Steering system

Abstract

The invention relates to a steering system, which can improve the practicability of a steering system capable of steering front wheels and rear wheels. When a front wheel (10F) passes through an unevenness R, a rear wheel avoidance control for avoiding the passage of a rear wheel (10R) through the unevenness is executed, and in the rear wheel avoidance control, a rear wheel avoidance sideslip angle [beta] A, which is a vehicle center-of-gravity sideslip angle to be achieved, is determined. And determines a target steering angle, which is a steering angle at which each of the front wheel and the rear wheel should be steered, on the basis of the rear wheel sideslip avoidance angle. According to the present invention, it is possible to execute rear wheel avoidance control while executing target line travel control in which front wheels and rear wheels are steered so that the vehicle travels along a travel line on which the vehicle should travel, i.e., a target line L *, so that it is possible to cause the vehicle to travel along an appropriate travel line while avoiding the passage of rear wheels through irregularities.

Description

Technical Field

[0001] The present invention relates to a steering system provided in a vehicle. Background Art

[0002] A technology described in the following patent document is being studied, that is, a technology for detecting the lifting of the wheels while the vehicle is running and preventing the vehicle from turning sideways by warning the driver and braking the vehicle.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2005-239078 Summary of the invention

[0004] In the technology described in the above patent document, for example, when the front wheel passes through the unevenness of the road, it is impossible to avoid the rear wheel passing through the unevenness, and it is difficult to say that the stability of the vehicle can be well maintained. If a steering system that can well ensure the driving stability of the vehicle is realized, the steering system becomes a steering system with high practicality. The present invention is completed in view of such actual conditions, and its subject is to provide a steering system with high practicality.

[0005] In order to solve the above-mentioned problems, the steering system of the present invention is a steering system provided in a vehicle, and comprises:

[0006] a front wheel steering device for steering the front wheels; a rear wheel steering device for steering the rear wheels; and a controller for controlling the front wheel steering device and the rear wheel steering device in a manner that the front wheels and the rear wheels can be steered independently of each other,

[0007] The above-mentioned controller is configured to execute rear wheel avoidance control for avoiding the rear wheel passing through the bump when the front wheel passes through the bump. In the rear wheel avoidance control, the vehicle center of gravity side slip angle that should be achieved, that is, the rear wheel avoidance side slip angle, is determined, and based on the rear wheel avoidance side slip angle, the steering angle at which each of the front and rear wheels should be turned, that is, the target steering angle, is determined.

[0008] The "vehicle center of gravity side slip angle" can also be called the body slip angle, which is the angle formed by an axis that passes through the center of gravity of the vehicle and extends in the front-to-rear direction of the vehicle (hereinafter sometimes referred to as the "vehicle front-to-rear axis") and a line that extends in the direction of travel of the vehicle (hereinafter sometimes referred to as the "driving direction line"). In the "rear wheel avoidance control", the vehicle center of gravity side slip angle is set to an appropriate angle in a manner that the rear wheels do not pass through bumps and depressions. This angle is the above-mentioned "rear wheel avoidance side slip angle". In the rear wheel avoidance control, the steering angle of the front wheels and the steering angle of the rear wheels are controlled in a manner to achieve the rear wheel avoidance side slip angle. Through this control, the rear wheels can be prevented from passing through bumps and depressions that the front wheels have passed through. As a result, the driving stability of the vehicle is improved.

[0009] When the steering system of the present invention (hereinafter sometimes referred to as "the present steering system") is applied to a front-rear-left-right four-wheel vehicle having two left and right front wheels and two left and right rear wheels, the "front-wheel steering device" may be a device that steers the two front wheels as a whole, or may be a device that steers the two front wheels independently of each other, that is, a device that is configured to include two single-wheel steering devices. Similarly, the "rear-wheel steering device" may be a device that steers the two rear wheels as a whole, or may be a device that steers the two rear wheels independently of each other, that is, a device that is configured to include two single-wheel steering devices. The "controller" may be a single structure, for example, it may be a structure that is configured to include a controller that controls the front-wheel steering device, a controller that controls the rear-wheel steering device, and a controller that controls them in an integrated manner. In addition, the present steering system is a system in which both the front wheels and the rear wheels can be steered by the control of the controller, and is suitable for vehicles that are automatically driven.

[0010] The "unevenness" to be avoided by the rear wheel avoidance control is a general term for the concave part, depression, convex part, ridge, protrusion, step difference, etc. of the road surface that disturbs the vehicle's travel due to the wheel passing through. The unevenness to be avoided by the rear wheel can also be limited to the unevenness that greatly disturbs the vehicle's travel. Specifically, it is also possible to target the unevenness that makes the front and rear wheels not share the load of the vehicle body when the front wheel passes through the unevenness, in short, the so-called unevenness that makes the front and rear wheels float. It is sufficient to target the unevenness that makes the front and rear wheels float on either the left or right side of the above-mentioned front, rear, left and right four-wheel vehicle. That is, the steering system can be configured to perform the rear wheel avoidance control under the condition that the float of both the front and rear wheels is detected. Among them, as a method for detecting the float of the front and rear wheels, a method based on ZMP (zero moment point) can be adopted. This method will be described later.

[0011] In the rear wheel avoidance control, in order to avoid the rear wheel passing through the bump, the rear wheel avoidance side slip angle can be determined based on, for example, the distance that the rear wheel should be displaced laterally from the bump (hereinafter, sometimes referred to as the "rear wheel displacement distance") and the wheelbase of the vehicle. The specific determination method will be described later. By the way, in the rear wheel avoidance control, the rear wheel can be displaced to the outside of the turn relative to the front wheel, or to the inside of the turn, and can also be displaced to the vicinity of the center position of the vehicle, or can be displaced to the outside of the vehicle.

[0012] In order to reliably avoid the rear wheel passing the bump, the rear wheel avoidance control can be performed after the front wheel passes the bump until the vehicle travels a distance equivalent to the wheelbase of the vehicle. In other words, the rear wheel avoidance control can be terminated when the vehicle travels a distance equivalent to the wheelbase of the vehicle. The vehicle's travel distance can be obtained by estimating the vehicle's own position based on mileage information obtained by sensors that measure wheel rotation, GPS, cameras, etc.

[0013] In this steering system, a "target line driving control" can be executed to steer the front and rear wheels so that the vehicle travels along the target line, which is the driving line that the vehicle should travel. The target line driving control allows the vehicle to travel along the appropriate driving line. Furthermore, when the front wheel passes through a bump during the execution of the target line driving control, the rear wheel avoidance control can be executed while the target line driving control is continued. By executing these two controls in parallel, the vehicle can be driven along the appropriate driving line while avoiding the rear wheel passing through the bump.

[0014] Specifically, for example, target line driving control can be performed by setting a target point on the target line in front of the vehicle and determining the target steering angles of the front and rear wheels based on the positional relationship between the target point and the vehicle and the pre-set vehicle center of gravity side slip angle, i.e., the "standard side slip angle". The standard side slip angle characterizes the turning characteristics of the vehicle. For example, if the standard side slip angle is set to 0°, the front and rear wheels are turned in opposite directions to each other, and a so-called zero beta turn can be performed. By the way, if this zero beta turn is achieved, the delay in responsiveness can be reduced and the steering maneuverability can be improved. Among them, the standard side slip angle can be set to be fixed, and it can also be set to be variably according to the vehicle's driving speed (hereinafter sometimes referred to as "vehicle speed"), turning radius, etc.

[0015] In order to execute the rear wheel avoidance control while performing the target line traveling control as described above, for example, the rear wheel avoidance sideslip angle may be used instead of the standard sideslip angle and the target steering angles of the front and rear wheels may be determined based on the rear wheel avoidance sideslip angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram showing the hardware configuration of the steering system of the embodiment.

[0017] Figure 2 This is a schematic diagram showing the front and rear wheel models related to the steering of the wheels and the situation of traveling on the target line.

[0018] Figure 3It is a schematic diagram for explaining the avoidance of unevenness by the rear wheels based on the rear wheel avoidance control, and a schematic diagram showing the behavior of the vehicle when the rear wheel avoidance control is performed while the target line running control is performed.

[0019] Figure 4 This is a schematic diagram for explaining a method of detecting the lifting of a wheel using the ZMP.

[0020] Figure 5 This is a flowchart of a target steering angle determination processing routine executed in the steering system of the embodiment. DETAILED DESCRIPTION

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

[0022] [Example]

[0023] [A] Hardware composition of the steering system

[0024] like Figure 1 As shown, the steering system of the embodiment (hereinafter, sometimes referred to as "this system") is mounted on a left front and rear four-wheel vehicle having a left front wheel 10FL, a right front wheel 10FR, a left rear wheel 10RL, and a right rear wheel 10RR. This system is provided with a left front wheel steering device 12FL, a right front wheel steering device 12FR, a left rear wheel steering device 12RL, and a right rear wheel steering device 12RR in order to independently steer the above four wheels 10FL, 10FR, 10RL, and 10RR, that is, to rotate the kingpin axis. In addition, it is provided with four steering electronic control units (hereinafter, sometimes referred to as "steering ECUs") 14 for controlling the above four wheel steering devices 12FL, 12FR, 12RL, and 12RR, and an integrated electronic control unit (hereinafter, sometimes referred to as "integrated ECU") 16 for comprehensively controlling this system. The controller of this system is configured to include the above four steering ECUs 14 and the integrated ECU 16.

[0025] In the following description, when there is no need to distinguish between the left and right front wheels 10FL and 10FR, each of them is collectively referred to as the front wheel 10F, when there is no need to distinguish between the left and right rear wheels 10RL and 10RR, each of them is collectively referred to as the rear wheel 10R, and when there is no need to distinguish between the front wheel 10F and the rear wheel 10R, each of them is collectively referred to as the wheel 10. In addition, the wheel steering device is also similarly sometimes collectively referred to as the front wheel steering device 12F, the rear wheel steering device 12R, and the wheel steering device 12. In addition, when there is no need to distinguish between the left and right, front and back, etc., the suffixes F, R, FL, FR, RL, and RR are sometimes omitted. By the way, it can also be considered that the left front wheel steering device 12FL and the right front wheel steering device 12FR constitute a front wheel steering device, and the left rear wheel steering device 12RL and the right rear wheel steering device 12RR constitute a rear wheel steering device.

[0026] Since each wheel steering device 12 has a general structure, the description of the structure is omitted. The wheel steering device 12 includes a steering motor 18 which is a DC brushless motor as a driving source, and steers the wheel 10 to an angle corresponding to the rotation amount of the steering motor 18 .

[0027] Each steering ECU 14 includes a computer having a CPU, ROM, RAM, etc. as a main component, and has an inverter as a drive circuit (driver) of the steering motor 18. The integrated ECU 16 is configured to include a computer having a CPU, ROM, RAM, etc. as a main component. Each steering ECU 14 and the integrated ECU 16 are connected to a CAN (car area network or controllable area network) 20, and can communicate with each other via the CAN 20.

[0028] Among them, various equipment, devices, and systems are provided in this vehicle. The following briefly describes the structure related to this system. The vehicle provided with this system travels in automatic driving, and therefore has an automatic driving electronic control unit (hereinafter, sometimes referred to as "automatic driving ECU") 22 that controls the driving under the automatic driving (hereinafter, sometimes referred to as "automatic driving"). The vehicle is provided with a driving information acquisition device 24 that is configured to include a camera that monitors the surroundings, LiDAR, a communication device for communicating information with the outside, a GPS device, etc. The driving information acquisition device 24 acquires the information required for automatic driving, that is, driving information. The above-mentioned automatic driving ECU 22 and driving information acquisition device 24 are also connected to CAN 20. The automatic driving ECU 22 determines the driving line that the vehicle should travel, that is, the target line, the vehicle speed, etc. based on the driving information acquired by the driving information acquisition device 24. In addition, the vehicle is provided with a sensor for detecting the posture, behavior, etc. of the vehicle. Specifically, a stroke sensor 26 for detecting the vertical separation distance between the wheel 10 and the vehicle body, i.e., the stroke, and a rotation speed sensor 28 for detecting the rotation speed of the wheel 10 are provided corresponding to each wheel 10. In addition, an IMU (inertial measurement unit) 30 for detecting the acceleration of the front-back, left-right, and vertical axes of the vehicle and the rotation speed around the front-back, left-right, and vertical axes is provided. These sensors 26, 28, and IMU 30 are also connected to CAN 20.

[0029] [B] Control in the steering system

[0030] In simple terms, this system determines a target steering angle δ* that is a target of the steering angle δ of each wheel 10, and steers each wheel 10 in such a way that the steering angle δ of each wheel 10 becomes the determined target steering angle δ*. In detail, as a basic control that is always performed, a target line driving control is performed for causing the vehicle to travel along a driving line L, that is, a target line L*, on which the vehicle should travel. Furthermore, when any front wheel 10F passes through a bump, while executing the target line driving control, a rear wheel avoidance control is performed for causing the rear wheel 10R located behind the front wheel 10F to not pass through the bump. Below, the above-mentioned target line driving control and rear wheel avoidance control are described in detail, and then the process of the target steering angle determination process performed in these controls is described.

[0031] (a) Target line driving control

[0032] In the target line driving control, the integrated ECU 16 executes a target steering angle determination process which is a process for determining a target steering angle δ* of each wheel 10, and each steering ECU 14 executes a process for steering each wheel 10 so that the steering angle δ of each wheel 10 becomes the target steering angle δ*, i.e., a wheel steering process. These processes are described in detail below.

[0033] i) Target steering angle determination process for driving on the target line

[0034] Comprehensive ECU16 according to Figure 2 The front wheel steering angle δ is determined by using the front and rear wheel models shown in (a) of FIG. F The target front wheel steering angle δ F *, the steering angle δ of the rear wheel 10R is also referred to as the rear wheel steering angle δ R The target rear wheel steering angle δ R Therefore, in this system, for the sake of convenience, both the front wheel 10F and the rear wheel 10R are turned to the same left and right steering angle δ.

[0035] In the above front and rear two-wheel model, under stable conditions, the following two equations of motion hold true.

[0036] [Formula 1]

[0037]

[0038] [Formula 2]

[0039]

[0040] In the front and rear two-wheel model, in the above two equations, C is the center of gravity of the vehicle, l is the wheelbase, and l F , 1 R are the distance between the front and rear wheel centers of gravity, β is the side slip angle of the vehicle center of gravity, M is the vehicle weight (vehicle weight), V is the vehicle speed (vehicle speed), γ is the yaw rate, and K F , K R They are the front wheel cornering stiffness and the rear wheel cornering stiffness, respectively. In the attached figure, X represents the front-rear axis of the vehicle, X' represents the driving direction line, and the front wheel 10F and the rear wheel 10R are turned in the same phase with each other. In other words, the steering directions of the front wheel 10F and the rear wheel 10R are depicted as being the same as each other. In this system, the front wheel 10F and the rear wheel 10R can also be turned in a manner that they are in opposite phases, that is, the steering directions are opposite to each other. In this case, the steering angle δ of the front wheel 10F is F The steering angle δ of the rear wheel 10R R The positive and negative values ​​are different from each other.

[0041] Here, the curvature κ is defined as follows.

[0042] [Formula 3]

[0043]

[0044] By using the turning curvature K, the above two equations of motion are expressed as follows.

[0045] [Formula 4]

[0046] 2(K F +K R )β+{MV 2 +2(l F K F -l R K R )}κ

[0047] =2K F δ F +2K R δ R …(4)

[0048] [Formula 5]

[0049] 2(l F K F -l R K R )β+2(l F 2 K F +l R 2 K R )κ

[0050] =2l F K F δ F +2l F K R δ F …(5)

[0051] By solving the above two motion equations, the front wheel steering angle δ can be obtained as follows: F , rear wheel steering angle δ R .

[0052] [Formula 6]

[0053]

[0054] [Formula 7]

[0055]

[0056] On the other hand, in this system, Figure 2As shown in (b), the target line driving control is performed to make the vehicle drive along the target driving line L, that is, the target line L*. In other words, the control is performed to make the vehicle drive in a manner such that the center of gravity C moves on the target driving line. Therefore, a target point G is set on the target line L* in front of the vehicle. That is, the target point G is set in a manner to have a specific positional relationship with the vehicle. If the distance between the target point G and the center of gravity C of the vehicle in the front-rear direction of the vehicle, that is, the target distance is set to S G , the angle between the line connecting the target point G and the center of gravity of the vehicle C and the front and rear axis X of the vehicle, that is, the target point angle, is set to δ G , then the curvature K can be expressed as follows.

[0057] [Formula 8]

[0058]

[0059] In addition, in this system, the target distance S G The target side slip angle β* is set according to the vehicle speed V, and specifically, is set to a distance that reaches the target point G in a few seconds (e.g., 2 seconds). In addition, the vehicle center of gravity side slip angle β in the above formula is set to the target side slip angle β* that is the target of the vehicle center of gravity side slip angle β. The target side slip angle β* determines the turning characteristics of the vehicle. Therefore, the target side slip angle β* can be set arbitrarily according to the desired steering characteristics, but in this system, during turning, the target side slip angle β* is set to the standard side slip angle β*. REF Specifically, the standard sideslip angle β REF It can be set to, for example, 0° in order to achieve a so-called zero beta turn. By the way, the standard sideslip angle β REF The target sideslip angle β* may be set to change according to the vehicle speed V or the like. The integrated ECU 16 substitutes the standard sideslip angle β for the target sideslip angle β* during a turn. REF , the turning curvature κ is obtained according to the above formula, and the front wheel steering angle δ is determined according to the above two formulas based on the turning curvature κ and the target side slip angle β*. F The target front wheel steering angle δ F *, becomes the rear wheel steering angle δ R The target rear wheel steering angle δ R *. In this system, the target line driving control is performed regardless of whether the vehicle is traveling straight or turning. Therefore, when traveling straight, that is, when the target point angle δ G When β is 0°, the target sideslip angle β* is set to 0°.

[0060] Alternatively, the front wheel target steering angle δ may be determined so that the steering angle δ of the wheel 10 varies according to the vehicle speed V. F *、Rear wheel target steering angle δ R*. Specifically, for example, the front wheel target steering angle δ F *、Rear wheel target steering angle δ R *It can be determined so that the higher the vehicle speed V, the smaller it is, and the lower the vehicle speed V, the larger it is. In addition, in at least one of the left and right front wheels 10F and the left and right rear wheels 10R, the target steering angle δ* of these wheels 10 can be determined so that the steering angle δ of the left and right wheels 10 is different from each other. For example, the target steering angle δ* of the left and right wheels 10 can be determined so that the steering ratio of the left and right wheels 10 approaches Ackerman geometry when the vehicle speed V is low, and approaches parallel geometry when the vehicle speed V is high.

[0061] ii) Wheel steering process

[0062] The wheel steering process is a process performed by each of the four steering ECUs 14, and is a process for steering the corresponding wheel 10 in such a way that the steering angle δ of the corresponding wheel 10 becomes the target steering angle δ* transmitted via the CAN 20. Specifically, the steering ECU 14 determines the deviation of the actual steering angle δ from the target steering angle δ*, that is, the steering angle deviation Δδ (=δ*-δ). The actual steering angle δ is proportional to the motor rotation angle of the steering motor 18, and the steering ECU 14 detects the actual steering angle δ based on the motor rotation angle.

[0063] Then, the steering torque T required for steering the wheel 10, that is, the target steering torque T*, is determined based on the steering angle deviation Δδ according to the following equation, that is, according to the PID control law. P , G I , G D They are proportional gain, integral gain, and differential gain respectively.

[0064] [Formula 9]

[0065]

[0066] It can be considered that the steering torque T is substantially proportional to the steering current I, which is the current supplied to the steering motor 18. Accordingly, the steering ECU 14 calculates the steering current determination coefficient K by I The target steering current I*, which is a target steering current I, is determined by multiplying the determined target steering torque T*, and a current is supplied to the steering motor 18 based on the target steering current I*.

[0067] (b) Rear wheel evasive control

[0068] When either of the left and right front wheels 10F passes through a bump that disturbs the running of the vehicle, the running of the vehicle will be extremely unstable if the rear wheel 10R located on the same side of the left and right also passes through the bump. In view of this, in this system, the rear wheel avoidance control is performed so that the rear wheel 10R does not pass through the bump that the front wheel 10F passes through. The processing in the rear wheel avoidance control is described below.

[0069] i) Change of target sideslip angle

[0070] In the rear wheel avoidance control, the integrated ECU 16 changes the target side slip angle β* in the target line driving control from 0° during straight driving or the standard side slip angle β during turning to REF Changed to rear wheel side slip angle β A . Reference Figure 3 (a) is used to illustrate that the rear wheel avoids the side slip angle β A It is determined according to the following formula. Figure 3 (a) shows the situation in which the left front wheel 10FL passes the unevenness R while the vehicle is turning left. A Incidentally, the rear wheel 10R can be displaced to either the left or right, but in this system, the rear wheel 10R is displaced toward the center of the vehicle relative to the front wheel 10F.

[0071] [Formula 10]

[0072]

[0073] Rear wheel avoidance control, that is, the target sideslip angle β* to the rear wheel avoidance sideslip angle β A The change is performed until the rear wheel 10R passes the bump. Specifically, the change is performed from the moment when the front wheel 10F passes the bump R until the vehicle travels a distance equivalent to the wheelbase l. The integrated ECU 16 obtains the travel distance D of the vehicle based on the mileage information. Specifically, for example, based on the wheel speed v of each wheel 10 W When the vehicle has traveled a distance equivalent to the wheelbase l, if it is traveling straight, the integrated ECU 16 changes the target side slip angle β* from the rear wheel avoidance side slip angle β A Return to 0°, or return to the standard sideslip angle β when turning REF .

[0074] By the rear wheel avoidance control as described above, Figure 3 As schematically shown in (b), the vehicle can avoid passing the unevenness R of the rear wheel 10R while the vehicle travels along the target line L*, that is, while the vehicle travels with the center of gravity C moving on the target line L*.

[0075] ii) Starting conditions

[0076] The rear wheel avoidance control is started with the passage of the bump R by any of the front wheels 10F as a trigger. The bump R that becomes the trigger is a bump to the extent that it is estimated that the vehicle's travel becomes very unstable if the rear wheel 10R also passes through the bump R. The load of the vehicle body is shared by the four wheels 10, but when one front wheel 10F passes through a bump, depending on the extent of the bump, a state may occur in which not only the front wheel 10F but also the rear wheel 10R located on the same side of the left or right does not share the weight of the vehicle body. In simple terms, the front wheel 10F and the rear wheel 10R on one side of the left or right are both floating (hereinafter sometimes referred to as the "single-sided two-wheel floating state"). In this system, the execution of the rear wheel avoidance control is started on the condition that the above-mentioned single-sided two-wheel floating state is achieved.

[0077] The above detection of the floating state of the two wheels on one side can be performed based on the method based on ZMP (zero moment point). Since this method is a general method, the following reference Figure 4 Here, "ZMP" refers to the point where the combined force of gravity and inertia on the vehicle intersects the road surface.

[0078] In the (x, y, z) coordinate system, if the center of gravity position vector "C", vehicle momentum vector "P", vehicle angular momentum vector "L", gravity acceleration vector "g", and ZMP position vector "p" are defined as follows,

[0079] 《C》=[xyz] T

[0080] 《P》=[P X P Y P Z ] T

[0081] 《L》=[L X L Y L Z ] T

[0082] 《g》=[00-g] T

[0083] 《p》=[p X p Y p Z ] T

[0084] Then, regarding the position of ZMP, the following two equations hold. By the way, M is the vehicle weight and g is the acceleration due to gravity.

[0085] [Formula 11]

[0086]

[0087] [Formula 12]

[0088]

[0089] In the accompanying drawings, the sprung center of gravity C is shown. S , the unsprung center of gravity C corresponding to each wheel 10 U The plane formed by connecting the points where each of the four wheels 10 contacts the road surface is defined as the support plane PL. The position of the projection point p of ZMP onto the support plane PL (p X , p Y ) moves on the support plane PL. When one of the two front wheels 10F passes through the bump R, when the height or depth of the bump R is relatively large, the ZMP moves significantly, and the projection point p moves to a position on either side of the support plane PL. At this time, the vehicle is in a state of floating on one side of the two wheels on either side. In this system, when the projection point p of the ZMP moves to a position on either side of the support plane PL, it is considered that the front wheel 10F has passed through the bump R that should be dealt with, and the rear wheel avoidance control is started.

[0090] (c) Target steering angle determination process

[0091] The target steering angle determination process in the target line driving control including the above-mentioned rear wheel avoidance control is repeatedly executed by the integrated ECU 16 at short time intervals (for example, several to several tens of milliseconds). Figure 5 The target steering angle determination processing procedure shown in the flowchart is performed. The flow of the target steering angle determination processing is described below according to the flowchart.

[0092] Data related to the target line L* of the vehicle is always sent from the automatic driving ECU 22. In the process according to the above program, first, in step 1 (hereinafter abbreviated as "S1". The same applies to other steps), the target point angle δ is determined based on the data. G In the next S2, it is determined whether the rear wheel avoidance flag FL is 1. The rear wheel avoidance flag FL is a flag which is set to 1 when the above-mentioned rear wheel avoidance control is being performed, and is set to 0 when the rear wheel avoidance control is not being performed.

[0093] When the rear wheel avoidance control is not performed, in S3, it is detected whether any of the left and right front wheels 10F has passed the bump R to be dealt with based on the above-mentioned ZMP method. When neither of the front wheels 10F has passed the bump R, in S4, the rear wheel avoidance flag FL is reset to 0. Next, in S5, it is determined whether the vehicle is going straight or turning. Specifically, at the target point angle δ GWhen it is 0, it is determined to be straight driving, and when it is not 0, it is determined to be turning. In the case of straight driving, the above-mentioned target sideslip angle β* is set to 0 in S6, and in the case of turning, the target sideslip angle β* is set to the standard sideslip angle β in S7. REF .

[0094] If it is determined in S3 that any of the front wheels 10F has passed the unevenness R, in S8, the rear wheel avoidance flag FL is set to 1, and the rear wheel avoidance control is started. Then, in S9, the rear wheel avoidance side slip angle β is determined as described above. A In S10, the target side slip angle β* is set to the rear wheel avoidance side slip angle β A Next, in S11, the travel distance D is reset to 0. The travel distance D is the distance traveled by the vehicle after the front wheel 10F passes over the unevenness R.

[0095] If it is determined in S2 that the rear wheel avoidance flag FL is 1, that is, when the rear wheel avoidance control is executed, in S12, the travel distance D is updated by an update distance ΔD. The update distance ΔD is based on the execution time interval of the program and the wheel rotation speed v of each wheel 10. W When the rear wheel avoidance control is performed, it is determined in S13 whether the travel distance D exceeds the distance corresponding to the wheelbase l of the vehicle. If the travel distance D exceeds the distance corresponding to the wheelbase l, the rear wheel avoidance flag FL is reset to 0 in S4, and the execution of the rear wheel avoidance control is terminated.

[0096] Based on the target sideslip angle β* and the target point angle δ set as described above G And the target distance S G In S14, the front wheel target steering angle δ is determined according to the above method. F *、Rear wheel target steering angle δ R *, in S15, the front wheel target steering angle δ determined by these F *、Rear wheel target steering angle δ R * is transmitted to each steering ECU 14 via the CAN 20. Each steering ECU 14 receiving the signal regarding the target steering angle δ* steers the corresponding wheel 10 as described above so that the steering angle δ of the corresponding wheel 10 becomes the target steering angle δ*.

[0097] Description of reference numerals:

[0098] 10F: front wheel; 10R: rear wheel; 12F: front wheel steering device; 12R: rear wheel steering device; 14: steering electronic control unit (steering ECU) [controller]; 16: integrated electronic control unit (integrated ECU) [controller]; β A : rear wheel avoidance slip angle; SA : rear wheel displacement; L*: target line; X: vehicle front and rear axis; l: wheelbase; δ F : front wheel steering angle; δ R : rear wheel steering angle; R: bump; C: vehicle center of gravity.

Claims

1. A steering system, provided in a vehicle, wherein: have: Front wheel steering device, to steer the front wheels; a rear-wheel steering device for steering the rear wheels; and a controller for controlling the front-wheel steering device and the rear-wheel steering device in a manner capable of steering the front wheels and the rear wheels independently of each other, The controller is configured to execute rear wheel avoidance control for avoiding the rear wheel from passing through the bump when the front wheel passes through the bump. In the rear wheel avoidance control, the vehicle center of gravity side slip angle to be achieved, i.e., the rear wheel avoidance side slip angle, is determined, and based on the rear wheel avoidance side slip angle, the steering angle at which each of the front and rear wheels should be turned, i.e., the target steering angle, is determined.

2. The steering system according to claim 1, wherein: The controller is configured to determine the rear wheel avoidance sideslip angle based on a distance by which the rear wheel should be displaced in the lateral direction from the unevenness and the wheelbase of the vehicle during the rear wheel avoidance control.

3. The steering system according to claim 1, wherein: The controller is configured to execute target line driving control to steer the front and rear wheels so that the vehicle travels along a target line, which is a driving line that the vehicle should travel. When the front wheel passes over a bump, the rear wheel avoidance control is executed while continuing to execute the target line driving control.

4. The steering system according to claim 3, wherein: The controller is configured to set a target point on the target line in front of the vehicle during the target line driving control, and determine the target steering angles of the front wheels and the rear wheels based on the positional relationship between the target point and the vehicle and a predetermined vehicle center of gravity side slip angle, i.e., a standard side slip angle. The target steering angles of the front wheels and the rear wheels are determined based on the rear wheel avoidance sideslip angle instead of the standard sideslip angle, thereby executing the rear wheel avoidance control while executing the target line traveling control.

5. The steering system according to claim 1, wherein: The controller is configured to execute the rear wheel avoidance control on the condition that lift of both the front wheel and the rear wheel is detected.

6. The steering system according to claim 1, wherein: The controller is configured to execute the rear wheel avoidance control until the vehicle travels a distance corresponding to the wheelbase of the vehicle after the front wheels pass over the unevenness.

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