Steering system

Abstract

To provide a steer-by-wire system having high practicality.SOLUTION: The steer-by-wire system is configured such that, when a stored neutral position (ω0mi + Δωm), which is a neutral steering position stored for controlling steering actuators, is shifted from an actual neutral position, which is an actual neutral steering position, a neutral position shift elimination process for bringing the stored neutral position closer to the actual neutral position (S27) is executed in a state (S26) in which an operation of an operation member for causing a vehicle to travel straight is maintained by a driver. Since the neutral position shift elimination process is executed in a state where the driver is driving the vehicle straight, the process is relatively simple.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] This invention relates to a steer-by-wire type steering system mounted on a vehicle. [Background technology]

[0002] In a steer-by-wire steering system installed in a vehicle (hereinafter sometimes referred to as "steer-by-wire system"), the steering wheel and other operating components are generally not mechanically connected to the wheels being steered. Therefore, the wheels are steered by the power source of the steering actuator, rather than by the force applied to the operating components by the driver (hereinafter sometimes referred to as "operating force"). In a steer-by-wire system, wheel steering is mainly performed in response to the operation of the operating components, so the relationship between the operating position of the operating components and the steering position of the wheels is important in controlling wheel steering (hereinafter sometimes referred to as "steering control"). Specifically, if the operating position of the operating components that the vehicle should be in when traveling straight is defined as the neutral operating position, then when the operating components are in that neutral operating position, the attitude of the wheels being steered should also be the attitude when traveling straight. In other words, the steering position of the wheels should also be in the neutral steering position.

[0003] The controller that performs steering control stores the neutral operating position and the neutral steering position, and performs steering control based on these stored neutral operating position and neutral steering position. However, if the toe angle of the wheel to be steered is adjusted, or if a relatively large force is applied to the wheel to be steered from the outside, the stored neutral position may deviate from the actual neutral steering position. If this deviation (hereinafter sometimes referred to as "neutral position deviation") occurs, it is expected that the steering wheel may not be steered properly in response to the driver's operation of the control member, or that the driver may feel uncomfortable with the operation. Therefore, in steer-by-wire systems, for example, the processing described in the following patent document is being considered. This processing is a technology in which, in target line following control that steers the wheels so that the vehicle travels along a target line, the neutral steering position is set based on the difference between the target steering position based on the target line and the steering position detected by the sensor. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-177128 [Overview of the project] [Problems that the invention aims to solve]

[0005] The technology described in the above-mentioned patent document relates to target line following control, which is one type of driver assistance control, and requires a certain degree of accuracy in setting the neutral steering position. On the other hand, there are also driver assistance controls that steer the steering wheels for safety, such as vehicle stabilization control and lane departure prevention control, and it is desirable that these controls be executed even before a highly accurate neutral steering position is obtained by executing target line following control, that is, even when there is a certain degree of neutral position deviation. Furthermore, the setting of the neutral steering position in target line following control is based on complex methods and learning, and it is also desirable to eliminate the neutral position deviation in a simple way instead of such a setting. In other words, it is thought that the practicality of the steer-by-wire system will be improved if the neutral position deviation can be easily eliminated. The present invention has been made in view of such circumstances and aims to provide a highly practical steer-by-wire type steering system for vehicles. [Means for solving the problem]

[0006] To solve the above problems, the steering system of the present invention is Operating components operated by the driver, A steering actuator that has a power source and steers the wheels using the force of that power source, A controller that controls the steering actuator in order to achieve wheel steering in response to the operation of the operating member. A steer-by-wire steering system mounted on a vehicle, comprising: The controller is configured to perform a neutral position correction process to bring the stored neutral position closer to the actual neutral position when the stored neutral position, which is the neutral steering position stored for controlling the steering actuator, deviates from the actual neutral steering position, while the driver is maintaining operation of the operating member to move the vehicle straight. Assuming that, The first steering system is The steering system includes an operating reaction force applying device that applies an operating reaction force, which is a reaction force to the operation of the operating member, The aforementioned controller Control is performed to apply an operating reaction force that includes a component to return the operating position of the operating member to the neutral operating position, which is the position that the vehicle should be in when moving straight. The system is configured to terminate the neutral position displacement correction process when the operating reaction force is eliminated, or when the driver's operating force to resist the operating reaction force is eliminated. The second steering system is In the vehicle in question, multiple driver assistance controls are implemented, each involving automatic steering of the wheels. The steering system is configured to allow at least one of the multiple driver assistance controls even while the neutral position misalignment correction process is being executed. [Effects of the Invention]

[0007] In the steering system of the present invention, the neutral position deviation correction process is performed while the driver is driving the vehicle straight, making the process relatively simple. As a result, the steering system of the present invention is highly practical. (Aspects of the Invention)

[0008] In this invention, the "operating member" is generally a steering wheel, but it may be various other things such as a steering wheel, control stick, or joystick. The steering system of this invention is a steer-by-wire system, and generally, the "steering actuator" is not mechanically connected to the operating member. Therefore, the steering actuator has a "power source" (which can also be called a "driving source") such as an electric motor or hydraulic cylinder, and steers the wheels by the force of that power source, without relying on the force applied by the driver to the operating member (hereinafter sometimes referred to as "operating force"). The structure of the steering actuator is not particularly limited, but for example, in a vehicle in which a pair of left and right wheels are steered, it may have a steering rod that connects a pair of steering knuckles that hold each of those wheels, and a structure that moves the steering rod from side to side. In a steering system equipped with a steering actuator of such a structure, for example, a mechanism for adjusting the toe angle of the wheel is provided between the end of the steering rod and the steering knuckle, and the toe angle is adjusted by that mechanism. If such toe angle adjustment is performed, the actual neutral steering position is likely to change. Therefore, the above-mentioned process for correcting the neutral position misalignment is highly significant when performed after adjusting the toe angle.

[0009] In a narrow sense, "steering position" refers to the attitude of the wheel being steered (e.g., "rotation position," "toe angle," etc.). However, in the steering system of the present invention, it is interpreted more broadly to also refer to the operating position of the steering actuator. Therefore, "neutral steering position" refers to the attitude of the wheels that the vehicle should take when moving straight, or the operating position of the steering actuator. Specifically, for example, the toe angle of the wheel being steered (or the toe angle of each wheel if there is a pair of wheels being steered) or the operating position of the steering rod in the steering actuator of the above structure when the vehicle is moving straight corresponds to the neutral steering position. Similarly, with respect to the operating member, the position of the operating member (for example, the rotation angle of the steering wheel if the operating member is a steering wheel) is called the "operating position," and the operating position when trying to move the vehicle straight is called the "neutral operating position."

[0010] In a steer-by-wire system, the wheels are steered by the driver's operation of control components. In other words, the steering of the wheels (hereinafter sometimes referred to as "steering control") is controlled based on the driver's operation of the control components. In this steering control, for example, when the control component is in the neutral position, the steering position is set to the neutral steering position, and when the control component is operated by a certain amount from the neutral position, the steering position is changed from the neutral steering position by an amount of steering corresponding to that amount of operation. This steering control is performed by a "controller." Incidentally, the controller is composed of, for example, a computer as the main component and includes a driver (drive circuit) for the steering actuator.

[0011] The controller performs the steering control described above based on the stored neutral position, which is the neutral steering position it has memorized. Therefore, in a state of "neutral position deviation," where the stored neutral position deviates from the actual neutral steering position, even if the driver positions the control member in the neutral control position, the vehicle will not move straight, that is, it will deviate to either the left or the right.

[0012] The above "neutral position deviation elimination process" in the present invention is performed when a neutral position deviation occurs, while the driver maintains the operation of driving the vehicle straight. In other words, it is performed in a state where the driver has shifted the operation member from the neutral operation position to make the vehicle go straight. That is, in the neutral position deviation elimination process, the controller shifts (offsets) the stored neutral position in the direction in which the vehicle goes straight, on the condition that the driver is performing an operation to maintain that state. That is, the stored neutral position is brought closer to the actual neutral position. According to this neutral position deviation elimination process, although an operation for the driver to drive the vehicle straight is required, it is possible to simply adjust the neutral steering position.

[0013] The neutral position deviation elimination process may be a process that instantaneously brings the stored neutral position closer to the actual neutral position. However, a sudden change in the neutral steering position may give the driver a sense of discomfort and may also hinder the running stability of the vehicle. Therefore, in this steering system, it is desirable to perform a neutral position deviation elimination process that gradually changes the stored neutral position toward the actual neutral position. In other words, it is desirable to shift it step by step little by little, that is, to shift it so that the neutral steering position changes continuously over a relatively long period of time.

[0014] It is desirable to end the neutral position deviation elimination process when the stored neutral position coincides with the actual neutral position or when it can be regarded as coinciding. The determination of whether the stored neutral position coincides with the actual neutral position or can be regarded as coinciding can be made, for example, by whether the stored neutral position has been shifted by that amount when the amount of neutral position deviation can be grasped in advance. Specifically, when the difference between the stored neutral position and the actual neutral position becomes smaller than the set threshold value, the neutral position deviation elimination process may be ended. It may also be performed by the method described below.

[0015] During the execution of the neutral position deviation elimination process, the driver attempts to keep the operating position of the operating member at the position where the vehicle goes straight. Therefore, when the neutral position deviation is eliminated, the operating position of the operating member will naturally be at the neutral operating position. Taking advantage of this, the neutral position deviation elimination process may be terminated on the condition that the operating position of the operating member is at the neutral operating position. This condition may be that the operating position is generally at the neutral operating position. Also, in a steer-by-wire system, since the steered wheel and the operating member are not mechanically connected, generally, a reaction force applying device that applies an operating reaction force, which is the reaction force to the operation of the operating member, is provided to the operating member. The controller also controls the reaction force applying device. Specifically, for example, the reaction force applying device is controlled to apply an operating reaction force having a component for returning the operating member to the neutral operating position to the operating member. When such control is being performed, when the above neutral position deviation occurs, the driver needs to position the operating member at a position shifted from the neutral operating position by an operating force that resists the operating reaction force in order to make the vehicle go straight. However, in a state where such an operating reaction force is applied, as the neutral position deviation elimination process progresses, the operating reaction force gradually becomes smaller. Taking advantage of this, the neutral position deviation elimination process may be terminated when the operating reaction force disappears or when the operating force that resists the operating reaction force disappears. Specifically, when the operating reaction force has almost disappeared or when the operating force that resists the operating reaction force has almost disappeared, if the stored neutral position is considered to have coincided with the actual neutral position, the neutral position deviation elimination process may be terminated. According to these methods, it is possible to appropriately terminate the neutral position deviation elimination process without knowing the amount of the neutral position deviation.

[0016] In many vehicles, various driver assistance controls are implemented. Specifically, these include controls to keep the vehicle along a target line (target line following control), controls to prevent the vehicle from deviating from its lane (lane departure prevention control), controls to keep the vehicle stable along the line during turns (vehicle stabilization control), and controls to avoid collisions with obstacles ahead (collision avoidance control). All of these driver assistance controls involve automatic steering of the wheels, that is, steering that does not depend on the driver's operation of control members. It is safer not to perform such controls when the above-mentioned neutral position deviation occurs. However, for controls that prioritize safety, such as lane departure prevention control, vehicle stabilization control, and collision avoidance control, it is desirable to perform them even if there is a slight neutral position deviation and the accuracy of the control itself is somewhat poor. Therefore, in the steering system of the present invention, it is desirable to allow at least one of the multiple driver assistance controls even while the neutral position deviation correction process is being performed.

[0017] To explain in more detail, the various driver assistance controls can be classified into two categories. One category is safety-focused assistance control, which prioritizes vehicle safety even if the accuracy of the neutral steering position is low, and includes lane departure prevention control, vehicle stabilization control, and collision avoidance control. The other category is high-precision-required assistance control, which requires accurate determination of the steering neutral position, and is the target line following control. In light of this, it is desirable to allow the execution of at least safety-focused control even while the neutral position deviation correction process is being performed. [Brief explanation of the drawing]

[0018] [Figure 1] This figure shows the overall configuration of the steering system in the embodiment. [Figure 2] This is a flowchart of the steering control program executed in the steering system of the embodiment. [Figure 3] This is a flowchart of the reaction force control program executed in the steering system of the embodiment. [Figure 4] This is a schematic diagram illustrating the stopper that defines the operating range of the steering actuator, and the adjustment of the wheel toe angle. [Figure 5] This is a flowchart of the neutral position misalignment correction program executed in the steering system of the embodiment. [Figure 6] This is a flowchart of the IG-OFF program and IG-ON program executed in the steering system of the embodiment in relation to the neutral position misalignment correction process. [Figure 7] This diagram shows one specific example of the process for correcting neutral position misalignment. [Figure 8] This diagram shows another specific example of the neutral position misalignment process. [Modes for carrying out the invention]

[0019] Hereinafter, a steering system, which is an embodiment of the present invention, will be described in detail with reference to the drawings as an embodiment for carrying out the present invention. In addition to the embodiments described below, the present invention can be carried out in various forms by making various changes and improvements based on the knowledge of those skilled in the art, starting with the forms described in the section [Embodiments of the Invention] above. [Examples]

[0020] [1] Overall configuration of the steering system The steering system of this embodiment (hereinafter sometimes referred to as "this steering system" or "this system") is a steer-by-wire type steering system that can steer the wheels without the driver's operating force applied to the operating member. As shown in Figure 1, it is composed of a reaction force actuator 12 to which the steering member, the handle 10, is connected, and a steering actuator 16 to which the two left and right wheels 14 are connected and which steer them together. Incidentally, the handle 10 is shaped like a modified steering wheel and is rotated by the driver. The reaction force actuator 12 receives this operation and is configured to apply a reaction force (hereinafter sometimes referred to as "operating reaction force") to the handle 10, or more specifically, to the operation of the handle 10.

[0021] The reaction force actuator 12 comprises a steering column 20 supported by the reinforcement of the instrument panel, a steering shaft 22 rotatably held in the steering column 20, and a reaction force motor 24, which is an electric motor for applying rotational torque to the steering shaft 22 via a power transmission mechanism. The steering wheel 10 is attached to the rear end of the steering shaft 22. The power transmission mechanism, although a detailed structural description is omitted, comprises a worm attached to the motor shaft of the reaction force motor 24 and a worm wheel attached to the steering shaft 22 that meshes with the worm. The reaction force motor 24 is a three-phase brushless DC motor and functions as the power source for the reaction force actuator 12. The torque generated by the reaction force motor 24 applies a reaction force torque as an operating reaction force to the steering wheel 10 connected to the steering shaft 22. The steering shaft 22 functions as a movable member of the reaction force actuator 12, and the reaction force actuator 12 functions as an operating reaction force application device.

[0022] The steering actuator 16 comprises a generally cylindrical housing 30 supported on the chassis in an orientation extending to the left and right, a steering rod 32 held in the housing 30 so as to be non-rotatable and movable from side to side, and a pair of tie rods 34 connected to the left and right ends of the steering rod 32 via ball joints. The ends of each tie rod 34 are connected to the wheels 14 via ball joints. More specifically, each tie rod 34 is connected via ball joints to the knuckle arm of a steering knuckle, which is held rotatably on the suspension arm and holds the wheel 14 so as to be rotatable.

[0023] The steering rod 32 has a screw groove 36 formed therein. Although not shown in the illustration, a nut that holds bearing balls and screws into the screw groove 36 is held inside the housing 30 so as to be immovable from side to side but rotatable. In other words, the steering rod 32 and the nut constitute a ball screw mechanism. An electric motor, the steering motor 38, is attached to the housing 30, and the steering motor 38 rotates the nut via a power transmission mechanism. Incidentally, although not shown in the illustration, the power transmission mechanism includes a pulley attached to the motor shaft of the steering motor 38 and a timing belt wrapped around the pulley and the outer circumference of the nut. The steering motor 38 is a three-phase brushless DC motor and functions as a power source for the steering actuator 16. By rotating the steering motor 38, the steering rod 32 is moved from side to side, and the left and right wheels 14 are steered together. The steering rod 32 functions as a movable member of the steering actuator 16.

[0024] The reaction force actuator 12 is controlled by a reaction force electronic control unit (hereinafter sometimes referred to as "reaction force ECU") 40 attached to the reaction force motor 24. The reaction force ECU 40 consists of a computer consisting of a CPU, ROM, RAM, etc., and an inverter which is the driver (drive circuit) for the reaction force motor 24, and is powered by a battery. Similarly, the steering actuator 16 is controlled by a steering electronic control unit (hereinafter sometimes referred to as "steering ECU") 42 attached to the steering motor 38. The steering ECU 42 consists of a computer consisting of a CPU, ROM, RAM, etc., and an inverter which is the driver (drive circuit) for the steering motor 38, and is powered by a battery.

[0025] The reaction force ECU 40 and the steering ECU 42 work in coordination with each other, and together they constitute a single controller for the steering system. Therefore, the reaction force ECU 40 and the steering ECU 42 are connected by a dedicated high-speed communication line 44. Incidentally, both are also connected to the CAN (car area network or controllable area network) 46 provided by the vehicle.

[0026] In relation to control, the reaction actuator 12, although a detailed structural description will be omitted, has an operating torque sensor 50 that detects the amount of twist of the steering shaft 22 to detect the operating torque To, which is the operating force applied by the driver to the steering wheel 10. It also has an operating angle sensor 52 that detects the operating angle δ of the steering wheel 10 by detecting the rotation angle of the steering shaft 22, and a reaction motor rotation angle sensor 54 for detecting the rotation angle (rotation phase) φc of the reaction motor 24 for purposes such as switching the energized phase.

[0027] Furthermore, since there is a specific relationship between the steering angle ω of the wheel 14 and the lateral movement position of the steering rod 32, the steering actuator 16 has a steering angle sensor 56 that detects the movement position of the steering rod 32 in order to detect the steering angle ω of the wheel 14. Briefly, a rack 58 is formed on the steering rod 32, and a pinion shaft 60 that meshes with the rack 58 is held in the housing 30. The steering angle sensor 56 detects the amount of lateral movement of the steering rod 32 by detecting the rotation angle of the pinion shaft 60, and thereby detects the steering angle ω of the wheel 14. Incidentally, the movement position of the steering rod 32 is the operating position of the steering actuator 16, that is, the steering position of the wheel 14. The steering actuator 16 also has a steering motor rotation angle sensor 62 for detecting the rotation angle (rotation phase) φs of the steering motor 38 for purposes such as switching the energized phase.

[0028] [2] Control of the steering system In this steering system, the steering ECU 42 performs steering control to steer the wheels 14, and the reaction force ECU 40 performs reaction force control to apply a reaction force torque as an operating reaction force to the steering wheel 10. The steering control and reaction force control are described below.

[0029] (a) Steering control Steering control is a control mechanism that directs the steering actuator 16 to steer the wheels 14 to a steering angle ω corresponding to the operating angle δ. This is performed by the steering ECU 42 computer repeatedly executing the steering control program, shown in the flowchart in Figure 2, at short time intervals (for example, several meters to tens of milliseconds). The steering control will be explained below in accordance with this program. For the sake of ease of understanding, the operating angle δ will sometimes be referred to as "the operating angle δ of the steering wheel 10" below.

[0030] In the process following the steering control program, first, in step 1 (hereinafter abbreviated as "S1"; the same applies to the other steps), the steering ECU 42 obtains the operating angle δ of the steering wheel 10 from the reaction force ECU 40 via a dedicated high-speed communication line 44. To explain the operating angle δ, the operating angle δ as the operating position of the operating member is determined as the operating position of the reaction force actuator 12, that is, the rotational angle position of the steering shaft 22, which is a movable member. The operating position of the reaction force actuator 12 is defined with respect to the neutral operating position, that is, the operating position that the vehicle should be in when it is moving straight. As will be explained in detail later, the reaction force ECU 40 identifies the displacement angle from the neutral operating angle δ0, which is the neutral operating position of the steering shaft 22, based on the motor rotation angle φc of the reaction force motor 24, as the operating angle δ, and transmits a signal about that operating angle δ to the steering ECU 42 via the dedicated high-speed communication line 44. The steering ECU 42 obtains the operating angle δ based on that signal. The neutral operating angle δ0 is stored in the reaction force ECU40.

[0031] In the subsequent S2, the steering ECU 42 determines the target steering angle ω, which is the steering angle ω at which the wheel 14 should be steered, based on the acquired steering angle δ. * This is determined. To explain the steering angle ω, similar to the operating angle δ, the steering angle ω as the steering position is determined as the operating position of the steering actuator 16, that is, the movement position of the steering rod 32, which is a movable member. The operating position of the steering actuator 16 is defined based on the neutral steering position, that is, the operating position that the vehicle should be in when it is moving straight. Based on the detection by the steering angle sensor 56, the steering ECU 42 detects the amount of movement of the steering rod 32 from the neutral position, that is, the displacement angle of the pinion shaft 60 from the neutral angular position, as the steering angle ω. Incidentally, the neutral steering position can be called the neutral steering angle ω0, and it will be referred to as the neutral steering angle ω0 below. As will be explained in detail later, the neutral steering angle ω0 is stored in the steering ECU 42, and this stored neutral steering position is conceptual, and will be referred to as the "stored neutral position" or "stored neutral steering angle ω0m" below.

[0032] Since the steering angle δ and the steering angle ω are related in a way that satisfies the set steering gear ratio Ns, in S2, the target steering angle ω * This is determined according to the following formula. ω * =Ns·δ The steering gear ratio Ns may be set to a fixed value, or it may be set to change according to, for example, the vehicle speed.

[0033] Since the steering angle ω and the steering motor rotation angle φs have a specific gear ratio relationship Nms, steering control is performed based on the steering motor rotation angle φs, taking into consideration detection accuracy, etc. Therefore, in S3, the steering ECU 42 sets the target steering motor rotation angle φs, which is the control target for the steering motor rotation angle φs, according to the following equation. * To decide. φs * =Nms·ω * The steering angle sensor 56 is capable of detecting absolute angles, and even if the ignition switch is turned OFF, it can detect the steering angle ω relative to the neutral steering position (memorized neutral position) when it is turned ON. In this steering system, the steering ECU 42 is configured to calibrate the steering motor rotation angle φs detected by the steering motor rotation angle sensor 62 based on the steering angle ω detected by the steering angle sensor 56 each time the ignition switch is turned ON. Incidentally, the steering motor rotation angle sensor 62 only detects a rotation phase of 360°, or one full rotation, but the steering ECU 42 is configured to detect steering motor rotation angles φs exceeding 360° through integration processing.

[0034] Next, in S4, the steering ECU 42 detects the current steering motor rotation angle φs using the steering motor rotation angle sensor 62, and in S5, it sets the target steering motor rotation angle φs according to the following equation. * Identify the steering motor rotation angle deviation Δφs, which is the deviation of the steering motor rotation angle φs at the current time relative to the given value. Δφs = φs * -φs

[0035] In the subsequent S6, the steering ECU 42 determines the torque that the steering motor 38 should generate, i.e., the steering torque Ts that the steering actuator 16 should generate, based on the steering motor rotation angle deviation Δφs and in accordance with the PID feedback control law, specifically according to the following equation. Ts=Gsp·Δφs+Gsi·∫(Δφs)dt+Gsd·d(Δφs) / dt Incidentally, Gsp, Gsi, and Gsd are the proportional term gain, integral term gain, and differential term gain, respectively.

[0036] Since the steering torque Ts and the steering current Is, which is the current supplied to the steering motor 38 as a power source, are roughly proportional, the steering ECU 42 determines the steering current Is in S7 based on the steering torque Ts and using the coefficient of current determination Ks, according to the following equation. Is=Ks·Ts

[0037] The determined steering current Is is supplied from the inverter to the steering motor 38 in S8. Then, in S9, the steering ECU 42 transmits a signal regarding the steering current Is to the reaction force ECU 40 via a dedicated high-speed communication line 44 for use in the reaction force control described later, and one execution of the steering control program is completed.

[0038] (b) Control of reaction force Reaction force control is a control method that applies a reaction force torque to the reaction force actuator 12 as a reaction force to the steering wheel 10, with the aim of providing the driver with an appropriate steering feel and returning the steering wheel 10 to the neutral position. Reaction force control is performed by the computer of the reaction force ECU 40 repeatedly executing the reaction force control program, which is shown in the flowchart in Figure 3, at short time intervals (for example, several meters to tens of milliseconds). The reaction force control will be explained below in accordance with that program.

[0039] In the process according to the reaction force control program, first, in S11, the reaction force ECU 42 detects the motor rotation angle φc of the reaction force motor 24 using the reaction force motor rotation angle sensor 54. Since the operating angle δ and the reaction force motor rotation angle φc have a specific gear ratio Nmc relationship, the reaction force control is performed based on the reaction force motor rotation angle φs, taking into consideration the detection accuracy, etc. Therefore, in S12, the reaction force ECU 40 determines the operating angle δ based on the reaction force motor rotation angle φc according to the following equation. δ = Nmc·φc The operating angle sensor 52 is capable of detecting absolute angles, and even if the ignition switch is turned OFF, it can detect the operating angle δ at the time it is turned ON. In this steering system, the reaction force ECU 40 is configured to calibrate the reaction force motor rotation angle φc detected by the reaction force motor rotation angle sensor 54 based on the operating angle δ detected by the operating angle sensor 52 each time the ignition switch is turned ON. Incidentally, the reaction force motor rotation angle sensor 54 only detects a rotation phase of 360°, i.e., one rotation, but the reaction force ECU 40 is configured to detect the reaction force motor rotation angle φc exceeding 360° through integration processing. In S13, the reaction force ECU 40 transmits a signal for the specified operating angle δ to the steering ECU 42 via a dedicated high-speed communication line 44 for use in the steering control described above.

[0040] The reaction torque Tc consists of two components. One is the neutral position return component Tcc, which returns the operating position of the reaction actuator 12, i.e., the steering wheel 10, to the neutral operating position, and the other is the steering load dependent component Tcs, which simulates the load on the steering actuator 16. In S14, the reaction force ECU 40 uses the neutral position return component determination coefficient Cc and determines the neutral position return component Tcc according to the following equation. Tcc = Cc·δ According to the above formula, the neutral position return component Tcc is determined such that the reaction torque Tc required to return the handle 10 to the neutral position increases as the operating angle δ increases.

[0041] The load on the steering actuator 16 can be considered to be roughly proportional to the steering current Is, which is the current supplied to the steering motor 38. In the following S15, the reaction force ECU 40 acquires the steering current Is based on the signal transmitted from the steering ECU 42. Then, in S16, the reaction force ECU 40 uses the steering load component determination coefficient Cs to determine the steering load dependent component Tcs according to the following equation. Tcs=Cs·Is According to the above formula, the steering load-dependent component Tcs is determined such that the larger the steering current Is, that is, the larger the load on the steering actuator 16, the greater the reaction torque Tc applied.

[0042] Based on the neutral position return component Tcc and steering load dependent component Tcs determined as described above, in S17, the reaction force ECU 40 determines the reaction force torque Tc according to the following equation. Tc = Tcc + Tcs Since the reaction torque Tc and the reaction current Ic, which is the current supplied to the reaction motor 24 as a power source, are roughly proportional, the reaction ECU 40 determines the reaction current Ic in S18 based on the reaction torque Tc and using the coefficient of current determination Kc, according to the following equation. Ic=Kc·Tc The determined reaction force current Ic is supplied from the inverter to the reaction force motor 24 in S19, and one execution of the reaction force control program is completed.

[0043] (c) Driver assistance control Vehicles equipped with this steering system are also equipped with a driver assistance system that performs multiple driver assistance controls to support the driver's operation of the vehicle. These multiple driver assistance controls include target line following control (LTA), lane departure prevention control (LDA), vehicle stability control (VSC), and pre-collision control (PCS). All of these controls involve automatic steering of the wheels 14, that is, steering of the wheels 14 without relying on the driver's operation of the steering wheel 10.

[0044] Briefly explaining each driving support control, the target lane tracking control is a control for driving the vehicle along the target driving line set in the center of the driving lane when the vehicle is driving on, for example, a highway. According to this control, when the vehicle deviates from the target driving line due to the driver's steering of the wheel 14, the steering angle ω of the wheel 14 is adjusted. The lane departure prevention control is a control for preventing the vehicle from leaving the driving lane. According to this control, when the vehicle protrudes into either the left or right of the driving lane in which it is driving, a warning is issued to the driver, and the wheel 14 is forcibly steered to keep the vehicle within the driving lane. This control is executed only when the vehicle is traveling at a speed of a certain level or more (for example, 50 km / h or more). The vehicle stabilization control is a control for stabilizing the running or posture of the vehicle when the vehicle is turning. According to this control, when the vehicle tends to be understeer or oversteer beyond the limit, in addition to operations such as braking and accelerating, the wheel 14 is steered to suppress the understeer or oversteer. The collision avoidance control is a control for preventing the vehicle from colliding with an obstacle ahead. According to this control, when there is a high possibility that the vehicle will collide with an obstacle ahead even by braking, the wheel 14 is steered to avoid the collision. The vehicle stabilization control and the collision avoidance control are executed regardless of whether the vehicle is driving on an ordinary road or the driving speed of the vehicle.

[0045] Each of the above driving support controls is executed by a driving support electronic control unit (hereinafter sometimes referred to as "driving support ECU"). As shown in FIG. 1, the driving support ECU 66 (denoted as "DA-ECU" in the figure) is connected to the CAN 46. Although shown as one unit in the figure, actually, a plurality of electronic control units corresponding to a plurality of driving support controls are mounted. The driving support ECU 66 transmits a steering command to the steering ECU 42 via the CAN 46. More specifically, it intervenes in the above-described steering control to steer the wheel 14. Specifically, the target steering angle ω *A command regarding this is sent from the driver assistance ECU 66, and the steering ECU 42 determines the target steering angle ω as described above based on the steering angle δ. * Instead, the target steering angle ω that was sent to it * Based on this, steering control is performed.

[0046] While a detailed explanation is omitted, for each driver assistance control, the driver assistance ECU66 stores a unique neutral steering position, i.e., a neutral steering angle ω0, for each control. These neutral steering angles ω0 are acquired through learning. Each driver assistance control requires a different level of control accuracy, and therefore the learning accuracy, specifically the accuracy of the neutral steering angle ω0 acquired through learning, also differs. Specifically, target lane following control requires the highest accuracy, followed by lane departure prevention control, vehicle stabilization control, and collision avoidance control, in that order of decreasing accuracy. Conversely, the necessity of executing the control is set in inverse proportion to the accuracy, considering the safety of vehicle operation, with collision avoidance control being the most necessary, followed by vehicle stabilization control, lane departure prevention control, and target lane following control, in that order of decreasing necessity. Generally, the higher the required accuracy of a control, the longer the learning time for the neutral steering angle ω0 is required.

[0047] In light of the above, the driver assistance control systems in vehicles equipped with this steering system are classified into two types. One is safety-focused assistance control, which includes lane departure prevention control, vehicle stabilization control, and collision avoidance control. The other is high-precision required assistance control, which is target line following control. As will be explained in more detail later, these two types of control differ in how they handle the neutral position deviation correction process.

[0048] [3] Neutral rudder position and its setting The steering actuator 16 has an operating range for the steering of the left and right wheels, and the center of this operating range, that is, the exact middle position, is set as the mechanical neutral position. Figure 4(a) is a schematic diagram showing the right and left portions of the steering actuator 16. As shown in this figure, the steering actuator 16 has locking rings 74R and 74L attached to the portion of the steering rod 32, which is a movable member, that extends from the housing 30. When the steering rod 32 is moved to the right to a certain extent, the locking ring 74L comes into contact with the left end of the housing 30, as shown by the dashed line, and further movement of the steering rod 32 to the right is prohibited. In this state, the operating position of the steering rod 32 is at one end of the operating range of the steering actuator 16, that is, the right end. On the other hand, when the steering rod 32 is moved to the left to a certain extent, the locking ring 74R comes into contact with the right end of the housing 30, as shown by the dashed line, and further leftward movement of the steering rod 32 is prohibited. This state means that the operating position of the steering rod 32 is at the other end of the operating range of the steering actuator 16, that is, the left end. In this way, one end and the other end of the operating range are defined. When the locking rings 74R and 74L are located at the positions shown by the solid lines in Figure 4(a), the operating position of the steering actuator 16 is at the center of the above operating range, that is, the operating position of the steering actuator 16 is at the mechanical neutral steering position. This neutral steering position is the operating position where the steering actuator 16 is expected to be maintained when the vehicle is moving straight. Incidentally, the right and left ends of the housing 30, which the locking rings 74R and 74L abut against, function as a pair of stoppers that lock the locking rings 74R and 74L.

[0049] After the vehicle is manufactured, that is, after the steering actuator 16 is mounted on the vehicle body, the toe angle of the wheels 14 is adjusted in the factory before shipment. In short, the toe angle of the wheels 14 should ideally be approximately 0° when the vehicle is moving straight, as schematically shown in Figure 4(b). The toe angle of the wheels 14 is adjusted by adjusting the tie rod length L, which is the length of the tie rod 34, while maintaining the operating position of the steering actuator 16 in the mechanically neutral steering position described above. The specific adjustment method can be followed according to general procedures and will not be explained here.

[0050] After the toe angle adjustment described above, the steering ECU 42 is instructed to store the value detected by the steering angle sensor 52 at that time as the neutral steering angle ω0, which is the neutral steering position. Through this process, the neutral steering angle ω0 at that time is set as the initial stored neutral steering angle ω0mi, which is the initial stored neutral position. As explained earlier, the stored neutral steering angle ω0m, which is the stored neutral position, is conceptual and may be changed after shipment. In practice, the initial stored neutral steering angle ω0mi is added to the stored steering offset angle Δωm, which is the stored steering offset angle Δω, to obtain the neutral steering angle ω0, and steering control is executed. Therefore, the steering ECU 42 stores the initial stored neutral steering angle ω0mi and the stored steering offset angle Δωm, and changes to the stored neutral steering angle ω0m, that is, the neutral steering angle ω0 used for steering control, are made by changing the stored steering offset angle Δωm. Incidentally, the memory steering offset angle Δωm is set to 0° immediately after toe angle adjustment following vehicle manufacturing. Furthermore, in the following explanation, the sum of the initial memory neutral steering angle ω0mi and the memory steering offset angle Δωm may be treated as the memory neutral steering angle ω0m.

[0051] The neutral operating position of the steering wheel 10, which is an operating component, is set in the same way as the neutral steering position when the steering wheel 10 is attached to the steering shaft 22, but this explanation will be omitted here.

[0052] [4] Neutral position shift and the process to correct it (a) Deviation from the neutral steering position The toe angle of the steering wheel 14 may need to be readjusted at the dealership that sold the vehicle, for example, due to some reason. Also, even if it does not reach the point where readjustment at the dealership is necessary, it is expected that the toe angle will change slightly due to some reason (for example, the wheel 14 hitting a curb, the wheel 14 getting stuck in a groove, or aging). As explained earlier, steering control is performed using the stored neutral steering angle ω0m as the neutral steering angle ω0, but if the toe angle of the wheel 14 is readjusted or the toe angle changes, the actual neutral steering position (which can also be simply called the "actual neutral position"), that is, the actual neutral steering angle ω0r, which is the actual neutral steering angle ω0, will change. In other words, the stored neutral steering angle ω0m, which is set based on the mechanical neutral operating position of the steering actuator 16 as described above, will deviate from the actual neutral steering angle ω0r. In other words, a shift in the neutral position occurs.

[0053] As explained earlier, steering control is performed using the stored neutral steering angle ω0m as the neutral steering angle ω0. However, if the neutral position deviation occurs, even if the driver maintains the steering wheel 10 in the neutral position, the vehicle will deviate to either the left or the right. In other words, it is expected that the wheels 14 will not be properly steered. Conversely, if the driver operates the steering wheel 10 to make the vehicle go straight, the steering wheel 10 must be maintained in a position deviating from the neutral position, and the reaction force actuator 12 generates a reaction force torque Tc corresponding to the operating angle δ at that time, based on the neutral position return component Tcc mentioned above. In that case, the driver must maintain the steering wheel 10 against that reaction force torque Tc, and will feel discomfort with the steering operation.

[0054] (b) Overview of the process for correcting neutral position misalignment To correct the above-mentioned neutral position deviation, this steering system performs a neutral position deviation correction process while the vehicle is in motion, more specifically, while the steering control and reaction force control described above are being performed. This neutral position deviation correction process may be performed, for example, as part of the work of a dealer's adjuster after toe angle adjustment at the dealership, or it may be performed by the vehicle's user. When performed by an adjuster, the neutral position deviation correction process is performed by connecting an operation terminal 80 to the vehicle, as shown in Figure 1. The operation terminal 80 consists of a display, keyboard, etc., and is connected to a connector installed in the vehicle, and is connected to the steering ECU 42 via CAN 46. This operating terminal 80 is capable of accessing various information related to the steering system, such as the stored steering offset angle Δωm currently stored in the steering ECU 42. Although a detailed explanation is omitted, in the neutral position deviation correction process using this operating terminal 80, the adjuster can correct the neutral position deviation with greater accuracy while observing the change in the stored neutral steering angle ω0m. On the other hand, when the correction is based on the operation of the vehicle user, the neutral position deviation correction process is performed using the position deviation correction process start switch 82 provided on the instrument panel.

[0055] In simple terms, the neutral position deviation correction process is a process that brings the stored neutral steering angle ω0m, which is the stored neutral steering position, closer to the actual neutral steering angle ω0r. In other words, it is a process that changes the stored steering offset value Δωm so that the stored neutral steering angle ω0m approaches the actual neutral steering angle ω0r. The neutral position deviation correction process is performed when the steering control and reaction force control described above are being executed, and when the adjuster or user (hereinafter sometimes collectively referred to as "driver") maintains an operation of the steering wheel 10 that causes the vehicle to move straight. When a neutral position deviation occurs, in order to move the vehicle straight, as described above, the operating angle δ of the steering wheel 10 will be in a state that deviates from the neutral operating angle δ0, and a reaction force torque Tc corresponding to that deviation is generated. Therefore, the neutral position deviation correction process is performed when the driver applies an operating torque To to the steering wheel 10 that opposes that reaction force torque Tc.

[0056] The neutral position misalignment correction process is initiated by the driver operating the operation terminal 80 or the position misalignment correction process start switch 82. When the neutral position misalignment correction process is initiated, the steering ECU 42 first determines whether the execution conditions are met. The execution conditions are that the vehicle speed v, which is the vehicle's travel speed, is within the set speed range and the vehicle is traveling in a straight line. The vehicle speed v is obtained from the brake electronic control unit (brake ECU), which is not shown in the figure, via CAN 46, and whether the vehicle is traveling in a straight line is determined based on the yaw rate γ detected by the yaw rate sensor 84 installed on the vehicle. If the execution conditions are met, the steering ECU 42 executes the initial processing. In this initial process, the steering offset angle Δωt for shifting the neutral steering angle ω0 is set to the currently stored steering offset angle Δωm. Then, instead of the stored neutral steering angle ω0m, the initial stored neutral steering angle ω0mi is added to the steering offset angle Δωt to obtain the neutral steering angle ω0, and steering control is performed based on this neutral steering angle ω0.

[0057] Next, the steering ECU 42 determines whether the neutral steering angle ω0, that is, the currently stored neutral steering angle ω0m, has shifted to the left or right from the actual neutral steering angle ω0r. In other words, the steering ECU 42 determines whether to shift the stored steering offset value Δωm to the left or right from its current value, i.e., the direction of the shift of the neutral steering angle ω0. This determination of the shift direction may be performed, for example, based on the detected value of the steering angle sensor 56. More specifically, at the present time, the steering angle ω is the actual neutral steering angle ω0r, or approximately the actual neutral steering angle ω0r. Therefore, by comparing the stored neutral steering angle ω0m with the detected value of the current steering angle ω by the steering angle sensor 56, the deviation angle dω0 of the neutral steering angle ω0, which is the amount of deviation of the neutral steering position, can be determined, and the shift direction can be determined. Furthermore, the shift direction may be determined based, for example, on the operating angle δ of the steering wheel 10 detected by the operating angle sensor 52, the operating torque To detected by the operating torque sensor 50, the value of the reaction force torque Tc being generated, etc.

[0058] Based on the shift direction identified as described above, the steering ECU 42 gradually changes the neutral steering angle ω0 toward the actual neutral steering angle ω0r, provided that the above execution conditions are met. Specifically, the shift steering offset angle Δωt is changed by the set shift angle dΔω, and this changed shift steering offset angle Δωt is added to the initial stored neutral steering angle ω0mi to determine the neutral steering angle ω0, and the steering control continues. This change of the shift steering offset angle Δωt is repeated until the change termination condition (hereinafter sometimes simply referred to as the "termination condition") described later is met.

[0059] The termination condition is that the value of the judgment parameter P is a value that can be considered approximately 0. The judgment parameter P can be the deviation angle dω0 of the neutral steering angle ω0, the detected operating angle δ of the steering wheel 10 by the operating angle sensor 52, the detected operating torque To by the operating torque sensor 50, the value of the generated reaction torque Tc, etc., as explained in relation to the identification of the shift direction. Regarding the steering of the wheels 14 and the operation of the steering wheel 10, various numerical parameters such as the steering angle ω and operating angle δ will be treated with a + for values ​​corresponding to left turns and a - for values ​​corresponding to right turns, and the judgment parameter P will be treated similarly. If treated in this way, |P| <Pt This can be used as the termination condition. The threshold Pt is set to a value that allows us to consider that the neutral position shift has been resolved.

[0060] Specifically, if the judgment parameter P is the misalignment angle dω0, then as the shift steering offset angle Δωt is changed, the absolute value of the misalignment angle |dω0| decreases, and when it becomes smaller than the threshold dω0t, it can be considered that the neutral position misalignment has been resolved. Furthermore, if the reaction force control described above is performed, the absolute values ​​of the detected operating angle δ of the steering wheel 10, the detected operating torque To by the operating torque sensor 50, and the generated reaction force torque Tc, |δ|, |To|, and |Tc|, respectively, can all be considered to have resolved the neutral position misalignment when they become smaller than the thresholds δt, Tot, and Tct, which are set close to 0. In short, the neutral position misalignment can be considered to have been resolved when the steering wheel 10 is in the neutral operating position, which is the position the vehicle should be in when moving straight, and there is no longer any operating force applied to the steering wheel 10 by the driver, or when there is no operating reaction force applied to the steering wheel 10. Incidentally, the latter method has the advantage of being able to estimate the deviation from the neutral steering angle ω0 without detecting the actual steering angle ω.

[0061] Simply put, the steering ECU 42 terminates the change of the shift steering offset angle Δωt when the determination parameter P satisfies the above termination condition. In practice, when the above termination condition is satisfied, the shift steering offset angle Δωt is changed once more in the shift direction. If this change does not make |P| greater than the absolute value of the previous value Pp (|Pp|), the change of the shift steering offset angle Δωt is terminated. If |P| becomes greater than |Pp|, the change of the shift steering offset angle Δωt is terminated by returning it to the shift steering offset angle Δωt as it was before the change was made. This type of change of the shift steering offset angle Δωt allows, for example, a change of the shift steering offset angle Δωt to the opposite side of the actual neutral steering angle ω0r, and makes it possible to set the neutral steering angle ω0 to a value closer to the actual neutral steering angle ω0r.

[0062] The neutral position misalignment correction process in this steering system is performed as part of the work of the adjuster, and is carried out in connection with the operation of the vehicle's ignition switch (hereinafter sometimes referred to as "IG"). Specifically, considering that the adjuster confirms that the above termination conditions are met by the operation terminal 80 before turning IG OFF, the steering ECU 42 determines that the neutral position misalignment correction process is complete when IG is turned OFF. More specifically, the difference between the shift steering offset angle Δωt and the currently stored stored steering offset angle Δωm is determined as the change angle (|Δωt-Δωm|), and if this change angle (|Δωt-Δωm|) is greater than the threshold angle Δωs, that is, if the stored neutral steering angle ω0m is changed relatively significantly, the shift steering offset angle Δωt at that time is stored as the stored steering offset angle Δωm. In other words, the stored neutral steering angle ω0m is updated, and thereafter, steering control is performed using the updated stored neutral steering angle ω0m as the neutral steering angle ω0. On the other hand, if the angle of change (|Δωt-Δωm|) is less than or equal to the threshold angle Δωs, that is, if there is almost no difference between the steering offset angle Δωt for the shift at that time and the stored steering offset angle Δωm, the stored neutral steering angle ω0m is not updated.

[0063] Furthermore, considering that the driver, if they are also a steering engineer, will need to confirm the elimination of the neutral position deviation, when the driver turns the ignition ON, the steering ECU 42 maintains the certification that the neutral position deviation elimination process is complete for a set time (hereinafter sometimes referred to as the "completion certification maintenance time ts"). This completion certification maintenance time ts should be set to, for example, 30 seconds to 1 minute, which is the time required for the engineer to confirm. The process related to the operation of the ignition will be explained in detail later. As mentioned above, if the angle of change (|Δωt-Δωm|) is less than or equal to the threshold angle Δωs, that is, if the stored neutral steering angle ω0 has not been updated, the certification that the neutral position deviation elimination process is complete will not be made.

[0064] The relationship between the aforementioned driver assistance control and the neutral position deviation correction process is as follows: As explained earlier, each driver assistance control is performed based on the neutral steering angle ω0 that is independently learned and stored. In the target line following control (LTA), which is a high-precision request assistance control, when the neutral position deviation correction process starts, the neutral steering angle ω0 that is independently stored in that control is reset, and the execution of the control itself is prohibited. After the certification that the neutral position deviation correction process has finished is maintained for a completion certification period ts, learning of the neutral steering angle ω0 is started, and after a highly accurate neutral steering angle ω0 is obtained through learning, the execution of the control is resumed.

[0065] On the other hand, in the case of the safety-focused support controls, namely Lane Departure Prevention (LDA), Vehicle Stabilization Control (VSC), and Pre-Collision System (PCS), the stored neutral steering angle ω0 is not reset even when the neutral position deviation correction process is initiated, and the control itself is permitted. However, as mentioned above, if the change angle (|Δωt-Δωm|) is greater than the threshold angle Δωs, that is, if the stored neutral steering angle ω0m is changed relatively significantly, even in the case of safety-focused support controls, when the IG is turned ON, the neutral steering angle ω0 stored in that control is reset and the execution of that control is prohibited. After a more accurate neutral steering angle ω0 is acquired through learning, the execution of that control is resumed. Note that for safety-focused support controls, the execution of the control may not be prohibited regardless of the change angle (|Δωt-Δωm|). Also, the learning of the neutral steering angle ω0 may be started from the time the neutral position deviation correction process is completed.

[0066] (c) Flowchart for correcting neutral position misalignment The neutral position deviation correction process described above is performed by the steering ECU 42 executing the neutral position deviation correction process program, which is shown in the flowchart in Figure 5. This program is started when the driver operates the operation terminal 80 or the position deviation correction process start switch 82 while the vehicle is moving straight. The flow of the neutral position deviation correction process will be briefly explained below with reference to the flowchart.

[0067] In the process following the above program, first, in S21, it is determined whether the execution conditions are met. As mentioned above, the execution conditions are that the vehicle is traveling within a certain speed range and the vehicle is moving in a straight line. If these execution conditions are met, in S22, as an initial process, the steering offset angle Δωt for shifting is set to the stored steering offset angle Δωm, and the neutral steering angle ω0 in steering control is set to the value obtained by adding the initial stored neutral steering angle ω0mi and the steering offset angle Δωt for shifting.

[0068] Next, in S23, as described above, the direction of the neutral position deviation is determined by identifying, for example, whether the stored neutral steering angle ω0m deviates to the left or right from the actual neutral steering angle ω0r. Then, in S24, the processing flag Fm is set to "ON". The processing flag Fm is, simply put, a flag that indicates that the neutral position deviation correction process is being performed. It is set to "ON" when the process is in progress and to "OFF" when the process is not in progress. Subsequently, in S25, a command is sent to the driver assistance ECU 66 to prohibit the execution of high-precision request support control (for example, target line following control) and to reset the value of the neutral steering angle ω0 that has been learned in that control.

[0069] Next, in S26, it is determined whether the above execution conditions are met. If the execution conditions are met, in S27, the steering offset angle Δωt for shifting is changed by a set shift angle dΔω in the direction opposite to the direction of the neutral position deviation. This change is repeated until it is determined in S28 that the termination conditions have been met. The determination of the termination conditions in S28 is made by whether the absolute value of the determination parameter P described above is smaller than the threshold Pt. The determination parameter P is, as described above, the deviation angle dω0 of the neutral steering angle ω0, the operating angle δ of the steering wheel 10, the operating torque To of the steering wheel 10, the reaction torque Tc, etc.

[0070] If the above termination conditions are met, in S29 the execution conditions are further determined, and if the execution conditions are met, in S30 the shift steering offset angle Δωt is changed again by the set shift angle dΔω. The result of this change is confirmed in S31. Specifically, the absolute value of the determination parameter P is compared with the previous determination parameter P (previous value Pp). If the absolute value of the determination parameter P is greater than the absolute value of the previous value Pp, in S32 the shift steering offset angle Δωt is changed in the opposite direction by the set shift angle dΔω. In other words, the shift steering offset angle Δωt is returned to the value before the last change. On the other hand, if the absolute value of the determination parameter P is not greater than the absolute value of the previous value Pp, the shift steering offset angle Δωt is not changed.

[0071] The process according to the neutral position deviation correction program is as described above, but as explained earlier, the neutral position deviation correction process is related to the operation of the ignition (IG). Therefore, in this steering system, when the IG is turned OFF and when the IG is turned ON, the steering ECU 42 executes the IG-OFF program and the IG-ON program, respectively, as shown in the flowchart in Figure 6. The flow of the process according to these programs is briefly explained below.

[0072] In the process following the IG-OFF program, first, in S41, the extent to which the shift steering offset angle Δωt has ultimately changed from the stored steering offset angle Δωm is confirmed, i.e., the change angle (|Δωt-Δωm|). If this change angle (|Δωt-Δωm|) is greater than the threshold angle Δωs, in S42, the stored steering offset angle Δωm is set to the shift steering offset angle Δωt. Subsequently, in S43, a command is sent to the driver assistance ECU66 to disable safety-oriented support control (e.g., lane departure prevention control, vehicle stabilization control, collision avoidance control) and to reset the neutral steering angle ω0 that has already been learned for that control. Then, in S44, the post-processing flag Fa is set to "ON". The post-processing flag Fa is a flag used to determine that the neutral position shift correction process, specifically the gradual change from the stored neutral position to the actual neutral position, has effectively been completed. This flag is set to "ON" when it is determined that the process has been completed.

[0073] In S45, the neutral steering angle ω0 is set to the initial stored neutral steering angle ω0mi plus the stored steering offset angle Δωm. From this point onward, steering control is performed based on the neutral steering angle ω0 set in this way. Incidentally, if the change angle (|Δωt-Δωm|) is determined to be less than or equal to the threshold angle Δωs in S41, the stored steering offset angle Δωm is not changed, and steering control is performed with the original neutral steering angle ω0. In this case, the post-processing flag Fa is not set to "ON".

[0074] In the process according to the IG-ON program, first, in S51, the processing flag Fm is reset to "OFF". In the following S52, a command is issued to the driver assistance ECU 66 to start learning the neutral steering angle ω0 in the prohibited driver assistance control. If safety-focused assistance control is also prohibited and the neutral steering angle ω0 in that control has also been reset, the learning of that neutral steering angle ω0 is also started based on the command. The driver assistance control is restarted on the condition that an appropriate neutral steering angle ω0 has been acquired through learning. Then, in S53, it is determined whether the post-processing flag Fa is "ON" or not. If it is "ON", in S54 the time counter t is reset to 0, and in S55 the time counter t is incremented by Δt. This increment continues until in S56 the time counter t exceeds the estimated termination time ts. After the estimated termination time ts has elapsed, in S57, the post-processing flag Fa is reset to "OFF".

[0075] (d) Specific examples of neutral position misalignment correction processes The following explains a specific example of the neutral position misalignment correction process, referring to the diagrams in Figures 7 and 8.

[0076] The diagram in Figure 7 shows the case where the neutral steering angle ω0 is changed relatively significantly during the neutral position misalignment correction process. Before the neutral position misalignment correction process is executed, the misalignment angle dω0 of the neutral steering angle ω0 is 1.6°. In other words, the neutral steering angle ω0 is misaligned by 1.6° in the left turn direction. At time t0, the neutral position misalignment correction process is started. At that time, the stored steering offset angle Δωm is 0.0°, and when the neutral position misalignment correction process is started, the shift steering offset angle Δωt is set to 0.0°. At that time, the processing flag Fm is set to "ON", and high-precision request support control is disabled. The learned neutral steering angle ω0 (0.3°) in that control is reset to its value at that time.

[0077] At times t1, t2, and t3, the steering offset angle Δωt for shifting is repeatedly changed in the direction of a right turn by 0.5°, which is the set shift angle dΔω. In other words, the steering offset angle Δωt for shifting is sequentially changed from 0.0° to -0.5°, -1.0°, and -1.5°. As a result, the deviation angle dω0 of the neutral steering angle ω0 is gradually reduced from 1.6° to 1.1°, 0.6°, and 0.1°. At time t3, the change in the steering offset angle Δωt for shifting causes the aforementioned determination parameter P (for example, the deviation angle dω0 of the neutral steering angle ω0) to become smaller than the threshold Pt (for example, a deviation angle of 0.2°), and the change in the steering offset angle Δωt for shifting is terminated.

[0078] After the change to the shift steering offset angle Δωt is completed, the ignition (IG) is turned OFF. In this neutral position shift correction process, the change angle (|Δωt-Δωm|), which is the difference between the shift steering offset angle Δωt and the stored steering offset angle Δωm, is ultimately greater than the threshold angle Δωs (for example, 0.4°). Therefore, when the IG is turned OFF, the stored steering offset angle Δωm is set to -1.5°, which is the shift steering offset angle Δωt at that time, and the post-processing flag Fa is set to "ON". Also, from that point onward, the execution of safety-focused support control is prohibited, and the neutral steering angle ω0 (0.3°) that was learned in that control is reset to its value.

[0079] Next, when the IG is turned ON, the processing flag Fm is reset to "OFF", and the learning of the neutral steering angle ω0 for the previously prohibited driver assistance control (high-precision required assistance control and safety-focused control) begins. After the appropriate neutral steering angle ω0 (0.1°) is obtained through this learning, the learning is terminated, and the previously prohibited driver assistance control is permitted to be executed. Also, when the estimated completion time ts has elapsed since the IG was turned ON, the post-processing flag Fa is reset to "OFF".

[0080] The diagram in Figure 8 shows the case where, although the neutral position shift correction process was performed, the aforementioned change angle (|Δωt-Δωm|) was less than or equal to the threshold angle Δωs (for example, 0.4°), and therefore the neutral steering angle ω0 was effectively not changed. Unlike the case in Figure 7, the set shift angle dΔω is set to 0.3°.

[0081] In the case of Figure 8, before the neutral position deviation correction process is executed, the deviation angle dω0 of the neutral steering angle ω0 is 0.4°. In other words, the neutral steering angle ω0 is shifted by 0.4° in the left turning direction. At time t0, the neutral position deviation correction process is started. At that time, the stored steering offset angle Δωm is 0.0°, and when the neutral position deviation correction process is started, the shift steering offset angle Δωt is set to 0.0°. At that time, the processing flag Fm is set to "ON", and high-precision request support control is disabled. The neutral steering angle ω0 (0.3°) that was learned during that control is reset to its value at that time.

[0082] At time t1, the steering offset angle Δωt for shifting is changed 0.3° in the rightward turning direction, which is the set shift angle dΔω. This change causes the judgment parameter P (e.g., the deviation angle dω0 of the neutral steering angle ω0) to become smaller than the threshold Pt (e.g., the deviation angle of 0.2°). According to the program described above, at time t2, the steering offset angle Δωt for shifting is changed again 0.3° in the rightward turning direction, which is the set shift angle dΔω. As a result, the absolute value of the judgment parameter P (the deviation angle dω0, which is -0.2°) becomes larger than the previous value Pp (0.1°), and at time t3, the steering offset angle Δωt for shifting is returned to its value before the change (-0.3).

[0083] After the above-mentioned change in the steering offset angle Δωt for shifting, the ignition (IG) is turned OFF. However, in this neutral position shift correction process, since the changed angle (|Δωt-Δωm|, which is 0.3) is ultimately less than or equal to the threshold angle Δωs (for example, 0.4°), the stored steering offset angle Δωm is not changed even when the IG is turned OFF, and the post-processing flag Fa is not set to "ON". Furthermore, the execution of safety-focused support control is not prohibited, and the learned neutral steering angle ω0 (0.3°) is maintained in that control.

[0084] Next, when IG is turned ON, the processing flag Fm is reset to "OFF", and the learning of the neutral steering angle ω0 in the previously prohibited driver assistance control (high-precision required assistance control) begins. After the appropriate neutral steering angle ω0 (0.1°) is obtained through this learning, the learning is terminated, and the previously prohibited driver assistance control is permitted to be executed. [Explanation of Symbols]

[0085] 10: Handle [operating member] 12: Reaction actuator [reaction force application device] 14: Wheel 16: Steering actuator 24: Reaction motor [power source] 32: Steering rod [movable member] 34: Tie rod 38: Steering motor [power source] 40: Reaction electronic control unit (reaction ECU) [controller] 42: Steering electronic control unit (steering ECU) [controller] 44: Dedicated high-speed communication line 46: CAN 56: Steering angle sensor 60: Pinion shaft 66: Driving support electronic control unit (driving support ECU) 74R, 74L: Locking ring L: Tie rod length 80: Operation terminal 82: Position misalignment correction processing start switch 84: Yaw rate sensor ω: Steering angle ω0: Neutral steering angle [neutral steering position] ω0m: Stored neutral steering angle [stored neutral position] ω0mi: Initial stored neutral steering angle ω0r: Actual neutral steering angle [actual neutral position] dω0: Deviation angle of neutral steering angle ω0 Δω: Steering offset angle Δωm: Memory steering offset angle Δωt: Steering offset angle for shift dΔω: Set shift angle |Δωt-Δωm|: Change angle Δωs: Threshold angle P: Parameter for judgment Pt: Threshold v: Vehicle speed γ: Yaw rate Fm: Processing flag Fa: Post-processing flag

Claims

1. Operating components operated by the driver, A steering actuator that has a power source and steers the wheels using the force of that power source, An operating reaction force applying device that applies an operating reaction force, which is a reaction force to the operation of the operating member, to the operating member, A controller that controls the steering actuator to achieve wheel steering in response to the operation of the operating member, and also performs control to apply an operating reaction force that includes a component to return the operating position of the operating member to the neutral operating position, which is the position the vehicle should be in when moving straight. A steer-by-wire steering system mounted on a vehicle, comprising: The aforementioned controller When the stored neutral position, which is the neutral steering position stored for controlling the steering actuator, deviates from the actual neutral steering position, the system is configured to perform a neutral position deviation correction process to bring the stored neutral position closer to the actual neutral position while the driver is maintaining the operation of the control member to move the vehicle straight, and A steering system configured to terminate the neutral position displacement correction process when the operating reaction force is eliminated, or when the driver's operating force to resist the operating reaction force is eliminated.

2. Operating components operated by the driver, A steering actuator that has a power source and steers the wheels using the force of that power source, A controller that controls the steering actuator in order to achieve wheel steering in response to the operation of the operating member. A steer-by-wire steering system mounted on a vehicle, comprising: The controller is configured to perform a neutral position correction process to bring the stored neutral position closer to the actual neutral position when the stored neutral position, which is the neutral steering position stored for controlling the steering actuator, deviates from the actual neutral steering position, while the driver is maintaining operation of the operating member to move the vehicle straight. A steering system in which, in the vehicle, a plurality of driver assistance controls are performed, each involving the automatic steering of the wheels, and the steering system is configured to allow at least one of these plurality of driver assistance controls even while the neutral position deviation correction process is being performed.

3. The aforementioned multiple driver assistance controls include safety-focused assistance controls that prioritize vehicle driving safety over the accuracy of the neutral steering position, The steering system according to claim 2, wherein the steering system is configured to allow at least the safety-focused support control even while the neutral position deviation correction process is being executed.

4. The aforementioned controller The steering system according to claim 2, configured such that the neutral position deviation correction process is terminated on the condition that the operating position of the operating member is located in the neutral operating position, which is the position that the vehicle should be in when moving straight.

5. The steering system includes an operating reaction force applying device that applies an operating reaction force, which is a reaction force to the operation of the operating member, The aforementioned controller Control is performed to apply an operating reaction force that includes a component to return the operating position of the operating member to the neutral operating position, which is the position that the vehicle should be in when moving straight. The steering system according to claim 2, configured to terminate the neutral position displacement correction process when the operating reaction force is eliminated, or when the driver's operating force to resist the operating reaction force is eliminated.

6. The steering system according to claim 1 or claim 2, wherein the neutral position deviation correction process is a process that gradually changes the stored neutral position toward the actual neutral position.

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