Vehicle control method and vehicle control device

Abstract

Determine the optimal wheel speed for the drive wheels to free the vehicle from being stuck in sand. [Solution] In the vehicle control method, it is determined whether or not the vehicle is stuck in the sand (S1), and if it is determined that the vehicle is stuck in the sand, the amount of tire sinking in the sand is estimated (S5), the target wheel speed of the drive wheels is determined based on the estimated amount of sinking (S8, S9), and the drive wheels are driven to rotate at the determined target wheel speed (S12).

Description

Technical Field

[0006]

[0001] The present invention relates to a vehicle control method and a vehicle control device.

Background Art

[0002] Patent Document 1 proposes a running control device that controls the driving force and braking force of driving wheels so as to maintain the vehicle speed at a preset very low speed target vehicle speed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in a scene where the vehicle escapes from a state of being stuck in sandy soil, if the preset very low speed target vehicle speed is too high, the wheels will dig into the sand and the vehicle will sink further. On the contrary, if the very low speed target vehicle speed is too low, the driving force of the vehicle will be insufficient and it will be difficult to escape from the sandy soil. An object of the present invention is to determine a target wheel speed of a driving wheel suitable for the vehicle to escape from a state of being stuck in sandy soil.

Means for Solving the Problems

[0005] In a vehicle control method according to an aspect of the present invention, it is determined whether the vehicle is stuck in sandy soil. When it is determined that the vehicle is stuck in sandy soil, the amount of tire sinkage in the sandy soil is estimated, a target wheel speed of the driving wheel is determined based on the estimated sinkage amount, and the driving wheel is driven to rotate at the determined target wheel speed.

Effects of the Invention

[0006] According to the present invention, it is possible to determine the optimal wheel speed of the drive wheels for a vehicle to escape from a state where it is stuck in sand. [Brief explanation of the drawing]

[0007] [Figure 1] This figure shows a schematic example of the configuration of a vehicle control device according to an embodiment. [Figure 2] Figure 1 is a block diagram showing an example of the controller's functional configuration. [Figure 3] This figure shows an example of a map that defines estimated values ​​for settlement amount in relation to steering current. [Figure 4] This graph illustrates the relationship between wheel speed, steering speed, and lift speed. [Figure 5] (a) to (f) are time charts illustrating the operation of the vehicle control method of the embodiment. [Figure 6] This is a flowchart of an example of a vehicle control method according to the embodiment. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the drawings. Note that the drawings are schematic and may differ from actual ones. Furthermore, the embodiments of the present invention described below are illustrative examples of devices and methods for realizing the technical concept of the present invention, and the technical concept of the present invention is not limited to the structure, arrangement, etc., of the components described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims described in the patent claims.

[0009] (First Embodiment) (composition) Figure 1 shows a schematic configuration example of a vehicle control device according to an embodiment. Vehicle 1 is equipped with a vehicle control device 10 that assists vehicle 1 in escaping from a stuck state when vehicle 1 gets stuck in sand. The vehicle control device 10 includes a front wheel drive power source 11F, a rear wheel drive power source 11R, a steering motor 12, a current sensor 13, an on-board sensor 14, a stuck escape mode selection switch 15, and a controller 16. In the drawing, the stuck escape mode selection switch 15 is denoted as "SW".

[0010] The front-wheel drive source 11F generates driving force to the right front wheel 2FR and the left front wheel 2FL of the vehicle 1, and the rear-wheel drive source 11R generates driving force to the right rear wheel 2RR and the left rear wheel 2RL. The front-wheel drive source 11F and the rear-wheel drive source 11R may be, for example, electric motors or internal combustion engines. The front wheel drive source 11F is connected via a reduction gear (not shown) to the front drive shaft 3F, which is connected to the drive wheels, the right front wheel 2FR and the left front wheel 2FL. By rotating the front drive shaft 3F, it provides driving force to the right front wheel 2FR and the left front wheel 2FL.

[0011] The rear-wheel drive source 11R is connected to the drive shaft 3R, which is connected to the drive wheels, the right rear wheel 2RR and the left rear wheel 2RL, via a reduction gear (not shown). By rotating the rear drive shaft 3R, it provides driving force to the right rear wheel 2RR and the left rear wheel 2RL. In the example shown in Figure 1, the front wheel drive source 11F drives both the right front wheel 2FR and the left front wheel 2FL, and the rear wheel drive source 11R drives both the right rear wheel 2RR and the left rear wheel 2RL. However, it is also possible to use in-wheel motors to drive each of the right front wheel 2FR, left front wheel 2FL, right rear wheel 2RR, and left rear wheel 2RL separately.

[0012] Furthermore, the system may be configured to drive only one of the following: the right front wheel 2FR and the left front wheel 2FL, or the right rear wheel 2RR and the left rear wheel 2RL, out of the right front wheel 2FR, left front wheel 2FL, right rear wheel 2RR, and left rear wheel 2RL. For example, the system may be configured to drive only the steering wheels (e.g., the right front wheel 2FR and the left front wheel 2FL).

[0013] The steering motor 12 applies steering force to the steering wheels. For example, the steering motor 12 may be a motor that generates steering assist force in the steering system of the vehicle 1 in an electric power steering (EPS) system. For example, the steering motor 12 may be a motor that is connected via a reduction gear (not shown) to the steering shaft 5 that connects the steering wheel 4 and the steering wheels 2FR and 2FL, and applies steering assist force to the steering shaft 5.

[0014] For example, vehicle 1 may also be equipped with a steer-by-wire system in which the steering wheel 4 and the steering wheels 2FR and 2FL are mechanically separated. In this case, the steering motor 12 may be a motor that is connected to a mechanism for steering the steering wheels 2FR and 2FL (for example, a rack and pinion mechanism) and provides steering force to steer the steering wheels 2FR and 2FL. The current sensor 13 detects the steering current Is, which is the drive current flowing to the steering motor 12.

[0015] The in-vehicle sensor 14 includes an external sensor that detects ambient environment information, which is information about the surrounding environment of the vehicle 1, and a vehicle sensor that detects various information (vehicle information) obtained from the vehicle 1. For example, the external sensor may include multiple different types of object detection sensors, such as cameras, radar, and sonar, that detect objects around the vehicle 1. For example, the vehicle sensor may include a wheel speed sensor that detects the rotational speed of the vehicle's tires, a steering angle sensor that detects the steering angle of the steering wheels (e.g., the right front wheel 2FR and the left front wheel 2FL), and a three-axis acceleration sensor (G sensor) that detects the acceleration (including deceleration) of the vehicle in three axes.

[0016] The stack escape mode selection switch 15 is a switch that accepts a selection operation by an occupant (e.g., a driver) of the vehicle 1 to select the operation mode of the vehicle 1 between the normal driving mode and the stack escape mode. The normal driving mode is an operation mode in which the vehicle 1 is driven by computer-aided autonomous driving control or manual driving operation by a driver. The stack escape mode is an operation mode in which when the vehicle 1 gets stuck in sand, the vehicle control device 10 automatically rotates the drive wheels and reciprocally steers the steering wheels, which are the drive wheels, to assist the vehicle 1 to escape from the stuck state.

[0017] The controller 16 is an electronic control unit (ECU: Electronic Control Unit) that controls the operation of the vehicle control device 10. The controller 16 includes a processor 17 and peripheral components such as a storage device 18. The processor 17 may be, for example, a CPU (Central Processing Unit) or a MPU (Micro-Processing Unit). The storage device 18 may be equipped with a semiconductor storage device, a magnetic storage device, an optical storage device, etc. The storage device 18 may include memories such as registers, cache memories, a ROM (Read Only Memory) and a RAM (Random Access Memory) used as a main memory. The functions of the controller 16 described below are realized, for example, when the processor 17 executes a computer program stored in the storage device 18.

[0018] Note that the controller 16 may be formed by dedicated hardware for executing each information processing described below. For example, the controller 16 may include a functional logic circuit set in a general-purpose semiconductor integrated circuit. For example, the controller 16 may have a programmable logic device (PLD) such as a field-programmable gate array (FPGA).

[0019] Figure 2 is a block diagram of an example of the functional configuration of the controller 16. The controller 16 comprises a stack determination unit 20, a sinking amount estimation unit 21, a target wheel speed determination unit 22, a steering angle width determination unit 23, a steering speed determination unit 24, a drive force source control unit 25, and a steering control unit 26. The stuck detection unit 20 determines whether or not vehicle 1 is stuck in the sand. For example, the stuck detection unit 20 may determine that vehicle 1 is stuck in the sand when the stuck escape mode is selected by the stuck escape mode selection switch 15, and determine that vehicle 1 is not stuck in the sand when the normal driving mode is selected.

[0020] Alternatively, the stack determination unit 20 may determine whether the vehicle 1 is stuck in the sand based on the distance detection result to the ground by the camera, radar, or sonar of the on-board sensor 14. For example, it may determine that the vehicle 1 is stuck in the sand if the height of the ground visible to the camera is higher than a threshold. Alternatively, the stack determination unit 20 may determine that the vehicle 1 is stuck in the sand if the longitudinal acceleration is small relative to the increase in wheel speed, based on the detection results of the wheel speed sensor and acceleration sensor of the on-board sensor 14.

[0021] The stuck determination unit 20 also determines whether or not the vehicle 1 has escaped from being stuck in the sand. For example, the stuck determination unit 20 may determine that the vehicle 1 has escaped from being stuck in the sand when the stuck escape mode is selected by the stuck escape mode selection switch 15 and the vehicle changes to the normal driving mode. Alternatively, the stack detection unit 20 may determine that the vehicle 1 has escaped from being stuck in the sand when the steering current detected while the steering motor 12 is being driven falls below a threshold.

[0022] The settlement amount estimation unit 21 estimates the amount of tire settlement in the sand (hereinafter simply referred to as "settlement amount S") when the stuck determination unit 20 determines that the vehicle 1 is stuck in the sand. For example, the settlement amount estimation unit 21 may estimate the settlement amount S based on the steering current Is (i.e., the steering reaction force acting on the steering motor 12) flowing through the steering motor 12 when the steering wheels (e.g., the right front wheel 2FR and the left front wheel 2FL) are steered at a predetermined steering speed by the steering motor 12.

[0023] For example, the settlement amount estimation unit 21 may estimate the settlement amount S based on a table or map that defines estimated values ​​of the settlement amount S for a given steering current Is, and the steering current Is detected by the current sensor 13. Figure 3 shows an example of a map defining the estimated value of the amount of settlement S in relation to the steering current Is. The larger the amount of settlement S, the greater the steering reaction force acting on the steering motor 12, and therefore the larger the steering current Is required for steering.

[0024] Therefore, the settlement estimation unit 21 calculates a larger settlement amount S estimate when the steering current Is is larger than when it is smaller. For example, the larger the steering current Is, the larger the settlement amount S estimate it calculates. Alternatively, the subsidence estimation unit 21 may estimate the subsidence amount S based on the detection result of the distance to the ground surface by the camera, radar, or sonar of the on-board sensor 14.

[0025] Furthermore, the settlement estimation unit 21 estimates the change in settlement amount S per unit time (hereinafter referred to as "settlement change ΔS") based on the settlement amount S estimated at multiple points in time at predetermined time intervals. For example, the settlement amount estimation unit 21 may estimate the settlement amount S at a predetermined control cycle. The settlement amount estimation unit 21 may estimate the difference between the settlement amount S estimated in the previous control cycle and the settlement amount S estimated in the current control cycle as settlement amount change ΔS = (current settlement amount S - previous settlement amount S). For example, the settlement amount change ΔS may be estimated as the difference between the settlement amount S estimated based on the steering current Is obtained from the current sensor 13 in the previous control cycle and the settlement amount S estimated based on the steering current Is obtained in the current control cycle.

[0026] The target wheel speed determination unit 22 determines the target wheel speed Vtw (i.e., the driving speed of drive shafts 3F and 3R), which is the target value of the wheel speed of the drive wheels when the vehicle control device 10 rotates the drive wheels in the stuck escape mode. As described above, if vehicle 1 is stuck in the sand, a wheel speed that is too high could cause the tires to dig into the sand, potentially causing vehicle 1 to sink further.

[0027] Therefore, the target wheel speed determination unit 22 determines the target wheel speed Vtw in such a way that the amount of sinking S does not increase (for example, so that the change in amount of sinking ΔS is negative). In other words, the target wheel speed determination unit 22 determines the target wheel speed Vtw based on the amount of sinking S estimated by the amount of sinking estimation unit 21. To put it another way, the target wheel speed Vtw is determined based on the steering current Is (steering reaction force acting on the steering motor 12) flowing through the steering motor 12. The target wheel speed determination unit 22 may determine different target wheel speeds Vtw for the right front wheel 2FR and the left front wheel 2FL, and for the right rear wheel 2RR and the left rear wheel 2RL.

[0028] Figure 4 is a graph illustrating the relationship between the speed at which a stuck tire lifts off the sand (hereinafter referred to as "lift speed Vr"), wheel speed, and steering speed of the drive wheels. As can be seen from the graph in Figure 4, within the range where the amount of sinking S does not increase, the higher the wheel speed, the higher the lift speed Vr. Therefore, for example, the target wheel speed determination unit 22 may determine the highest wheel speed within the range where the amount of settlement S does not increase as the target wheel speed Vtw. For example, the target wheel speed determination unit 22 may determine the target wheel speed Vtw by increasing the target wheel speed Vtw when the change in amount of settlement ΔS estimated by the amount of settlement estimation unit 21 is negative or 0, and by decreasing the target wheel speed Vtw when the change in amount of settlement ΔS becomes positive.

[0029] For example, the target wheel speed determination unit 22 may set a lower target wheel speed Vtw when the amount of sinking S is small compared to when the amount of sinking S is large, based on the amount of sinking S (i.e., based on the steering current Is). For example, the target wheel speed determination unit 22 may set a lower target wheel speed Vtw the smaller the amount of sinking S is. For example, if the target wheel speed determination unit 22 detects that the amount of settlement S estimated by the settlement amount estimation unit 21 has fallen from a state of being above a predetermined threshold to below a predetermined threshold, it may determine the target wheel speed Vtw such that it decreases as the amount of settlement S decreases.

[0030] For example, a table or map defining the relationship between the amount of settlement S and the target wheel speed Vtw may be prepared so that the target wheel speed Vtw is lower when the amount of settlement S is small compared to when it is large (for example, the smaller the amount of settlement S, the lower the target wheel speed Vtw becomes). The target wheel speed determination unit 22 may set the target wheel speed Vtw based on such a table or map and the amount of settlement S estimated by the amount of settlement estimation unit 21. Then, if the change in amount of settlement ΔS becomes positive when the drive wheels are rotated at the set target wheel speed Vtw, the target wheel speed Vtw may be reduced.

[0031] Refer to Figure 2. The steering angle width determination unit 23 determines the steering angle width Δθ, which is the range of change in the steering angle θ when the vehicle control device 10 steers the steerable drive wheels (e.g., the right front wheel 2FR and the left front wheel 2FL) back and forth in the stuck escape mode. When the drive wheels are steered back and forth while being driven, the sand around the drive wheels is gathered under the drive wheels, and the lift velocity Vr can be increased by the drive wheels kicking up this sand.

[0032] In this specification, "reciprocating steering" means repeatedly steering the steering wheel, which is a steerable wheel, to the right and then to the left from the neutral position. Furthermore, the steering angle range Δθ is the sum of the steering angle at the point where the vehicle is steered furthest to the right and the steering angle at the point where it is steered furthest to the left during the reciprocating steering in the stuck-out mode.

[0033] For example, the steering angle width determination unit 23 may determine the steering angle width Δθ in such a way that a so-called "end hit" occurs, where the rack axis of the steering mechanism reaches the end of its stroke. Furthermore, the steering angle Δθ may be determined such that it becomes smaller when the amount of settlement S is small compared to when it is large. For example, the smaller the amount of settlement S, the smaller the steering angle Δθ may be determined. In other words, the steering angle width determination unit 23 may determine the steering angle width Δθ based on the amount of settlement S estimated by the settlement amount estimation unit 21. To put it another way, the steering angle width Δθ may be determined based on the steering current Is (steering reaction force acting on the steering motor 12) flowing through the steering motor 12.

[0034] For example, a table or map may be prepared that defines the relationship between the amount of settlement S and the steering angle Δθ so that the steering angle Δθ becomes smaller when the amount of settlement S is small compared to when the amount of settlement S is large (for example, the smaller the amount of settlement S, the smaller the steering angle Δθ becomes). The steering angle determination unit 23 may set the steering angle Δθ based on such a table or map and the amount of settlement S estimated by the amount of settlement estimation unit 21.

[0035] Alternatively, the steering angle width determination unit 23 may determine the steering angle width Δθ based on the steering current Is flowing through the steering motor 12. For example, if the steering current Is exceeds a threshold, the unit may determine that the steering wheel is in contact with an obstacle and steering is being hindered, and determine the steering angle width Δθ such that the amount of steering is smaller than the steering angle at the time the steering current Is exceeded the threshold.

[0036] The steering speed determination unit 24 determines the steering speed Vθ for reciprocating steering of the steerable drive wheels (e.g., the right front wheel 2FR and the left front wheel 2FL) in the stuck escape mode. The ascent velocity Vr is affected by the steering speed Vθ (i.e., the change in sinking amount ΔS is affected by the steering speed Vθ). When the steering speed Vθ is below a boundary value, the ascent velocity Vr increases, and when it exceeds the boundary value, the ascent velocity Vr decreases. In the example shown in Figure 4, the ascent velocity Vr peaks when the steering speed Vθ is at the boundary value V1. Ascent velocity Vr increases when the steering speed Vθ is below the boundary value V1, and decreases when it is above the boundary value V1.

[0037] Therefore, the steering speed determination unit 24 determines the steering speed Vθ such that it is within the range in which the ascent speed Vr increases with increasing steering speed Vθ (i.e., the range in which the change in sinking amount ΔS is negative and the absolute value |ΔS| increases with increasing steering speed Vθ). In other words, the steering speed determination unit 24 determines the steering speed Vθ based on the sinking amount S estimated by the sinking amount estimation unit 21. To put it another way, it determines the steering speed Vθ based on the steering current Is (steering reaction force acting on the steering motor 12) flowing through the steering motor 12.

[0038] For example, the steering speed determination unit 24 may monitor the ascent speed Vr based on the change in sinking amount ΔS while changing the steering speed Vθ, and determine the relationship between the direction of change of the steering speed Vθ and the direction of change of the ascent speed Vr. For example, the steering speed determination unit 24 may decrease the steering speed Vθ if the ascent speed Vr decreases as the steering speed Vθ increases. This allows the value of the steering speed Vθ to be adjusted so that it is within the range in which the ascent speed Vr increases as the steering speed Vθ increases. In other words, the steering speed Vθ may be changed in a direction that increases the ascent speed Vr.

[0039] Furthermore, the steering speed Vθ at which the buoyancy velocity Vr peaks is affected by the wheel speed of the steering drive wheels and the amount of sinking S. For this reason, the steering speed determination unit 24 may determine the steering speed Vθ based on the target wheel speed Vtw determined by the target wheel speed determination unit 22 and the amount of sinking S estimated by the sinking amount estimation unit 21. In other words, the steering speed determination unit 24 may determine the steering speed Vθ after the target wheel speed determination unit 22 has determined the target wheel speed Vtw.

[0040] For example, the surfacing velocity Vr for each combination of conditions—sinking amount S, target wheel speed Vtw, and steering speed Vθ—may be determined in advance through experiments or simulations, and a table or map defining the relationship between the combination of conditions—sinking amount S, target wheel speed Vtw, and steering speed—and the surfacing velocity Vr may be prepared. The steering speed determination unit 24 may determine the steering speed at which the surfacing velocity Vr peaks, based on such a table or map and the sinking amount S and target wheel speed Vtw estimated by the sinking amount estimation unit 21, and then determine the steering speed Vθ so that it is less than or equal to the determined steering speed.

[0041] Furthermore, the steering speed determination unit 24 may determine the steering speed Vθ such that it is lower when the amount of sinking S is small compared to when the amount of sinking S is large. For example, the smaller the amount of sinking S, the lower the steering speed Vθ may be determined. For example, if the steering speed determination unit 24 detects that the amount of settlement S estimated by the settlement amount estimation unit 21 has fallen from a state of being above a predetermined threshold to below a predetermined threshold, it may determine the steering speed Vθ to decrease as the amount of settlement S decreases.

[0042] Alternatively, the steering speed determination unit 24 may determine the steering speed Vθ based on the temperature of the steering motor 12 and its drive circuit, and the steering current Is. When limiting the steering current Is based on the temperature conditions of the steering motor 12 and its drive circuit, the steering speed Vθ may be reduced. Alternatively, the steering speed determination unit 24 may reduce the steering speed Vθ based on the steering angle θ and the steering angle width Δθ.

[0043] For example, the steering speed determination unit 24 may lower the steering speed Vθ when the absolute value of the steering angle θ is large compared to when it is small (for example, the steering speed Vθ may be lower the larger the absolute value of the steering angle θ). This reduces the impact when the steering direction is reversed. Alternatively, the steering speed Vθ may be increased when the steering angle Δθ is large compared to when it is small (for example, the larger the steering angle Δθ, the higher the steering speed Vθ may be). This allows more sand to be gathered under the drive wheels in a shorter time, increasing the lift speed Vr.

[0044] The drive force source control unit 25 controls the front wheel drive force source 11F and the rear wheel drive force source 11R so that the right front wheel 2FR, left front wheel 2FL, right rear wheel 2RR, and left rear wheel 2RL rotate at the target wheel speed Vtw determined by the target wheel speed determination unit 22. The steering control unit 26 drives the steering motor 12 so that the steering wheels (for example, the right front wheel 2FR and the left front wheel 2FL) are steered to the left or right by a steering angle Δθ determined by the steering angle determination unit 23, and are steered at a steering speed Vθ determined by the steering speed determination unit 24.

[0045] (action) Figures 5(a) to 5(f) are time charts illustrating the operation of the vehicle control method of the embodiment. Figure 5(a) is a time chart showing the setting state of the stuck escape mode, and Figures 5(b) to 5(f) are time charts for the estimated value of the sink amount S, the target wheel speed Vtw, the steering speed Vθ, the steering angle width Δθ, and the steering angle θ, respectively.

[0046] At time t0, the stack determination unit 20 determines whether or not vehicle 1 is stuck in the sand. If it is determined that vehicle 1 is stuck in the sand, the operating mode of vehicle 1 switches to the stack escape mode. When the stuck escape mode is initiated, the target wheel speed determination unit 22, the steering angle width determination unit 23, and the steering speed determination unit 24 set the initial values ​​of the target wheel speed Vtw, steering angle width Δθ, and steering speed Vθ, respectively, to predetermined values. The drive force source control unit 25 rotates the right front wheel 2FR, the left front wheel 2FL, the right rear wheel 2RR, and the left rear wheel 2RL at the initial value of the target wheel speed Vtw.

[0047] Furthermore, the steering control unit 26 steers the steering wheels (for example, the right front wheel 2FR and the left front wheel 2FL) back and forth at an initial value of the steering speed Vθ such that the width of the steering angle θ for steering the steering wheels left and right becomes the initial value of the steering angle width Δθ. At time t1, the settlement estimation unit 21 estimates the settlement amount S and the settlement amount change ΔS based on the steering current Is of the steering motor 12 detected by the current sensor 13 when the steering wheels were steered between time t0 and time t1.

[0048] The target wheel speed determination unit 22, the steering angle width determination unit 23, and the steering speed determination unit 24 determine the target wheel speed Vtw, the steering angle width Δθ, and the steering speed Vθ based on the amount of settlement S and the change in amount of settlement ΔS estimated by the settlement amount estimation unit 21. From time t1 onward, the drive force source control unit 25 rotates the right front wheel 2FR, left front wheel 2FL, right rear wheel 2RR, and left rear wheel 2RL at a target wheel speed Vtw determined based on the amount of settlement S and the change in amount of settlement ΔS.

[0049] Furthermore, the steering control unit 26 steers the steering wheels back and forth based on the steering angle width Δθ and steering speed Vθ determined based on the amount of settlement S and the change in the amount of settlement ΔS. If the estimated value of the settlement amount S falls below a predetermined threshold S1 at time t2, the steering angle width determination unit 23 starts a gradual reduction process of the steering angle width Δθ, which decreases in accordance with the decrease in the settlement amount S. From time t2 onward, the steering angle width determination unit 23 sets a smaller steering angle width Δθ as the amount of sinking S decreases.

[0050] Furthermore, if the estimated value of the settlement amount S falls below a predetermined threshold S2 at time t3, the target wheel speed determination unit 22 starts a process to gradually decrease the target wheel speed Vtw in accordance with the decrease in the settlement amount S. The steering speed determination unit 24 also starts a process to gradually decrease the steering speed Vθ in accordance with the decrease in the settlement amount S.

[0051] From time t3 onward, the target wheel speed determination unit 22 and the steering speed determination unit 24 set lower target wheel speed Vtw and steering speed Vθ, respectively, as the amount of sinking S decreases. Subsequently, at time t6, if the stuck detection unit 20 determines that vehicle 1 has escaped from being stuck in the sand, the stuck escape mode ends and the operating mode of vehicle 1 switches to normal driving mode.

[0052] (operation) Figure 6 is a flowchart of an example of a vehicle control method according to the embodiment. In step S1, the stack determination unit 20 determines whether the stack escape mode is selected by the stack escape mode selection switch 15. If the stack escape mode is not selected (step S1:N), the process ends. If the stack escape mode is selected (step S1:Y), the process proceeds to step S2.

[0053] In step S2, the settlement amount estimation unit 21 determines whether the system is in an initial state where the settlement amount S has not yet been estimated since the start of the stack escape mode. If it is not in an initial state (step S2:N), the process proceeds to step S7. If it is in an initial state (step S2:Y), the process proceeds to step S3. In step S3, the target wheel speed determination unit 22, the steering angle width determination unit 23, and the steering speed determination unit 24 set initial values ​​for the target wheel speed Vtw, the steering angle width Δθ, and the steering speed Vθ.

[0054] In step S4, the drive force source control unit 25 controls the front wheel drive force source 11F and the rear wheel drive force source 11R based on the initial value of the target wheel speed Vtw. The steering control unit 26 controls the steering motor 12 based on the initial values ​​of the steering angle width Δθ and the steering speed Vθ. In step S5, the settlement estimation unit 21 estimates the settlement amount S and the settlement change ΔS. In step S6, the stack determination unit 20 determines whether or not vehicle 1 has escaped from being stuck in the sand. If vehicle 1 has not escaped from being stuck (step S6:N), the process returns to step S2. If vehicle 1 has escaped from being stuck (step S6:Y), the process ends.

[0055] In step S7, the settlement estimation unit 21 estimates the settlement amount S and the settlement change ΔS. In step S8, the target wheel speed determination unit 22 determines the target wheel speed Vtw for the right front wheel 2FR and the left front wheel 2FL based on the change in sink amount ΔS. In step S9, the target wheel speed determination unit 22 determines the target wheel speed Vtw for the right rear wheel 2RR and the left rear wheel 2RL based on the change in sink amount ΔS.

[0056] In step S10, the steering angle determination unit 23 determines the steering angle Δθ based on the estimated value of the settlement amount S. The steering angle determination unit 23 may also determine the steering angle Δθ based on the steering current Is in addition to the estimated value of the settlement amount S. In step S11, the steering speed determination unit 24 determines the steering speed Vθ based on the estimated value of the settlement amount S. In addition to the estimated value of the settlement amount S, the steering speed determination unit 24 may also determine the steering speed Vθ based on the steering current Is, the steering angle θ, and the steering angle width Δθ.

[0057] In step S12, the drive source control unit 25 controls the front wheel drive source 11F and the rear wheel drive source 11R based on the target wheel speed Vtw determined in steps S8 and S9. The steering control unit 26 controls the steering motor 12 based on the steering angle width Δθ determined in step S10 and the steering speed Vθ determined in step S11. In step S13, the stack determination unit 20 determines whether or not vehicle 1 has escaped from being stuck in the sand. If vehicle 1 has not escaped from being stuck (step S13:N), the process proceeds to step S7. If vehicle 1 has escaped from being stuck (step S13:Y), the process ends.

[0058] (Effects of the embodiment) (1) The vehicle control method determines whether the vehicle is stuck in the sand. If it is determined that the vehicle is stuck in the sand, it estimates the amount of tire sinking in the sand. Based on the estimated amount of sinking, it determines a target wheel speed for the drive wheels and drives the drive wheels to rotate at the determined target wheel speed. This allows the drive wheels to rotate at a wheel speed suitable for escaping from the stuck state when the vehicle is stuck in the sand.

[0059] (2) The amount of sinking can be estimated based on the steering reaction force acting on the steering motor that applies steering force to the steering wheels. This makes it possible to estimate the amount of tire sinking in sandy ground. (3) If it is determined that the vehicle is stuck in the sand, the steering motor that applies steering force to the drive wheels, which are the steering wheels, may be controlled to steer the drive wheels back and forth, and the steering speed for reciprocating the drive wheels may be determined based on the amount of sinking. This can improve the lifting speed at which the rotation of the drive wheels lifts the tires off the sand.

[0060] (4) The steering speed may be determined after the target wheel speed has been determined. Differences in target wheel speed have a greater impact on the lift speed that lifts the tires off the sand than differences in steering speed. By determining the steering speed after the target wheel speed, the target wheel speed, which has a greater impact on the lift speed, can be prioritized, and by determining the steering speed appropriate for the determined target wheel speed, the combination of target wheel speed and steering speed that can increase the lift speed can be optimized.

[0061] (5) When the amount of sinking is small compared to when the amount of sinking is large, the range of steering angles used to steer the drive wheels back and forth may be set to be smaller. This can prevent the vehicle from moving in an unintended direction when the amount of sinking decreases and the vehicle starts to move forward. It can also reduce the energy consumed to get out of a stuck state. (6) When the amount of sinking is small compared to when it is large, the target wheel speed may be set lower. This helps to avoid sudden lurching when the amount of sinking decreases and the vehicle starts to move forward. It also reduces the energy consumed to get out of a stuck state. [Explanation of symbols]

[0062] 1...Vehicle, 2FL...Left front wheel, 2FR...Right front wheel, 2RL...Left rear wheel, 2RR...Right rear wheel, 3F...Front drive shaft, 3R...Rear drive shaft, 4...Steering wheel, 5...Steering shaft, 10...Vehicle control device, 11F...Front wheel drive source, 11R...Rear wheel drive source, 12...Steering motor, 13...Current sensor, 14...On-board sensor, 15...Stuck escape mode selection switch, 16...Controller, 17...Processor, 18...Memory device, 20...Stuck detection unit, 21...Sinking amount estimation unit, 22...Target wheel speed determination unit, 23...Steering angle width determination unit, 24...Steering speed determination unit, 25...Drive force source control unit, 26...Steering control unit

Claims

1. Determine whether the vehicle is stuck in the sand. If it is determined that the vehicle is stuck in the sand, the amount of tire sinking in the sand is estimated. Based on the estimated amount of sinking, the target wheel speed of the drive wheels is determined. The drive wheels are driven to rotate at the determined target wheel speed. A vehicle control method characterized by the following:

2. The vehicle control method according to claim 1, characterized in that the amount of sinking is estimated based on the steering reaction force acting on a steering motor that applies steering force to the steering wheels.

3. When it is determined that the vehicle is stuck in the sand, the steering motor that applies steering force to the drive wheels, which are the steering wheels, is controlled to steer the drive wheels back and forth. Based on the amount of sinking, the steering speed for reciprocating the drive wheel is determined. The vehicle control method according to feature 1.

4. The vehicle control method according to claim 3, characterized in that the steering speed is determined after the target wheel speed is determined.

5. The vehicle control method according to claim 3 or 4, characterized in that when the amount of sinking is small compared to when it is large, the range of steering angles for reciprocating steering of the drive wheels is reduced.

6. The vehicle control method according to any one of claims 1 to 4, characterized in that the target wheel speed is lowered when the amount of sinking is smaller than when it is larger.

7. The vehicle control method according to claim 5, characterized in that the target wheel speed is lowered when the amount of sinking is smaller than when it is larger.

8. A power source that drives the drive wheels, A controller that performs the following processes: determining whether a vehicle is stuck in the sand; if it is determined that the vehicle is stuck in the sand, estimating the amount of tire sinkage in the sand; determining a target wheel speed for the drive wheels based on the estimated amount of sinkage; and controlling the drive source so that the drive wheels rotate at the determined target wheel speed. A vehicle control device characterized by comprising the following:

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