Steering system

Abstract

To provide a steering system capable of detecting or correcting the deflection state of a wheel.SOLUTION: A steering system includes: a turn control device 51 that controls, in accordance with a turn request, a front-wheel turning device 3 and a rear-wheel turning device 4; a straight-running detecting device 6 that detects a straight-running state in which a vehicle is running straight; and a deflection determining device 7 that determines, when the straight-running detecting device 6 detects the straight-running state, whether or not the state of the vehicle is a deflection state in which the vehicle back-and-forth direction and the running direction of the vehicle are misaligned on the basis of an optical flow calculated from the detection result of a peripheral monitoring device 71 installed in the vehicle, or the respective moving trajectories of two GPSs 72 and 73 installed in the vehicle so as to be apart from each other. When the deflection determining device 7 determines that the state of the vehicle is the deflection state, the steering system executes a deflection correcting control that controls the rear-wheel turning device 4 so as to correct the deflection state or a warning control to warn a driver.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] When replacing vehicle suspension parts, a tester is used to measure the toe angle and other parameters in order to adjust the wheel alignment. Precise alignment adjustment using a tester takes time and costs money. For example, in commercial vehicles, it is not uncommon for the steering mechanisms of all four wheels to be replaced at once (e.g., as a unit). However, performing precise alignment adjustments every time a part that affects straight-line performance (e.g., the suspension mechanism or steering mechanism) is replaced would take a considerable amount of time and cost. Therefore, for example, Patent Publication No. 5313760 discloses a technology that automatically adjusts the toe angle while driving. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5313760 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above technology, adjustments are made based on driving with both the steering angle of the front wheels and the yaw rate of the vehicle body set to 0. Therefore, even if the yaw rate is 0, if the vehicle is traveling straight with the wheels biased relative to the fore-aft direction of the vehicle body, i.e., if the wheels are in a biased state, the toe angle of the rear wheels may be set while maintaining that biased state.

[0005] The deflected state is a state in which the vehicle is moving straight with the vehicle body longitudinal direction (front direction of the vehicle body) not coinciding with the traveling direction (so-called crab running state). In the deflected state, no yaw rate is generated. In the deflected state, the vehicle body can be said to have a vehicle body slip angle in terms of the relationship between the directions of the vehicle body and the wheels. The vehicle body longitudinal direction is, for example, a direction parallel to a straight line (center line) passing through the center point of the left-right width at the front end of the vehicle body and the center point of the left-right width at the rear end of the vehicle body. In the deflected state, the front wheels and the rear wheels are deflected in the same direction with the same steering angle with respect to the vehicle body. In particular, when the steering mechanism of the four wheels is replaced in its entirety, the possibility of such a deflected state occurring is relatively high unless strict alignment adjustment is performed. However, from the viewpoint of time and cost, it is desirable to reduce the number of times strict alignment adjustment is performed. SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide a steering system that is capable of detecting and correcting wheel deflection conditions. [Means for solving the problem]

[0006] The steering system of the present invention includes a front wheel steering device for steering front wheels, a rear wheel steering device for steering rear wheels, a steering control device for controlling the front wheel steering device and the rear wheel steering device in response to a steering request, a straight-line detection device for detecting a straight-line state in which a vehicle is traveling straight, and an optical flow meter calculated from the detection results of a surroundings monitoring device installed in the vehicle when the straight-line detection device detects the straight-line state. To and a deviation determination device for determining whether the state of the vehicle is in a deviation state in which the longitudinal direction of the vehicle body is misaligned with the traveling direction based on the deviation determination device, and for correcting the deviation state when the deviation determination device determines that the state of the vehicle is in the deviation state. The front wheel steering device, A deflection correction control for controlling the rear wheel steering device or a warning control for warning the driver is executed. Effect of the Invention

[0007] According to the present invention, by using optical flow or the movement trajectories of two GPS, it is possible to detect a deflection state in which the vehicle is moving straight and the longitudinal direction of the vehicle body is deviated from the traveling direction (for example, a state in which there is a difference of a predetermined angle or more). When a deflection state is detected, deflection correction control or warning control is executed. According to the present invention, it is possible to detect or correct the deflection state of the wheels.

[0008] In a configuration in which warning control is executed, alignment adjustment is performed only when a warning is issued, and the number of adjustments can be reduced. In a configuration in which deflection correction control is executed, deflection of the rear wheels is automatically corrected by controlling the steering angle of the rear wheels. This reduces the number of alignment adjustments. However, in a configuration in which the front wheel steering device and the operating member are mechanically connected, when driving the vehicle straight after deflection correction control is executed, the driver needs to maintain a state in which the operating member is operated a certain amount from the neutral position. On the other hand, when the front wheel steering device is of the steer-by-wire type, it is possible to correct the steering angle of the front wheels independently of the operating member, that is, without operating the operating member. According to this, by changing the steering angle of the front wheels relative to the neutral position of the operating member, it is possible to set the vehicle to go straight in the neutral position. [Brief description of the drawings]

[0009] [Figure 1] 1 is a conceptual diagram showing a configuration of a steering system according to an embodiment of the present invention; [Diagram 2] FIG. 4 is a conceptual diagram for explaining a deflection state of a vehicle in the embodiment. [Diagram 3] FIG. 2 is a conceptual diagram for explaining an optical flow in the embodiment. [Figure 4] 4 is a flowchart showing an example of control according to the embodiment. [Diagram 5] FIG. 13 is a conceptual diagram showing a modified embodiment of the deflection determining device according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A steering system 1 according to an embodiment of the present invention will be described in detail below with reference to the drawings. In addition to the embodiment described below, the present invention can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art.

[0011] As shown in FIG. 1, the steering system 1 of the embodiment includes three devices that are mechanically independent of one another, namely, an operation device 2, a front wheel steering device 3, and a rear wheel steering device 4. The front wheel steering device 3 is a device that steers a pair of front wheels 10F. The rear wheel steering device 4 is a device that steers a pair of rear wheels 10R. The steering system 1 also includes a steering ECU 5 that mainly controls the front wheel steering device 3 and the rear wheel steering device 4. The steering system 1 is a steer-by-wire type steering system. Note that hereinafter, the front wheels 10F and rear wheels 10R may be collectively referred to as wheels 10. The drive wheels are, for example, the rear wheels 10R.

[0012] (operating device) The operating device 2 includes a steering wheel 21 as an operating member, a steering shaft 22, a steering column 23, a reaction force imparting mechanism 24, and an operating angle sensor 25. The steering wheel 21 is an operating member that is steered by the driver. The steering shaft 22 is a shaft member having the steering wheel 21 attached to its tip. The steering column 23 is a member that rotatably holds the steering shaft 22 and is supported by an instrument panel reinforcement (not shown).

[0013] The reaction force applying mechanism 24 is a mechanism that applies a reaction force against a steering operation (hereinafter also referred to as "operation reaction force") to the steering wheel 21 via the steering shaft 22, using a reaction force motor 26, which is an electric motor supported by the steering column 23, as a power source. The reaction force applying mechanism 24 has a general structure including a reducer and the like. The reaction force motor 26 is provided with a rotation angle sensor 26a. The operation angle sensor 25 is a sensor that detects the operation angle of the steering wheel 21 as the amount of steering operation.

[0014] In addition, in the steering system 1, similar to a general so-called power steering system, a torsion bar 27 is incorporated in the steering shaft 22. The operation device 2 has an operation torque sensor 28 for detecting an operation torque as an operation force applied to the steering wheel 21 by the driver based on the amount of twist of the torsion bar 27.

[0015] (Steering device) Each of the wheels 10 is supported on the vehicle body so as to be steerable via a steering knuckle 90, which is one component of a suspension device. The front wheel steering device 3 steers the pair of front wheels 10F together by rotating the steering knuckle 90. The front wheel steering device 3 has a steering actuator 30 as a main component.

[0016] The steering actuator 30 includes a steering rod 31, a housing 32, and a rod moving mechanism 33. The steering rod 31 (also called a "rack bar") is a member connected at both ends to left and right steering knuckles 90 via link rods 34. The housing 32 is a member that supports the steering rod 31 so that it can move left and right, and is fixedly held to the vehicle body.

[0017] The rod moving mechanism 33 is a mechanism for moving the steering rod 31 left and right using the steering motor 35, which is an electric motor, as a drive source. The rod moving mechanism 33 mainly comprises a ball screw mechanism consisting of a ball groove screwed into the steering rod 31 and a nut that screws into the ball groove via a bearing ball and is rotated by the steering motor 35. Since it is of a general structure, a detailed description of the rod moving mechanism 33 will be omitted.

[0018] The steering motor 35 is provided with a rotation angle sensor 35a and a current sensor 35b that detects the current supplied to the motor 35. The front wheel steering device 3 also has a steering angle sensor 36 that detects the amount of movement of the steering rod 31 from the neutral position to the left and right, in order to detect the steering angle (amount of steering) of the front wheels 10F. In this way, the front wheel steering device 3 is mechanically independent from the operating force of the steering wheel 21, and constitutes a steer-by-wire type steering device that steers the front wheels 10F by the force of the steering motor 35.

[0019] The rear wheel steering device 4 has a similar configuration to the front wheel steering device 3. That is, the rear wheel steering device 4 is equipped with a steering actuator 40 equivalent to the steering actuator 30. The rear wheel steering device 4 steers the rear wheels 10R independently of the front wheels 10F under the control of the steering ECU 5. Since the rear wheel steering device 4 has a similar configuration to the front wheel steering device 3, a description thereof will be omitted.

[0020] (Control device) The steering ECU 5 is an electronic control unit including a CPU, a memory, etc. Although communication lines are not shown in the drawing, the steering ECU 5 is communicatively connected to each device and each sensor. A car area network or controllable area network (CAN) is used for communication within the vehicle.

[0021] The steering ECU 5 executes steering control for steering the wheels 10 in response to a steering request, i.e., the operation angle of the steering wheel 21 in the case of manual driving. The steering ECU 5 acquires the operation angle of the steering wheel 21 based on the rotation angle of the reaction force motor 26 detected by the rotation angle sensor 26a. The steering ECU 5 determines a target front wheel steering angle, which is a target for the steering angle of the front wheels 10F, based on the operation angle.

[0022] Based on the target front wheel steering angle, steering ECU 5 determines a target rotation angle, which is a target for the rotation angle of steering motor 35. Steer ECU 5 detects the actual rotation angle of steering motor 35 (hereinafter also referred to as "actual rotation angle") via rotation angle sensor 35a, and determines a rotation angle deviation, which is the deviation of the actual rotation angle from the target rotation angle. If the torque generated by steering motor 35 is called steering torque, steering ECU 5 determines the steering torque to be generated in accordance with a feedback control law based on the rotation angle deviation.

[0023] If the current supplied to the steering motor 35 is called the steering current, then the steering torque and the steering current are roughly proportional to each other. In accordance with this relationship, the steering ECU 5 determines the steering current to be supplied to the steering motor 35 based on the determined steering torque, and supplies the determined steering current to the steering motor 35.

[0024] The steering ECU 5 also determines a target rear wheel steering angle, which is a target for the steering angle of the rear wheels 10R, based on the operation angle and vehicle speed information. The vehicle speed is calculated, for example, based on the detection results of wheel speed sensors 82 provided for each wheel 10. The steering ECU 5 controls the steering actuator 40 based on the target rear wheel steering angle, similar to the steering control of the front wheels 10F. The steering ECU 5 can control the front wheels 10F and the rear wheels 10R to be in phase or in opposite phase depending on the running conditions such as the vehicle speed. The steering ECU 5 controls the steering angle of the rear wheels 10R as necessary. The steering ECU 5 may control only the steering angle of the front wheels 10F depending on the steering request and the running conditions.

[0025] The steering ECU 5 also executes reaction force control to give the driver a feeling of operation in response to the steering operation. The steering ECU 5 determines the operation reaction force based on two components, a steering load dependent component FS and an operation force dependent decrease component FA. The steering load dependent component FS is a component related to the steering force (the steering torque of the steering motor 35) required to steer the front wheels 10F, and is determined based on the steering current supplied to the steering motor 35. Although a detailed explanation is omitted, the larger the steering current, the greater the steering load on the front wheels 10F is recognized to be, and the steering load dependent component FS is determined to be a large value.

[0026] On the other hand, the operation force dependent decrease component FA can be considered as a component for providing the driver with an operation feeling in a so-called power steering system. In a power steering system, an assist torque corresponding to an operation torque is generally applied to the steering shaft 22. The steering ECU 5 detects the operation torque via an operation torque sensor 28. The steering ECU 5 determines a reaction force current, which is a current to be supplied to the reaction force motor 26, based on the operation reaction force, and supplies the determined reaction force current to the reaction force motor 26.

[0027] In this way, it can be said that the steering ECU 5 includes a steering control section 51 that executes steering control, and an operation control section 52 that controls the operation device 2, for example, by executing reaction force control. In addition, the steering ECU 5 further includes a straight-line determination section 53, an origin calculation section 54, a reference storage section 55, a deflection determination section 56, and an angle calculation section 57, which will be described in detail later. Note that the steering ECU 5 may be composed of a plurality of ECUs. For example, the steering ECU 5 may include an operation ECU that controls the operation device 2, a front wheel steering ECU that controls the front wheel steering device 3, and a rear wheel steering ECU that controls the front wheel steering device 3, which are connected to each other so as to be able to communicate with each other. In addition, the devices and ECUs in the steer-by-wire type steering system 1 are each made redundant.

[0028] (Detection of deflection state) The steering system 1 further includes a straight-line detection device 6 and a deflection determination device 7. The straight-line detection device 6 is a device that detects a straight-line state in which the vehicle is moving straight. The straight-line state can be, for example, a state in which the yaw rate is 0 and the vehicle speed is greater than 0, a state in which the movement trajectory of an arbitrary position of the vehicle is a straight line, or a state in which the left and right wheel speeds are the same.

[0029] The straight-line detection device 6 of the embodiment includes a yaw rate sensor 61, a wheel speed sensor 82 as a vehicle speed sensor, and a straight-line determination unit 53. The straight-line determination unit 53 determines whether the vehicle is in a straight-line state based on the detection results of the yaw rate sensor 61 and the wheel speed sensor 82 (i.e., yaw rate information and vehicle speed information). When the yaw rate is equal to or lower than a predetermined value and the vehicle speed is equal to or higher than a predetermined value for a predetermined time or more, the straight-line determination unit 53 determines that the vehicle is traveling without a yaw rate, and determines that the vehicle is in a straight-line state. Note that the difference between the detection values ​​of the left and right wheel speed sensors 82 may be used as an element for determining the straight-line state.

[0030] When the straight-line detection device 6 detects a straight-line state, the deflection determination device 7 determines whether the state of the vehicle is a deflection state in which the vehicle's forward and backward directions are misaligned with the vehicle's traveling direction, based on the optical flow calculated from the detection result of the surroundings monitoring device. In other words, the deflection determination device 7 determines whether the state of the vehicle is a deflection state in which the traveling direction of the vehicle is tilted at a predetermined angle or more with respect to the vehicle's forward and backward directions, based on the optical flow. The vehicle's forward and backward directions are parallel to the center line CL that is a virtual straight line passing through the center of the left and right sides of the vehicle (direction along the center line CL). As shown in FIG. 2, the deflection state is a state in which the angle β between the vehicle's forward and backward directions and the traveling direction, in other words, the angle β between a straight line parallel to the traveling direction and the center line CL, is equal to or greater than a predetermined angle (threshold value). In the deflection state, the front wheels 10F and the rear wheels 10R are deflected in the same direction with respect to the vehicle body at the same steering angle.

[0031] The deflection determination device 7 includes a camera 71, an origin calculation unit 54, a reference storage unit 55, a deflection determination unit 56, and an angle calculation unit 57. The camera 71 is a periphery monitoring device that captures an image of the area in front of the vehicle body in the longitudinal direction of the vehicle body. The camera 71 captures digital images (e.g., video) that are continuous in time, and transmits the captured image results to the origin calculation unit 54. As shown in Fig. 3, the origin calculation unit 54 calculates an optical flow based on the captured image results of the camera 71, and calculates a measurement origin MP that is the origin of the optical flow (also called the center of expansion, vanishing point, or intersection).

[0032] The optical flow is a known technique as described in, for example, Japanese Patent Application Laid-Open No. 2016-122381, and detailed description thereof will be omitted. The optical flow is a technique that expresses the movement of an object as a vector in an imaging result (continuous digital images). The optical flow can be said to be a technique that expresses (captures) the movement of an object between adjacent frames (between consecutive images) caused by the movement of an imaged object or a camera 71 as a vector. As shown in FIG. 3, for example, when a vehicle is moving straight forward, in the optical flow based on the camera 71 that captures the image in front of the vehicle body, the vector indicating the change in the position of the object extends radially from the origin (center of expansion). The origin calculation unit 54 creates an optical flow for an object in the imaging area E based on the continuous digital images, and calculates the origin of the optical flow as the measurement origin MP.

[0033] The reference storage unit 55 stores the reference position RP in advance. The reference position RP is a position (point, line, or area) set in the imaging area of ​​the camera 71 so as to include the origin Or of the optical flow when the vehicle is not in a deflected state and is moving straight ahead. The reference position RP in the embodiment is set to a straight line that includes the origin Or and extends in the vertical direction of the imaging screen. In other words, the reference position RP is a reference straight line that divides the imaging screen into a left area and a right area. In this way, the "reference position RP set to include the origin Or" includes, for example, a straight line passing through the origin Or and a certain area in which the origin Or is located inside.

[0034] When the camera 71 is installed in the center of the vehicle in the left-right direction and captures an image of the area in front of the vehicle body, the origin Or of the optical flow is located on a straight line passing through the center of the image capture area in the left-right direction (see FIG. 3). The reference line, which is the reference position RP, can be estimated in advance from the installation position and image capture direction of the camera 71, and can be set in advance in the reference storage unit 55. When the vehicle is traveling straight and not in a crab-like state, the measurement origin MP is theoretically located on the reference position RP. The reference position RP can also be said to be the position where the front of the vehicle (vehicle body) is captured.

[0035] The deflection determination unit 56 determines whether the vehicle state is deflected based on a comparison between the measurement origin MP and the reference position RP. For example, when the difference (separation distance) between the measurement origin MP and the reference position RP is equal to or greater than a threshold value, the deflection determination unit 56 determines that the vehicle state is deflected. The difference between the measurement origin MP and the reference position RP can also be considered as the horizontal deviation of the measurement origin MP from the reference position RP. The deflection determination unit 56 may determine that the vehicle state is deflected when an angle β (absolute value) described later is equal to or greater than a threshold value. The deflection determination unit 56 transmits the determination result to the steering control unit 51.

[0036] The angle calculation unit 57 calculates the inclination angle β of the traveling direction of the vehicle with respect to the vehicle body longitudinal direction based on the difference between the measurement origin MP and the reference position RP. The angle β can also be called the vehicle body slip angle, and is the angle between a straight line parallel to the vehicle body longitudinal direction (for example, the center line CL) and a straight line parallel to the vehicle traveling direction. The angle calculation unit 57 converts the horizontal (left-right) deviation between the measurement origin MP and the reference position RP into an angle β. There is a positive correlation between the horizontal deviation and the angle β. For example, the angle calculation unit 57 may store a map showing the relationship between the horizontal deviation and the angle β, or may store a calculation formula for calculating the angle β from the horizontal deviation. The angle calculation unit 57 transmits information on the angle β to the steering control unit 51. In the crab running state of FIG. 2, with the steering wheel 21 in the neutral position, all the wheels 10 are deflected in the same direction (right side) by the angle β. In the state shown in FIG. 2, the left wheel 10 is toe-in, and the right wheel 10 is toe-out.

[0037] (Deflection correction control) When the deflection determination device 7 determines that the vehicle state is in a deflection state, the steering control unit 51 executes deflection correction control for controlling the rear wheel steering device 4 so as to correct the deflection state. More specifically, when the deflection determination device 7 determines that the vehicle state is in a deflection state, the steering control unit 51 records information at the time of the determination (measurement origin MP, angle β, etc.) and executes deflection correction control at a predetermined timing. The predetermined timing is set, for example, when the vehicle is stopped or when the vehicle is in a low-speed state where it is traveling at or below a predetermined vehicle speed.

[0038] The steering control unit 51 determines whether the wheel 10 is deflected to the left or right with respect to the vehicle body, based on information from the origin calculation unit 54 and / or the deflection determination unit 56. In the example of Fig. 3, the measurement origin MP is located to the right of the reference position RP, so the wheel 10 is deflected to the right with respect to the vehicle body (see Fig. 2). In this case, in the deflection correction control, the steering control unit 51 controls the rear wheel steering device 4 to steer the rear wheel 10R to the left so as to reduce (cancel) the inclination of the rear wheel 10R with respect to the vehicle body.

[0039] The steering control unit 51 executes the deflection correction control based on the inclination angle β calculated by the angle calculation unit 57. The steering control unit 51 steers the rear wheels 10R by the angle β in a direction that cancels the deflection of the wheels 10. Furthermore, in executing the deflection correction control, the steering control unit 51 controls the front wheel turning device 3 so as to correct the front wheels 10F in the same manner as the correction to the rear wheels 10R, without operating the steering wheel 21. That is, the steering control unit 51 steers the front wheels 10F by the angle β in a direction that cancels the deflection of the wheels 10, similar to the rear wheels 10R. At this time, the steering control unit 51 and the operation control unit 52 cooperate to execute the deflection correction control so that the steering wheel 21 does not rotate in response to the steering of the front wheels 10F.

[0040] In this way, the steering ECU 5 executes the deflection correction control on the front wheels 10F and the rear wheels 10R while maintaining the rotation angle of the steering wheel 21. The steering ECU 5 records the state of the wheels 10 after the deflection correction control is executed as the state of the wheels 10 in a straight-ahead state (e.g., a state in which the toe angle is 0 degrees). Therefore, in the next and subsequent driving, the state of the wheels 10 after the deflection correction control corresponds to the state of the wheels 10 when the steering wheel 21 is in the neutral position (a state in which the steering wheel 21 is not being operated).

[0041] An example of the flow of control by the steering ECU 5 will be described with reference to FIG. 4. Based on the calculation result of the straight-line detection device 6, it is determined whether the vehicle is in a straight-line state (S1). If it is determined that the vehicle is in a straight-line state (S1: Yes), it is determined whether the angle β (absolute value) is equal to or greater than a predetermined threshold value based on the angle β calculated by the angle calculation unit 57 (S2). If the angle β is equal to or greater than the threshold value (S2: Yes), the information is recorded, and it is determined whether a predetermined execution condition for the deviation correction control (for example, the vehicle is stopped or in a low-speed state) is satisfied (S3). If the execution condition is satisfied (S3: Yes), the deviation correction control is executed, and at least the rear wheel 10R is steered by the angle β so that the angle β becomes 0 (S4). In this embodiment, the front wheel 10F is also steered by the angle β at the same time as the rear wheel 10R without operating the steering wheel 21. Then, the state of the wheels 10 after the deviation correction control is executed is recorded, and thereafter, the relationship between the neutral position of the steering wheel 21 and the steering angle of the wheels 10 is changed (S5).

[0042] (Warning Control) The steering ECU 5 may execute a warning control to warn the driver when the deflection determination device 7 determines that the vehicle state is in a deflection state. The warning control is a control to inform the driver that the vehicle state is in a deflection state, for example, by display or sound. Furthermore, when the steering ECU 5 executes the deflection correction control, it may inform the driver that the deflection correction control has been executed, for example, by display or sound.

[0043] (summary) In this way, the steering system 1 is configured to execute bias correction control for controlling the rear wheel steering device 4 to correct the bias state, or warning control for warning the driver, when the bias determination device 7 determines that the vehicle state is in a bias state. This steering system 1 can detect the bias state of the wheels (so-called crab running state) by utilizing optical flow. Furthermore, when a bias state is detected, warning control or bias correction control is executed. In this way, this configuration makes it possible to detect or correct the bias state of the wheels.

[0044] In the configuration in which the warning control is executed, alignment adjustment needs to be performed only when a warning is issued, and the number of adjustments can be reduced. In the configuration in which the deviation correction control is executed, deviation of the rear wheels is corrected by controlling the steering angle of the rear wheels 10R. This allows the number of alignment adjustments to be reduced.

[0045] However, unlike the embodiment, in a configuration in which the front wheel steering device 3 and the steering wheel 21 are mechanically connected, such as in power steering, the driver needs to keep the steering wheel 21 operated a certain amount from the neutral position when driving the vehicle straight after the deflection correction control is executed. On the other hand, in a case in which the front wheel steering device 3 is of the steer-by-wire type as in the embodiment, it is possible to correct the front wheels 10F independently of the steering wheel 21. This allows the vehicle to be set to go straight in the neutral position by changing the steering angle of the front wheels 10F with respect to the neutral position of the steering wheel 21.

[0046] By making the inclination angle β during straight driving 0 (approaching 0) through automatic alignment adjustment (deflection correction control) as in the embodiment, the projected area of ​​the vehicle as seen from the direction of travel while going straight can be reduced, making it possible to improve fuel efficiency by reducing air resistance. Furthermore, this automatic adjustment makes it possible to more accurately guide the vehicle to the target position when driving on narrow roads or when pulling over to the side of a car.

[0047] According to the embodiment, the deflection determination device 7 determines the presence or absence of a deflection state by utilizing the optical flow, so that the presence or absence of a deflection state can be determined with high accuracy with a simple configuration. According to the embodiment, the angle calculation unit 57 calculates the angle β, and the deflection correction control is executed based on the angle β, so that the deflection correction control is executed with high accuracy.

[0048] According to the embodiment, since the yaw rate is used to determine whether the vehicle is moving straight, it is possible to directly and accurately determine whether the vehicle is moving straight. According to the embodiment, the deflection correction control is executed when the vehicle is stopped or moving at a low speed, which can reduce discomfort felt by the driver.

[0049] (others) The present invention is not limited to the above embodiment. For example, the straight-line detection device 6 may detect the straight-line state of the vehicle based on at least one of the vehicle movement trajectory acquired by GPS, the detection value of the lateral acceleration sensor, and the difference between the detection values ​​of the left and right wheel speed sensors 82, instead of or in addition to the yaw rate information and the vehicle speed information. The straight-line detection device 6 can detect the straight-line state of the vehicle, for example, when the vehicle movement trajectory is linear, the lateral acceleration (acceleration in the left and right direction) is equal to or less than a predetermined value, or the difference between the left and right wheel speeds is equal to or less than a predetermined value. In addition, the straight-line detection device 6 may detect the straight-line state of the vehicle based on the movement trajectory of the vehicle in the self-position estimation result during automatic driving (for example, estimation based on information acquired by radio waves from infrastructure or magnets on the road surface).

[0050] The deflection determination device 7 may also calculate the optical flow and the measurement origin MP (the origin in this case is also called the reduction center) based on the imaging result of a camera that images the rear of the vehicle body. The deflection determination device 7 may not use the optical flow. For example, as shown in FIG. 5, instead of the configuration of the embodiment, the deflection determination device 7 may include GPS 72, 73 installed apart from each other on the vehicle, and a determination unit 74 (ECU) that determines whether or not the vehicle is in a deflected state based on the movement trajectories (position information) of the GPS 72, 73.

[0051] The GPS 72, 73 are arranged, for example, at a distance L apart in the front-rear direction of the vehicle body so that a straight line connecting the GPS 72 and the GPS 73 is parallel to the center line CL. When the straight-line traveling state of the vehicle is detected based on the above-mentioned determination elements related to straight-line traveling (yaw rate, position information, etc.), the determination unit 74 calculates the deviation x of the movement trajectory of the GPS 73 relative to the movement trajectory of the GPS 72. The deviation x is the distance between the two detected parallel movement trajectories. The determination unit 74 calculates the tilt angle β based on the deviation x, for example, based on the following equation. β = a sin(x / L)

[0052] In this way, the deflection state of the vehicle can be detected by using the movement trajectories of the two GPS 72, 73. The installation positions of the GPS 72, 73 are not limited to the direction along the front-rear direction of the vehicle body, but may be in the left-right direction. If the installation positions of the two GPS 72, 73 relative to the vehicle body can be grasped, the angle β can be calculated.

[0053] The steering system is not limited to a steer-by-wire type system, but may be a system in which the operating force applied to the steering wheel is mechanically transmitted to a front wheel steering device (e.g., a steering rod, etc.), such as a power steering system. The steering system may be a left / right independent steering type system in which the left and right wheels 10 can be steered independently. The deflection correction control can be performed at any timing without causing discomfort to the driver, for example, during automatic driving, by being performed together with the route correction.

[0054] Also, the correction of the angle of the wheels 10 in the deflection correction control may be performed gradually. Also, the steering request may be transmitted from another ECU to the steering ECU 5, for example, in the case of automatic driving. Also, the deflection determination device 7 may use the detection result of a radar device provided in the vehicle as a periphery monitoring device when determining the deflection state. The periphery monitoring device may be a radar device. Also, the steering system 1 may execute control to correct the steering angle of the wheels 10 by a predetermined amount in a direction to cancel the deflection as the deflection correction control, for example, when the angle β is not calculated. The steering system 1 may repeatedly execute the deflection correction control until the deflection state is eliminated. [Explanation of symbols]

[0055] 1: steering system, 10F: front wheels, 10R: rear wheels, 2: operating device, 21: steering wheel (operating member), 3: front wheel steering device, 4: rear wheel steering device, 5: steering ECU, 51: steering control unit (steering control device), 53: straight line determination unit, 54: origin calculation unit, 55: reference memory unit, 56: deflection determination unit, 57: angle calculation unit, 6: straight line detection device, 61: yaw rate sensor, 7: deflection determination device, 71: camera, 82: wheel speed sensor, CL: center line.

Claims

1. A front wheel steering device for steering the front wheels; A rear wheel steering device for steering the rear wheels; a steering control device that controls the front wheel steering device and the rear wheel steering device in response to a steering request; a straight-line detection device for detecting a straight-line state in which the vehicle is traveling straight; a deviation determination device that, when the straight-line state is detected by the straight-line detection device, determines whether or not the state of the vehicle is a deviation state in which the longitudinal direction of the vehicle body is misaligned with the traveling direction of the vehicle, based on an optical flow calculated from the detection result of a surroundings monitoring device installed on the vehicle; Equipped with the steering control device executes a bias correction control for controlling the front wheel steering device and the rear wheel steering device so as to correct the bias state when the bias determination device determines that the state of the vehicle is the bias state, the front wheel steering device constitutes a steer-by-wire type steering device that is mechanically independent of the operating force of an operating member and steers the front wheels by the force of a steering motor, the steering control device controls the front wheel steering device so as to correct the front wheels in the same manner as the correction to the rear wheels, without operating the operating member, in executing the deflection correction control. Steering system.

2. A front wheel steering device for steering the front wheels; A rear wheel steering device for steering the rear wheels; a steering control device that controls the front wheel steering device and the rear wheel steering device in response to a steering request; a straight-line detection device for detecting a straight-line state in which the vehicle is traveling straight; a deviation determination device that, when the straight-line state is detected by the straight-line detection device, determines whether or not the state of the vehicle is a deviation state in which the longitudinal direction of the vehicle body is misaligned with the traveling direction of the vehicle, based on an optical flow calculated from the detection result of a surroundings monitoring device installed on the vehicle; Equipped with When the deviation determination device determines that the state of the vehicle is in the deviation state, a warning control is executed to warn a driver. Steering system.

3. The deflection determination device includes: a camera as the periphery monitoring device that captures an image of a front or rear of the vehicle body in a longitudinal direction of the vehicle body; an origin calculation unit that calculates the optical flow based on the imaging result of the camera and calculates a measurement origin that is the origin of the calculated optical flow; a reference storage unit that stores in advance a reference position that is set in an imaging area of ​​the camera and is set so as to include an origin of the optical flow when the vehicle is not in the deflected state and is moving straight; a deflection determination unit that determines whether or not the state of the vehicle is in the deflected state based on a comparison between the measurement origin and the reference position; Equipped with A steering system according to claim 1 or 2.

4. An angle calculation unit is further provided that calculates an inclination angle of the traveling direction of the vehicle with respect to the vehicle body longitudinal direction based on a difference between the measurement origin and the reference position, The deflection determination unit determines that the state of the vehicle is in the deflected state when the tilt angle is equal to or greater than a predetermined threshold value.

4. The steering system of claim 3.

5. when the deflection determination device determines that the vehicle is in the deflected state, the turning control device executes the deflection correction control based on the inclination angle calculated by the angle calculation unit. A steering system according to claim 4 not dependent on claim 2.

6. The straight-line detection device is A yaw rate sensor and a vehicle speed sensor, a straight-line determination unit that determines whether the vehicle is in the straight-line state based on detection results of the yaw rate sensor and the vehicle speed sensor; Equipped with A steering system according to any one of claims 1 to 5.

7. When the deflection determination device determines that the vehicle is in the deflection state, the steering control device records information at the time of the determination, and when the vehicle is in a stopped state or in a low-speed state where the vehicle is traveling at or below a predetermined vehicle speed, executes the deflection correction control based on the recorded information at the time of the determination. A steering system according to claim 1 or according to any one of claims 3 to 6 not dependent on claim 2.

8. Recording the state of the wheels after the deflection correction control is executed, and changing the relationship between the neutral position of the operating member and the steering angle of the wheels based on the record.

8. A steering system according to claim 7.

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