JP2748287B2 - 4-wheel steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel steering system capable of maximizing evasion ability in an emergency evasion.

[0002]

2. Description of the Related Art There is widely known a four-wheel steering system in which the rear wheels are steered in the same or opposite phases in accordance with the steering of the front wheels to improve the steerability of the vehicle. Such a four-wheel steering device determines a steering angle of a rear wheel according to a vehicle state such as a vehicle speed and a yaw rate.
The rear wheels are steered.

[0003]

However, since the steering angle of the rear wheel is not physically configured to be able to be physically steered to the maximum angle in the conventional device, the steering angle of the rear wheel is insufficient during an emergency avoidance. There was a problem. The present invention has been made in view of the above points, and an object of the present invention is to provide a four-wheel steering device capable of exerting the evasion ability to the maximum during an emergency evasion.

[0004]

4-wheel steering system according to the present invention SUMMARY OF THE INVENTION comprises a vehicle locus calculating means for calculating a trajectory of the vehicle, car
A forward obstacle sensor that detects the state of obstacles in front of each other,
The trajectory of the vehicle calculated by the vehicle trajectory calculation means and the front
Collision danger determining means for determining the danger of colliding with an obstacle in front of the vehicle based on the state of the obstacle detected by the vehicle obstacle sensor, and the state of the moving body on the side of the vehicle. The moving object state detecting means for detecting, and the front obstacle sensor
An avoidance space for calculating an avoidance space for avoiding an obstacle ahead of the vehicle in consideration of the state of the obstacle and the state of the moving body on the side of the vehicle detected by the moving body state detection means. The vehicle turns around an obstacle ahead in consideration of the avoidance space calculated by the space calculation means and the avoidance space calculation means.
Avoidance trajectory calculating means for calculating a avoid possible trajectories, and front and rear wheel steering ratio calculating means for calculating a front and rear wheel steering ratio in accordance with avoidance trajectory of the vehicle calculated by the avoidance locus calculating means, front wheel steering angle and the rear wheel And rear wheel steering means for steering rear wheels so that a ratio of the steering angle to the steering angle is equal to the rear wheel steering ratio.

[0005]

The trajectory of the vehicle is calculated based on data such as the vehicle speed and the steering wheel angle, and the inter-vehicle distance and the relative speed of the front obstacle detected by the front obstacle sensor are calculated. Determine the risk of collision. Further, the distance to the moving body on the side of the vehicle and the relative speed to the moving body are calculated, and the avoidance space that the vehicle can avoid is calculated. If it is determined that there is a risk of collision, an avoidance trajectory that allows the vehicle to avoid an obstacle in front is calculated in consideration of the avoidance space, and the front and rear wheel steering ratio according to the avoidance trajectory is calculated. calculate. The rear wheels are steered so that the ratio between the front wheel steering angle and the rear wheel steering angle becomes the front and rear wheel steering ratio.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A four-wheel steering system according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a four-wheel steering device, FIG. 2 is a perspective view of a vehicle showing a mounting location of sensors mounted on the vehicle, and FIG. 3 is a diagram showing an avoidance trajectory of the vehicle in an emergency. 4 and FIG.
FIG. 6 is a block diagram showing a detailed configuration of the steering wheel, and FIG.
It is a figure which shows a / d characteristic.

In FIG. 1 and FIG. 2, reference numeral 11 denotes a front obstacle sensor formed by, for example, a CCD camera provided for capturing an obstacle ahead of the vehicle and a white line on the road, and 12 denotes an obstacle behind the vehicle. A rear obstacle sensor 13 comprising a CCD camera, for example, is provided for detecting a distance from a moving body on the side of the vehicle, and a side obstacle detection comprising, for example, a plurality of ultrasonic transceivers. Means 1
Reference numeral 4 denotes a vehicle speed sensor for detecting a vehicle speed, and reference numeral 15 denotes a steering wheel angle sensor for detecting a steering angle of a steering wheel.

[0008] side obstacle sensor 13 described above is one that is composed of a plurality of ultrasonic transceivers _131-134, ultrasound in the direction and obliquely forward orthogonal to the side surface of the vehicle on both sides of the vehicle It is set up to be transmitted.

The detection signals from the sensors 11, 12, 14, and 15 and the detection means 13 are input to a controller 20. The detailed configuration of the controller 20 is shown in FIGS.
It will be described later with reference to FIG.

The controller 20 includes a braking device 21 for braking the front and rear wheels, a rear wheel steering actuator 22 for controlling the steering of the rear wheels, and a warning device 23 for warning that an obstacle in front cannot be avoided. Connected.

Next, a detailed configuration of the controller 20 will be described with reference to FIGS. Vehicle speed sensor 1
The vehicle speed detected in 4 and the steering wheel angle detected by the steering wheel angle sensor 15 are input to the vehicle trajectory calculation unit 31. A memory 32 for storing driving characteristic data of the vehicle is connected to the vehicle trajectory calculation unit 31. The driving characteristic data is data necessary for estimating the trajectory of the vehicle when the vehicle speed and the steering wheel angle are specified, and is data such as vehicle weight and wheelbase. .

The vehicle trajectory calculation unit 31 reads the vehicle speed and the steering wheel angle at every predetermined sampling time,
The trajectory of the vehicle is calculated in consideration of the driving characteristic data of the vehicle stored in 2.

A forward video signal taken by the front obstacle sensor 11 is output to an inter-vehicle distance / relative speed calculation unit 33, a vehicle recognition unit 34, and a white line recognition unit 35. The inter-vehicle distance / relative speed calculation unit 33 calculates the inter-vehicle distance L and the relative speed Vr between the vehicle and the obstacle ahead of the vehicle based on the input video signal. Further, the vehicle recognizing unit 34 calculates the left / right position x of the vehicle with respect to the obstacle based on the input video signal. Further, the white line recognition unit 35 performs a recognition process of recognizing a white line on the road from the input video signal. This recognition processing data is used in a corner R calculating section 36 for calculating a turning radius R of the road.
Is output to

The inter-vehicle distance L and the relative speed Vr calculated by the inter-vehicle distance / relative speed calculation unit 33 and the left and right position X of the vehicle with respect to the obstacle calculated by the vehicle recognition unit 34 are output to a collision risk determination unit 37, respectively. You. The collision danger determining unit 37 calculates the inter-vehicle distance L, the relative speed Vr between the preceding obstacle and the vehicle based on the vehicle trajectory data calculated by the vehicle trajectory calculating unit 31, the left and right position x of the vehicle with respect to the obstacle. The risk of collision of the vehicle is determined in consideration of the above. Specifically, when it is predicted that the vehicle will collide with an obstacle ahead even after the maximum braking (for example, 0.4 g) is performed, a determination signal indicating a danger of collision is output. Then, a judgment signal having no risk of collision is output.

The reception signals of the ultrasonic signals transmitted from the ultrasonic transmitters / receivers 13 _{1 to} 13 ₄ constituting the side obstacle detecting means 13 are output to the distance calculator 38. This distance calculator 3
8 _{1-38 4} denotes a distance between the transmission time and the ultrasound is mobile and the vehicle in consideration of the reception time input is reflected by the movement of the output ultrasonic signal from the side obstacle sensor 13 x1 to x4 are calculated respectively.

The distance calculator 38 _{1-38 4} distance x1~x4 calculated in is output to the moving body recognition unit 39. The mobile recognition unit 39 calculates a relative speed Vr1~Vr4 a mobile present on the sides of the vehicle in consideration of the installation location and the installation direction of the ultrasonic transducer _131-134, avoiding space - Output to the calculation unit 40.

A video signal of the rear vehicle taken by the rear obstacle sensor 12 is output to an inter-vehicle distance calculating unit 41 and a vehicle recognizing unit 42. The inter-vehicle distance calculating unit 41 calculates the inter-vehicle distance L1 to the vehicle behind the vehicle based on the input video signal and outputs it to the avoidance space calculating unit 40. Further, the vehicle recognizing unit 42 calculates the left / right position x5 of the vehicle with respect to the vehicle behind the vehicle based on the input video signal, and calculates the avoidance space calculating unit 4.
Output to 0.

The avoidance space calculating unit 40 is output from the inter-vehicle distance / relative speed calculating unit 33 and the inter-vehicle distance L and the relative speed Vr output from the vehicle recognizing unit 34, the left / right position x and the moving object recognizing unit 39, respectively. Based on the relative velocities Vr1 to Vr4 with respect to the moving body on the side of the vehicle, the inter-vehicle distance L1 with the rear vehicle output from the inter-vehicle distance calculation unit 41, and the left and right position x5 with respect to the rear vehicle output from the vehicle recognition unit 42. An avoidance space for avoiding an obstacle ahead is calculated.

The avoidance space data output from the avoidance space calculation unit 40 and the above-described collision danger determination unit 3
7 is input to the avoidance trajectory calculation unit 43. The avoidance trajectory calculating unit 43 is connected to the memory 32 for storing the vehicle motion characteristic data. When the collision danger determination signal output from the collision danger determination unit 37 is a signal for determining that there is a danger of collision, the avoidance locus calculation unit 43 is input from the avoidance space calculation unit 40. Based on the avoidance space data, an avoidance trajectory for the vehicle to avoid an obstacle ahead is calculated. This avoidance trajectory is calculated by estimating a trajectory capable of minimizing the lateral G that occurs when avoiding, and as shown in FIG. 3, a trajectory that maximizes the distance d to the obstacle in front is calculated. Is done.

If the collision risk judgment signal output from the collision risk judgment unit 37 is a signal for judging that there is no collision risk, the avoidance trajectory calculation unit 43 eliminates the risk of collision. The amount of braking required for (1) is determined, and braking data is created.

The avoidance trajectory calculator 43 includes a braking controller 4
The braking device 45 is connected via the switch 4. Further, a front wheel steering unit 47 is connected to the avoidance trajectory calculation unit 43 via a front wheel steering control unit 46 that automatically steers the front wheels.

Further, the avoidance trajectory calculating section 43 is connected to a front and rear wheel turning ratio control section 48. The front / rear wheel turning ratio control unit 48 receives the front wheel steering angle signal θf output from the front wheel steering control unit 46, the turning radius R of the road calculated by the corner R calculation unit 36, and the vehicle speed sensor 14. Is input.

The avoidance trajectory calculator 43 calculates the vehicle speed V and the turning radius R.
A more necessary yaw rate number 1 is calculated. And
The maximum front and rear wheel steering ratio Kmax (Equation 2) according to the yaw rate is obtained. Further, according to the avoidance trajectory data calculated by the avoidance trajectory calculation unit 43, the steering ratio K of the front and rear wheels is calculated. The steering ratio K is represented by a function of w / d shown in FIG.

[0024]

(Equation 1)

[0025]

(Equation 2)

That is, K = f (w / d), and the relationship between the steering ratio K and w / d is as shown in FIG. As shown in FIG. 6, when w / d is small, the steering ratio is 4 w
The steering ratio Ko of s is set to Ko (however, Ko is a function of the vehicle speed V), and gradually increases to 1 as w / d increases. The turning ratio K is a ratio between the steering angles of the front wheels and the rear wheels, and is a value equal to or less than “1”. If the turning ratio K calculated by the front / rear wheel turning ratio control unit 48 is smaller than Kmax, the turning ratio K is determined as the final turning ratio.

The front / rear wheel turning ratio controller 48 calculates the rear wheel steering angle θr by multiplying the front wheel steering angle θr by the turning ratio K, and outputs it to the rear wheel steering actuator 22. The rear wheel steering actuator 22 controls the rear wheel steering angle so as to be the input rear wheel steering angle θr.

Next, the operation of the embodiment of the present invention configured as described above will be described. Vehicle trajectory calculation unit 31
Reads the vehicle speed and the steering wheel angle at predetermined sampling times, and calculates the trajectory of the vehicle in consideration of the driving characteristic data of the vehicle stored in the memory 32 each time.

The collision danger determining unit 37 is a vehicle trajectory calculating unit 3
Based on the vehicle trajectory data calculated in step 1, the risk of collision of the vehicle is determined in consideration of the following distance L, the relative speed Vr, and the lateral position x of the vehicle with respect to the obstacle. . Specifically, when it is predicted that the vehicle will collide with an obstacle ahead even after the maximum braking (for example, 0.4 g) is performed, a determination signal indicating a danger of collision is output. Then, a judgment signal having no risk of collision is output.

The moving body recognizing section 39 includes the side obstacle sensor 13.
The relative speeds Vr1 to Vr4 with respect to the moving object existing on the side of the vehicle are calculated in consideration of the installation location and the installation direction of the vehicle, and output to the avoidance space calculation unit 40.

The avoidance space calculation unit 40 is output from the inter-vehicle distance / relative speed calculation unit 33 and the inter-vehicle distance L and the relative speed Vr output from the vehicle recognition unit 34, the left / right position x, and the moving body recognition unit 39, respectively. Based on the relative velocities Vr1 to Vr4 with respect to the moving body on the side of the vehicle, the inter-vehicle distance L1 with the rear vehicle output from the inter-vehicle distance calculation unit 41, and the left and right position x5 with respect to the rear vehicle output from the vehicle recognition unit 42. An avoidance space for avoiding an obstacle ahead is calculated.

The avoidance trajectory calculation unit 43 includes the collision danger determination unit 3
If the collision risk determination signal output from 7 is a signal for determining that there is a collision risk, the vehicle is determined based on the avoidance space data input from the avoidance space calculation unit 40. Calculate traces that can avoid obstacles ahead. This trajectory is calculated by estimating a trajectory capable of minimizing the lateral G generated at the time of avoidance. As shown in FIG. 3, a trajectory in which the distance d to the obstacle in front is maximum is calculated. You.

If the collision danger determination signal output from the collision danger determination unit 37 is a signal for determining that there is no danger of collision, the avoidance trajectory calculation unit 43 eliminates the danger of a collision. The amount of braking required for (1) is determined, and braking data is created.

The avoidance trajectory calculator 43 calculates the vehicle speed V and the turning radius R
A more necessary yaw rate number 3 is calculated. And
The maximum front and rear wheel steering ratio Kmax (Equation 4) according to the yaw rate is obtained. Further, according to the avoidance trajectory data calculated by the avoidance trajectory calculation unit 43, the steering ratio K of the front and rear wheels is calculated. If the turning ratio K is smaller than Kmax, the turning ratio K is determined as the final turning ratio.

[0035]

(Equation 3)

[0036]

(Equation 4)

The front wheels are automatically steered by the front wheel steering controller 46. The front / rear wheel turning ratio control unit 48 calculates the rear wheel steering angle θr by multiplying the front wheel steering angle θr output from the front wheel steering control unit 46 by the turning ratio K, and outputs the result to the rear wheel steering actuator 22. I do. The rear wheel steering actuator 22 controls the rear wheel steering angle so as to be the input rear wheel steering angle θr. Although the above embodiment is an apparatus for automatically steering the front wheels, the present invention can be similarly applied to an apparatus for the driver to steer the front wheels.

As described above, the avoidance trajectory calculated by the avoidance trajectory calculation unit 43 is calculated by estimating a trajectory capable of minimizing the lateral G generated at the time of avoidance. Therefore, the yaw rate generated in the vehicle when avoiding an obstacle can be suppressed to a minimum necessary size. If the avoidance trajectory shown in FIG. 3 is d = d1, w = w1, the steering ratio K at this time is as shown in FIG.
It becomes K1. Since the steering ratio K is larger than the conventional steering ratio Ko, it is possible to set the avoidance ability to be larger than before.

Further, the required number of yaw rates 5 is calculated from the vehicle speed V and the turning radius R, and the maximum front and rear wheel steering ratio Kmax (Equation 6) according to the yaw rate is obtained. Since it is set within a range smaller than the maximum front and rear wheel steering ratio Kmax (Equation 7), divergence due to excessive turning in an emergency can be reduced. That is, the maximum evasion ability among the physically possible evasion abilities can be exhibited.

[0040]

(Equation 5)

[0041]

(Equation 6)

[0042]

(Equation 7)

[0043]

As described in detail above, according to the present invention, it is possible to maximize the evasion ability at the time of emergency evasion.
A wheel steering device can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a four-wheel steering device according to one embodiment of the present invention.

FIG. 2 is a perspective view showing a mounting location of sensors mounted on a vehicle body.

FIG. 3 is a diagram showing an avoidance locus of a vehicle in an emergency.

FIG. 4 is a block diagram showing a part of the detailed configuration of the controller in FIG. 1;

FIG. 5 is a block diagram showing a part of the detailed configuration of the controller in FIG. 1;

FIG. 6 is a diagram showing a steering ratio Kw / d characteristic.

[Description of Signs] 11: Forward obstacle sensor, 12: Rear obstacle sensor, 1
3 ... side obstacle sensor, 14 ... vehicle speed sensor, 15 ... handle angle sensor.

Claims (1)

(57) [Claims] 1. Vehicle trajectory calculating means for calculating a trajectory of a vehicle
When,A front obstacle sensor that detects the state of an obstacle ahead of the vehicle
When,  The trajectory of the vehicle calculated by the vehicle trajectory calculation means andBefore
Based on the obstacle state detected by the obstacle sensor
Collision danger to determine the danger of colliding with an obstacle ahead of the vehicle
Gender determining means;
Steps andThe state of the obstacle detected by the front obstacle sensor, Up
The lateral movement of the vehicle detected by the moving body state detection means
Moving body conditionWhenTo avoid obstacles ahead of the vehicle
Avoidance space calculating means for calculating an avoidance space for calculating the avoidance space calculated by the above avoidance space calculating means.
Considering vehicleCan avoid obstacles aheadCalculate the trajectory
Avoidance trajectory calculating means;
A front and rear wheel steering ratio calculating means for calculating a front and rear wheel steering ratio, and a ratio between a front wheel steering angle and a rear wheel steering angle is the rear wheel steering ratio.
And rear wheel steering means for steering the rear wheels.
Characteristic four-wheel steering system.