ Specifically, the present steering system is a vehicle speed-sensitive steering system. The higher the vehicle speed V, the higher the target steering angle δ even if the operating angle θ is the same. L ＊ , δ R ＊ Specifically, refer to Figure 4 The target steering angle determination map schematically shown in (a) of FIG. 1 determines the target steering angle δ L ＊ , δ R ＊ .

[0039] Furthermore, in S4, it is determined whether any one of the left and right front wheels 10FL, 10FR is not properly turned, that is, a one-wheel improper turning state. In other words, it is determined whether any one of the left and right front wheels 10FL, 10FR has become an improperly turned wheel that is not properly turned during turning. In the case of the one-wheel improper turning state, in S5, a one-wheel improper turning state response process is executed. The above-mentioned one-wheel improper turning state and one-wheel improper turning state response process will be described in detail later.

[0040] In S6, the target steering angle δ determined in S3 or changed in S5 is transmitted to the steering ECUs 16L and 16R via the CAN 22. L ＊ , δ R ＊ After the sending action, the execution of this program ends.

[0041] (b) Single-wheel steering

[0042] The steering ECUs 16L and 16R corresponding to the left and right front wheels 10FL and 10FR respectively repeatedly execute the control at short time intervals (for example, several to several tens of μsec). Figure 3 The single-wheel steering processing program shown in the flowchart is used to perform the single-wheel steering processing. According to the flowchart, in the single-wheel steering processing performed by each steering ECU 16, first, in S11, the target steering angle δ is obtained from the operating ECU 18 via the CAN 22. ＊ In the next step S12, the actual steering angle δ of the front wheel 10F is detected, and in step S13, the steering angle δ is determined relative to the target steering angle δ. ＊ The deviation of the steering angle is Δδ(=δ ＊ -δ).

[0043] Next, in S14, the steering torque T required to steer the front wheel 10F, that is, the target steering torque T is determined according to the following equation: ＊ In addition, the steering torque T is a kind of steering force, which is the torque around the kingpin axis KP. Based on the steering angle deviation Δδ, the target steering torque T is determined according to the PID control rule by the following formula: ＊ In addition, GP, GI, and GD in the following formula are proportional gain, integral gain, and differential gain, respectively.

[0044]

Formula 1

[0045]

[0046] It is considered that the steering torque T is substantially proportional to the current supplied to the steering motor 46a, that is, the steering current I. Based on this, in S15, the target steering torque T is determined. ＊ Multiply by the steering current determination coefficient K I , which determines the target steering current I, i.e., the target steering current I ＊ Furthermore, in S16, based on the target steering current I ＊ , supplies current to the steering motor 46a, and ends one execution of this program.

[0047] (c) Response to improper steering of one wheel

[0048] It is also assumed that one of the pair of front wheels 10F becomes unable to perform proper steering due to some reason, for example, failure of the driving circuit of the steering motor 46a. In the present steering system, when one of the pair of front wheels 10F becomes an improperly steered wheel, the other front wheel 10F is used as a steering compensation wheel, and the target steering angle δ of the front wheel 10F is changed. ＊ , thus coping with this state.

[0049] As described above, in S4 of the target steering angle determination process, it is determined whether one wheel is in an inappropriate steering state. As a premise, the steering ECU 16 corresponding to the front wheel 10F determines whether the front wheel 10F is an inappropriate steering wheel. In short, the target steering angle δ of the corresponding front wheel 10F is ＊ When the difference between the steering angle δ and the actual detected steering angle δ is greater than the threshold difference for a certain period of time, or when the target steering current I ＊ When the difference between the actual supplied current I and the current I is greater than the threshold difference for a certain period of time, the front wheel 10F is determined to be an improperly steered wheel. When it is determined to be an improperly steered wheel, the steering ECU 16 that has been determined sends this information 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 improper steering state.

[0050] As described above, in the case of one wheel improper steering state, in S5 of the target steering angle determination process, one wheel improper steering state response process (hereinafter referred to as "response process") is performed. Figure 5 The countermeasure processing is performed according to the countermeasure processing sub-routine of the flowchart shown in . Before explaining the processing according to the sub-routine, the general theory related to the steering of the wheel 10 is explained.

[0051] Edge Reference Figure 4In the two-wheel model shown in (b), it is explained that in a vehicle in which only the front wheel 10F can turn, corresponding to the turning of the front wheel 10F, a front wheel turning force F expressed by the following formula is generated in one front wheel 10F and one rear wheel 10R respectively. CF , rear wheel turning force F CR In the following equation, β is the body slip angle (vehicle slip angle), γ is the yaw rate of the vehicle, and l F is the distance between the axle line of the front wheel 10F and the center of gravity of the vehicle body in the front-rear direction (hereinafter, sometimes referred to as “the distance between the centers of gravity of the front wheels”), R is the distance between the axle line of the rear wheel 10R and the center of gravity of the vehicle body in the front-rear direction (hereinafter, sometimes referred to as “the distance between the centers of gravity of the rear wheels”), K F is the front wheel cornering stiffness, K R is the rear wheel cornering stiffness. In addition, the front wheel turning force F CF , rear wheel turning force F CR These are one type of lateral force generated by one front wheel 10F and one rear wheel 10R respectively.

[0052]

Formula 2

[0053]

[0054]

Formula 3

[0055]

[0056] Furthermore, if the entire vehicle is considered, the following equation holds true: wherein m is the weight of the vehicle (hereinafter sometimes referred to as "vehicle weight").

[0057]

Formula 4

[0058]

[0059] In the above equation, the right side can use the lateral acceleration G of the vehicle Y , and is expressed as follows.

[0060]

Formula 5

[0061]

[0062] On the other hand, for a four-wheel vehicle turning with only the front wheels 10F turned, the following two basic equations also hold: Wherein, J is the inertia moment about the vertical axis of the vehicle.

[0063]

Formula 6

[0064]

[0065]

Formula 7

[0066]

[0067] In the processing according to the handling processing sub-routine, first, in S21, it is determined which of the left and right front wheels 10FL and 10FR is the inappropriate steering wheel, and the other one that is not the inappropriate steering wheel is determined as the steering compensation wheel. In addition, in the following description, there is a case where the inappropriate steering wheel is denoted as 10FD and the steering compensation wheel is denoted as 10FC. In addition, there is a case where the steering angle of the inappropriate steering wheel 10FD and the target steering angle are denoted as δ D , δ D ＊ , and the steering angle of the steering compensation wheel 10FC and the target steering angle are respectively denoted as δ C , δ C ＊ situation.

[0068] Next, in S22, the target steering angles δ of the left and right front wheels 10FL and 10FR determined in S3 are determined. L ＊ , δ R ＊ , set each target steering angle equal, for example, determine a target steering angle δ by finding the average value, etc. ＊ Then, in S23, the above equations (6) and (7) are regarded as simultaneous equations, and based on the target steering angle δ ＊ By solving these, the standard yaw rate γ is deduced when it is assumed that both the left and right front wheels 10FL and 10FR are not the inappropriately steered wheels 10FD. REF 、Standard body slip angle β REF Next, in S24, based on these standard yaw rates γ REF 、Standard body slip angle β REF and the target steering angle δ ＊ According to the above formula (2), the turning forces F that the left and right front wheels 10FL and 10FR should generate respectively are determined. CF That is, the standard front wheel turning force F CFREF Wherein, the standard front wheel turning force F CFREF The doubled turning force is a turning force to be generated in the entire front wheel 10F, that is, a total standard front wheel turning force which is a total lateral force.

[0069] In the next S25, the turning force actually generated by the improperly steered wheel 10FD, that is, the improperly steered wheel turning force F CFD As a method for this estimation, two methods can be considered, but in S25, any one method may be adopted. The two methods are described below.

[0070] The first method is based on the actual yaw rate γ, the actual vehicle body slip angle β, and the actual steering angle δ of the improperly steered wheel 10FD. D To infer the inappropriate steering wheel turning force F CFD Specifically, the method is based on the above formula (2). The actual steering angle δ D Based on the steering motor rotation angle δ M To detect. Figure 1 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 change speed of the vehicle body slip angle β can be calculated 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 according to the above formula (5). Y Therefore, the actual vehicle body slip angle β is estimated based on the change speed of the estimated vehicle body slip angle β.

[0071] The second method is a method of inferring based on the following formula (8). Figure 4 (c) is the state equation of the wheel steering motion model. In addition, in the following equation, J S represents the moment of inertia about the kingpin axis of the wheel 10, C S represents the attenuation coefficient in the steering action, and ξ represents the tire trail.

[0072]

Formula 8

[0073]

[0074] The steering torque T as the steering force can be determined based on the steering current I actually supplied to the steering motor 46a. That is, the method according to the above formula can be said to be based on the steering angle δ of the improperly steered wheel 10. D The inappropriate steering wheel turning force F is inferred from the changes in CFD The second method is to estimate the change in the steering angle δ of the improperly steered wheel 10FD in the near future to estimate the improperly steered wheel turning force F CFD According to this method, it is possible to make an inference without delay, in other words, it is possible to make an inference taking into account the delay of steering.

[0075] In the case of improper steering wheel turning force F CFD After the inference, in S26, the turning force that the steering compensation wheel 10FC should generate, that is, the steering compensation wheel turning force F CFC Specifically, by converting the turning force to be generated by the entire front wheel 10F, that is, the standard front wheel turning force F CFREFThe doubled turning force, i.e., the total standard front wheel turning force minus the inappropriate steering wheel turning force F CFD To determine the steering compensation wheel turning force F CFC .

[0076] In the next S27, based on the steering compensation wheel turning force F CFC According to the above formula (2), the target steering angle δ of the steering compensation wheel 10FC is determined C ＊ In this case, the actual yaw rate γ and the actual vehicle body slip angle β are used. 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 set. ＊ The value determined in S3 is replaced by the target steering angle δ of the steering compensation wheel 10FC. C ＊ The value of decision.

[0077] Through the above-described processing, in the case of one wheel improper steering state, the target steering angle δ for the steering compensation wheel 10FC is changed. ＊ , thereby ensuring the turning force that should be generated by the entire front wheel 10F corresponding to the turning request. As a result, even in a state where one wheel is not properly turned, the vehicle can be properly turned and turned.

Claims

1. A vehicle steering system, mounted on a vehicle having a plurality of steerable wheels, wherein: The vehicle steering system comprises: a wheel steering device for steering the plurality of wheels independently of one another; and a controller for controlling the wheel steering device in such a manner that the steering amount of each of the plurality of wheels becomes a target steering amount determined for each of the plurality of wheels according to a steering request, The controller is composed of: In an improper steering state in which one of the multiple wheels becomes an improperly steering wheel that is inappropriate during steering, in order to ensure the sum of the lateral forces that the multiple wheels should generate respectively according to the steering requirement, that is, the total lateral force, at least one or more wheels among the multiple wheels except the improperly steering wheel is used as a steering compensation wheel, and the target steering amount for the steering compensation wheel is changed.

2. The vehicle steering system according to claim 1, wherein: The controller is composed of: In the one-wheel improperly steered state, an improper lateral force, which is a lateral force generated by the improperly steered wheel, is estimated, and based on the estimated improper lateral force, the target steering amount of the steering compensation wheel is changed.

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

4. The vehicle steering system according to claim 2, wherein: The controller is composed of: The inappropriate lateral force is estimated based on the steering force applied to the inappropriately steered wheel in the one-wheel inappropriately steered state.

5. The vehicle steering system according to any one of claims 1 to 4, wherein: The vehicle has four wheels, front, rear, left and right, and the plurality of wheels capable of turning are left and right front wheels. The controller is configured to change a 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 becomes the improperly steered wheel in the one-wheel improperly steered state.

Images