JP7534262B2 - Vehicle driving control device - Google Patents

Description

The present invention relates to a vehicle driving control device.

Conventionally, there is known technology that makes it easy to switch from a normal driving mode to a non-normal driving mode, in which the vehicle turns on the spot or moves laterally, in an independently steerable vehicle in which each wheel can be steered independently.

For example, the automobile disclosed in Patent Document 1 has a joystick equipped with multiple input operation means for switching driving modes by the driver's operation. This operation makes it possible to switch between a normal driving mode and an abnormal driving mode, and furthermore, in the abnormal driving mode, it is possible to select a rotation mode and a lateral movement mode.

JP 2013-112102 A

In this specification, "linear movement" refers to movement in which the angle of the vehicle's front and rear axes relative to an imaginary line on the road surface is maintained constant. Of linear movements, movement in a direction along the vehicle's front and rear axes is "straight ahead." In contrast to linear movement, movement in which the angle of the vehicle's front and rear axes relative to an imaginary line on the road surface changes is "turning." Independently steered vehicles are capable of lateral and diagonal movement as linear movements other than straight ahead. However, during lateral or diagonal movement, turning may be necessary to avoid obstacles or other obstacles jumping out. However, the conventional technology of Patent Document 1 does not take into consideration turning during linear movement other than straight ahead.

The present invention was created in consideration of the above points, and its purpose is to provide a vehicle driving control device that appropriately performs cornering during linear motion other than straight ahead travel by an independently steered vehicle.

The vehicle driving control device according to the present invention controls the driving of an independently steering vehicle (100) in which three or more tires (91-94) can be steered independently. The steering angle range in which each tire of an independently steering vehicle can be steered is finite. This vehicle driving control device includes a turning target instruction unit (14), a steering angle control unit (15), and a braking/driving force control unit (16).

The linear movement direction indicating unit indicates the direction of "linear movement," which is movement in which the angle of the vehicle's front and rear axes relative to a virtual line on the road surface is maintained constant. The turning target indicating unit indicates the turning center and turning radius as turning target indicating values when the vehicle turns. The turning angle control unit and braking/driving force control unit acquire vehicle characteristics from a vehicle characteristic storage device (20). In response to the indicating values from the linear movement direction indicating unit and turning target indicating unit, the turning angle control unit steers each tire individually, and the braking/driving force control unit brakes/drives each tire individually.

The steering angle control unit calculates the steering angle of each tire from the commanded linear movement direction and the turning target command value when turning the vehicle in the linear movement direction commanded by the linear movement direction command unit. When the calculated steering angle for at least one tire exceeds the turning angle range in which the tire can be turned, the steering angle control unit recalculates the steering angle of each tire by adjusting the turning center while maintaining the turning radius of the turning target command value.

If we define x and y coordinates with the vehicle's center of gravity as the origin and the vehicle's straight-line direction as the y axis, when turning while moving in a straight line other than a straight line, the x and y coordinates of the center of each tire are different from when turning while moving straight. Therefore, if the vehicle is steered at the same steering angle as when turning while moving straight, unnecessary forces will be generated due to tire slippage, and the turning radius will shift. Therefore, smoother turning is possible by calculating the steering angle using the x'y' coordinates converted to the linear movement direction.

1 is a block diagram of a vehicle driving control device according to an embodiment; FIG. 2 is a diagram showing an example of a steering angle limit information presentation device. FIG. 4 is a diagram showing the relationship between a turning center, a turning radius, and a steering angle. 1A and 1B are diagrams showing (a) diagonal movement and (b) lateral movement by an independently steered vehicle; 4A to 4C are diagrams showing a steering operation when turning left relative to a linear movement direction. 1A shows a state in which the right wheel exceeds the steering angle limit when turning right relative to the linear movement direction, and FIG. 1B shows a state in which the turning center has moved and the left wheel has been steered in the opposite direction. FIG. 1 is a diagram for explaining task example 1. FIG. 13 is a diagram illustrating task example 2. FIG. 1 is a diagram illustrating a solution to a problem according to an embodiment. 4 is a diagram for explaining calculation of a steering angle when turning while traveling straight. 6A and 6B are diagrams for explaining calculation of a steering angle when turning during linear movement other than straight ahead; FIG. 13 is a diagram showing the results of a simulation analysis of the turning radius when turning during linear movement. 4 is a flowchart of a driving control process according to one embodiment.

A vehicle driving control device according to one embodiment of the present invention will be described below with reference to the drawings. The vehicle driving control device of this embodiment controls the driving of an independently steering vehicle in which each tire can be steered independently. Here, movement in which the angle of the vehicle's front and rear axes with respect to an imaginary line on the road surface is maintained constant is defined as "linear movement." Of linear movement, movement in a direction along the vehicle's front and rear axes is called "straight ahead."

Conventionally, in a typical vehicle, the pair of left and right tires are mechanically connected via a link, and the tires are turned by turning the steering wheel. In the future, it is expected that developments will progress to steer-by-wire, in which the steering wheel and the link between the pair of left and right tires are mechanically separated, and to four-wheel independently steering vehicles in which the left and right rear wheels can be steered independently in addition to the left and right front wheels. For example, four-wheel independently steering vehicles are capable of lateral and diagonal movement, i.e., "linear movement other than straight ahead," making it easy to parallel park in narrow parking spaces.

However, during lateral or diagonal movement, turning may be necessary to avoid obstacles or objects jumping out. In addition, in a four-wheel independently steering vehicle, it is possible to freely set the turning center and turning radius when turning. The purpose of this embodiment is to take advantage of the characteristics of such an independently steering vehicle and to appropriately perform turning while moving in a straight line other than a straight line.

(One embodiment)
The configuration of a vehicle driving control device 10 according to one embodiment will be described with reference to Figures 1 and 2. In the independently steering vehicle 100 shown in Figure 1, all four tires 91-94 can be steered independently. Each tire 91-94 is equipped with an in-wheel motor ("IWM" in the figure) and a brake mechanism that generate braking/driving force, and a steering mechanism that steers the tire. The front left tire 91 is marked with "FL", the front right tire 92 with "FR", the rear left tire 93 with "RL", and the rear right tire 94 with "RR".

In addition to the vehicle driving control device 10, the vehicle 100 is equipped with a vehicle characteristics storage device 20 that stores vehicle characteristics, and a steering angle limit information presentation device 70. The vehicle characteristics stored in the vehicle characteristics storage device 20 include vehicle dimensions such as wheelbase and tread width, and steering angle limit values. The steering angle limit information presentation device 70 is a device that notifies the driver that the steering angle is approaching the limit, and a specific example will be described later.

The vehicle driving control device 10 includes a linear movement direction indicator 13, a turning target indicator 14, a steering angle control unit 15, and a braking/driving force control unit 16. The linear movement direction indicator 13 indicates the direction of linear movement. The turning target indicator 14 indicates the turning center and turning radius as turning target indication values when the vehicle 100 turns. As shown in FIG. 2, the linear movement direction indicator 13 is, for example, a joystick, and the turning target indicator 14 is, for example, a steering wheel.

The steering angle control unit 15 and the braking/driving force control unit 16 acquire vehicle characteristics from the vehicle characteristics storage device 20. The steering angle control unit 15 outputs a command signal to the steering mechanism to steer each tire 91-94 individually according to the instruction values from the linear movement direction instruction unit 13 and the turning target instruction unit 14. The braking/driving force control unit 16 outputs a command signal to the in-wheel motor and the brake mechanism to brake/drive each tire 91-94 individually according to the instruction values. In detail, the steering angle control unit 15 steers all tires 91-94 in the instructed linear movement direction. When the braking/driving force control unit 16 outputs a driving force in that linear movement direction, the vehicle 100 starts moving linearly.

When turning the vehicle 100 in the linear movement direction instructed by the linear movement direction instructing unit 13, the turning angle control unit 15 calculates the turning angle of each tire 91-94 from the instructed linear movement direction and the turning target instruction value. A specific calculation formula for the turning angle will be described later with reference to FIG. 11.

However, when considering wiring for brakes and the like, it is not possible to provide a mechanism for infinite steering, so the steering angle of the vehicle 100 is finite. The limit of the steering angle range at which the tires can be steered is called the "steering angle limit." If the steering angle in the clockwise direction is defined as positive, the steering angle limit includes a positive upper limit value in the clockwise direction and a negative lower limit value in the counterclockwise direction. If each tire 91-94 could be steered ±90°, linear movement in all directions would be possible, so the steering angle limit is assumed to be ±90°, or ±(90°+α) with a margin angle α of a few degrees added.

If the steering angle calculated by the steering angle control unit 15 exceeds the limit, the turning radius cannot be maintained. Therefore, when the calculated steering angle for at least one tire exceeds the steering angle limit, the steering angle control unit 15 adjusts the turning center while maintaining the turning radius and recalculates the steering angle for each tire 91-94. Furthermore, when the steering angle control unit 15 predicts that the calculated steering angle for at least one tire will exceed the steering angle limit, it notifies the steering angle limit information presentation device 70 to inform the driver.

As a specific example of the steering angle limit information presentation device 70, as shown in FIG. 2, a click sensation can be provided on the steering wheel to inform the driver by touch that at least one tire is about to exceed the steering angle limit. In this configuration example, it may be interpreted that the turning target indication unit 14, which also functions as the steering angle limit information presentation device 70, is provided inside the vehicle driving control device 10. Alternatively, the steering angle limit information presentation device 70, which is composed of a buzzer, indicator lamp, etc., may be used to inform the driver by audio or visual information.

Next, Figure 3 shows the relationship between the turning center, turning radius, and steering angle. The turning radius corresponds to the distance from the turning center to the center of gravity of the vehicle. The rotation direction of each tire 91-94 is set so that it is perpendicular to the line connecting the center of each tire 91-94 and the turning center. In this way, with a four-wheel independently steering vehicle, the turning center and turning radius during turning can be freely set.

Next, referring to FIG. 4, "linear movement other than straight ahead" by the independently steered vehicle 100 will be described. The angle with respect to the vehicle's longitudinal axis y is expressed with the rightward direction (clockwise direction) relative to the front as positive. FIG. 4(a) shows diagonal movement, which is linear movement 45° to the right and forward with respect to the vehicle's longitudinal axis y. FIG. 4(b) shows lateral movement, which is linear movement 90° to the right with respect to the vehicle's longitudinal axis y, i.e., in the x-axis direction. Assuming an imaginary straight line on the road surface extending in the linear movement direction, the angle of the vehicle's longitudinal axis y with respect to the imaginary straight line on the road surface is maintained constant during diagonal movement and lateral movement.

In linear motion, as a rule, all tires 91-94 are driven with their steering angles set to the same angle parallel to the linear motion direction. However, as an exception, the idea of toe-in or toe-out may be used, with the tires on both sides straddling the center line of the linear motion direction facing symmetrically inward or outward.

Here, in linear movement, the tires located forward of the vehicle's center of gravity in the direction of travel are called pseudo front wheel sections, and the tires located rearward of the vehicle's center of gravity in the direction of travel are called pseudo rear wheel sections. For example, in the lateral movement shown in FIG. 4(b), the right front wheel 92 and right rear wheel 94, which correspond to the pseudo front wheel sections, may be toe-in. Note that exceptional toe-in and toe-out are not taken into account in the calculation of the steering angle described below.

Next, referring to Figures 5 and 6, we will explain turning while moving diagonally in the right front direction as an example of linear movement other than going straight. As shown in Figure 5, when turning left relative to the linear movement direction, the steering angle is calculated from the center of turning and the position of each tire 91-94 relative to the center of gravity of the vehicle, and the vehicle can be turned without any problems.

In contrast, as shown in Figure 6(a), when turning right in the linear motion direction, if the right front wheel 92 and right rear wheel 94, which correspond to the pseudo front wheel section, exceed their steering angle limits, the vehicle cannot turn right. However, as shown in Figure 6(b), by moving the turning center forward in the linear motion direction while maintaining the turning radius, and steering the left front wheel 91 and left rear wheel 93, which correspond to the pseudo rear wheel section and have not reached their limits, in the opposite direction, the vehicle can turn right while maintaining the turning radius.

This control by the steering angle control unit 15 of this embodiment is called "turning control at the steering angle limit." The vehicle driving control device 10 of this embodiment can minimize the turning radius when turning during linear movement other than straight ahead by controlling turning at the steering angle limit, and can perform appropriate turning.

With reference to Figures 7 to 9, an example of a problem solved by the turning control at the steering angle limit of this embodiment will be described. Figures 7 to 9 are plan views seen from above, with the top of the page showing the front and the bottom showing the rear. Two other vehicles 801, 803 are parked along the wall or shoulder at the right end with a space between them. Assume a situation in which the host vehicle 100 is parked in parallel by moving laterally from the left side in the space between the two other vehicles 801, 803. The front-to-rear distance of the parking space is slightly longer than the overall length of the host vehicle 100.

In problem example 1 shown in FIG. 7, a situation is assumed in which the vehicle 100 notices an obstacle such as garbage in front of the parking space while moving sideways to park directly behind the vehicle 801 in front, or an obstacle such as garbage appears in front of the parking space due to falling or being blown by wind, etc. In this case, even if the vehicle tries to avoid the obstacle, the right front wheel 92 and right rear wheel 94 of the vehicle 100 have reached their steering angle limits, so the vehicle cannot move diagonally to the target position (two-dot chain line) to the right rear.

In the example of the problem shown in FIG. 8, the location is a downhill slope, and even though the vehicle 100 intends to move sideways toward the parking space, it slips and falls forward, and if it continues to slide, it will collide with the rear of the vehicle 801 in front. At this time, even if the vehicle tries to avoid the collision, the right front wheel 92 and right rear wheel 94 of the vehicle 100 have reached their steering angle limits, so the vehicle cannot move diagonally to the right rear.

Figure 9 shows an example of the turning control at the steering angle limit of this embodiment in the same situation as Figure 7. When the right front wheel 92 and right rear wheel 94 reach the steering angle limit during lateral movement of the vehicle 100, the left front wheel 91 and left rear wheel 93 are steered leftward to make a right turn (*1), and the right front wheel 92 and right rear wheel 94 are further steered leftward to make a left turn (*2), thereby allowing the vehicle 100 to park in the parking space while avoiding obstacles.

Next, with reference to Figures 10 and 11, the calculation of the steering angle during turning by the steering angle control unit 15 will be described. First, with reference to Figure 10. When turning while traveling straight, an xy coordinate is defined with the vehicle's center of gravity as the origin (0,0), the vehicle's left-right axis as the x-axis, and the vehicle's front-rear axis as the y-axis. On the x-axis, the right is positive and the left is negative, and on the y-axis, the front is positive and the rear is negative. The coordinates of the turning center are (x1, y1). The turning angle is calculated so that the rotation direction of each tire 91-94 is perpendicular to a straight line connecting the center of each tire 91-94 and the turning center.

The turning radius Rt is the distance between the turning center and the center of gravity, and is expressed by equation (1).
Rt=√(x1 ² +y1 ² )...(1)

The wheelbase L and tread widths Df, Dr of the vehicle are obtained from the vehicle characteristics storage device 20. The distance from the center of gravity to the axles of the front wheels 91, 92 in the y-axis direction is represented as Lf, and the distance from the center of gravity to the axles of the rear wheels 93, 94 is represented as Lr. The steering angles δFL, δFR, δRL, δRR of each tire 91-94 are expressed as tangent values using equations (2.1) to (2.4), with the clockwise direction being positive. The subscripts "FL, FR, RL, RR" in Figures 10 and 11 will be written in normal characters in the specification.

tanδFL= (Lf-y1)/{x1+(Df/2)}...(2.1)
tan δFR= (Lf-y1)/{x1-(Df/2)}...(2.2)
tanδRL=-(Lr+y1)/{x1+(Dr/2)}...(2.3)
tan δRR=-(Lr+y1)/{x1-(Dr/2)}...(2.4)

Next, let us refer to Figure 11. When turning during linear motion other than straight ahead, x'y' coordinates that are rotationally transformed around the origin are used instead of the xy coordinates used when turning while moving straight ahead. The y' axis is the axis of linear motion, and the x' axis is perpendicular to the y' axis. The angle of the rotational transformation, i.e., the angle of the linear motion direction relative to the straight ahead direction, is θo.

The calculation of the steering angle will be described using the right front wheel 92 as an example. The vehicle wheelbase L and the front wheel tread width Df use the symbols in Fig. 10. The distance Lfro from the vehicle center of gravity to the axis of the right front wheel 92 is expressed by equation (3.1).
Lfro=√{(Df/2) ² +Lf ² } ...(3.1)

The x'y' coordinates of the axis of the right front wheel 92 are (Dfr, Lfr). If the angle of the axis of the right front wheel 92 relative to the y axis is θfr, Dfr and Lfr are expressed by equations (3.2) and (3.3), respectively. As with each steering angle δ, the clockwise direction is considered positive for θo and θfr.

Dfr=Lfro×sin(θfr−θo) (3.2)
Lfr=Lfro×cos(θfr−θo) (3.3)

The steering angle δFR of the right front wheel 92 is expressed as a tangent value by equation (4). The steering angles δFL, δRL, δRR of the other tires 91, 93, 94 can be calculated in a similar manner based on the x'y' coordinates of the tire axes.
tanδFR= (Lfr-y'1)/(x'1-Dfr)...(4)

Figure 12 shows the results of a simulation analysis of the turning radius when turning while moving in a straight line. Assume that the vehicle turns from a state in which it is moving in a straight line at an angle of 85° to the vehicle's longitudinal axis y. When turning left, the turning angle does not reach its limit, so the turning radius is approximately 4 m, as shown by the long dashed line. In contrast, when turning right, the turning angle reaches its limit, and the turning radius increases to approximately 14 m, as shown by the two-dot chain line. In this case, there is a risk that it will not be possible to avoid obstacles by turning.

However, as shown in FIG. 6(b), by adjusting the turning center by the turning control at the steering angle limit and turning using tires 91 and 93 with a steering angle margin, the turning radius (solid line) becomes about 4 m, which is the same as in the case of turning left. Therefore, it is more likely that obstacles can be avoided by turning.

The flowchart in Figure 13 shows a routine for driving control according to this embodiment. In the explanation of the flowchart, the symbol "S" means a step. In S1, the steering angle control unit 15 obtains a linear movement direction instruction value from the linear movement direction instruction unit 13. If linear movement is to be performed, a YES determination is made in S2, and linear movement is started in S3. If a turning instruction is given during linear movement, a YES determination is made in S4, and the process moves to S5. If no turning instruction is given, the process returns to before S2.

In S5, the steering angle control unit 15 calculates the steering angle based on the calculation formula in FIG. 11 from the linear movement direction and turning command values (turning center, turning radius). In S6, it is determined whether all tires 91-94 are within the steering angle limit. If all tires 91-94 are within the steering angle limit, YES is determined in S6, and in S7 the steering angle control unit 15 steers the tires at the calculated steering angle.

If the calculated steering angle for at least one tire exceeds the steering angle limit, the result in S6 is NO. In this case, in S8, the steering angle control unit 15 holds the turning radius command value and adjusts the turning center according to the steering angle limit. Then, in S9, the steering angle control unit 15 recalculates the steering angle from the adjusted turning center.

(Effects of this embodiment)
(1) When turning the vehicle 100 in the linear movement direction instructed by the linear movement direction instructing unit 13, the turning angle control unit 15 calculates the turning angle of each of the tires 91-94 from the instructed movement direction and the turning target instruction value.

As shown in FIG. 10, if the xy coordinate system is defined with the center of gravity of the vehicle as the origin and the straight-line direction of the vehicle as the y axis, when turning during linear motion other than straight-line motion, the xy coordinates of the center of each tire are different from when turning while moving straight. Therefore, if the vehicle is turned at the same turning angle as when turning while moving straight, unnecessary forces are generated due to tire slippage, and the turning radius is shifted. Therefore, as shown in FIG. 11, the turning angle is calculated using the x'y' coordinates converted to the linear motion direction, making it possible to turn smoothly. Therefore, the vehicle driving control device 10 of this embodiment can improve vehicle driving performance such as obstacle avoidance, response to road gradients, and path following for path planning during automatic driving.

(2) The steering angle range within which each tire 91-94 of the independently steering vehicle 100 can be steered is finite. When the calculated steering angle for at least one tire exceeds the steering angle limit, which is the limit of the steering angle range, the steering angle control unit 15 recalculates the steering angle for each tire 91-94 by adjusting the turning center while maintaining the turning radius, which is the turning target command value.

When wiring and other factors are taken into consideration, the steering angle of a vehicle is usually finite. Therefore, depending on the turning conditions, the steering angle may exceed the limit, making it impossible to maintain the turning radius. Therefore, the steering angle control unit 15 can calculate a steering angle that allows the turning radius to be maintained without exceeding the steering angle limit by adjusting the turning center while maintaining the turning radius.

(3) The vehicle driving control device 10 of this embodiment is mounted on a vehicle 100 equipped with a steering angle limit information presentation device 70. When the steering angle control unit 15 predicts that the calculated steering angle for at least one tire will exceed the steering angle limit, it notifies the steering angle limit information presentation device 70 to inform the driver.

If the turning center is suddenly adjusted after the steering angle of one of the tires has reached its limit, the driver may feel uncomfortable. Therefore, the steering angle control unit 15 can eliminate the driver's sense of discomfort by notifying the driver in advance that the steering angle of one of the tires is about to exceed its limit.

Other Embodiments
(a) The independently steered vehicle controlled by the vehicle travel control device 10 of the present invention is not limited to a four-wheeled vehicle, but may be any vehicle with three or more wheels that can be independently steered.

(b) In the configuration example of FIG. 1, the vehicle 100 does not need to be equipped with a steering angle limit information presentation device 70.

The present invention is not limited to the above-mentioned embodiment, and can be implemented in various forms without departing from the spirit of the invention.

10... Vehicle driving control device,
13... linear movement direction indicator,
14...Turning target indication unit,
15...Steering angle control unit,
16: Braking/driving force control unit,
20... Vehicle characteristic storage device,
91-94... Tires,
100...Vehicle with independent steering.

Claims (2)

A vehicle driving control device controls driving of an independently steering vehicle (100) in which tires (91-94) of three or more wheels can be independently steered, the independently steering vehicle having a finite steering angle range in which each tire can be steered,
a linear movement direction indicator (13) for indicating a direction of linear movement in which the angle of the front and rear axes of the vehicle with respect to a virtual straight line on a road surface is kept constant;
A turning target indicating unit (14) that indicates a turning center and a turning radius as turning target indicating values when the vehicle is turning;
a steering angle control unit (15) that acquires vehicle characteristics from a vehicle characteristics storage device (20) and steers each tire individually in response to instruction values from the linear movement direction instruction unit and the turning target instruction unit, and a braking/driving force control unit (16) that brakes/drives each tire individually;
Equipped with
The steering angle control unit, when turning the vehicle in a commanded linear movement direction, calculates a steering angle of each tire from the commanded linear movement direction and the turning target command value , and, when the calculated steering angle for at least one tire exceeds a steering angle limit that is the limit of a steering angle range in which steering is possible, adjusts the turning center while maintaining a turning radius that is the turning target command value, and recalculates the steering angle of each tire . The steering angle limit information presentation device (70) is mounted on a vehicle equipped with the steering angle limit information presentation device (70) for notifying a driver that the steering angle is approaching the limit,
2. The vehicle driving control device according to claim 1 , wherein when it is predicted that the calculated steering angle for at least one tire will exceed the steering angle limit, the steering angle control unit notifies the steering angle limit information presentation device to inform the driver.

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