Patent Application
20160152237
The invention relates to a vehicle control system configured to recognize a travel environment in which a vehicle travels, and provide drive assist.
Patent Document 1 discloses the technology of detecting a guardrail by using a camera to avoid contact with the guardrail and then generating yaw moment in an ego vehicle when the vehicle and the guardrail come into predetermined positional relationship.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2012-84038
It has been difficult for the conventional technology, however, to ensure the stability of vehicle behavior in spite of yaw moment when the ego vehicle travels off a travel path without a guardrail.
It is an object of the invention to provide a vehicle control system which is capable of ensuring the stability when the vehicle runs off course.
To accomplish the above object, according to the invention, when yaw moment control is carried out to reduce a formed angle between a travel-path defining line of a travel path, which is recognized from information about an area located in a traveling direction of an ego vehicle, and a traveling-direction virtual line extending from the ego vehicle in the traveling direction and if it is judged that the ego vehicle has departed from the travel-path defining line, the yaw moment control is suspended.
A vehicle of the Embodiment 1 includes a travel environment recognition system 1, an electrically-assisted power steering 2, a hydraulic brake unit 3, a brake booster 4, a steering wheel 5, a front left wheel 6, a front right wheel 7, a rear left wheel 8, a rear right wheel 9, an electronic control unit 10, and a vehicle motion detector 11.
The travel environment recognition system 1 takes an image of a view ahead of an ego vehicle by using stereo cameras 310a and 310b placed in a substantially middle position in the vicinity of a rearview mirror located in an upper front portion in an interior of the ego vehicle, and creates travel environment data.
The electrically-assisted power steering 2 calculates an assist torque on the basis of a command according to a driver steering torque and a steering angle or steering angle speed of the steering wheel 5, assists the steering torque by means of an electric motor, and turns the front right and left wheels 6 and 7. The electrically-assisted power steering 2 further executes steering-torque assist control which applies yaw moment to a vehicle through after-mentioned vehicle attitude stabilizing control. It is possible to employ a steer-by-wire system capable of turning the front right and left wheels 6 and 7 independently of a driver's steering wheel operation. There is no particular limitation.
The hydraulic brake unit 3 independently controls wheel-cylinder pressure which applies a braking torque to the four wheels according to a driver's brake operation force or a vehicle condition. The hydraulic brake unit 3 may be a VDC unit which carries out vehicle behavior control, such as vehicle dynamics control and vehicle stability control, which are existing controls. Alternatively, the hydraulic brake unit 3 may be a unique hydraulic unit. There is no particular limitation.
The brake booster 4 is a booster which boosts a driver's brake pedal force with respect to a piston in a master cylinder, which is activated by the brake pedal, and thus electrically assists a stroke force of the piston. Master-cylinder pressure is generated by the force boosted by the brake booster 4, and outputted to the hydraulic brake unit 3. The brake booster 4 does not have to be configured to electrically assist the force, and may be a negative-pressure booster using negative pressure of an engine. There is no particular limitation.
The vehicle motion detector 11 detects the speed of vehicle (vehicle speed), longitudinal acceleration, lateral acceleration, yaw rate, steering angle, steering torque, and the like.
The electronic control unit 10 controls the travel environment recognition system 1, the electrically-assisted power steering 2, and the hydraulic brake unit 3 in accordance with detection values of the vehicle motion detector 11. When a travel-path defining line which defines a travel path on a road recognized from an image taken by the travel environment recognition system 1 and a traveling direction of the ego vehicle (traveling-direction virtual line extending from the ego vehicle in the traveling direction, for example) intersect with each other, the electronic control unit 10 activates the electrically-assisted power steering 2 and/or the hydraulic brake unit 3, and applies the yaw moment and/or deceleration to the vehicle, to thereby carry out the vehicle attitude stabilizing control so that the traveling direction of the vehicle and a traffic lane are parallel to each other. The “travel-path defining line” here means a center line, a traffic lane line if white lines are recognized, a line connecting positions where guardrails are installed if guardrails are recognized, a line or the like indicating a boundary between a flat area and a slope area of a road embankment (hereinafter, also simply referred to as a “road edge”). The vehicle attitude stabilizing control will be later described in details.
If driven by the driver's brake operation force, the hydraulic brake unit 3 applies equal braking forces to the front right and left wheels 6 and 7 and to the rear right and left wheels 8 and 9. According to the vehicle attitude stabilizing control, right and left braking forces are generated while the braking forces are differentiated between the front right and left wheels 6 and 7 and between the rear right and left wheels 8 and 9, to thereby apply the yaw moment to the vehicle.
(Vehicle Attitude Stabilizing Control System)
The departure-tendency calculating unit 20 includes a travel-path defining line recognition unit (road-edge line recognition unit) 22, a vehicle's current position recognition unit 23, an intersect time calculation unit 24, a virtual travel-path defining line calculation unit (virtual road-edge line recognition unit) 25, and an activation necessity judgment unit 26.
The travel-path defining line recognition unit 22 recognizes boundary lines (including a center line) of road edges existing on right and left sides of a traffic lane on which the ego vehicle travels, which include white lines, guardrails and curbs, from an image of a view ahead of the ego vehicle, which is taken by the travel environment recognition system 1.
The vehicle's current position recognition unit 23 recognizes a current position of a vehicle, which is a forward end of the vehicle as viewed in a traveling direction of the ego vehicle, and also recognizes the traveling-direction virtual line from the vehicle's current position in the traveling direction of the ego vehicle. The current position of the vehicle may be a substantially central position of the ego vehicle, instead of the forward end of the vehicle as viewed in the traveling direction. If the ego-vehicle traveling direction (traveling-direction virtual line) intersects with a travel-path defining line on the right, a right forward position of the ego vehicle may be the current position of the vehicle. If the ego-vehicle traveling direction intersects with a travel-path defining line on the left, a left forward position of the ego vehicle may be the current position of the vehicle. The current position of the vehicle may also be set at a position located with leeway as compared to the position of the actual end of the vehicle. There is no particular limitation.
The intersect time calculation unit 24 computes an intersect time, namely, a time period in which the ego vehicle travels at current speed from the vehicle's current position to an intersection of the traveling-direction virtual line and the travel-path defining line.
The virtual travel-path defining line calculation unit 25 calculates the virtual travel-path defining line which is in the direction of tangent to the travel-path defining line at the intersection of the travel-path defining line and the traveling-direction virtual line. If there are a plurality of intersections of the travel-path defining line and the traveling-direction virtual line in the traveling direction of the ego vehicle, the virtual travel-path defining line calculation unit 25 calculates the virtual travel-path defining line which is in the direction of tangent at an intersection point closest to the ego vehicle.
The activation necessity judgment unit 26 makes a judgment on the basis of the intersect time as to whether the activation of the vehicle attitude stabilizing control is necessary, that is, whether control intervention by the vehicle attitude stabilizing control should be carried out. More specifically, a judgment is made as to whether the intersect time is equal to or longer than predetermined time. If the intersect time is equal to or longer than the predetermined time, it is judged that safety is secured, that there is no need for control intervention, and that the vehicle attitude stabilizing control is unnecessary. To the contrary, if the intersect time is shorter than the predetermined time, it is judged that the vehicle attitude stabilizing control is necessary.
If it is judged by the activation necessity judgment unit 26 that the vehicle attitude stabilizing control is necessary, the vehicle attitude stabilizing control unit 21 conducts the vehicle attitude stabilizing control. If judged unnecessary, the vehicle attitude stabilizing control is not conducted.
(Recognition of the Travel-Path Defining Line)
The recognition of the travel-path defining line will be explained in details.
The travel environment recognition system 1 is configured to obtain distance to an object captured in an image on the basis a triangulation principle using difference in vision (hereinafter, referred to as “disparity”) which occurs when an image is taken by the plurality of cameras 310a and 310b. For example, a relational expression below is true, where Z denotes distance to the object; B denotes distance between the cameras; f denotes a focal length of the cameras; and δ is disparity.
Z=(B×f)/δ
The travel environment recognition system 1 includes a RAM 320 which stores images taken, a CPU 330 which executes computational processing, a data ROM 340 which stores data, and a program ROM 350 in which a recognition processing program is stored. The stereo camera 310 is fixed to a rearview mirror portion in a vehicle interior and configured to take the image of the view ahead of the ego vehicle at a predetermined depression angle at the fixed position. The image of the view ahead of the ego vehicle, which is taken by the stereo camera 310 (hereinafter, referred to as an “image taken”) is scanned into the RAM 320. The CPU 330 executes the recognition processing program stored in the program ROM 350 with respect to the image taken which is scanned into the RAM 320, to thereby detect a traffic lane and a three dimensional object ahead of the ego vehicle, and estimate a road configuration. A result of the estimation by the CPU 330 (computation result) is outputted to the data ROM 340 and/or ECU 10.
Step 201 executes processing of inputting images taken by the camera 310a situated on the left. Data of the images taken by the camera 310a are inputted into the RAM 320.
Step 202 executes processing of inputting images taken by the camera 310b situated on the right. Data of the images taken by the camera 310b are inputted into the RAM 320.
In Step 203, the CPU 330 executes processing of calculating corresponding points captured in the images.
In Step 204, the CPU 330 executes processing of calculating distance to the calculated corresponding points. The distance calculation processing is carried out on the basis of the relational expression, Z=(B×f)/δ. Step 205 executes processing of outputting distance information.
In Step 206, the CPU 330 makes a judgment as to presence of an image input signal. If there is the image input signal, the routine returns to Step 201 and repeats the present flow. If there is no image input signal, the routine terminates the computation processing and enters a wait state.
(Recognition Processing on a Road with a Steep Slope)
The following description explains image processing in a case where outside zones located outside a road (such as both sides of the road on which the ego vehicle travels) are lower than a road surface.
(Improvement of Accuracy in Image Processing)
If the road and the outside zones are visually completely homogenous, it is difficult to extract a certain place in the same zone in images taken by the two cameras.
Since there are many visually characteristic points on the road, the outside areas, and the boundaries therebetween, it is possible to make a comparison of these zones with one another within the images taken by the cameras 310a and 310b, calculate a direction and distance from the cameras 310a and 310b, and find a position of each characteristic point. This makes it possible to understand that an aggregate of the characteristic points on the road lies in substantially the same plane and that the characteristic points on the areas lower than the road are located on the outside zones.
(Overlay Processing)
Concerning a road surface configuration, a characteristic point on the screen, such as not only a road marking but a small crack and a tire mark on the road, is extracted from the images of the view ahead of the ego vehicle, which are taken by the stereo camera 310. On the basis of a position gap of the images taken by the two cameras on the screen, distance to the point is measured. On the other hand, characteristic points do not always evenly exist on the entire road surface. Even if they do exist, it is unsure whether the characteristic points can be detected all the time. Also in the zones lower than the road surface, the characteristic points are not necessarily detectable in every place of the zones. It is then required to further improve accuracy. To that end, the obtained distance data are accumulated in the data ROM 340 and overlaid on data obtained from the image taken with a subsequent or later timing.
If the images taken have different distance data with respect to a position recognized as the same place, priority may be given to newer data. The use of the newer data improves accuracy in recognition. An average of a plurality of data may also be used. This eliminates an effect of disturbance included in the data and the like, and stabilizes the recognition. It is also possible to extract data which does not much vary from other proximate data. This enables computation based on stable data and improvement in recognition accuracy. There are various methods of processing as described above. It is possible to combine the methods or employ any one of the methods.
(Road Edge Recognition Processing)
Referring to
(Road Edge Recognition Processing on a Road with a Moderate Slope)
(Improvement of Accuracy in Recognition of the Road Edge)
If the road and the outside area are connected to each other with a moderate inclination intervening therebetween, the inclined portion can be imaged by the stereo camera 310 to obtain the distance information thereof. This makes it possible to detect that the inclined portion is a slope area that is not suitable for a vehicle to pass along, and also consider that a boundary between the inclined area and the road area is a road boundary (namely, a road edge).
Even if the zone lower than the road is considerably low and therefore impossible to be detected, for example, as in a case where the road is formed along a precipitous cliff or where contrast between a road and a zone on the side of the road is weak, it is still possible to recognize that the lower zone is outside the road.
Although the detected road edge is expected to be the actual edge of the road, there actually is a gap due to a detection error. Because a road edge has a weak base structure, it is sometimes inappropriate to drive along the road edge. An effective way to cope with such possibilities is to output as a road edge a position located further on the inner side of the road than the detected road edge, as necessary. Contrary to the foregoing case, when the vehicle attitude stabilizing control system is used in combination as in the Embodiment 1, it is effective to output as a road edge a position located further on the outer side of the road than the road edge, as necessary, from the standpoint of prevention of excessive control or warning.
(Handling During Virtual-Image Photographing)
The following is a case where the presence of a zone lower than a road is extracted, and the zone is judged to be located outside the road. When there is a puddle of water in the road, and a virtual image reflected on the puddle is detected, the virtual image is seemingly located lower than the road surface, so that the puddle zone is likely to be incorrectly recognized as a zone lower than the road surface. The virtual image reflected on the puddle has characteristics different from those of a real image, and is therefore excluded in distinction from zones which are actually lower than the road surface. To be more specific, the characteristics are as listed below.
a) A virtual image is created by a distant object being reflected. Therefore, there is a road surface zone, which looks closer than apparent distance of the virtual image, at a point farther than a zone in which the virtual image exists on the screen.
b) Because a water surface is not completely flat, the virtual image is sometimes significantly distorted, which generates variation in distance of the puddle zone.
c) If the water surface is unstable, the apparent position of the virtual image varies with time
d) It looks as if there is an object in a symmetrical position to an object on the road, across the road surface (water surface).
e) If the virtual image is of a traveling vehicle, the image moves despite that it is located in the zone lower than the road surface.
The virtual image has the foregoing characteristics which are highly unlikely to be seen with real images. Detection of the foregoing characteristics makes it possible to determine that the image is not a real image but a virtual one.
[Vehicle Attitude Stabilizing Control]
In Step S1, the vehicle attitude stabilizing control unit 21 reads in detection values including vehicle speed, longitudinal acceleration, lateral acceleration, yaw rate, steering angle, and steering torque, received from the vehicle motion detector 11.
In Step S2, the travel-path defining line recognition unit 22 recognizes a position of the travel-path defining line from the image of the view ahead of the ego vehicle, which is received from the travel environment recognition system 1.
In Step S3, the vehicle's current position recognition unit 23 recognizes the vehicle's current position which is the forward end of the vehicle as viewed in the traveling direction of the ego vehicle. The vehicle's current position recognition unit 23 also obtains a traveling-direction virtual line extending from the ego vehicle in the traveling direction.
In Step S4, the intersect time calculation unit 24 computes an intersect time, namely, a time period in which the ego vehicle travels at current speed from the vehicle's current position to an intersection of the traveling-direction virtual line and the travel-path defining line. The virtual travel-path defining line calculation unit 25 calculates a virtual travel-path defining line. The virtual travel-path defining line is a tangent of the travel-path defining line at a point close to a vehicle's estimated position. The vehicle's estimated position is, for example, an intersection of the traveling-direction virtual line and the travel-path defining line.
In Step S5, the activation necessity judgment unit 26 makes a judgment as to whether the intersect time is shorter than a predetermined time. If the intersect time is shorter than the predetermined time, the routine advances to Step S6. If the intersect time is equal to or longer than the predetermined time, the routine ends. This is because a feeling of strangeness is given to the driver if a control amount is provided before the driver actually drives along the travel-path defining line ahead of the vehicle when the intersect time is longer than the predetermined time.
In Step S6, the vehicle attitude stabilizing control unit 21 activates the electrically-assisted power steering 2 and/or the hydraulic brake unit 3 according to a yaw moment control amount, applies yaw moment and/or deceleration to the vehicle, and executes the vehicle attitude stabilizing control. The vehicle attitude stabilizing control unit 21 uses one or more of the detection values including the vehicle speed, longitudinal acceleration, lateral acceleration, yaw rate, steering angle, and steering torque, which are read in at Step S1, to execute the vehicle attitude stabilizing control.
(Details of the Vehicle Attitude Stabilizing Control)
Details of the vehicle attitude stabilizing control processing will be explained below.
As illustrated in
It is therefore desired to impart a yaw moment control amount for making stable (stabilizing) the vehicle attitude upon consideration of the foregoing travel motions. Relationship between the yaw rate (dφ/dt) and vehicle speed V is expressed as follows:
(dφ/dt)=V/r
where r denotes a turning radius. Therefore, the following is true:
1/r=(dφ/dt)/V
where (1/r) is curvature. The curvature is a value indicative of a turning state of the vehicle, regardless of vehicle speed, and can be therefore handled in the same manner as the formed angle θ.
The evaluation function Ho(t) at a time t, which is obtained in light of the foregoing matters, is set as follows:
Ho(t)=A{(d/dt)/V}(t)−Bθ(t)
where A and B are constants.
The evaluation function Ho(t) represents the yaw moment control amount which should be imparted according to difference between the turning condition [A{(dφ/dt)/V}(t)] of the ego vehicle and the condition of the actual travel-path defining line. If the evaluation function Ho(t) indicates a large positive value while the vehicle is turning right, it is necessary to apply a left yaw moment. It is then required to apply a braking force to the left wheel or execute steering torque control which facilitates a left turn. If the evaluation function Ho(t) indicates a negative value with a large absolute value while the vehicle is turning left, it is necessary to apply a right yaw moment. It is therefore required to apply a braking force to the right wheel or execute steering torque control which facilitates a right turn.
Using the evaluation function Ho(t) eliminates the feeling of strangeness because the value of the evaluation function Ho(t) is small, and the yaw moment control amount to be imparted is also small when the driver drives along the travel-path defining line. If the driver drives toward the travel-path defining line, the value of the evaluation function Ho(t) is large, and the yaw moment control amount to be imparted is also large. This firmly secures the stability of the vehicle attitude.
As a comparative example to be compared with the invention according to the Embodiment 1, the following description explains a technology of calculating a target yaw rate by dividing the formed angle between a travel locus along the recognized travel-path defining line and the traveling-direction virtual line by an arrival time which is time that elapses before arrival to the travel-path defining line. As in the comparative example, if a value resulted from the division by the arrival time is used as the yaw moment control amount, the yaw rate is gradually corrected in the process where the vehicle approaches the travel-path defining line. This causes the problem that it takes time until a travel motion along the travel-path defining line is achieved.
According to the Embodiment 1, the yaw moment control amount is imparted according to the evaluation function Ho(t) based on difference between the curvature (i/r) indicative of a current turning state of the vehicle and the formed angle θ. For that reason, it is output such a control amount that the vehicle immediately becomes parallel to the travel-path defining line before the vehicle actually reaches the travel-path defining line, regardless of distance to the travel-path defining line (regardless of the intersect time). This enables highly safe control. Furthermore, since the control amount is computed using the relationship between the curvature and the formed angle θ, when control is not required as in a situation where the vehicle travels along the travel-path defining line, the vehicle attitude stabilizing control does not intervene even if the formed angle θ is created, so that the driver is not given the feeling of strangeness.
Step S101 computes the formed angle θ between the traveling direction of the ego vehicle and the travel-path defining line. More specifically, Step S101 obtains the formed angle between the traveling-direction virtual line and the virtual travel-path defining line, which are calculated in Steps S3 and S4 of
Step S102 computes the yaw rate (dφ/dt) of the ego vehicle. The yaw rate may be a yaw rate sensor value detected by the vehicle motion detector 11. The yaw rate may be computed from vehicle speed or steering angle according to a vehicle motion model. There is no particular limitation.
Step S103 computes the evaluation function Ho(t) from the formed angle θ, the yaw rate (dφ/dt), and the vehicle speed V.
Step S104 makes a judgment as to whether the evaluation function Ho(t) is positive. If the evaluation function Ho(t) is positive, the routine proceeds to Step S105. If the evaluation function Ho(t) is zero or smaller, the routine advances to Step S108.
Step S105 makes a judgment as to whether the evaluation function Ho(t) is larger than a predetermined value δ indicative of a dead band which is set in advance, and if the evaluation function Ho(t) is larger, the routine proceeds to Step S106. If the evaluation function Ho(t) is smaller than the predetermined value δ, the routine advances to Step S107.
Step S106 sets the control amount H(t) at a value obtained by subtracting the predetermined value δ from the evaluation function Ho(t).
Step S107 sets the control amount H(t) at zero.
Step S108 makes a judgment as to whether a value obtained by multiplying the evaluation function Ho(t) by minus (the evaluation function Ho(t) is a negative value and turns into a positive value if being multiplied by minus) is larger than the predetermined value δ. If the value is larger, the routine moves to Step S109. If the value is smaller than the predetermined value δ, the routine proceeds to Step S110.
Step 3109 sets the control amount H(t) at a value obtained by adding the predetermined value δ to the evaluation function Ho(t).
Step S110 sets the control amount H(t) at zero.
Step S110A makes a judgment as to whether the vehicle speed is equal to or higher than predetermined vehicle speed Vo. If the vehicle speed is equal to or higher than the predetermined vehicle speed Vo, it is judged that the yaw moment control using a brake braking torque is effective. The routine then advances to Step S111. If the vehicle speed V is lower than the predetermined vehicle speed Vo, it is judged that the yaw moment control by the steering rather than the brake is effective. The routine then moves to Step S121.
Step S111 makes a judgment as to whether the control amount H(t) is equal to or larger than zero. If the control amount H(t) is equal to or larger than zero, the routine proceeds to Step S112. If the control amount H(t) is negative, the routine proceeds to Step S113.
In Step S112, it can be judged that a right turn needs to be suppressed. A right-wheel base control amount TR is thus set at zero, and a left-wheel base control amount TL at H(t).
In Step S113, it can be judged that a left turn needs to be suppressed. The right-wheel base control amount is set at H(t), and the left-wheel base control amount TL at zero.
Step S114 calculates the braking torque with respect to each wheel according to the following relational expressions.
Front-right wheel braking torque TFR=TR×α
Rear-right wheel braking torque TRR=TR−TFR
Front-left wheel braking torque TFL=TL×α
Rear-left wheel braking torque TRL=TL−TFL
where α is a constant and a value that is set according to brake force distribution to the front and rear wheels.
Step S115 calculates a wheel-cylinder hydraulic pressure of each wheel according to the following relational expressions.
Front-right wheel cylinder hydraulic pressure PFR=K×TFR
Front-left wheel cylinder hydraulic pressure PFL=K×TFL
Rear-right wheel cylinder hydraulic pressure PRR=L×TRR
Rear-left wheel cylinder hydraulic pressure PRL=L×TRL
where K and L are constants and conversion constants for converting torque into hydraulic pressure.
Step S121 makes a judgment as to whether the vehicle is in a regular travel condition. If it is judged that the vehicle is in the regular traveling condition, the routine proceeds to Step S122. In cases other than the foregoing state (post-collision state, spinning state, a state where the vehicle departs from the road surface), the present control flow is terminated.
Step S122 makes a judgment as to whether a hand is on the steering wheel. If it is judged that a hand is on the steering wheel, the routine advances to Step S125, If it is judged that no hand is on the steering wheel, the routine moves to Step S123. Whether a hand is on the steering wheel may be checked, for example, by analyzing inertia of the steering wheel on the basis of resonance frequency components of a torque sensor or by providing a touch sensor or the like to the steering wheel to judge if a hand is on the wheel.
Step S123 makes a judgment as to whether a no-hands-on-wheel time exceeds predetermined time. If the no-hands-on-wheel time exceeds the predetermined time, the routine moves to Step S128 where automatic control release is executed. If the no-hands-on-wheel time does not exceed the predetermined time, the routine advances to Step S124 where the no-hands-on-wheel time is incremented. The routine then moves to Step S125. If automatic steering is allowed while no hand is on the steering wheel, the driver might overly rely on the present control system and lose attention during driving.
Step S125 makes a judgment as to whether a state in which the steering torque is equal to or higher than a predetermined value continues for predetermined time. If such a state continues for the predetermined time, it is judged that the driver steers the vehicle with the intention, and the routine moves to Step S128 where the automatic control release is carried out. When the state in which the steering torque is equal to or larger than the predetermined value does not continue for the predetermined time, namely, when the steering torque is low or not continuously applied even if high, the routine proceeds to Step S126 where a high steering torque continuation timer is incremented.
Step S127 executes semi-automatic steering control. The semi-automatic steering control is control which carries out automatic steering according to the travel motion of the vehicle, regardless of the driver's intention, and switches the automatic steering control to regular steering assist control when the no-hands-on-wheel state is confirmed or a high steering torque is applied in a continuous manner. According to the automatic steering control, a target steering angle and the target yaw rate for achieving the control amount H(t) are set. Electric motor control switches from torque control for applying an assist torque to rotation angle control, and an activate command is outputted to the electric motor so as to turn the steering wheel up to the target steering angle according to target steering-wheel turning speed.
At time t1, the left yaw rate dφ/dt is generated by crosswind, and simultaneously, the formed angle θ starts being created in the travel-path defining line on the left. The value of the evaluation function Ho(t) also starts changing. In this situation, because of the left turn state which increases the formed angle, the sign of the yaw rate dφ/dt and that of the formed angle θ disagree with each other. The evaluation function Ho(t) changes so that the absolute value is large on the negative side. The vehicle attitude stabilizing control is not executed until the absolute value becomes larger than the predetermined value δ. This suppresses an excessive control intervention and thus prevents the driver from having the feeling of strangeness.
At time t2, the evaluation function Ho(t) becomes equal to or larger than the predetermined value δ, and the control amount H(t) is calculated. Thereafter, the right-wheel base control amount TR is calculated, and the front right-wheel braking torque TFR and the rear right-wheel braking torque TRR are calculated. At this time, the front left-wheel braking torque TFL and the front left-wheel braking torque TRL are set at zero. The vehicle is thus applied with the right yaw moment and makes a turn so that the vehicle traveling direction (traveling-direction virtual line) is parallel to the direction of the travel-path defining line.
At time t21, the travel-path defining line of the curved roadway appears ahead of the vehicle, and the formed angle θ starts being created between the travel-path defining line and the vehicle traveling direction (traveling-direction virtual line). At this point of time, the vehicle does not yet enter the curve, so that the driver does not operate the steering wheel, and the yaw rate dφ/dt is not generated. Although the evaluation function Ho(t) begins indicating negative values, these values are smaller than the predetermined value δ.
At time t22, the driver operates the steering wheel to drive along the curved roadway, the yaw rate dφ/dt then starts being generated in the vehicle. The sign of yaw rate dφ/dt agrees with that of the formed angle θ, and the absolute value of the evaluation function Ho(t) becomes small. If the vehicle travels along the travel-path defining line, the value of the evaluation function Ho(t) is substantially zero, and remains within a range of plus or minus δ. The vehicle attitude stabilizing control is therefore basically not executed. It is thus possible to avoid the feeling of strangeness which is caused by unnecessary control intervention.
(Off-Course Behavior Control)
Off-course behavior control processing will now be described. The processing is executed in a case where the ego vehicle travels beyond the travel-path defining line (hereinafter, referred to as “off course”) when the travel-path defining line is recognized not as an obstacle, such as a guardrail, but as a boundary between an upper side portion and a slope portion of the road embankment. The off-course behavior control controls an off-course behavior before the occurrence of off-course travel to prevent the vehicle from running off course. After the vehicle runs off course, only regular control is conducted, and the off-course behavior control is inhibited.
Step S301 makes an off-course behavior estimation judgment and judges whether the vehicle will travel off course. If it is judged that the vehicle will travel off course, the routine advances to Step S301a. If there is no judgment of collision, the routine moves to Step S305. The off-course behavior estimation judgment estimates and judges before the vehicle travels off course that it is difficult to avoid the off-course travel. For example, when the current intersect time is less than the predetermined time, and the formed angle is equal to or larger than the predetermined angle which can be suppressed by the yaw moment control (corresponding to an off-course behavior control zone shown in
Step S301a (corresponding to a recording unit) initiates image recording processing which records images taken by the stereo camera 310 in a memory installed in the ECU 10. More specifically, Step S301a initiates the image recording prior to the off-course travel and continues the image recording for a predetermined time period after the vehicle travels off course, to thereby allow the stereo camera 310 to serve as a drive recorder. Since the image recording is initiated prior to the off-course travel, it is possible to efficiently record an actual traveling condition at the time of the off-course travel, as compared to when images are constantly recorded. This saves a storage capacity of the memory.
Step S302 makes a judgment as to whether the vehicle has traveled off course. It is judged that the vehicle has traveled off course, the routine moves to Step S304. If it is judged that the vehicle has not traveled off course, that is, before the off-course travel, the routine proceeds to Step S303. The off-course behavior judgment judges an expected timing which is immediately before the off-course travel, the timing at which the vehicle travels beyond the travel-path defining line into the slope portion of the road embankment or the like while traveling substantially in a current travelling state even if the driver takes any steering operation or braking operation.
The off-course behavior judgment is made on the basis of the images taken by the stereo camera 310. In light of a viewing angle of the camera, it is difficult to recognize from the images the relationship between the ego vehicle and the travel-path defining line at the time of the off-course travel. Therefore, a time point when an intersect position between the traveling-direction virtual line and the travel-path defining line is last recognized by the stereo camera 310 (hereinafter, referred to as “final recognition timing”) is memorized. At the same time, an intersect time (value of dividing distance to the intersect position by current vehicle speed) at the final recognition timing is counted down from the final recognition timing. It is judged that the vehicle travels off course when the countdown is finished.
Step S303 conducts automatic steering control. To be more specific, Step S303 sets the target steering angle and the target yaw rate for achieving the control amount H(t), switches from the torque control for applying the assist torque to the rotation angle control as electric motor control, and outputs the activate command to the electric motor so as to turn the steering wheel up to the target steering angle at the target steering-wheel turning speed. Besides the automatic steering control, an after-mentioned brake control is executed.
Step S304 deactivates the automatic steering control due to the off-course travel.
Step S305 executes the vehicle-attitude stabilizing control processing because the off-course behavior judgment has not been made.
[Automatic Steering Control]
If the off-course travel cannot be avoided (if S301 estimates the occurrence of the off-course travel), that is, before the vehicle travels off course, both the brake control and the steering control are conducted (S303). The brake control multiplies the control amount H(t) by a gain larger than 1 to increase an absolute value of the yaw moment control amount, in which a braking force is generated. The steering control carries out automatic steering which performs forced steering according to the sign of the control amount H(t).
In general, a ground surface onto which the vehicle travels after running off course is not always as flat as a road, and is considerably bumpy or inclined in many cases. If the yaw moment control by steering or braking which is programmed for a flat road surface is carried out on such a ground surface, a vehicle behavior is likely to be different from what the driver expects. For that reason, the control is deactivated.
In view of the accident cases which have previously been reported, there are cases in which when the vehicle runs off the road on the embankment, and yaw moment is generated carelessly, for example, with the intention of returning to the course while the vehicle is traveling on the slope portion of the embankment, and the generation of yaw moment increases lateral acceleration to cause the vehicle to overturn. At the same time, it is considered in some cases that when the vehicle travels off the road on the embankment due to drowsy driving, it is safer if the vehicle moves from the slope portion to a lower portion by remaining off course because the vehicle is moderately decelerated. In this light, it is preferable to inhibit the yaw moment control which makes the vehicle travel along the travel-path defining line when the vehicle travels off course to prevent the destabilization of vehicle behavior and the turnover of the vehicle. Even if the vehicle is on the road embankment, therefore, the yaw moment control is carried out during the off-course behavior estimation judgment before the vehicle travels off course, and the yaw moment control is suspended after the vehicle travels off course. This makes it possible to ensure the stability of vehicle behavior since the control which makes the vehicle travel along the travel-path defining line as much as possible is automatically executed before the vehicle runs off the travel path, and also makes it possible to ensure the stability of vehicle behavior by suppressing the generation of unnecessary yaw moment after the vehicle runs off course.
(Positioning and Technical Purposes of the Controls)
As illustrated in
If the travel-path defining line is a traffic lane, and the vehicle merely crosses the lane due to negligent driving, that does not immediately incur an accident or the like. It is then simply required to conduct the lane keeping control which previously imparts a relatively small yaw moment control amount. If the travel-path defining line is not a traffic lane and there is a steep slope outside the road, the securing of safety is more important than the prevention of feeling of strangeness. Therefore, in an area where a large yaw moment control amount is required to be imparted because the formed angle θ exceeds the lane keeping control area, the Embodiment 1 sets a vehicle attitude stabilizing control area and imparts a relatively large yaw moment control amount at an early stage, regardless of the intersect time.
In an area where the intersect time is shorter or the formed angle θ is larger, as compared to the vehicle attitude stabilizing control area, the avoidance of off-course travel is considered to be difficult. In such a case, a braking torque and a cornering force are created using a control amount which is much larger than the control amount imparted during the vehicle attitude stabilizing control, for example, up to the vicinity of a performance limit of friction circle of a tire. Before the vehicle travels off course, the steering control is executed to make the vehicle parallel to the travel-path defining line in a forced manner to some extent, which further secures safety. To control the vehicle after the off-course travel by imparting as great a yaw moment control amount as before the off-course travel is unlikely to contribute to the stability of vehicle behavior. For that reason, the yaw moment control is suspended after the vehicle travels off course.
As described above, the Embodiment 1 provides operation and advantages listed below.
(1) The vehicle control system includes:
the travel-path defining line recognition unit 22 (travel-path defining line recognition unit) configured to recognize the travel-path defining line of the travel path from the information about the area located in the traveling direction of the ego vehicle;
the vehicle's current position recognition unit 23 (traveling-direction virtual line recognition unit) configured to recognize the traveling-direction virtual line extending from the ego vehicle in the traveling direction;
the automatic steering control flow (yaw moment control unit) of Step S303, which is configured to impart the control amount H(t) (yaw moment control amount) to reduce the formed angle θ between the traveling-direction virtual line and the travel-path defining line;
Step S302 (departure judgment unit) configured to make a judgment as to whether the ego vehicle has departed from the travel-path defining line; and
Steps S302 and S304 (control suspension unit) configured to suspend the automatic steering control when it is judged that the ego vehicle has departed from the travel-path defining line.
Since the yaw moment control is suspended after the departure of the vehicle from the travel-path defining line, the driver can operate the vehicle to return to the travel path, pull over to an edge of a road, or the like. This enables highly safe control.
(2) Step S302 (departure judgment unit) is configured to make a judgment of departure on the basis of the speed of the ego vehicle before departure and distance between the ego vehicle and the travel-path defining line before departure.
For example, when the off-course travel is judged on the basis of the images taken by the stereo camera 310, it is difficult to recognize from the images the relationship between the ego vehicle and the travel-path defining line at the time of the off-course travel in light of the viewing angle of the camera. Therefore, the final recognition timing at which the intersect position between the traveling-direction virtual line and the travel-path defining line is last recognized by the stereo camera 310 is memorized. At the same time, the intersect time (value of dividing distance to the intersect position by current vehicle speed) at the final recognition timing is counted down from the final recognition timing. It is judged that the vehicle has traveled off course when the countdown is finished. This enables a highly accurate judgment of off-course travel.
(3) There is provided Step S301a (recording unit) configured to record images taken (information) before and after the departure of the ego vehicle from the travel-path defining line, which are recognized by the stereo camera 310, when it is judged that the ego vehicle has departed from the travel-path defining line.
Since the image recording is initiated before the vehicle travels off course, and the image recording is continued for the predetermined time period after the off-course travel, it is possible to make the stereo camera 310 serve as a drive recorder. Furthermore, since the image recording is initiated prior to the off-course travel, it is possible to efficiently record the actual traveling condition at the time of the off-course travel, and thus save the storage capacity of the memory.
(4) There is provided Step S301 (departure estimation unit) configured to estimate whether the ego vehicle will depart from the travel-path defining line, and
according to the automatic steering control flow, if it is estimated that the ego vehicle will depart from the travel-path defining line, the yaw moment control which reduces the formed angle θ is carried out, regardless of the driver's steering operation.
For example, in a situation where the vehicle is about to run off the travel path due to drowsy driving, that is, before the off-course travel, the control which makes the vehicle travel along the travel-path defining line as much as possible is automatically carried out. This makes it possible to ensure more safety.
(5) There is provided the electrically-assisted power steering 2 (steering actuator) configured to control the steering torque applied by the driver, and
the automatic steering control (yaw moment control unit) of Step S303 is configured to carry out the yaw moment control by automatically controlling the electrically-assisted power steering 2.
More specifically, when the driver falls asleep at the wheel, it is difficult to accurately correct the relationship between the traveling-direction virtual line and the travel-path defining line simply by guiding the steering. To solve this, the steering angle is controlled so that the vehicle is forced to become parallel to the travel-path defining line by the steering control before the off-course travel. This makes it possible to ensure more safety. If the electrically-assisted power steering 2 is switched from the regular torque control to the rotation angle control, a desired steering turning angle and yaw rate can be achieved.
The Embodiment 1 is provided with the electrically-assisted power steering 2. If the vehicle is installed with a steer-by-wire system, however, it is simply required to carry out automatic control on a turning actuator side, regardless of the steering operation of the driver. It is also possible to control a reaction motor to guide the wheels to a necessary steering angle. There is no particular limitation.
(6) The automatic steering control (yaw moment control unit) of Step S303 is configured to carry out the yaw moment control through the brake control which applies the braking torque to the wheels, in addition or instead of the automatic steering control.
This makes it possible to impart the yaw moment control amount to the vehicle while decelerating the vehicle, and thus improve safety.
(7) The travel-path defining line recognition unit 22 includes a stereo camera configured to measure distance by using the disparity created when a plurality of cameras 310a and 310b take an image of the same object.
This makes it possible to stereoscopically perceive distance and obstacle ahead of the vehicle, and set control gains which differ between obstacles, such as guardrails, and white lines. If there is the possibility of collision with an obstacle, a larger gain is set to achieve highly safe control.
(8) The automatic steering control of Step S303 is configured to impart the yaw moment control amount according to an intersection angle which is difference between the formed angle θ between the traveling-direction virtual line and the travel-path defining line, and the curvature (1/r) according to the turning radius of the ego vehicle.
This makes it possible to output such a control amount that the vehicle quickly becomes parallel to the travel-path defining line before actually reaching the travel-path defining line, regardless of distance from the ego vehicle to the travel-path defining line, so that highly safe control can be achieved. Furthermore, the control amount is computed using the relationship between the curvature and the formed angle θ. Therefore, when control is unnecessary as in a situation where the vehicle travels along the travel-path defining line, the collision control does not intervene even if the formed angle θ is generated. The driver is therefore not given the feeling of strangeness.
The invention has been described on the basis of the embodiment. The configuration of the invention is not limited to the above-described configuration, and may be optionally modified within the scope of the invention. According to the Embodiment 1, for example, the yaw moment control through the brake control is not executed when the vehicle travels at low speed. However, the yaw moment control through the brake control may be executed also when the vehicle travels at low speed. In this case, it is also possible to calculate a yaw rate equivalent value as a yaw rate on the basis of the formed angle θ recognized by the stereo camera 310, instead of the sensor value obtained by the vehicle motion detector 11, and then calculate a brake control amount on the basis of the yaw rate equivalent value.
According to the above-described embodiment, the yaw moment control is suspended after the vehicle departs from the travel-path defining line. The driver therefore can operate the vehicle to return to the travel path, pull over to a curb, or the like. This enables highly safe control.
A vehicle control system according to one aspect of the invention includes a travel-path defining line recognition unit configured to recognize a travel-path defining line of a travel path from information about an area located in a traveling direction of an ego vehicle; a traveling-direction virtual line recognition unit configured to recognize a traveling-direction virtual line extending from the ego vehicle in the traveling direction; a yaw moment control unit configured to carry out yaw moment control to reduce a formed angle between the traveling-direction virtual line and the travel-path defining line;
a departure judgment unit configured to make a judgment as to whether the ego vehicle has departed from the travel-path defining line on the basis of the information about the area located in the traveling direction of the ego vehicle; and
a control suspension unit configured to suspend the yaw moment control when it is judged that the ego vehicle has departed from the travel-path defining line.
According to the vehicle control system, the departure judgment unit may be configured to make a judgment of departure on the basis of speed of the ego vehicle before departure and distance between the ego vehicle and the travel-path defining line before departure.
According to the vehicle control system, there may be provided a recording unit configured to record information before and after departure, which is recognized by the travel-path defining line recognition unit, when it is judged that the ego vehicle has departed from the travel-path defining line.
According to the vehicle control system, there may be provided a departure estimation unit configured to estimate whether the ego vehicle will depart from the travel-path defining line, and the yaw moment control unit may carry out yaw moment control to reduce the formed angle, regardless of a driver's steering operation, when it is estimated that the ego vehicle will depart from the travel-path defining line.
According to the vehicle control system, there may be provided a steering actuator configured to control a steering torque applied by the driver, and the yaw moment control unit may carry out yaw moment control by automatically controlling the steering actuator.
According to the vehicle control system, the yaw moment control unit may be configured to carry out yaw moment control at least either by automatically controlling the steering actuator or by carrying out brake control which applies a braking torque to wheels.
According to the vehicle control system, the travel-path defining line recognition unit may include a stereo camera configured to measure distance by using disparity created when a plurality of cameras take an image of the same object.
According to the vehicle control system, the yaw moment control unit may be configured to carry out yaw moment control according to an intersection angle which is difference between the formed angle between the traveling-direction virtual line and the travel-path defining line, and curvature according to a turning radius of the ego vehicle.
According to the vehicle control system, there may be provided a departure estimation unit configured to estimate whether the ego vehicle will depart from the travel-path defining line, and the yaw moment control unit may include a recording unit configured to initiate recording of information recognized by the travel-path defining line recognition unit, when it is estimated that the ego vehicle will depart from the travel-path defining line.
A vehicle control system according to one aspect of the invention includes a travel-path defining line recognition unit configured to recognize a travel-path defining line of a travel path from information about an area located in a traveling direction of an ego vehicle; a yaw moment control unit configured to carry out yaw moment control so that the ego vehicle is parallel to the travel-path defining line; a departure judgment unit configured to make a judgment as to whether the ego vehicle has departed from the travel-path defining line; and a control suspension unit configured to suspend the yaw moment control when it is judged that the ego vehicle has departed from the travel-path defining line.
According to the vehicle control system, the departure judgment unit may be configured to make a judgment of departure on the basis of speed of the ego vehicle before departure and distance between the ego vehicle and the travel-path defining line before departure.
According to the vehicle control system, a traveling-direction virtual line recognition unit configured to recognize the traveling-direction virtual line extending from the ego vehicle in the traveling direction, and the yaw moment control unit may be configured to carry out the yaw moment control to reduce the formed angle between the traveling-direction virtual line and the travel-path defining line.
According to the vehicle control system, there may be provided a departure estimation unit configured to estimate whether the ego vehicle will depart from the travel-path defining line, and the yaw moment control unit may be configured to carry out the yaw moment control to reduce the formed angle, regardless of a driver's steering operation, when it is estimated that the ego vehicle will depart from the travel-path defining line.
According to the vehicle control system, the departure judgment unit may be configured to make a judgment of departure on the basis of the speed of the ego vehicle before departure and the distance between the ego vehicle and the travel-path defining line before departure.
According to the vehicle control system, there may be provided the departure estimation unit configured to estimate whether the ego vehicle will depart from the travel-path defining line, and the yaw moment control unit may include a recording unit configured to initiate recording of information recognized by the travel-path defining line recognition unit when it is estimated that the ego vehicle will depart from the travel-path defining line.
According to the vehicle control system, the recording unit may be configured to record information before and after departure, which is recognized by the travel-path defining line recognition unit.
A vehicle control system according to one aspect of the invention includes a yaw moment control unit configured to carry out yaw moment control to reduce a formed angle between a traveling-direction virtual line and a travel-path defining line of a travel path on the basis of information from a travel-path defining line recognition unit configured to recognize the travel-path defining line from information about an area located in a traveling direction of an ego vehicle and a traveling-direction virtual line recognition unit configured to recognize the traveling-direction virtual line extending from the ego vehicle in the traveling direction; a departure judgment unit configured to make a judgment as to whether the ego vehicle has departed from the travel-path defining line; and a control suspension unit configured to suspend the yaw moment control when it is judged that the ego vehicle has departed from the travel-path defining line.
The foregoing description merely explains several embodiments of the invention. Those skilled in the art could easily understand that the embodiments described above may be changed or modified in various ways without substantially deviating from new teachings and advantages of the invention. Therefore, it is intended to include within the technological scope of the invention all aspects added with such changes or modifications.
The present patent application claims priority to Japanese Patent Application No. 2013-126113 filed on Jun. 14, 2013. The entire disclosure of Japanese Patent Application No. 2013-126113 filed on Jun. 14, 2013 including description, claims, drawings and abstract is incorporated herein by reference in its entirety.
The entire disclosure of Japanese Unexamined Patent Application Publication No. 2012-84038 (Patent Document 1) including description, claims, drawings and abstract is incorporated herein by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-126113 | Jun 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/064674 | 6/3/2014 | WO | 00 |
