JP3567761B2 - Vehicle steering control method and vehicle obstacle avoidance device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for controlling the turning (steering) of a vehicle, and more particularly, to a method for avoiding an obstacle using the theory of friction circles of wheels. The present invention also relates to a device for avoiding an obstacle by turning control.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a vehicle control device that avoids an obstacle has been proposed, and an obstacle is recognized by a radar or a camera to avoid the obstacle. In the present invention, “avoidance” means avoiding an obstacle, and includes stopping the vehicle before reaching the obstacle (hereinafter the same). Conventionally, devices that avoid by steering or devices that avoid by braking have been individually proposed.
[0003]
For example, an automatic braking control device described in Japanese Patent Application Laid-Open No. H10-138894 proposes to control a braking force using a friction circle. As shown in FIG. 8, the friction circle is a circle having a radius of a maximum value of the wheel acting force that can be generated between the wheel and the road surface. This maximum acting force is determined by the vehicle weight and the like. The wheel acting force is a resultant force of the wheel longitudinal force (braking force) and the wheel lateral force.
[0004]
In the device disclosed in the above publication, the turning angle of the wheel is detected, and the wheel lateral force is obtained from the turning angle. Then, the longitudinal force on the friction circle corresponding to the lateral force is obtained using the friction circle, and the brake is controlled so as to obtain the longitudinal force. In short, the maximum braking force that can be generated under the current steering angle is generated.
[0005]
[Problems to be solved by the invention]
However, with the conventional method, the vehicle may not be able to stop before reaching the obstacle in some circumstances. In the situation illustrated in FIG. 9, it is assumed that the driver finds an obstacle (guardrail) in front of the vehicle, turns the steering wheel to a large extent, and moves the vehicle along a locus shown in the figure. In this case, since the steering angle is large, the wheel lateral force is also considerably large. Therefore, the maximum possible braking force determined from the friction circle is considerably small. Even if such a braking force is applied to the brake, the braking distance (the traveling distance until the vehicle stops) may be long, and the vehicle may not be able to sufficiently decelerate before reaching the obstacle.
[0006]
As a background that causes such a situation, it is cited that the steering of the wheels is mainly controlled by the driver. Conventionally, generally, a steering wheel and a wheel are mechanically connected, and the wheel does not change its direction independently of a driver's operation of the steering wheel. Therefore, if the steering wheel is set large, only a small braking force can be generated. However, if the conventional assumption, that is, the assumption that the steering is left to the driver, is removed and the steering control is performed on the vehicle side, the vehicle can be more appropriately stopped.
[0007]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a steering control method and a related device capable of appropriately controlling the direction of a wheel and appropriately avoiding an obstacle.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a relative positional relationship between a vehicle and an obstacle is required. Based on the detected relative positional relationship and the friction circle of the wheel, a combination of the wheel lateral force and the wheel braking force suitable for obstacle avoidance is obtained. Here, the combination of the lateral force and the braking force (wheel acting force) can be generated if it is included in the friction circle. Further, the stop position of the vehicle differs depending on the combination of the lateral force and the braking force. Therefore, a combination of a lateral force and a braking force within a friction circle is required so that the stop position is closer to the obstacle. Then, by turning the wheel according to the obtained wheel lateral force, an obstacle can be appropriately avoided.
[0009]
As an example, consider a situation in which the driver has fully covered the steering wheel but cannot avoid an obstacle as it is. Even in this situation, if the steering angle is reduced and the braking force is increased, the braking distance may be shortened and the vehicle may be stopped short of an obstacle. In such a case, appropriate steering control is performed by applying the present invention, and an obstacle is appropriately avoided.
[0010]
In the present invention, the adjustment of the braking force may be performed by the driver, or may be automatically performed on the vehicle side. In the latter case, the brake may be controlled so that the wheel braking force determined together with the lateral wheel force is generated, and the vehicle automatically controls steering and braking to avoid obstacles.
[0011]
According to the present invention, (1) the trajectory from the vehicle to the obstacle is obtained, and (2) the wheel braking force required to stop along the trajectory before traveling to the obstacle before reaching the obstacle is calculated. (3) The wheel lateral force required to travel along the trajectory is obtained, and (4) it is determined whether or not the resultant force of the calculated wheel braking force and wheel lateral force is included within the friction circle. Thereby, an appropriate combination of the wheel lateral force and the wheel braking force can be obtained.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention (hereinafter, referred to as embodiments) will be described with reference to the drawings.
[0013]
FIG. 1 is a block diagram showing the overall configuration. The obstacle avoiding device 1 includes a steering control device and a brake control device, and the control unit 10 includes a steering ECU 12 and a brake ECU 14. The turning ECU 12 controls the turning actuator 16 to change the direction of the steered wheels (steered wheels) 18. The brake ECU 14 controls the hydraulic brake actuator 20 to operate the brake 22.
[0014]
In the present embodiment, a by-wire type steering system is employed. The by-wire system is a system in which a steering wheel operated by a driver and wheels are not directly mechanically connected by a cable or the like. The handle sensor 24 detects an operation amount (rotation angle) of a steering wheel (not shown) and sends an electric signal indicating the operation amount to the steering ECU 12. The turning ECU 12 sends an electric signal to the turning actuator 16 to generate a turning angle according to the steering wheel operation amount.
[0015]
Similarly, the brake system employs a by-wire system. The brake sensor 26 detects a depression force of a brake pedal (not shown) and sends an electric signal indicating the depression force to the brake ECU 14. The brake ECU 14 sends an electric signal to the brake actuator 20 to generate a braking force according to the brake depression force.
[0016]
In addition, the obstacle radar 28 detects an obstacle in front of the vehicle and notifies the steered ECU 12. From the detection signal of the obstacle radar 28, the relative positional relationship between the vehicle and the obstacle can be known. The vehicle speed sensor 30 detects the traveling speed of the vehicle and outputs the detected traveling speed to the steering ECU 12. Another vehicle speed sensor for engine control or the like may be shared. The wheel turning angle sensor 32 detects the turning angle of the steered wheel 18 (the direction of the wheel with respect to the vehicle body) and outputs it to the turning ECU 12. Further, the brake braking pressure sensor 34 detects a braking pressure (oil pressure) generated by the brake actuator 20 and sends it to the steering ECU 12 and the brake ECU 14. The braking pressure is used as a parameter representing the current braking force.
[0017]
The turning ECU 12 obtains a target turning angle and a target braking force suitable for avoiding an obstacle based on the input information. Then, the steering actuator 16 is controlled so that the target steering angle is achieved. Further, the target braking force is sent to the brake ECU 14, and the brake ECU 14 controls the brake actuator 20 to achieve the target braking force. In addition, the turning ECU 12 displays the current turning state on the steering indicator 36 (described later).
[0018]
"Steering control of the present invention"
Next, the steering control of the present invention will be described with reference to FIGS. FIG. 2 shows a wheel acting force R acting on the wheel T and a steady friction circle C. The maximum value Rmax of the wheel acting force that can be generated is determined by the vehicle weight W and the friction coefficient μ. The wheel working force Rmax is set using an appropriate standard coefficient of friction. A circle having a radius of Rmax is a steady friction circle. Therefore, the acting force R (including the circumference) included in the friction circle C can be generated between the wheel and the road surface, and the acting force generated in total moves on the friction circle.
[0019]
Instead of the standard friction coefficient, the actual friction circle may be applied to the control of the present invention by using a detected value or an estimated value of the friction coefficient of the road surface of the traveling road. The detection and estimation of the friction coefficient may be performed by a known method. For example, the coefficient of friction can be estimated based on weather conditions, frozen conditions, pavement conditions, and the like.
[0020]
In FIG. 2, the direction F of the vehicle body and the direction Fw of the wheels form a steering angle α. The wheel acting force R can be decomposed into a longitudinal force X and a lateral force Y. The longitudinal force X is an acting force along the direction of the wheel. Since braking is considered in the present invention, the longitudinal force = braking force. The lateral force Y is a force in a direction perpendicular to the direction of the wheel. The lateral force Y is a function of the steering angle α, and the lateral force Y can be calculated from the steering angle α, the vehicle speed V, and the like using a known equation. As the calculation formula, for example, the formulas (3) to (5) of JP-A-10-138894 described above can be applied (shown in FIG. 10).
[0021]
Now, as an example, it is assumed that the traveling situation of FIG. 3 has occurred. There is a guardrail 102 as an obstacle in front of the vehicle. The driver who notices the approach of the guardrail 102 usually first tries to avoid the vehicle by steering. The steering wheel is largely turned, and the vehicle travels along a solid path 104. However, when the vehicle speed is high, it is difficult to avoid only by steering.
[0022]
Therefore, the driver applies the brake as the next measure for steering. However, when the steering wheel operation amount is large, the steering angle α and the lateral force Y are large. As is evident from FIG. 2, since the friction circle is limited, the maximum braking force Xmax is small when the lateral force Y is large. Therefore, the braking distance becomes long, and the vehicle 100 cannot stop before reaching the guardrail 102.
[0023]
As described above, if the steering operation of the driver is directly reflected on the steering angle (non-control), it may be difficult to avoid an obstacle. However, even in the situation of FIG. 3, if the steering is automatically controlled to suppress the lateral force Y and increase the braking force X, an obstacle may be able to be appropriately avoided.
[0024]
That is, the vehicle 100 follows different trajectories and stops at different positions depending on the combination of the lateral force Y and the braking force X. When the lateral force Y is reduced and the braking force X is increased, the radius of the trajectory is increased, but the braking distance is significantly reduced. The vehicle 100 travels along a locus 106 shown by a dotted line in the figure, and can stop before reaching the guardrail 102.
[0025]
FIG. 4 shows the above control on a friction circle. When the steering angle corresponding to the steering wheel rotation angle is generated without applying the control of the present invention, the lateral force becomes Y1 and the braking force becomes small as X1. However, when the steering control of the present invention is applied, the wheel acting force R moves on the friction circle, and instead of the lateral force decreasing to Y2, the braking force increases to X2, and the braking distance can be reduced. .
[0026]
As shown in the above example, according to the present invention, focusing on the fact that the stop position of the vehicle is different depending on the combination of the lateral force and the braking force, the lateral force and the braking force are set such that the stop position is closer to the obstacle. Is required. An obstacle can be appropriately avoided by the control according to the acting force.
[0027]
The reason why such avoidance control can be performed is that the conventional assumption that the driver turns the vehicle is removed and the direction of the wheels is appropriately controlled. This control can be easily realized by employing a by-wire type steering system.
[0028]
"Calculation of braking force X and lateral force Y"
Next, a specific example of a process for obtaining an appropriate combination of the lateral force and the braking force will be described with reference to FIG. The relative positional relationship between the vehicle 100 and the guardrail 102 is detected by a radar having appropriate directivity. For example, it is preferable to determine the shape of the guardrail 102 from the positions of the reflectors installed at equal intervals on the guardrail 102.
[0029]
A plurality of points Pi (i = 1 to n) are appropriately set on the guardrail 102. For example, an arrival point when traveling at the maximum steering angle is set to a point P1, an arrival point when traveling straight ahead is set to a point Pn, and a predetermined number of points Pi are set at equal intervals. The point Pi may be the position of the reflector. Then, a locus (OPi) (route) from the current position O of the vehicle to each point Pi is obtained. Here, an arc that passes through the point Pi and is in contact with the center line in the front-rear direction of the vehicle is determined.
[0030]
The deceleration ai that can be stopped before reaching the point Pi when traveling along each trajectory OPi can be calculated by the equation “ai = V ² / 2Li”. V is the vehicle speed, and Li is the length of the trajectory. Next, a braking force Xi required to generate the deceleration ai is calculated.
[0031]
On the other hand, once the shape of the trajectory OPi is determined, the wheel lateral force Yi required to travel along the trajectory OPi is determined. For example, the steering angle required to pass through the trajectory OPi may be obtained, and the steering angle may be converted into the lateral force Yi.
[0032]
If the resultant force of the braking force Xi and the lateral force Yi, that is, the wheel acting force Ri is generated, the vehicle can be stopped before reaching the guardrail 102. However, if the acting force Ri is not within the friction circle, such a force cannot be generated. Therefore, it is determined whether or not the acting force Ri is within the friction circle.
[0033]
Here, the lateral force Yi is applied to the friction circle, and the maximum braking force Ximax on the friction circle C corresponding to the lateral force Yi is obtained. Ximax is the square root of (Rmax ² -Yi ^2). If Xi ≦ Ximax, the braking force Xi and the lateral force Yi can be generated. On the other hand, if Xi> Ximax, such a force cannot be generated and is not adopted.
[0034]
The above processing is performed for each of the points P1 to Pn on the guardrail 102, and appropriate “point Pa, lateral force Ya, braking force Xa” is selected. The selected lateral force Ya and braking force Xa are set as target values, and steering control and brake control are performed to achieve the target.
[0035]
It should be noted that a plurality of pairs of the braking force X and the lateral force Y may satisfy the above-described conditions. In this case, one that is considered optimal is selected. For example, (1) a combination having the largest lateral force Y is adopted. Thereby, it is possible to follow the driver's intention to make the steering wheel larger as much as possible. Alternatively, (2) a combination that maximizes "Xmax-X" is selected. Thereby, the vehicle 100 can be stopped at a position as far away from the guardrail 102 as possible.
[0036]
When performing the above-described processing, the trajectory O-Pi, the braking force Xi, and the lateral force Yi may be calculated for all the points Pi (i = 1 to n), and an appropriate combination may be selected from n combinations. Alternatively, the arithmetic processing may be performed for each trajectory in order from i = 1, or from n = 1, or in another order, and the process may be terminated when an appropriate acting force is found.
[0037]
Furthermore, in order to allow for safety, it is preferable to obtain an acting force that can be stopped slightly before the guardrail 102. For this purpose, for example, it is preferable to subtract a predetermined value from the trajectory length Li.
[0038]
"Use of tables and maps"
A table (may be a map or the like) based on the above-described processing method is prepared, and an appropriate braking force X and a lateral force Y may be obtained using the table. The table is stored in the memory of the steering ECU 12.
[0039]
A suitable table is, for example, for determining the braking force X and the lateral force Y from “trajectory (radius and length)” and “vehicle speed”. The above arithmetic processing is performed from these elements in advance, and the braking force X and the lateral force Y as the calculation results are written in a table. The combination of the trajectory shape and the vehicle speed that gives the braking force X and the lateral force Y running off the friction circle is not set on the table.
[0040]
When this table is used, an obstacle is recognized, a trajectory is determined, and the trajectory and the vehicle speed are applied to the table. The trajectory is sequentially changed, and the braking force X and the lateral force Y are read from the table.
[0041]
"Overall processing of obstacle avoidance"
Next, the operation of the present embodiment will be described with reference to FIG. The turning ECU 12 reads the vehicle speed V, the braking force X, and the turning angle α (S10). These are detected by the respective sensors and input to the steering ECU 12. The braking force X is obtained by converting a braking pressure detection value. Further, the turning ECU 12 recognizes an obstacle ahead of the vehicle based on input information from the obstacle radar 28 (S12). Then, it is determined whether or not an obstacle can be avoided by the current braking force X and the turning angle α (S14).
[0042]
The calculation using the trajectory described above can be applied to the determination in S14. The traveling locus when traveling at the current steering angle α is calculated. On the other hand, the braking distance is obtained from the vehicle speed V and the braking force X. If the vehicle can be stopped before reaching the obstacle when traveling along the traveling locus, the determination in S14 is YES. S14 is also YES when an obstacle can be avoided when traveling along the traveling locus. If the determination in S14 is YES (can be avoided), the process returns to S10.
[0043]
If it is impossible to avoid in S14, it is determined whether the turning angle α is the maximum value αmax and the braking force X is the maximum value Xmax (S16, S18). If α = αmax and X = Xmax, the process proceeds to S20 to perform the control of the present invention, but otherwise returns to S10.
[0044]
αmax is the turning angle when the driver turns the steering wheel to the maximum. Xmax is the braking force when the driver depresses the brake pedal to the maximum. The above determination may be made based on the steering wheel operation amount and the brake depression force instead of the steering angle α and the braking force X.
[0045]
The determination steps of S16 and S18 are provided to determine whether or not the obstacle avoidance control is really necessary. Obstacle avoidance is essentially an emergency control, and if there is room for the driver to handle by his / her own operation, do not perform avoidance control and avoid the obstacle in accordance with the driver's will (operation) Is considered desirable. However, if the driver has fully closed the steering wheel and fully depressed the brake pedal, it can be said that the driver cannot avoid obstacles by himself. Therefore, the control of the present invention is applied to such a case.
[0046]
That is, in S20, an appropriate combination of the braking force Xa and the lateral force Ya (wheel acting force Ra) that can stop the vehicle before reaching the obstacle is obtained by the method described with reference to FIG. The target turning angle αa required to obtain the lateral force Ya is calculated. The braking force Xa becomes the target value of the brake control as it is.
[0047]
Then, the turning control is performed so that the actual turning angle α = the target turning angle αa (S22). The turning ECU 12 controls the turning actuator 16 to adjust the direction of the steered wheels 18 to achieve the target turning angle αa.
[0048]
Further, the brake is controlled such that the actual braking force X becomes the target braking force Xa (S24). The target value Xa is sent to the brake ECU 14. The brake ECU 14 controls the brake actuator 20 to adjust the brake operation state to achieve the target braking force Xa.
[0049]
By such steering control and brake control, the vehicle travels on the trajectory assumed in FIG. 5, and the vehicle stops before reaching the obstacle.
[0050]
In addition, the turning ECU 12 displays the neutral position (neutral point) of the steering wheel on the steering indicator 36. The neutral position is a position in the rotation direction of the steering wheel when the steering angle α = 0. Referring to FIG. 7, a circular electric display unit (LED) 202 is provided at the center of the handle 200. Then, the display unit 202 lights up a portion corresponding to the current neutral position. In FIG. 7, the handle is in the neutral state, and the indicator is also illuminated at the center. During normal running, the neutral position is fixed and does not change even when the steering wheel is rotated.
[0051]
However, when the avoidance control according to the present invention is performed, a steering angle different from a value corresponding to a normal steering wheel rotation angle is generated. As a result, the neutral position also deviates from the original position. An indicator is used to display the shifted neutral position. The driver can recognize the current neutral position and operate the steering wheel appropriately. It is preferable to return the neutral position to the original position at an appropriate timing after the end of the avoidance control.
[0052]
Next, a modified example of the present embodiment will be described.
[0053]
(1) In the present embodiment, both the turning control and the brake control are performed as the avoidance control. On the other hand, the steering control may be performed on the vehicle side, and the brake control may be left to the driver. That is, the wheels are oriented in an appropriate direction on the vehicle side, and the driver can freely adjust the deceleration.
[0054]
In this modification, the turning ECU 12 does not have to send the target braking force to the brake ECU 14, and in this case, the brake system itself is not an essential component of the present invention. However, preferably, only the maximum value of the braking force should be managed by the brake ECU 14 so that the wheel acting force does not protrude from the friction circle.
[0055]
(2) The steering ECU 12 and the brake ECU 14 may be integrated. Further, the processing of each step in FIG. 6 is performed exclusively by the turning ECU 12 in the above embodiment. However, some or all of these processes may be performed by the brake ECU 14. For example, the processing up to the calculation of the target braking force Xa and the target turning angle αa may be performed by the brake ECU 14.
[0056]
(3) The obstacle detection means is not limited to radar, and may be of any type. For example, the front may be photographed by a camera, and an obstacle may be detected by image processing. Further, the obstacle may transmit a signal indicating its own position, and the vehicle may receive the signal. Further, the obstacle is not limited to a fixed object, but may be a moving object such as a vehicle.
[0057]
(4) The handle device is typically a steering wheel, but may be any other type. A handle device other than a rotary type, for example, a control stick, may be applied.
[0058]
【The invention's effect】
As described above, according to the present invention, paying attention to the fact that the stop position of the vehicle changes depending on the combination of the wheel lateral force and the wheel braking force, by performing the steering control or the steering and brake control, Obstacles can be properly avoided.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an overall configuration of an embodiment of the present invention.
FIG. 2 is a diagram showing a steady friction circle of a wheel.
FIG. 3 is a diagram illustrating obstacle avoidance control according to the present invention.
FIG. 4 is a diagram illustrating the control of FIG. 3 on a friction circle.
FIG. 5 is a diagram showing a process for obtaining an appropriate combination of a wheel lateral force and a wheel braking force used in the control of FIG. 3;
FIG. 6 is a flowchart showing an operation of the apparatus of FIG. 1;
FIG. 7 is a diagram showing a steering indicator.
FIG. 8 is a diagram showing a friction circle of a wheel.
FIG. 9 is a diagram showing a behavior of the vehicle when an obstacle appears.
FIG. 10 is a diagram illustrating an example of a process of calculating a wheel lateral force from a wheel steering angle.
[Explanation of symbols]
1 Obstacle Avoidance Device, 10 Control Unit, 12 Steering ECU, 14 Brake ECU, 16 Steering Actuator, 18 Steering Wheel, 20 Brake Actuator, 22 Brake, 24 Handle Sensor, 26 Brake Sensor, 28 Obstacle Radar, 30 Vehicle speed sensor, 32 wheel steering angle sensor, 34 brake braking pressure sensor, 36 steering indicator.

Claims (6)

An obstacle detection step of obtaining a relative positional relationship between the vehicle and the obstacle,
Wheel working force calculation that calculates the combination of wheel lateral force and wheel braking force that can stop the vehicle before it reaches an obstacle based on a friction circle with the radius of the maximum value of the wheel working force that can be generated between the wheel and the road surface Process and
A steering step of adjusting the direction of the wheel according to the wheel lateral force,
Only including,
The wheel acting force calculating step,
A trajectory calculating step of obtaining a plurality of trajectories having different steering angles of the wheels from the vehicle to the obstacle,
A braking force calculation step of calculating a wheel braking force required to stop before traveling along each of the trajectories and reaching an obstacle,
A lateral force calculation step of determining a wheel lateral force required to travel along each of the trajectories,
A determining step of determining whether the resultant force of the calculated wheel braking force and wheel lateral force is included within a friction circle,
Steering control method for the wheel characterized in that it comprises a. Obstacle detection means for determining a relative positional relationship between the vehicle and the obstacle,
Wheel working force calculation that calculates the combination of wheel lateral force and wheel braking force that can stop the vehicle before it reaches an obstacle based on a friction circle with the radius of the maximum value of the wheel working force that can be generated between the wheel and the road surface Means,
Turning means for adjusting the direction of the wheel according to the wheel lateral force,
Including
The wheel acting force calculating means,
Trajectory calculation means for obtaining a plurality of trajectories from the vehicle to the obstacle,
Braking force calculation means for calculating a wheel braking force required to stop before traveling along each of the trajectories and reaching an obstacle,
Lateral force calculating means for determining wheel lateral force required to travel along each of the trajectories,
Determining means for determining whether the calculated resultant force of the wheel braking force and the wheel lateral force is included within a friction circle,
An obstacle avoidance device for a vehicle, comprising: The obstacle avoidance device for a vehicle according to claim 2,
An obstacle avoidance device for a vehicle, comprising: a braking control unit that automatically generates a wheel braking force obtained by the wheel acting force calculation unit . The obstacle avoidance device for a vehicle according to claim 2,
The trajectory calculation means,
An obstacle avoidance device for a vehicle , wherein a trajectory from a vehicle to an obstacle is set between a trajectory when traveling at a current steering angle and a trajectory when traveling straight . The obstacle avoidance device for a vehicle according to claim 2,
  From the combination of the braking force and the lateral force determined by the wheel acting force calculating means,
An obstacle avoidance device for a vehicle, wherein a combination that maximizes a lateral force is selected, and steering control is performed based on the combination of the values. The obstacle avoidance device for a vehicle according to claim 2,
  From the combination of the braking force and the lateral force determined by the wheel acting force calculating means,
An obstacle avoidance device for a vehicle, wherein a combination that maximizes a braking force is selected, and steering control is performed based on the combination of the values.

Images