Vehicle control device and vehicle control method

Abstract

To provide a technique which prevents changes in a steering angle that are not intended by a driver, and which increases stability of vehicle behavior, also when a wheel floating state of a vehicle has occurred.SOLUTION: Provided is a vehicle control device for controlling a vehicle. The vehicle control device executes: processing for determining whether or not one of a plurality of wheels of a vehicle is in a wheel floating state of not contacting the ground; and processing for holding a steering angle of the vehicle during occurrence of the wheel floating state.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a technique for controlling a vehicle when wheel lift occurs.

Background Art

[0002] Patent Document 1 discloses a rollover determination device that determines the presence or absence of a vehicle rollover. The rollover determination device includes detection means for detecting a state in which one wheel of the vehicle has lifted off the road surface, and predicts the rollover behavior of the vehicle when the wheel is in a state of having lifted off the road surface.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a vehicle is running, a wheel lift state may occur in which one of the wheels floats due to riding over an obstacle or the like. When the wheel lift state occurs, the resistance from the road surface to the floating wheel disappears, so that an unintended change in the steering angle is likely to occur. When the wheel lands in a situation where such an unintended change in the steering angle has occurred, the vehicle posture may become unstable. One object of the present disclosure is to provide a technique capable of enhancing the stability of vehicle behavior even when a wheel lift state occurs.

Means for Solving the Problems

[0005] The first aspect of the present disclosure relates to a vehicle control device that controls a vehicle.

[0006] The vehicle control device relating to the first aspect is characterized by being configured to perform a process of determining whether a wheel-lift condition has occurred in which any of the vehicle's multiple wheels are not in contact with the ground, and a process of maintaining the steering angle of the vehicle while the wheel-lift condition has occurred.

[0007] The second aspect of this disclosure relates to a vehicle control method for controlling a vehicle.

[0008] The vehicle control method relating to the second aspect is characterized by including determining whether a wheel-lift condition has occurred in which any of the vehicle's multiple wheels are not in contact with the ground, and maintaining the steering angle of the vehicle while the wheel-lift condition is occurring. [Effects of the Invention]

[0009] According to this disclosure, the steering angle of the vehicle is maintained while the wheel is lifted off the ground. Maintaining the steering angle prevents unintended changes in the steering angle. In this way, the stability of the vehicle's behavior can be enhanced. [Brief explanation of the drawing]

[0010] [Figure 1] This is a block diagram showing examples of vehicle configurations. [Figure 2] This is a diagram to explain the state of a wheel floating. [Figure 3] This flowchart shows an example of the processing performed by the vehicle control device according to this embodiment. [Figure 4] This diagram illustrates the reference direction used in determining the yaw angle by the vehicle control device according to this embodiment. [Figure 5] This figure shows an example of ground load information. [Figure 6] This flowchart shows an example of processing in an application. [Modes for carrying out the invention]

[0011] Embodiments of this disclosure will be described with reference to the attached drawings.

[0012] 1. Overview of Vehicle Control Systems The vehicle control device according to this embodiment controls the vehicle. Figure 1 is a block diagram showing an example configuration of a vehicle 1 to which the vehicle control device 10 according to this embodiment is applied.

[0013] Vehicle 1 comprises a vehicle control device 10, sensors 20, and actuators 30. The vehicle control device 10 is configured to communicate information with the sensors 20 and actuators 30. For example, the vehicle control device 10 is connected to these devices by an in-vehicle network consisting of wire harnesses, etc.

[0014] The sensors 20 include an IMU (Inertial measurement unit) 21, an on-board camera 22, a steering angle sensor 23, and a wheel speed sensor 24. The IMU 21 is a sensor that detects angular velocity and acceleration in three axes. This allows the vehicle 1's attitude angle (yaw angle, roll angle, and pitch angle), direction of travel, and vehicle speed to be acquired. The on-board camera 22 includes, for example, a front camera that images the area in front of the vehicle 1 and a foot-level camera that images the wheels of the vehicle 1. The foot-level camera is mounted under the floor of the vehicle 1 and its imaging range includes the contact area where the wheels touch the ground. The foot-level camera is mounted on the vehicle 1, for example, to detect wheel failures. The steering angle sensor 23 detects the steering angle of the vehicle 1. The wheel speed sensor 24 detects the wheel speed of each of the multiple wheels of the vehicle 1. The sensors 20 may also include a sensor that detects suspension stroke.

[0015] The actuator 30 includes, for example, a steering motor that controls the wheels.

[0016] The vehicle control device 10 includes at least one processor 11 (hereinafter simply referred to as the processor 11) and at least one storage device 12 (hereinafter simply referred to as the storage device 12) coupled to the processor 11. The processor 11 performs various calculations necessary for the processing by the vehicle control device 10. The storage device 12 stores at least one program executable by the processor 11 and various data related thereto. When the program stored in the storage device 12 is executed by the processor 11, various processes by the vehicle control device 10 are realized. The vehicle control device 10 may include one or more ECUs (Electronic Control Unit).

[0017] When the vehicle 1 is running, a wheel lift state may occur. The wheel lift state is a state in which any one of a plurality of wheels of the vehicle 1 is not in contact with the ground, and is caused by the vehicle 1 climbing over a convex portion or an obstacle on the ground. In particular, when the vehicle 1 is running on an unpaved road or an uneven road, the frequency of the vehicle 1 climbing over an obstacle or the like tends to increase, and the wheel lift state also tends to occur.

[0018] FIG. 2 is a diagram schematically showing the state of the vehicle 1 when the wheel lift state occurs. (A) of FIG. 2 shows the state of the vehicle 1 viewed from the side, and (B) of FIG. 2 shows the state of the vehicle 1 viewed from above.

[0019] At time T1, the wheel lift state has not yet occurred, and the vehicle 1 is traveling in a straight-ahead direction. At time T2, due to the vehicle 1 climbing over an obstacle, the front wheels are in a floating state separated from the ground. This state is the wheel lift state. After climbing over the obstacle, the front wheels are again grounded, and the wheel lift state is eliminated at time T3.

[0020] Here, while the wheel lift state is occurring, a change in the steering angle of the vehicle 1 unintended by the driver is likely to occur. This is because while the wheel lift state is occurring, the resistance of the road surface to the change in the steering angle of the wheels disappears, so the load of the steering operation becomes lighter compared to when grounded. For this reason, the driver may operate the steering wheel too large more than necessary, and as a result, it becomes easy to steer the vehicle 1 in an unintended direction. Also, due to the difficulty in grasping the feeling of steering because there is no resistance, the driver is likely to steer the vehicle 1 in an unintended direction.

[0021] Even at the time point T2 in FIG. 2, a change in the steering angle of the vehicle 1 unintended by the driver has occurred. Therefore, when the front wheels touch the ground at T3, there is a risk of causing a sudden steering of the vehicle 1. Also, due to the occurrence of an unintended change in the steering angle, at T3, the yaw angle of the vehicle 1 is also facing a direction different from the direction intended by the driver, that is, the straight-ahead direction. Also due to this, the vehicle behavior at T3 may become unstable.

[0022] The vehicle control device 10 according to the present embodiment holds the steering angle of the vehicle 1 while the wheel lift state is occurring in order to prevent such a situation. By holding the steering angle of the vehicle 1, it is possible to prevent a change in the steering angle unintended by the driver from being caused by the occurrence of the wheel lift state and the vehicle behavior from becoming unstable.

[0023] FIG. 3 is a flowchart showing the process executed by the vehicle control device 10, more specifically, the process executed by the processor 11. The flowchart shown in FIG. 3 starts, for example, together with the start of the operation of the vehicle 1 and is repeatedly executed at a predetermined cycle.

[0024] In step S110, the vehicle control device 10 acquires information about the attitude angles (yaw angle, roll angle, and pitch angle) of the vehicle 1 from the IMU 21. The acquired information about the attitude angles is temporarily stored by the storage device 12.

[0025] In step S120, the vehicle control device 10 determines whether or not a wheel lift condition has occurred. The method by which the vehicle control device 10 detects a wheel lift condition will be explained in Chapter 2. If a wheel lift condition is detected (step S120; Yes), the process proceeds to step S130. On the other hand, if a wheel lift condition has not occurred (step S120; No), the process ends.

[0026] In step S130, the vehicle control device 10 compares the attitude angle of vehicle 1 immediately before the wheel lift condition occurs with the attitude angle of vehicle 1 after the wheel lift condition occurs, i.e., the current attitude angle of vehicle 1. In step S130, the vehicle control device 10 obtains the attitude angle of vehicle 1 immediately before the wheel lift condition occurs from the storage device 12. The vehicle control device 10 also obtains the current attitude angle of vehicle 1 from the IMU 21.

[0027] In step S140, the vehicle control device 10 makes a determination regarding the yaw angle among the attitude angles of vehicle 1 acquired in step S130. The vehicle control device 10 determines whether the yaw angle with respect to the reference direction has changed between the moment immediately before the wheel lift condition occurs and the moment after the wheel lift condition occurs. If there is no change in the yaw angle, or if the change is within a threshold (step S140; Yes), the process proceeds to step S160. On the other hand, if the yaw angle has changed by more than a threshold (step S140; No), the process proceeds to step S150.

[0028] Here, the reference direction is the intended direction of travel for vehicle 1 as intended by the driver. That is, the reference direction is the actual direction of travel of vehicle 1 before the wheel lift condition occurs. After the wheel lift condition occurs, the reference direction is the direction of travel if vehicle 1 continues the same movement as it was just before the wheel lift condition occurred. For example, as in Figure 4(A), if vehicle 1 was moving in a straight line just before the wheel lift condition occurred, the straight-ahead direction is the reference direction. Alternatively, as in Figure 4(B), if vehicle 1 was turning when the wheel lift condition occurred, the turning direction is the reference direction.

[0029] Refer to Figure 3 again. In step S150, the vehicle control device 10 controls the steering angle so that the attitude of vehicle 1 immediately before wheel lift-off occurs is maintained. In other words, if the attitude (yaw angle) of vehicle 1 changes by more than a threshold due to wheel lift-off, the vehicle control device 10 controls the steering angle to return it to the attitude (yaw angle) of vehicle 1 before wheel lift-off occurred. For example, if vehicle 1 was moving in a straight line as in Figure 4(A), the vehicle control device 10 controls the steering angle so that vehicle 1 remains facing the straight direction even after the wheels touch the ground. Alternatively, if vehicle 1 was turning as in Figure 4(B), the vehicle control device 10 controls the steering angle so that the attitude of vehicle 1 with respect to the turning direction is maintained even after the wheels touch the ground. After step S150, the process proceeds to step S160.

[0030] In step S160, the vehicle control device 10 maintains the steering angle of the vehicle 1. Maintaining the steering angle may be done by keeping the steering angle of the steering wheel unchanged, or by keeping the wheel turning angle unchanged.

[0031] In step S170, the vehicle control device 10 determines whether the wheel lift condition has been resolved. In step S170, the determination is made using the wheel lift condition detection method described in Chapter 2, similar to step S120. If the wheel lift condition has been resolved (step S170; Yes), the process proceeds to step S180. On the other hand, if the wheel lift condition persists (step S170; No), the process returns to step S160.

[0032] In step S180, the vehicle control device 10 releases the steering angle hold of vehicle 1. Once the steering angle hold is released, the driver can steer vehicle 1 as in normal driving conditions. When the steering angle hold is released, this process ends.

[0033] Thus, with the vehicle control device 10, the steering angle of the vehicle 1 is maintained when the wheels are off the ground. This prevents the vehicle 1 from being steered in a direction unintended by the driver and suppresses instability in the vehicle's behavior after landing. Furthermore, the steering angle is released when the wheels are off the ground, so it does not interfere with the driver's operation.

[0034] Furthermore, in step S150, the steering angle is controlled to maintain the attitude just before the wheels lift off the ground. This suppresses sudden changes in the vehicle's attitude after landing, even if an unintended change in the yaw angle of vehicle 1 occurs before the steering angle is maintained. In this way, vehicle 1 can be landed in a safer state.

[0035] It should be noted that steps S140 and S150 are not mandatory processes performed by the vehicle control device 10. In other words, the vehicle control device 10 may maintain the steering angle without controlling the steering angle based on the yaw angle comparison result while the wheel lift condition occurs. Even if steps S140 and S150 are not performed, the effect of suppressing instability in vehicle behavior can be obtained, as it is possible to prevent unintended steering of the vehicle 1 at least while the steering angle is maintained.

[0036] 2. Method for detecting wheel lift-off status The following section explains specific methods for detecting wheel lift. One of the detection methods described below may be used, or a combination of several may be employed.

[0037] The first example is a case where each of the multiple wheels of vehicle 1 is independently controlled by a steering motor. The vehicle control device 10 determines whether or not a wheel is in contact with the ground by calculating the ground load of each wheel from the steering angle and current value of the steering motor.

[0038] The vehicle control device 10 acquires the current value flowing through the steering motor. For example, an ammeter may be attached to the steering motor, and the vehicle control device 10 may acquire the current value from the ammeter. The vehicle control device 10 also acquires the steering angle of each wheel. The steering angle of each wheel is acquired, for example, by a steering angle sensor 23. In this case, the steering angle sensor 23 may be provided on the steering motor that controls each wheel.

[0039] The vehicle control device 10 calculates the ground load for each wheel based on the acquired current value and wheel steering angle, using the "ground load information". The ground load information is information that shows the correspondence between the current value flowing to the steering motor, the wheel steering angle, and the ground load for each wheel. Figure 5 shows an example of ground load information. The magnitude of the current value represents the magnitude of the steering force that the steering motor applies to the wheel. When the ground load is small, the resistance from the road surface is small, so the change in wheel steering angle with respect to the current value is large. Therefore, the relationship between the current value, wheel steering angle, and ground load can be determined and stored as ground load information. The ground load information is acquired in advance and stored in the storage device 12.

[0040] If the calculated ground load is greater than 0, it indicates that the wheel is in contact with the ground; if the ground load is 0 or less, it indicates that the wheel is not in contact with the ground. If there is one or more wheels that are not in contact with the ground, it is determined that a wheel-off condition has occurred.

[0041] In the second method, the wheel lift condition is detected by analyzing the images captured by the foot camera of the in-vehicle camera 22.

[0042] When a wheel lift occurs, the shape of the wheel and the position of the shadow it casts change compared to when the wheel is in contact with the ground. For example, when the wheel is in contact with the ground, the part of the wheel that touches the ground is deformed by the weight of the vehicle, so its width is larger compared to when the wheel is not in contact with the ground. Also, the position of the shadow on the wheel changes when the wheel is in contact with the ground and when it is not. That is, when the wheel is in contact with the ground, the area occupied by the shadow cast by the wheel in the image is not detected because it is in contact with or hidden by the wheel. In contrast, when the wheel is lifted from the ground, the area occupied by the shadow of the wheel in the image is detected at a position away from the wheel. In the second method, if these changes are detected by image analysis of the image captured by the camera, it is determined that a wheel lift has occurred.

[0043] In the third method, the wheel lift condition is detected by combining the image captured by the foot camera with information about the suspension stroke detected by the sensors 20.

[0044] The vehicle control device 10 performs the following calculations. First, the vehicle control device 10 acquires images captured by the foot camera and detects the contact points where the wheels touch the ground from the images. The vehicle control device 10 also calculates the current positional relationship between the wheels and the foot camera from the suspension stroke value and estimates the position of the contact points in the images captured by the foot camera based on the calculated positional relationship. Then, it compares the estimated position of the contact points with the position of the contact points actually detected, and if they do not match, it is determined that the wheels are not in contact with the ground. If there is one or more wheels that are not in contact with the ground, it is determined that a wheel-lift condition has occurred.

[0045] In the fourth method, the wheel lift-off condition is detected by the rotation of the wheels.

[0046] Wheel slippage is detected, for example, as follows: The vehicle control device 10 obtains the wheel speed of each wheel from the wheel speed sensor 24. It also detects the vehicle speed of vehicle 1 from the IMU 21. If there is a wheel whose wheel speed and vehicle speed differ by more than a threshold, it is determined that the wheel is not in contact with the ground and is slipping. If there is one or more wheels that are not in contact with the ground, it is determined that a wheel lift condition has occurred.

[0047] While the detection method is not limited to the above, the above example is effective in the following respects. If a dedicated sensor were to be installed to determine whether or not the wheels are in contact with the ground, the unsprung weight would increase, potentially reducing driving performance and increasing costs. Using existing sensors for detection as described above offers advantages in terms of driving performance and cost.

[0048] 3. Application Examples Let's consider the case where multiple wheels of vehicle 1 are controlled independently. In this case, when a wheel lift-off condition occurs, the vehicle control device 10 may further control the wheels as follows.

[0049] Figure 6 is a flowchart showing an example of the process performed by the vehicle control device 10 to control the wheels.

[0050] In step S210, the vehicle control device 10 determines whether or not a wheel lift condition has occurred. The determination in step S210 can be made using the detection method described in Chapter 2. If a wheel lift condition is detected (step S210; Yes), the process proceeds to step S220. On the other hand, if a wheel lift condition has not occurred (step S210; No), the process ends.

[0051] In step S220, the vehicle control device 10 obtains the vehicle speed of vehicle 1. The vehicle speed can be obtained from the IMU 21.

[0052] In step S230, the vehicle control device 10 acquires the slip ratio of the road surface in front of the vehicle 1. The vehicle control device 10 can estimate the slip ratio of the road surface by, for example, analyzing the image obtained when the front camera captures the road surface in front of the vehicle 1.

[0053] In step S240, the vehicle control device 10 calculates the target wheel speed based on the slip ratio obtained in step S230 and the vehicle speed obtained in step S220. The target wheel speed is calculated taking into account the control of the wheels when they make contact with the ground. For example, in the case of a road surface where the slip ratio is large, such as sand, the target wheel speed is calculated to be higher than in the case of a road surface with a small slip ratio, anticipating that the wheels will slip when they make contact with the ground.

[0054] In step S250, the vehicle control device 10 controls the wheel speed of the wheels not in contact with the ground to the target wheel speed. Once the wheel speed control is complete, this process ends.

[0055] If a wheel lift occurs, the wheel speed may exceed the vehicle speed because there is no resistance from the road surface. If the wheel then lands, a snag may occur between the wheel and the road surface, potentially causing excessive input to the drive system. The control described above can suppress such excessive input.

[0056] Furthermore, the vehicle control device 10 may perform the following wheel steering angle control instead of steps S140 and S150 in Figure 3. First, the vehicle control device 10 obtains the direction of travel of the vehicle 1 from the IMU 21. Then, it controls the wheel steering angle so that the wheel steering angle of the floating wheel matches the direction of travel of the vehicle 1.

[0057] If a wheel lift occurs, the lifted wheel may turn in a direction different from the vehicle's direction of travel before the steering angle is maintained. If the wheel then lands, there is a risk of excessive input to the steering system. The control described above can suppress such excessive input.

[0058] 4. Other examples As another example, the wheels of vehicle 1 may be tracks. Even when the wheels are tracks, the vehicle control device 10 can detect the track lift condition and perform control such as maintaining the steering angle, in the same way as in the case of wheels. When a part of the track lifts off the ground, it is determined that the track is lifted, and the steering angle is maintained.

[0059] Furthermore, Vehicle 1 may be an autonomous vehicle. If Vehicle 1 is an autonomous vehicle and a wheel lift occurs during autonomous driving, the vehicle control device 10 will also perform control to maintain the steering angle once the wheel lift is detected. In this case, the driver's operation in the above explanation can be read as control by the autonomous driving system. While the wheel lift occurs, the steering angle control by the vehicle control device 10 takes precedence over the steering angle control by autonomous driving to maintain the steering angle, and once the wheel lift is resolved, steering by the autonomous driving system becomes possible. [Explanation of Symbols]

[0060] 1 vehicle 10. Vehicle control system 11 processors 12 Storage device 20 Sensors 21 IMU 22 In-car cameras 23. Steering angle sensor 24 Wheel speed sensors 30 Actuators

Claims

1. A vehicle control device for controlling a vehicle, The wheel speeds of the multiple wheels of the aforementioned vehicle can be controlled independently. The aforementioned vehicle control device is A process to determine whether a wheel-lifting state occurs in which any of the aforementioned multiple wheels are not in contact with the ground, While the wheel lift condition occurs, the process of maintaining the steering angle of the vehicle is performed. The process of obtaining the vehicle speed of the aforementioned vehicle, A process for obtaining the slip ratio of the road surface on which the vehicle is traveling, If the wheel lift condition occurs, before the wheel lift condition is resolved, a target wheel speed is calculated based on the vehicle speed and the slip ratio, and the wheel speed of the wheel that is not in contact with the ground among the plurality of wheels is controlled to become the target wheel speed. Configured to execute A vehicle control device characterized by the following features.

2. A vehicle control device for controlling a vehicle, The steering angle of each of the multiple wheels of the aforementioned vehicle is independently controlled by a steering motor. The vehicle control device includes a storage device that stores ground load information indicating the correspondence between the current value flowing to the steering motor, the wheel steering angle of one of the plurality of wheels, and the ground load of the one wheel. The aforementioned vehicle control device is A process to determine whether a wheel-lifting state occurs in which any of the aforementioned multiple wheels are not in contact with the ground, While the wheel lift condition occurs, the process of maintaining the steering angle of the vehicle is performed. It is configured to perform, The process for determining whether the wheel lift condition is occurring is performed for each of the multiple wheels, To obtain the aforementioned current value, To obtain the aforementioned wheel steering angle, Using the acquired current value, the wheel steering angle, and the ground load information, it is determined that the wheel lift condition occurs when the ground load on any of the multiple wheels is below a threshold. including A vehicle control device characterized by the following features.

3. A vehicle control device according to claim 1 or 2, If the wheel lift condition occurs, before maintaining the steering angle, The system is configured to further perform a process to control the steering angle so that the vehicle's posture is maintained immediately before the wheel lift condition occurs. A vehicle control device characterized by the following features.

4. A vehicle control device according to claim 1, The steering angle of each of the aforementioned wheels is independently controlled by a steering motor. The aforementioned vehicle control device is The system includes a storage device that stores ground load information indicating the correspondence between the current value flowing through the steering motor, the steering angle of one of the plurality of wheels, and the ground load of that one wheel. The process for determining whether the wheel lift condition is occurring is performed for each of the multiple wheels, To obtain the aforementioned current value, To obtain the aforementioned wheel steering angle, Using the acquired current value, the wheel steering angle, and the ground load information, it is determined that the wheel lift condition occurs when the ground load on any of the multiple wheels is below a threshold. including A vehicle control device characterized by the following features.

5. A vehicle control method for controlling a vehicle having a plurality of wheels and in which the wheel speed of the plurality of wheels can be independently controlled, To determine whether a wheel-lifting condition occurs in which any of the aforementioned multiple wheels are not in contact with the ground, While the wheel lift condition occurs, the steering angle of the vehicle is maintained. To obtain the vehicle speed of the aforementioned vehicle, Obtaining the slip ratio of the road surface on which the vehicle is traveling, If the aforementioned wheel lift condition occurs, before the wheel lift condition is resolved, a target wheel speed is calculated based on the vehicle speed and the slip ratio, and the wheel speed of the wheel that is not in contact with the ground among the plurality of wheels is controlled to reach the target wheel speed. A vehicle control method characterized by including the following:

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