Vehicle control method

Abstract

To provide a vehicle control method capable of mitigating impact when a four wheel independent steering vehicle stops an ultra-pivotal turn.SOLUTION: When braking force Fb is applied to a plurality of wheels and rotating speed V is lowered to thresholds V1 and V2 during an ultra-pivotal turn of a four wheel independent steering vehicle, the braking force Fb is reduced and a steering angle θ of the plurality of wheels is changed from steering angles θ1 and -θ1 during the ultra-pivotal turn.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a vehicle control method.

Background Art

[0002] Conventionally, a vehicle travel control device for controlling the travel of a vehicle in an independent steering vehicle in which three or more tires can be independently steered is known (for example, Patent Document 1 below).

[0003] In the above vehicle travel control device, at the time of acceleration, the driving force of the pseudo front wheel part is set to be larger than the driving force of the pseudo rear wheel part, and at the time of braking, the braking force of the pseudo rear wheel part is set to be larger than the braking force of the pseudo front wheel part, so that lift-up can be prevented.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the independent steering vehicle described in Patent Document 1 in which three or more tires can be independently steered, it is difficult to adjust the rotation speed during an extremely low-speed turn in which the vehicle turns on the spot, and the impact received by the vehicle occupants when stopping the extremely low-speed turn tends to increase.

[0006] The present disclosure provides a vehicle control method capable of reducing the impact received by the vehicle occupants when stopping an extremely low-speed turn of a four-wheel independent steering vehicle.

Means for Solving the Problems

[0007] One aspect of the present disclosure provides a vehicle control method that reduces braking force when braking force is applied to a plurality of wheels during ultra-low-speed turning of a four-wheel independently steerable vehicle and the rotational speed drops to a threshold value, and changes the steering angles of the plurality of wheels from the steering angles during ultra-low-speed turning.

Advantages of the Invention

[0008] According to the above aspect of the present disclosure, it is possible to provide a vehicle control method capable of reducing the impact received by the vehicle occupants when the ultra-low-speed turning of the four-wheel independently steerable vehicle stops.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings.

[0011] First, with reference to FIGS. 1 and 2, a four-wheel independently steerable vehicle 100 as a control target in an embodiment of the vehicle control method according to the present disclosure will be described, and then, with reference to FIG. 3, an embodiment of the vehicle control method according to the present disclosure will be described.

[0012] FIG. 1 is a schematic diagram of a four-wheel independently steerable vehicle 100 as a control target in an embodiment of the vehicle control method according to the present disclosure. FIG. 2 is a block diagram showing an example of the configuration of the four-wheel independently steerable vehicle 100 in FIG. 1.

[0013] The four-wheel independently steerable vehicle 100 has, for example, as shown in FIG. 1, a vehicle body 101 and four wheels 102. Further, the four-wheel independently steerable vehicle 100 includes, for example, as shown in FIG. 2, a positioning device 103, a speed sensor 104, an acceleration sensor 105, an angular velocity sensor 106, and an operation device 107. Further, the four-wheel independently steerable vehicle 100 includes, for example, a steering device 108, a driving device 109, a braking device 110, a user interface 111, and a control device 112. Further, the four-wheel independently steerable vehicle 100 may include, for example, an external sensor such as a camera or LiDAR.

[0014] The vehicle body 101 includes, for example, a platform that is a basic structure, and a body mounted on the platform to form a cabin. The vehicle body 101 has a generally rectangular shape having, for example, a front portion 101F, a rear portion 101R, a left side portion 101SL, and a right side portion 101SR. Note that the vehicle body 101 may have any shape without distinguishing the front portion 101F, the rear portion 101R, the left side portion 101SL, and the right side portion 101SR.

[0015] The four wheels 102 include, for example, a left front wheel 102FL, a right front wheel 102FR, a left rear wheel 102RL, and a right rear wheel 102RR. The left front wheel 102FL and the right front wheel 102FR are respectively attached to the corner on the left side portion 101SL side and the corner on the right side portion 101SR side of the front portion 101F. The left rear wheel 102RL and the right rear wheel 102RR are respectively attached to the corner on the left side portion 101SL side and the corner on the right side portion 101SR side of the rear portion 101R. Note that the four wheels 102 may not have distinctions of front, rear, left, and right.

[0016] The positioning device 103 is constituted by, for example, a receiver of a global navigation satellite system (GNSS) mounted on the vehicle body 101. The positioning device 103 acquires, for example, the position information of the four-wheel independently steerable vehicle 100 and outputs it to the control device 112.

[0017] The speed sensor 104 is composed of, for example, wheel speed sensors mounted on each wheel 102, and detects the speed of the four-wheel independent steering vehicle 100 based on the rotational speed of each wheel 102. The speed sensor 104 outputs the detected speed of the four-wheel independent steering vehicle 100 to the control device 112.

[0018] The acceleration sensor 105 is, for example, a piezoelectric or capacitive sensor mounted on the vehicle body 101, and detects the acceleration of the four-wheel independent steering vehicle 100 in the front-rear direction, left-right direction, and up-down direction by converting inertial force into an electrical signal. The acceleration sensor 105 outputs the detected acceleration of the four-wheel independent steering vehicle 100 to the control device 112.

[0019] The angular velocity sensor 106 is composed of, for example, an inertial sensor mounted on the vehicle body 101. The angular velocity sensor 106 detects the angular velocity around each axis of the roll axis, pitch axis, and yaw axis of the four-wheel independent steering vehicle 100, for example. The angular velocity sensor 106 outputs the detected angular velocity of the four-wheel independent steering vehicle 100 to the control device 112.

[0020] The operation device 107 is operated by the driver of the four-wheel independent steering vehicle 100 during manual driving, for example, and detects the amount of operation by the driver. The operation device 107 includes, for example, an accelerator pedal, a brake pedal, a steering wheel, a driving mode switching switch, an automatic driving switching switch, and the like.

[0021] Further, the operation device 107 includes, for example, an accelerator pedal sensor that detects the amount of operation of the accelerator pedal, a brake pedal sensor that detects the amount of operation of the brake pedal, a steering angle sensor that detects the rotation angle of the steering wheel, and the like. The operation device 107 outputs the detected amount of operation to the control device 112.

[0022] The driving mode switching switch of the operation device 107 is configured to be able to switch the driving mode of the four-wheel independent steering vehicle 100, for example. The driving mode of the four-wheel independent steering vehicle 100 includes, for example, a normal driving mode, a parallel driving mode, a front-rear reverse steering mode, a super-low-speed turning mode, and the like.

[0023] In the normal driving mode of the four-wheel independently steered vehicle 100, for example, similar to a normal automobile, the left rear wheel 102RL and the right rear wheel 102RR are fixed in the longitudinal direction of the four-wheel independently steered vehicle 100, and the left front wheel 102FL and the right front wheel 102FR are steered to perform forward movement SF, backward movement SB, and left and right turns.

[0024] The straight-line driving mode of the four-wheel independently steered vehicle 100 is a driving mode in which, for example, by steering the four wheels 102 in the same direction, it can move straight in all 360° directions. Specifically, in the straight-line driving mode, the four-wheel independently steered vehicle 100 can, for example, perform forward movement SF, backward movement SB, left straight movement LT, right straight movement RT, left diagonal forward movement LF, right diagonal forward movement RF, left diagonal backward movement LB, right diagonal backward movement RB, etc.

[0025] In the reverse steering mode of the four-wheel independently steered vehicle 100, for example, the left front wheel 102FL and the right front wheel 102FR and the left rear wheel 102RL and the right rear wheel 102RR are steered in opposite directions to perform right turns and left turns.

[0026] In the tight turning mode of the four-wheel independently steered vehicle 100, for example, as shown in FIG. 1, the four wheels 102 are steered so as to face the tangential direction of the turning circle centered on the vehicle body 101 and rotated in the same direction, and a left turn TL or a right turn TR is performed on the spot.

[0027] The automatic driving switch of the operation device 107, for example, when turned on, starts the automatic driving of the four-wheel independently steered vehicle 100 by the control device 112, and when turned off, enables manual driving by the driver of the four-wheel independently steered vehicle 100. When the automatic driving of the four-wheel independently steered vehicle 100 is started, the control device 112 autonomously drives the four-wheel independently steered vehicle 100 from the current location to a preset destination while appropriately switching the driving mode of the four-wheel independently steered vehicle 100.

[0028] The steering device 108 is composed of, for example, one or more steering motors and a steering mechanism driven by the steering motors to independently change the steering angle θ of each wheel 102. The steering device 108 adjusts the steering angle θ of each wheel 102 to an arbitrary independent steering angle based on, for example, the steering command of each wheel 102 input from the control device 112.

[0029] The drive device 109 includes, for example, one or more driving motors and a power transmission mechanism that transmits the driving force of the driving motors to rotate each wheel 102. More specifically, the drive device 109 includes, for example, an in-wheel motor provided on at least one of the left rear wheel 102RL and the right rear wheel 102RR. Further, the drive device 109 may include an in-wheel motor provided on at least one of the right front wheel 102FR and the right rear wheel 102RR. The drive device 109 adjusts the rotation direction and rotation speed of each wheel 102 based on, for example, the drive commands of the rotation direction and rotation speed of each wheel 102 input from the control device 112.

[0030] The braking device 110 is composed of, for example, an electric brake actuator and a friction brake, and brakes each wheel 102 independently. The braking device 110 adjusts the braking force applied to each wheel 102 based on, for example, the braking command input from the control device 112. That is, brake-by-wire is adopted for the braking device 110.

[0031] The user interface 111 includes, for example, an output device and an input device. The output device includes, for example, a display, a speaker, an indicator lamp, a buzzer, etc. The input device includes, for example, a touch panel, an operation switch, an operation dial, an operation button, a keyboard, etc.

[0032] The user interface 111, for example, displays an image on the display and outputs sound or a warning sound from a speaker or buzzer based on a control command input from the control device 112. Further, the user interface 111 receives, for example, the operation and voice of the occupants of the four-wheel independent steering vehicle 100 by an input device such as a touch panel or a microphone, and outputs a signal related to the operation and voice to the control device 112.

[0033] The control device 112 is constituted by, for example, one or more electronic control units (ECUs) including one or more microcontrollers. The control device 112 realizes various controls of the four-wheel independent steering vehicle 100 including the vehicle control method of the present embodiment described below by executing a program stored in a storage device such as a RAM or a ROM by a central processing unit (CPU).

[0034] In the four-wheel independent steering vehicle 100, for example, the difficulty of adjusting the rotation speed in the above-described super-creditable turning mode is higher than the speed adjustment in other driving modes such as the normal driving mode and the parallel driving mode described above. Therefore, for example, when manually driving the four-wheel independent steering vehicle 100, the driver tends to increase the rotation speed of the super-creditable turn more than necessary, and in order to decrease the rotation speed from that state, the driver tends to operate the brake pedal and the steering wheel more than necessary. As a result, the impact received by the occupants of the four-wheel independent steering vehicle 100 when stopping the super-creditable turn also tends to increase.

[0035] Hereinafter, the vehicle control method of the present embodiment capable of reducing the impact received by the occupants of the vehicle when stopping the super-creditable turn of the four-wheel independent steering vehicle 100 as described above will be described with reference to FIG. 3.

[0036] FIG. 3 is a graph for explaining an embodiment of the vehicle control method according to the present disclosure. The upper graph in FIG. 3 shows the temporal change in the rotation speed V when the four-wheel independent steering vehicle 100 is in super-creditable turning. The middle graph in FIG. 3 shows the temporal change in the braking force Fb applied to each wheel 102 by the braking device 110 of the four-wheel independent steering vehicle 100.

[0037] The graph in the lower part of FIG. 3 shows the temporal change of the steering angle θ at each wheel 102 of the four-wheel independently steerable vehicle 100 shown in FIG. 1. In this graph, the solid line represents the temporal change of the steering angle θ of the left front wheel 102FL and the right rear wheel 102RR, and the dotted line represents the temporal change of the steering angle θ of the right front wheel 102FR and the left rear wheel 102RL.

[0038] When the super-sticky turning mode is selected during manual driving or automatic driving and the four-wheel independently steerable vehicle 100 starts super-sticky turning, the control device 112 of the four-wheel independently steerable vehicle 100 starts the vehicle control method of the present embodiment.

[0039] When starting the vehicle control method of the present embodiment, the control device 112 acquires the rotational speed V of the four-wheel independently steerable vehicle 100 based on the detection results of, for example, the speed sensor 104 or the angular velocity sensor 106. Further, the control device 112 acquires the braking force Fb applied to each wheel 102, for example. Furthermore, the control device 112 acquires the steering angle θ of each wheel 102 from the steering device 108, for example. Here, the control device 112 may calculate the braking force Fb based on the detection value of the brake pedal sensor included in the operation device 107, or may calculate the braking force Fb based on the output of the brake actuator of the braking device 110.

[0040] In the example shown in FIG. 3, the driver or the control device 112 of the four-wheel independently steerable vehicle 100 performing super-sticky turning at a predetermined rotational speed V0 activates the braking device 110 at time t1 in order to stop the super-sticky turning. As a result, the braking force Fb applied to each wheel 102 gradually increases from time t1, and when the braking force Fb reaches a predetermined braking force Fb1 at time t2, the rotational speed V0 of the four-wheel independently steerable vehicle 100 gradually decreases and drops to a predetermined threshold value V1 at time t3.

[0041] Then, for example, at time t3, the control device 112 gradually reduces the braking force Fb applied to each wheel 102 regardless of the braking force Fb based on the driver's brake pedal operation indicated by the dashed-dotted line in the middle graph of FIG. 3. Thereafter, at time t4, when the rotational speed V of the four-wheel independent steering vehicle 100 decreases to a predetermined threshold value V2, the control device 112 outputs a steering command to the steering device 108 to change the steering angle θ of each wheel 102 from the steering angles θ1 and -θ1 during oversteering.

[0042] Specifically, as shown in FIG. 3, the control device 112 decreases the steering angle θ of the left front wheel 102FL and the right rear wheel 102RR from the steering angle θ1 to the steering angle θ2, and increases the steering angle θ of the right front wheel 102FR and the left rear wheel 102RL from the steering angle -θ1 to the steering angle -θ2. As a result, the directions of the left front wheel 102FL and the right rear wheel 102RR shown in FIG. 1 and the directions of the left rear wheel 102RL and the right rear wheel 102RR approach the front-rear direction of the four-wheel independent steering vehicle 100, and a force that hinders oversteering acts on each wheel 102.

[0043] As a result, it is possible to gently reduce the decreasing speed of the rotational speed V of the four-wheel independent steering vehicle 100, mitigate the impact at the time of stopping, and more surely stop the oversteering of the four-wheel independent steering vehicle 100. Thereafter, for example, when the oversteering mode is maintained and the braking force Fb becomes zero, the control device 112 returns the steering angle θ of each wheel 102 to the steering angles θ1 and -θ1 during oversteering from time t5 to time t6.

[0044] As described above, in the vehicle control method of the present embodiment, when a braking force Fb is applied to a plurality of wheels 102 during oversteering of the four-wheel independent steering vehicle 100 and the rotational speed V decreases to a threshold value V1, the braking force Fb is decreased and the steering angle θ of the plurality of wheels 102 is changed from the steering angles θ1 and -θ1 during oversteering.

[0045] With such a configuration, according to the vehicle control method of the present embodiment, when the super high-speed turning of the four-wheel independent steering vehicle 100 stops, the decreasing speed of the rotational speed V is moderated, and the impact on the vehicle occupants when the super high-speed turning stops can be reduced compared to the conventional vehicle control method. In addition, by changing the steering angle θ from the steering angles θ1 and -θ1 during super high-speed turning, the super high-speed turning can be stopped more reliably. Specifically, in the conventional vehicle control method, for example, as shown by the two-dot chain line in the middle graph of FIG. 3, the braking force Fb is gradually decreased and then increased again immediately before it becomes zero.

[0046] However, according to the vehicle control method of the present embodiment, not only can the impact on the occupants when the super high-speed turning stops be reduced more easily and reliably than the conventional vehicle control method, but also the need to increase the braking force Fb again can be eliminated or the increase amount of the braking force Fb can be suppressed. As described above, according to the present embodiment, a vehicle control method capable of reducing the impact received by the vehicle occupants when the super high-speed turning of the four-wheel independent steering vehicle 100 stops can be provided.

[0047] As described above, the preferred embodiments of the present invention have been described in detail. However, the present invention is not limited to the above-described embodiments. Various modifications or substitutions etc. can be applied without departing from the scope of the present invention.

[0048] For example, in the example shown in FIG. 3, the braking force Fb is decreased when the rotational speed V drops to the threshold value V1, and the steering angle θ is changed when the rotational speed V further drops to the threshold value V2, but the timing of decreasing the braking force Fb and the timing of changing the steering angle θ may be simultaneous.

[0049] Also, in the example shown in FIG. 3, the steering angle θ is changed in a direction approaching the front-rear direction of the four-wheel independent steering vehicle 100, but it may be changed in a direction approaching the left-right direction of the four-wheel independent steering vehicle 100. Also in this case, a force that hinders the super high-speed turning can be applied by each wheel 102.

Explanation of Reference Numerals

[0050] 100: Four-wheel independently steerable vehicle, 102: Wheel, Fb: Braking force, V: Rotational speed, V1, V2: Threshold values, θ: Steering angle, θ1, -θ1: Steering angles during skid steering.

Claims

【Claim 1】 A vehicle control method for reducing the braking force and changing the steering angles of a plurality of wheels from the steering angles during a tight turning when the braking force is applied to the plurality of wheels during a tight turning of a four-wheel independently steered vehicle and the rotational speed decreases to a threshold value.

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