JP7619207B2 - Steering system - Google Patents

Description

The present invention relates to a steering system.

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 adjustments using a tester are time-consuming and costly. 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.

Patent No. 5313760

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 zero. Therefore, even if the yaw rate is zero, if the wheels are traveling straight while 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.

The deflected state is a state in which the vehicle is moving straight with the vehicle body front-rear 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 direction of the vehicle body and the wheels. The vehicle body front-rear 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.

The steering system of the present invention comprises a front wheel steering device for turning the front wheels, a rear wheel steering device for turning the 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 the vehicle is traveling straight, and a deviation judgment device for, when the straight-line detection device detects the straight-line state, determining whether the state of the vehicle is in a biased state in which the fore-and-aft direction of the vehicle body is misaligned with the direction of travel, based on an optical flow calculated from the detection results of a surroundings monitoring device installed on the vehicle, and when the deviation judgment device determines that the state of the vehicle is in the biased state, executing deviation correction control for controlling the front wheel steering device and the rear wheel steering device to correct the biased state, or warning control for warning the driver.

According to the present invention, by using optical flow or the movement trajectories of two GPS devices, it is possible to detect a deflection state in which the vehicle is moving straight and the longitudinal direction of the vehicle body is misaligned with 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.

In a configuration in which warning control is executed, alignment adjustment is only required 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 keep the operating member operated a certain amount from the neutral position. On the other hand, when the front wheel steering device is a 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. This allows the vehicle to be set to go straight in the neutral position by changing the steering angle of the front wheels relative to the neutral position of the operating member.

1 is a conceptual diagram showing a configuration of a steering system according to an embodiment of the present invention; FIG. 4 is a conceptual diagram for explaining a deflection state of a vehicle in the embodiment. FIG. 2 is a conceptual diagram for explaining an optical flow in the embodiment. 4 is a flowchart showing an example of control according to the embodiment. FIG. 13 is a conceptual diagram showing a modified embodiment of the deflection determining device according to the embodiment.

Below, as a form 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. In addition to the embodiment described below, the present invention can be carried out in various forms with various modifications and improvements based on the knowledge of those skilled in the art.

As shown in FIG. 1, the steering system 1 of the embodiment includes three mechanically independent devices, namely, an operating 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.

(Operation device)
The operation device 2 includes a steering wheel 21 as an operation member, a steering shaft 22, a steering column 23, a reaction force imparting mechanism 24, and an operation angle sensor 25. The steering wheel 21 is an operation 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).

The reaction force applying mechanism 24 uses a reaction force motor 26, an electric motor supported on the steering column 23, as a power source to apply 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. The reaction force applying mechanism 24 has a general structure including a reduction gear 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.

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

(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.

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

The rod moving mechanism 33 is a mechanism for moving the steering rod 31 left and right using the steering motor 35, an electric motor, as a drive source. The rod moving mechanism 33 is mainly 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. As it has a general structure, a detailed explanation of the rod moving mechanism 33 will be omitted.

The steering motor 35 is provided with a rotation angle sensor 35a and a current sensor 35b that detects the current supplied to it. The front wheel steering device 3 also has a steering angle sensor 36 that detects the amount of movement of the steering rod 31 to the left and right from the neutral position 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 using the force of the steering motor 35.

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.

(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.

The steering ECU 5 executes steering control to steer 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 the target for the steering angle of the front wheels 10F, based on the operation angle.

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

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 this steering current to the steering motor 35.

The steering ECU 5 also determines a target rear wheel steering angle, which is the 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 rear wheels 10R to be in phase or in opposite phase depending on the driving 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 driving conditions.

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 reduction 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.

On the other hand, the operation force dependent reduction component FA can be considered as a component for providing the driver with the operation feel of a so-called power steering system. In a power steering system, an assist torque corresponding to the operation torque is generally applied to the steering shaft 22. The steering ECU 5 detects the operation torque via the operation torque sensor 28. The steering ECU 5 determines the reaction force current, which is the 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.

In this way, the steering ECU 5 can be said to include a steering control unit 51 that executes steering control, and an operation control unit 52 that controls the operation device 2, for example, by executing reaction force control. In addition, as will be described in detail later, the steering ECU 5 further includes a straight-line determination unit 53, an origin calculation unit 54, a reference memory unit 55, a deflection determination unit 56, and an angle calculation unit 57. Note that the steering ECU 5 may be composed of multiple ECUs. For example, the steering ECU 5 may be composed of 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, all of which are communicatively connected to each other. In addition, the devices and ECUs in the steer-by-wire steering system 1 are each made redundant.

(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 for detecting 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.

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). If the yaw rate is below a predetermined value and the vehicle speed is above a predetermined value for a predetermined time or more, the straight-line determination unit 53 can determine 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 a factor for determining the straight-line state.

When the straight-line detection device 6 detects a straight-line state, the deflection determination device 7 determines whether the vehicle is in a deflected state in which the longitudinal direction of the vehicle body is misaligned with the traveling direction of the vehicle, 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 vehicle is in a deflected state in which the traveling direction of the vehicle is tilted by a predetermined angle or more with respect to the longitudinal direction of the vehicle body, based on the optical flow. The longitudinal direction of the vehicle body is a direction parallel to the center line CL, which is a virtual straight line passing through the center of the left and right sides of the vehicle (a direction along the center line CL). As shown in FIG. 2, the deflected state is a state in which the angle β between the longitudinal direction of the vehicle body 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 deflected 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.

The deflection determination device 7 includes a camera 71, an origin calculation unit 54, a reference memory 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 in the longitudinal direction of the vehicle. The camera 71 captures digital images (e.g., video) that are continuous over time, and transmits the captured images to the origin calculation unit 54. As shown in FIG. 3, the origin calculation unit 54 calculates an optical flow based on the captured images of the camera 71, and calculates a measurement origin MP, which is the origin of the optical flow (also called the center of expansion, vanishing point, or intersection).

Optical flow is a known technology, as described in, for example, JP 2016-122381 A, and detailed description will be omitted. Optical flow is a vector representation of the movement of an object in the imaging result (continuous digital images). Optical flow can be said to be a technology that represents (captures) the movement of an object between adjacent frames (between consecutive images) caused by the movement of the imaged object or the 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 capturing an 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 consecutive digital images, and calculates the origin of the optical flow as the measurement origin MP.

The reference memory 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 moving straight and not deflected. In the embodiment, the reference position RP 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 that passes through the origin Or and a certain area in which the origin Or is located.

When the camera 71 is installed in the center of the vehicle in the left-right direction and captures the image 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 left-right direction of the image capture area (see Figure 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 memory 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.

The deflection determination unit 56 determines whether the vehicle is in a deflected state based on a comparison between the measurement origin MP and the reference position RP. For example, the deflection determination unit 56 determines that the vehicle is in a deflected state when the difference (distance) between the measurement origin MP and the reference position RP is equal to or greater than a threshold value. 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 is in a deflected state 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.

The angle calculation unit 57 calculates the inclination angle β of the vehicle's traveling direction relative to the vehicle's 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's slip angle, and is the angle between a straight line parallel to the vehicle's longitudinal direction (e.g., the center line CL) and a straight line parallel to the vehicle's 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. The angle calculation unit 57 may store, for example, a map showing the relationship between the horizontal deviation and the angle β, or may store a formula for calculating the angle β from the horizontal deviation. The angle calculation unit 57 transmits the angle β information 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 Figure 2, the left wheel 10 is toe-in and the right wheel 10 is toe-out.

(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 (such as the measurement origin MP and the angle β) 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.

Based on information from the origin calculation unit 54 and/or the deflection determination unit 56, the steering control unit 51 determines whether the wheel 10 is deflected to the left or right with respect to the vehicle body. 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.

The steering control unit 51 executes 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. In addition, in executing deflection correction control, the steering control unit 51 controls the front wheel steering device 3 to correct the front wheels 10F in the same way as the correction to the rear wheels 10R, without operating the steering wheel 21. In other words, 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, just like the rear wheels 10R. At this time, the steering control unit 51 and the operation control unit 52 work together to execute deflection correction control so that the steering wheel 21 does not rotate in response to the steering of the front wheels 10F.

In this way, the steering ECU 5 executes deflection correction control on the front wheels 10F and 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 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 deflection correction control corresponds to the state of the wheels 10 when the steering wheel 21 is in the neutral position (unoperated state).

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 deflection 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), deflection 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. The state of the wheels 10 after the deflection correction control is executed is then 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).

(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 is in a deflection state. The warning control is a control to inform the driver that the vehicle is in a deflection state, for example, by display or sound. Furthermore, when the steering ECU 5 executes the deflection correction control, the steering ECU 5 may inform the driver that the deflection correction control has been executed, for example, by display or sound.

(summary)
In this way, the steering system 1 is configured to execute a bias correction control for controlling the rear wheel steering device 4 to correct the bias state, or a warning control for warning the driver, when the bias determination device 7 determines that the vehicle state is 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 can detect or correct the bias state of the wheels.

In a configuration that executes warning control, alignment adjustments need only be performed when a warning is issued, reducing the number of adjustments required. In addition, in a configuration that executes deflection correction control, rear wheel deflection is corrected by controlling the steering angle of the rear wheels 10R. This reduces the number of alignment adjustments required.

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, when 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 relative to the neutral position of the steering wheel 21.

By automatically adjusting the alignment (deflection correction control) as in the embodiment, the inclination angle β during straight driving can be set to 0 (close to 0), thereby reducing the projected area of the vehicle as seen from the direction of travel while driving straight, 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 desired position when driving on narrow roads or when pulling over to the side of a car.

In addition, according to the embodiment, the deflection determination device 7 uses optical flow to determine the presence or absence of a deflection state, so that the presence or absence of a deflection state can be determined with high accuracy with a simple configuration.In addition, according to the embodiment, the angle β is calculated by the angle calculation unit 57, and deflection correction control is performed based on the angle β, so that deflection correction control is performed with high accuracy.

In addition, according to the embodiment, the yaw rate is used to determine whether the vehicle is traveling straight, so that it is possible to directly, i.e., accurately, determine whether the vehicle is traveling straight. In addition, according to the embodiment, the deflection correction control is executed when the vehicle is stopped or traveling at a low speed, so that the sense of discomfort felt by the driver can be suppressed.

(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 the 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 movement trajectory of the vehicle 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 (e.g., estimation based on information acquired by radio waves from infrastructure or magnets on the road surface).

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 image capture results of a camera that captures 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 at a distance from each other on the vehicle, and a determination unit 74 (ECU) that determines whether the vehicle is in a deflection state based on the movement trajectories (position information) of the GPS 72, 73.

The GPS 72, 73 are arranged at a distance L apart in the front-rear direction of the vehicle body, for example, 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=asin(x/L)

In this way, the vehicle's deflection state 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 determined, it is possible to calculate the angle β.

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 also be a left/right independent steering type system in which the left and right wheels 10 can be steered independently. In addition, the deflection correction control can be performed at any time without causing discomfort to the driver, for example, during automatic driving, by being performed together with the route correction.

The angle of the wheels 10 may be corrected gradually in the deflection correction control. A steering request may be sent from another ECU to the steering ECU 5, for example, in the case of autonomous driving. The deflection determination device 7 may use the detection results 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. 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 resolved.

1: Steering system, 10F: Front wheels, 10R: Rear wheels, 2: Operation device, 21: Steering wheel (operation 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 (8)

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. 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. 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 traveling 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 . 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 . 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 . 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. 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 . a state of the wheels after the deviation correction control is executed is recorded, and a relationship between the neutral position of the operation member and the steering angle of the wheels is changed based on the recorded state.
8. A steering system according to claim 7.

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