Steering system

Abstract

To facilitate detection of a steering angle of a toe-in amount becoming zero.SOLUTION: A steering system is configured in which a controller executes: symmetrical steering processing of changing consecutively or stepwise a left control current and a right control current while maintaining a steering angle of a left steering wheel 11 and a steering angle of a right steering wheel 12 symmetrically during a direct advance of a vehicle and under a state where no driving power moment occurs at the left steering wheel 11 and the right steering wheel 12; and reference set processing of setting a left steering angle and a right steering angle of a toe-in amount becoming zero on the basis of a detection value of a left steering angle sensor 224 when positive / negative of a detection value of a left current sensor 30 reverts and a detection value of a right steering angle sensor 224 when positive / negative of a detection value of a right current sensor 30 reverts, or the left steering angle and the right steering angle when a detection value of the left current sensor 30 and a detection value of the right current sensor 30 meet each other and a detection value of the left steering angle sensor 224 and a detection value of the right steering angle sensor 224 meet each other.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a steering system.

Background Art

[0002] As a technique for adjusting the toe angle of wheels, for example, a rear-wheel toe angle control device is disclosed in Japanese Patent Application Laid-Open No. 2010-260459. In this device, with the accelerator opening kept constant, the left and right electric actuators are driven while keeping the left and right rear wheels in a symmetric state, and the stroke amount detection value at which the vehicle speed becomes maximum is set as the reference stroke amount.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above device, in order to calculate an appropriate toe-in amount, the accelerator opening must be continuously kept constant. According to this, there is a possibility that driving according to the traffic flow cannot be performed. Also, on a slope or the like where the road surface gradient changes, the vehicle speed unintentionally changes, and there is a concern about a decrease in the detection accuracy of the reference. Thus, in the prior art, for example, after replacing the suspension, the steering angle at which the toe-in amount becomes 0 is not known, and it has not been easy to adjust the toe-in amount to a desired value.

[0005] An object of the present invention is to provide a steering system capable of easily detecting a steering angle at which the toe-in amount becomes 0 in single-wheel independent steering.

Means for Solving the Problems

[0006] In the steering system of the present invention, the controller is configured to execute a symmetric steering process and a reference setting process. The symmetric steering process is a process of continuously or stepwise changing the left control current and the right control current while maintaining the steering angles of the left steering wheel and the right steering wheel symmetrically in a state where the vehicle is going straight and no driving force moment is generated on the left and right steering wheels. The reference setting process is based on the detected value of the left steering angle sensor when the positive and negative of the detected value of the left current sensor are reversed, and the detected value of the right steering angle sensor when the positive and negative of the detected value of the right current sensor are reversed, or based on the left steering angle and the right steering angle when the detected value of the left current sensor and the detected value of the right current sensor are the same and the detected value of the left steering angle sensor and the detected value of the right steering angle sensor are the same, and is a process of setting the left steering angle and the right steering angle at which the toe-in amount becomes 0.

Effect of the Invention

[0007] When the vehicle is going straight, a moment (self-moment) around the kingpin axis is generated on the wheels by the pneumatic trail corresponding to the toe-in amount. In order for the controller to cancel the self-moment and maintain the toe-in amount, it is necessary to supply control currents with different polarities, that is, holding currents, to the left and right steering motors. On a flat road without a cross slope, when the vehicle is going straight, the left and right steering angles are the same and the left and right holding currents are the same only when the holding current is 0. When the holding current is 0, it can be estimated that no self-moment is generated, and it can be determined that the toe-in amount is 0. Also, it can be determined that the steering angle when the positive and negative of the value of the current sensor that detects the control current are reversed is the steering angle at which the toe-in amount becomes 0.

[0008] Also, on a road surface with a cross slope, the holding current as a whole shifts in the positive or negative direction by the amount of the moment due to gravity (gravity moment) applied to the wheels. However, since the left and right holding currents shift by the same amount, the steering angle at which the left and right steering angles match and the left and right holding currents match remains the steering angle at which the toe-in amount becomes zero. Therefore, whether on a flat road or an inclined plane, the controller sets the steering angle at which the left and right steering angles match and the left and right holding currents match as the steering angle at which the toe-in amount becomes zero based on the result of the symmetric steering process. Also, the midpoint between the left and right steering angles when the positive and negative values of the current sensor value are reversed can be determined as the steering angle with a toe-in amount of zero. Thus, according to the present invention, in single-wheel independent steering, for example, after replacing the suspension device, the steering angle at which the toe-in amount becomes zero can be easily detected.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0010] Hereinafter, as an embodiment for carrying out the present invention, a steering system 1 which is an embodiment of the present invention will be described in detail with reference to the drawings. It should be noted that the present invention can be implemented in various forms with various changes and improvements based on the knowledge of those skilled in the art in addition to the following examples.

[0011] The steering system 1 of the present embodiment is a steer-by-wire system of a single-wheel independent steering type (left and right independent steering type). As shown in FIG. 1, the steering system 1 includes a left steering device 2A, a right steering device 2B, a left steering controller (corresponding to a "left steering control unit") 3A, a right steering controller (corresponding to a "right steering control unit") 3B, an operating device 4, and a reaction force controller 5. The steering system 1 is a steer-by-wire system in which the left steering device 2A and the right steering device 2B are not mechanically connected to the operating device 4.

[0012] Communication within the vehicle is performed using CAN100. In the present embodiment, the steered wheels are the front wheels 11 and 12, the left steered wheel is the left front wheel 11, and the right steered wheel is the right front wheel 12. The left steering device 2A is a device for steering the left front wheel 11. The right steering device 2B is a device for steering the right front wheel 12 independently of the left steering device 2A. Since the left steering device 2A and the right steering device 2B have the same configuration, the configuration of the right steering device 2B will be described, and the description of the configuration of the left steering device 2A will be omitted. In addition, in the present embodiment, the rear wheels 13 and 14 are also steered wheels (toe-in amount adjusted) and are configured to be independently steered.

[0013] As shown in FIG. 2, the right steering device 2B includes a steering knuckle 21, a steering actuator 22, and a tie rod 23. The steering knuckle 21 is a member that rotatably holds the right front wheel 12. The steering knuckle 21 is a housing of an in-wheel motor unit 7 described later.

[0014] The steering actuator 22 is installed at a position on the base end side of the lower arm 91. The steering actuator 22 includes a steering motor 221, a speed reducer 222, an actuator arm 223, and a rotation angle sensor 224. The steering motor 221 is an electric motor as a drive source. The steering motor 221 is, for example, a brushless DC motor.

[0015] The speed reducer 222 is a gear device that reduces the rotation of the steering motor 221. The actuator arm 223 is an arm member that rotates by the rotation of the steering motor 221 via the speed reducer 222. The actuator arm 223 functions as a pitman arm. The tie rod 23 is a member that connects the knuckle arm 211 provided on the steering knuckle 21 and the actuator arm 223 of the steering actuator 22.

[0016] The rotation angle sensor 224 detects the rotation angle of the steering motor 221. There is a specific relationship between the rotation angle of the steering motor 221 and the steering angle of the right front wheel 12. Therefore, each of the steering controllers 3A and 3B can calculate the steering angle of the wheel corresponding to the steering motor 221 based on the rotation angle of the steering motor 221. That is, the rotation angle sensor 224 can be said to be a steering angle sensor. Note that the steering angle sensor may be a sensor that directly detects the steering angle.

[0017] The rotation angle sensor (hereinafter referred to as "left steering angle sensor") 224 of the left steering device 2A detects the steering angle of the left front wheel 11, and the rotation angle sensor (hereinafter referred to as "right steering angle sensor") 224 of the right steering device 2B detects the steering angle of the right front wheel 12. Hereinafter, the steering motor 221 that steers the left front wheel 11, which is the left steering wheel, is also referred to as "left steering motor 221", and the steering motor 221 that steers the right front wheel 12, which is the right steering wheel, independently of the left front wheel 11, is also referred to as "right steering motor 221".

[0018] The suspension devices 9 of the front wheels 11 and 12 each include a lower arm 91, a steering knuckle 21, a shock absorber 92, and a suspension spring 93. The suspension device 9 is, for example, a MacPherson strut type suspension device. The lower arm 91 is supported by a side member (not shown) of the vehicle body. The steering knuckle 21 is rotatably connected to the tip of the lower arm 91 via a ball joint 911. The shock absorber 92 is a member whose lower end is fixedly supported by the steering knuckle 21 and whose upper end is rotatably supported by the vehicle body via an upper support 94. The suspension spring 93 is a member whose upper end is rotatably supported by the vehicle body via an upper support 94 and whose lower end is supported by a lower support 95 provided on the shock absorber 92.

[0019] In the present embodiment, in-wheel motor units 7 are mounted on the front wheels 11 and 12, which are steered wheels, as drive devices. The in-wheel motor unit 7 includes a steering knuckle 21 that functions as a housing, a drive motor 71, a speed reducer 72, and an axle hub (not shown). The drive motor 71 is an electric motor built into the steering knuckle 21. A rotation angle sensor (not shown) is provided on the drive motor 71. The speed reducer 72 is a gear device that reduces the rotation of the drive motor 71. The axle hub is attached to the wheel of the vehicle. Each in-wheel motor unit 7 is supplied with a control current from a drive ECU (not shown) and is controlled by the drive ECU.

[0020] The steering system 1 of the present embodiment is mounted on a vehicle configured such that the kingpin offset δ1 is 0. In the present embodiment, the suspension device 9 is designed such that the kingpin offset δ1 is substantially 0.

[0021] As shown in Fig. 2, the kingpin axis KP is a straight line passing through the center of the upper support 94 and the center of the ball joint 911. When the longitudinal direction of the vehicle is the X direction, the lateral direction of the vehicle is the Y direction, and the vertical direction of the vehicle is the Z direction, the kingpin offset δ1 is, as shown in Fig. 3, in the YZ plane, the distance between the intersection of the kingpin axis KP and the ground contact surface and the ground contact surface center SC. The ground contact surface is the ground contact surface of the tire with the road surface.

[0022] Since the wheel drive device of this embodiment is the in-wheel motor unit 7, its driving force becomes the ground contact point input. Therefore, in a vehicle where the kingpin offset δ1 is set to 0, even when a driving force is applied to the wheel by the in-wheel motor unit 7, no moment (driving force moment) M1 around the kingpin axis KP is generated. That is, in this configuration, even in a situation where a driving force is applied, no driving force moment M1 is generated in the wheel, similar to a situation where no driving force is applied. According to this configuration, the reference adjustment control described later can be executed even during driving force application.

[0023] The operation device 4 has a general structure in a steer-by-wire system. As shown in Fig. 1, the operation device 4 includes a steering wheel (operation member) 41, a steering sensor 42, and a reaction force applying device 43. The steering sensor 42 is a sensor that detects the operation angle, which is the rotation angle of the steering wheel 41, as the operation position or operation amount of the steering wheel 41. For example, when the position that the steering wheel 41 takes in the straight-ahead state of the vehicle is set as the neutral position, the rotation angles in the left and right directions from the neutral position are the operation angles of the steering wheel 41. The reaction force applying device 43 is a device that applies a reaction force (reaction force to the operation) to the steering wheel 41. The reaction force controller 5 calculates a target reaction force based on the detection result of the steering sensor 42 and the vehicle speed, and controls the electric motor 431 of the reaction force applying device 43.

[0024] (Controller) The left steering controller 3A and the right steering controller 3B are connected to be communicable with each other, and are each an electronic control unit (ECU) including one or more processors 31a and one or more memories 31b.

[0025] The left steering controller 3A controls the left steering device 2A based on a steering request (for example, the detection result of the steering sensor 42 in manual driving or the command value from the automatic driving ECU in automatic driving). The right steering controller 3B controls the right steering device 2B based on the detection result of the steering request. In the case of manual driving, each of the steering controllers 3A and 3B calculates a target steering angle based on the detection result of the steering sensor 42, and calculates a target control current based on the target steering angle. Each of the steering controllers 3A and 3B supplies a control current to the steering motor 221 of the corresponding steering device (left steering device 2A or right steering device 2B) based on the target control current. Each of the steering controllers 3A and 3B calculates the target steering angle so that, for example, the detected value of the yaw rate sensor 61 approaches the target yaw rate.

[0026] Each of the steering controllers 3A and 3B is provided with a current sensor 30 for detecting the current value of the control current supplied to the steering motor 221. Hereinafter, the current sensor 30 for detecting the control current (also referred to as "left control current") supplied by the left steering controller 3A to the steering motor 221 is referred to as "left current sensor 30", and the current sensor 30 for detecting the control current (also referred to as "right control current") supplied by the right steering controller 3B to the steering motor 221 is referred to as "right current sensor 30".

[0027] The steering controllers 3A and 3B can acquire each other's calculation results and cooperate with each other to control the control target. That is, it can be said that the two steering controllers 3A and 3B constitute a set of controllers 3 related to steering. In the present embodiment, the controller 3 is composed of the left steering controller 3A and the right steering controller 3B.

[0028] The control current can be considered, by nature, as a change control current for changing the steering angle and a holding current for holding the steering angle. The holding current is a control current for continuously canceling out the moment generated on the wheels during driving in order to maintain the steering angle at the target steering angle. For example, when the wheels are set to travel straight with a predetermined toe-in amount, a moment (hereinafter also referred to as "self-moment") M2 in the direction of making the toe-in amount = 0 due to the pneumatic trail is applied to the wheels during straight travel. In this case, the controller 3 supplies a holding current to the steering motor 221 in order to cancel out the self-moment M2 during straight travel and maintain the toe-in amount. Hereinafter, the left control current for holding the left steering angle is also referred to as "left holding current", and the right control current for holding the right steering angle is also referred to as "right holding current".

[0029] In the vehicle of the present embodiment, when there is no driving force moment M1 generated on the left front wheel 11 and the right front wheel 12 and the toe-in amounts of the left front wheel 11 and the right front wheel 12 are 0 on a flat road without a cross slope, the left control current (left holding current) and the right control current (right holding current) for maintaining the straight travel of the vehicle are configured to be 0. The vehicle may be configured as described above theoretically or in design. The steering system 1 is mounted on such a vehicle. In the present embodiment, since the kingpin offset δ1 is 0 and the in-wheel motor unit 7 applies a driving force to the wheels, the driving force moment M1 is not generated. Also, during straight travel on a flat road, if the toe-in amount is 0, the self-moment M2 is not generated.

[0030] (Reference adjustment control) The controller 3 is configured to be able to execute reference adjustment control. The reference adjustment control is executed based on a user operation or a preset program, for example, after replacing the suspension device.

[0031] The reference adjustment control includes a symmetric steering process, a memory process, and a reference setting process. The symmetric steering process is a process of continuously or stepwise changing the left control current and the right control current while maintaining the steering angles of the left front wheel 11 and the right front wheel 12 symmetrically when the vehicle is going straight and no driving force moment M1 is generated on the left front wheel 11 and the right front wheel 12.

[0032] The memory process is a process of memorizing the correspondence between the detected value of the left current sensor 30 and the detected value of the left steering angle sensor 224, and the correspondence between the detected value of the right current sensor 30 and the detected value of the right steering angle sensor 224 in the symmetric steering process. The memory process is executed in parallel with the symmetric steering process. The controller 3 memorizes data in its own memory 31b, for example, in the memory process.

[0033] The reference setting process is a process of setting the left and right steering angles at which the toe-in amount becomes zero based on the detected value of the left steering angle sensor 224 when the positive and negative of the detected value of the left current sensor 30 are reversed (i.e., when the detected value = 0), and the detected value of the right steering angle sensor 224 when the positive and negative of the detected value of the right current sensor 30 are reversed, in the memory result of the memory process. Alternatively, the reference setting process is a process of setting the left and right steering angles at which the toe-in amount becomes zero based on the left and right steering angles when the detected value of the left current sensor 30 and the detected value of the right current sensor 30 are the same and the detected value of the left steering angle sensor 224 and the detected value of the right steering angle sensor 224 are the same, in the memory result of the memory process. The state of the vehicle going straight before the execution of the symmetric steering process is used as a temporary reference.

[0034] As an example, as shown in FIG. 4, immediately after the suspension device 9 is replaced, the toe-in amounts of the left and right front wheels 11, 12 may not be aligned. However, as shown in FIG. 5, when the controller 3 makes the vehicle go straight, it adjusts the steering angles of the left and right front wheels 11, 12 so that straight-line stability is ensured, that is, the same toe-in amount is achieved for the left and right front wheels 11, 12. Whether the vehicle is going straight can be determined based on, for example, the position information of the host vehicle (e.g., GPS), the detection value of the yaw rate sensor 61, the detection value of the lateral acceleration sensor 63, the detection values of the left and right wheel speed sensors 62, or the self-position estimation result during automatic driving. However, as shown in FIG. 5, even if the left and right front wheels 11, 12 have the same toe-in amount, it is unclear whether this is the desired toe-in amount, that is, the targeted toe-in amount, and it has been difficult to adjust to the desired toe-in amount during straight driving.

[0035] Therefore, the controller 3 detects the steering angle at which the toe-in amount becomes 0 by reference adjustment control, and sets this steering angle as a reference for the toe-in amount to become 0. The detected value of the steering angle sensor at which the toe-in amount becomes 0 can vary depending on the installation state (initial state) of each of the front wheels 11, 12. Therefore, for example, the detected values of each steering angle sensor 224 corresponding to the toe-in amount detected as 0 by the reference adjustment control are converted to toe-in amount = 0 (steering angle = 0) in subsequent calculations by the controller 3.

[0036] (Stepwise Symmetric Steering Process) First, the symmetric steering process in which the controller 3 changes the steering angle step by step (in steps) will be described. On the premise of executing the reference adjustment control, the controller 3 stores, as a temporary reference, the detected values of each steering angle sensor 224 in the state where the vehicle is going straight (the state in FIG. 5) as the same steering angle on the left and right (for example, steering angle = 0). In the reference adjustment control, until the reference setting process is completed, the controller 3 detects the current steering angle based on the temporary reference. In the symmetric steering process, the controller 3 first detects the holding current on each side (the detection value of each current sensor 30) at the steering angle of the temporary reference, and as a storage process, the correspondence between the steering angle and the holding current (for example, steering angle = 0, left holding current = Il0 , right holding current = I r0 ) is memorized. For example, as shown in FIG. 6, the steering angle is set with a temporary reference of 0, with changes in the toe-out direction being positive and changes in the toe-in direction being negative. Note that when the vehicle of this configuration is traveling straight on a road surface without a cross slope and the left and right front wheels 11, 12 have the same toe-in amount, theoretically, the absolute values of the left and right holding currents are the same value.

[0037] For the purpose of symmetric steering control, while the vehicle is traveling straight, the controller 3 detects (a) a state where the left and right holding currents match and the left and right steering angles (toe-in amounts) match, or (b) a left steering angle at which the left holding current becomes 0 and a right steering angle at which the right holding current becomes 0. In the state of (a), theoretically, it can be determined that the toe-in amounts of the left and right are 0. Therefore, when the controller 3 detects the state of (a), as a reference setting process, it sets the steering angle in that state as the steering angle with a toe-in amount of 0 (see FIGS. 6 and 8). In the case of (b), theoretically, the intermediate steering angle between the detected left and right steering angles corresponds to the steering angle with a toe-in amount of 0. For this reason, when the controller 3 detects the steering angle of (b), as a reference setting process, it sets the intermediate steering angle as the steering angle with a toe-in amount of 0 (see FIGS. 6 and 8). Note that the reference detection method may vary depending on whether the controller 3 determines the presence or absence of a cross slope of the road surface, etc., but in this example, it is assumed that the presence or absence of a cross slope is not determined.

[0038] holding current I l0 , I r0 When both are 0, the controller 3 sets the temporary reference steering angle as the steering angle with a toe-in amount of 0. Holding current I l0 , I r0When both are not zero, while the vehicle is going straight, as symmetric steering control, the controller 3 simultaneously changes the steering angles of the left front wheel 11 and the right front wheel 12 in the toe-out direction by a predetermined angle (for example, 0.1 degree). In a provisional reference state, in many cases, since it is assumed that the front wheels 11 and 12 are in the toe-in state, the controller 3 first changes the steering angle in the toe-out direction in the symmetric steering control. In this example, in order to change both steering angles in the toe-out direction, the controller 3 changes the left control current to the minus side and the right control current to the plus side. In the symmetric steering control, since the steering angles change symmetrically left and right, the straight-ahead state of the vehicle is maintained.

[0039] After the controller 3 changes the steering angles of the left and right front wheels 11 and 12, it holds the steering angles for a predetermined time (for example, several seconds) and stores the control current required to hold the steering angles, that is, the holding current. As a storage process, the controller 3 stores the correspondence relationship between the steering angle and the holding current (for example, steering angle = +0.1, left holding current = I l1 , right holding current = I r1 ). Hereinafter, the process of changing the steering angle in the symmetric steering control is also simply referred to as "steering angle change".

[0040] In the symmetric steering control and the storage process, the processes of holding the steering angle, storing the detected value, and changing the steering angle are repeated until the left and right steering angles in the state of (a) or the left and right steering angles in (b) are detected. When the vehicle of this configuration is going straight on a flat road without a cross slope (flat straight-ahead state), the direction of the self-aligning moment M2 is reversed with the toe-in amount 0 as the boundary, and the positive and negative of the holding current are also reversed. That is, in the flat straight-ahead state, the steering angle at which the holding current becomes 0 (including substantially 0) becomes the steering angle at which the toe-in amount becomes 0.

[0041] When giving priority to the detection of (b), the controller 3 compares the stored first holding current and the second holding current. If the positive and negative of the holding current are reversed between the first and the second in at least one of the left and right, it can be determined that there is a steering angle at which the holding current becomes 0 between the first steering angle and the second steering angle. In this case, the controller 3 executes a symmetric steering process in which a predetermined angle is made smaller than the initial value with respect to the range between the first steering angle and the second steering angle. That is, in the symmetric steering process, the controller 3 changes the steering angle more finely to detect the steering angle at which the holding current becomes 0. In the flat straight-ahead state, the holding currents on the left and right become 0 with the same toe-in amount on the left and right.

[0042] When the controller 3 cannot detect a positive / negative reversal with both holding currents, it continues to simultaneously change the steering angles of the left and right front wheels 11 and 12 by a predetermined angle in the toe-out direction. Then, the controller 3 holds the steering angle for a predetermined time, and stores the correspondence between the steering angle at that time and the holding current (for example, steering angle = +0.2, left holding current = I l2 , right holding current = I r2 ). The controller 3 repeatedly executes steering angle changes, executes fine steering angle changes in a section where the holding current reverses as necessary, and detects the steering angle in the state of (a) or the steering angle in (b). The controller 3 executes a symmetric steering process also in the toe-in direction as necessary.

[0043] The controller 3 may detect the steering angle in the state of (a) or the steering angle in (b) by representing a straight line or an approximate straight line passing through the stored values on a graph based on the stored values (measured values), as shown in FIG. 6 or FIG. 8, for example. In this way, the controller 3 detects the states of (a) and (b) based on the stored values, detects the steering angle with a toe-in amount of 0, and sets that steering angle as the true reference. The details of the graph will be described later.

[0044] (Continuous symmetric steering process) When the controller 3 executes symmetric steering control in which the steering angle is continuously changed, the controller 3 gradually (slowly) changes the steering angles of the left and right front wheels 11 and 12 simultaneously and symmetrically from a temporary reference state in the toe-out direction or the toe-in direction. For example, after changing the steering angles of the front wheels 11 and 12 to a predetermined steering angle in the toe-out direction, the controller 3 returns to the temporary reference, and then changes the angles to a predetermined steering angle in the toe-in direction. In the symmetric steering control in which the change is made step by step, the controller 3 holds the angle for a predetermined time after changing the steering angle. In this case, however, the steering angle is continuously changed at a predetermined speed, and the detection values of the respective sensors 30 and 224 are continuously stored.

[0045] In the symmetric steering control, the controller 3 changes the control current so as to continuously supply a control current having an absolute value slightly higher than the holding current at each steering angle to the steering motor 221. By supplying a control current having an absolute value slightly higher than the holding current to the steering motor 221, the wheels slowly steer from the held state. This control current is substantially the same value as the holding current, and the correspondence between the steering angle and the control current stored in the storage process can be regarded as the same as the correspondence between the steering angle and the holding current. Therefore, the controller 3 treats the stored correspondence as the correspondence between the steering angle and the holding current. The controller 3 detects the inversion of the holding current and sets a reference based on the detection result. Note that the change range of the steering angle is set to be smaller than the range from the upper limit to the lower limit of the steering angle.

[0046] As a memory process, the controller 3 stores the correspondence relationship (e.g., time-series data) between the steering angle and the control current. As shown in FIG. 6, the result of the memory process can be represented by a graph. In this graph, one axis (here the horizontal axis) represents the steering angle, and the other axis (here the vertical axis) represents the control current (holding current). In this graph, the left straight line, which is a straight line formed by the stored values of the left front wheel 11, and the right straight line, which is a straight line formed by the stored values of the right front wheel 12, intersect at the point where the control current reverses, that is, where the control current becomes 0 (steering angle). That is, the steering angle at which the control current becomes 0 is the same for both the left and right. The controller 3, as a reference setting process, sets the steering angle at which the control current becomes 0 as the steering angle at which the toe-in amount is 0 (steering angle = 0), that is, as the true reference. The graph is symmetric about the true reference. Note that even in the symmetric steering process in which the steering angle is changed step by step, a graph similar to that in FIG. 6 can be drawn based on the stored values.

[0047] In a graph in which one of the horizontal axis and the vertical axis is the steering angle and the other of the horizontal axis and the vertical axis is the current value of the control current, the controller 3 sets the steering angle corresponding to the intersection of the left straight line, which is a straight line representing the correspondence relationship between the left steering angle and the left holding current in the graph, and the right straight line, which is a straight line representing the correspondence relationship between the right steering angle and the right holding current in the graph, as the left and right steering angles at which the toe-in amount is 0. The straight line is a concept including the approximate straight line. Note that the controller 3 may set the reference based on the steering angle when the positive and negative of the holding current reverse, that is, the steering angle when the holding current is 0.

[0048] (Reference adjustment control on a road surface with a cross slope) As shown in FIG. 7, when a vehicle is traveling on a road surface with a transverse gradient (hereinafter also referred to as an "inclined surface"), a moment due to gravity (hereinafter also referred to as a "gravity moment") M3 is applied to the wheels of the vehicle traveling straight on the inclined surface. In the case of FIG. 7, a gravity moment M3 is applied to the wheels so as to turn to the left. Therefore, in order to maintain a straight-ahead state, in addition to the control current required in the flat straight-ahead state, the steering motor 221 requires a control current that cancels out the gravity moment M3. That is, the holding current in the inclined surface straight-ahead state, which is the state of traveling straight on the inclined surface, is a value obtained by adding a current that cancels out the gravity moment M3 to the holding current in the flat straight-ahead state.

[0049] When the controller 3 executes continuous symmetric steering processing in the inclined surface straight-ahead state, for example, a graph as shown in FIG. 8 is formed. In order to cancel the gravity moment M3 and travel straight, both the right straight line and the left straight line are shifted upward. Since the left and right values are shifted by the same amount, the steering angle at which the toe-in amount becomes 0 is the steering angle at the intersection of the right straight line and the left straight line. That is, when the left control current and the right control current match and the left steering angle and the right steering angle match, the left steering angle and the right steering angle are the steering angles (true reference) at which the toe-in amount = 0. As another way of obtaining it, the steering angle at the midpoint between the left steering angle when the left control current is inverted (left control current = 0) and the right steering angle when the right control current is inverted (right control current = 0) is the steering angle at which the toe-in amount = 0. In this way, even when the road surface is inclined, by calculating the steering angle corresponding to the intersection of the left straight line and the right straight line, the steering angle at which the toe-in amount becomes 0 can be detected.

[0050] As an example of the control of this embodiment, as shown in FIG. 9, the controller 3 determines whether the vehicle is going straight (S1). The determination is made based on, for example, the trajectory of the position data (GPS) of the host vehicle or the detected value of the yaw rate sensor 61. When the vehicle is going straight (S1: Yes), the controller 3 executes symmetric steering processing (S2). The controller 3 stores the result of the symmetric steering processing as storage processing (S3). The controller 3 sets a steering angle (reference) at which the toe-in amount becomes 0 based on the stored value stored in the storage processing as reference setting processing (S4). In straight running of the vehicle, the controller 3 executes symmetric steering processing based on the set reference so that the left and right front wheels 11 and 12 have a desired toe-in amount (S5).

[0051] In this way, whether on a flat road or an inclined surface, the controller 3 sets a steering angle at which the toe-in amount becomes 0 based on the result of the symmetric steering processing. According to this embodiment, in single-wheel independent steering, for example, after replacement of the suspension device, the steering angle at which the toe-in amount becomes 0 can be easily detected.

[0052] The present invention is not limited to the above embodiment. For example, the drive device may be an (on-board) engine or motor provided on the vehicle body instead of the in-wheel motor unit 7, rather than a wheel. In this case, for example, in a vehicle where the kingpin offset δ1 is 0, the caster trail is 0, and the camber angle is 0, when the driving force is not applied to the target wheel and the toe-in amount is 0, the suspension geometry is such that the control current (holding current) becomes 0. In an on-board drive device, since a driving force moment M1 is generated when a driving force is applied to the wheel, the reference adjustment control is executed in a state where the driving force is not applied to the wheel. In this case, the controller 3 can execute reference adjustment control on, for example, the front wheels in a rear-wheel drive vehicle or the wheels in a state where no driving force is applied and the vehicle is decelerating.

[0053] Further, the controller 3 may determine the presence or absence of a cross slope based on, for example, the detected value of the lateral acceleration sensor 63 or the absolute value of the left and right holding currents during symmetric steering processing. When the detected value of the lateral acceleration sensor is 0 while the vehicle is moving straight, the controller 3 can determine that there is no cross slope on the road surface. Also, when the absolute values of the left and right holding currents in the symmetric steering process are equal while the vehicle is moving straight, the controller 3 can determine that there is no cross slope on the road surface. When the controller 3 determines that there is no cross slope on the driving road surface, it may determine the steering angle at which the left and right holding currents become 0 as the steering angle at which the toe-in amount becomes 0. Further, when there is no cross slope, the controller 3 may change the control current in the direction in which the absolute values of the left and right holding currents decrease (toe-in direction or toe-out direction) in the symmetric steering process. For example, when the absolute values of the left and right holding currents are increasing in the symmetric steering process, the controller 3 may change the direction of change of the steering angle. Thereby, unnecessary symmetric steering processing can be omitted. When the controller 3 determines that there is a cross slope, it may detect a reference as in the above-described embodiment, for example. Also, when the cross slope changes, the controller 3 may interrupt the reference adjustment control.

Description of Signs

[0054] 1... Steering system, 221... Steering motor (left steering motor, right steering motor), 224... Steering angle sensor (left steering angle sensor, right steering angle sensor) 3... Controller, 3A... Left steering controller (left steering control unit), 3B... Right steering controller (right steering control unit), 30... Current sensor (left current sensor, right current sensor).

Claims

1. A left steering motor that steers a left steering wheel, A right steering motor that steers a right steering wheel independently of the left steering wheel, A controller including a left steering control unit that supplies a left control current, which is a control current, to the left steering motor, and a right steering control unit that supplies a right control current, which is a control current, to the right steering motor, A left steering angle sensor that detects a left steering angle, which is the steering angle of the left steering wheel, A right steering angle sensor that detects a right steering angle, which is the steering angle of the right steering wheel, A left current sensor that detects a current value of the left control current, A right current sensor that detects a current value of the right control current, A steering system mounted on a vehicle, comprising: in a flat road without a cross slope, in a state where no driving force moment, which is a moment around a kingpin axis due to a driving force, is generated on the left steering wheel and the right steering wheel, and when the toe-in amounts of the left steering wheel and the right steering wheel are both 0, the left control current and the right control current for maintaining straight travel of the vehicle are both configured to be 0, The controller is A symmetric steering process of continuously or stepwise changing the left control current and the right control current while maintaining the steering angles of the left steering wheel and the right steering wheel symmetrically in a state where the vehicle is traveling straight and no driving force moment is generated on the left steering wheel and the right steering wheel, Based on the detection value of the left steering angle sensor when the positive and negative of the detection value of the left current sensor are reversed, and the detection value of the right steering angle sensor when the positive and negative of the detection value of the right current sensor are reversed, or based on the left steering angle and the right steering angle when the detection value of the left current sensor and the detection value of the right current sensor match and the detection value of the left steering angle sensor and the detection value of the right steering angle sensor match, a reference setting process of setting the left steering angle and the right steering angle at which the toe-in amount becomes 0, configured to execute the steering system.

2. An in-wheel motor unit is provided as a driving device on the left steering wheel and the right steering wheel, The kingpin offset of the vehicle is set to 0, The steering system according to claim 1.

3. In a graph in which the controller uses one of the horizontal axis and the vertical axis as the steering angle and the other of the horizontal axis and the vertical axis as the current value of the control current, the steering angle corresponding to the intersection of a left straight line, which represents the correspondence between the left steering angle and the left control current as a straight line in the graph, and a right straight line, which represents the correspondence between the right steering angle and the right control current as a straight line in the graph, is set as the left steering angle and the right steering angle at which the toe-in amount is 0. The steering system according to claim 1 or 2.

4. When the controller determines that there is no lateral gradient on the road surface based on the lateral acceleration or the left control current and the right control current in the symmetric steering process, in the symmetric steering process, the controller changes the control current in the direction in which the absolute values of the left control current and the right control current become smaller, among the toe-in direction and the toe-out direction. The steering system according to claim 1 or 2.

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