Vehicle control apparatus

This application is based on and claims the benefit of priority from earlier Japanese Patent Application No. 2017-252545 filed Dec. 27, 2017, the description of which is incorporated herein by reference.

The present disclosure relates to a vehicle control apparatus that performs a steering control of a vehicle.

As a related art, for example, Japanese Patent Number 4217900 discloses an apparatus for performing a steering control of an own vehicle in which a curvature corresponding to a shape of the own lane is estimated to perform the steering control based on the estimated curvature. As a method for estimating a curvature of the own lane, a method is known in which a marking is detected from an image that captures ahead of the own vehicle and the curvature of the own lane is estimated using the detected marking.

However, depending on a road situation and the direction of the own vehicle, the curvature of the own lane may not be correctly estimated and thus cause deterioration of the steering control. For example, when a down slope is present ahead of the own vehicle on a road, the marking in the captured image is distorted. Moreover, in the case where the own vehicle is travelling on such a down slope road and approaches one of both left and right side markings when the own vehicle changes its direction in either the left or right direction, a degree of distortion differs between respective side markings in the captured image. Hence, due to the difference of degree of distortion of respective one side markings, an unnecessary steering amount may be applied to the own vehicle.

The present disclosure has been achieved in light of the above-described circumstances and provides a vehicle control apparatus that avoids unnecessary steering amount applied to the own vehicle when the own vehicle travels on a road having a road slope.

The vehicle control apparatus according to the present disclosure is provided with a marking detection unit that detects a marking defining an own lane based on an image of a region ahead of an own vehicle captured by an imaging device; a curvature estimation unit that estimates a curvature of the own lane ahead of the own vehicle based on both of left and right markings detected by the marking detection unit; a control unit that performs steering control of the own vehicle based on the curvature of the own lane estimated by the curvature estimation unit; a change determination unit that determines whether a direction of the own vehicle has changed with respect to a direction where the own lane extends; and a slope determination unit that determines whether a change in a road slope is present ahead of the own vehicle. The control unit is configured to apply a restriction to the steering control performed based on the curvature of the own lane during a state where a change in the direction of the own vehicle has been detected and a change in the road slope ahead of the own vehicle has been detected.

When the own vehicle travels on a road having a road slope and changes its direction to approach either of the left and right markings, in the captured image, an opposite side marking with respect to the direction of the own vehicle is distorted and deformed in the vehicle width direction compared to the own vehicle side marking. Hence, due to the difference of degree of distortion between respective one side markings, an error may occur on the estimated curvature of the road to cause an unnecessary steering amount to be applied to the own vehicle. In this regard, according to the above-described configuration, the apparatus determines whether a direction of the own vehicle has changed with respect to a direction in which the own lane extends, and determines whether a change in the road slope ahead of the own vehicle is present. Then, when determining that the direction of the own vehicle changes and the road slope changes ahead of the own vehicle, the apparatus applies a restriction to the steering control based on the curvature of the own lane. In this case, the own vehicle can be prevented from being applied with an unnecessary steering amount depending on a difference of degree of distortion between the left and right markings in the captured image.

In the accompanying drawings:

FIG. 1 is a diagram showing a steering control system according to embodiments of the present disclosure;

FIG. 2 is a graph showing a steering amount set by ECU (electronic control unit);

FIG. 3 is a diagram showing an own vehicle travelling on a road having a slope;

FIGS. 4A and 4B are diagrams each showing a captured image;

FIG. 5 is a flowchart showing a process of setting a steering amount;

FIG. 6 is a diagram showing a steering change rate set by ECU (electro control unit);

FIG. 7 is a diagram showing a steering change rate set by ECU;

FIGS. 8A to 8D are diagrams each showing a change in a position of the own vehicle when the own vehicle travels on a curved road;

FIGS. 9A and 9B are diagrams each showing a difference between cases where a road slope is changed;

FIG. 10 is a flowchart showing a process for setting a steering control value according to a second embodiment;

FIG. 11 is a diagram showing a theory of technique in a third embodiment; and

FIG. 12 is a diagram showing a target steering amount set by ECU according to a fourth embodiment.

First Embodiment

With reference to FIG. 1 , a steering control system 100 applied to a vehicle will be described. The steering control system 100 is provided with an ECU 10 , an imaging device 11 , a steering apparatus 13 and a yaw angle sensor 14 . According to the present embodiment, the ECU 10 corresponds to a vehicle control apparatus.

The imaging device 11 is attached to the own vehicle in a center position of the vehicle width direction at a predetermined height, whereby an area ahead of the own vehicle spreading in a predetermined angle range is captured as a bird's-eye view, and the captured image is outputted to the ECU 10 . The imaging device 11 is configured as, for example, a CCD (charge coupled device) camera, a CMOS (complementary metal oxide semiconductor) image sensor and an infrared camera. Note that the imaging device 11 is a monocular camera according to the present embodiment, but a stereo camera can be used.

The steering apparatus 13 is provided with a steering 13 b , and a steering motor 13 a . The steering motor 13 a generates a steering torque for steering the driving wheels included in the own vehicle. The larger the steering torque, the larger the steering amount of own vehicle is.

The ECU 10 is a computer provided with CPU, RAM, ROM and I/O. The CPU executes a program installed in the ROM, thereby performing a steering control to the vehicle. According to the present embodiment, the ECU 10 executes a lane keeping assist (LKA) control having the vehicle travel in accordance with a marking line that defines the own lane. In the LKA control, the ECU 10 estimates a road curvature of the own lane by using a detected marking in the captured image, and sets the steering amount of the steering apparatus 13 based on the estimated road curvature.

The ECU 10 detects the marking based on a feature quantity such as luminance in the captured image. Specifically, the ECU 10 extracts edge points of the marking from the captured image, performs Hough transformation to the extracted plurality of edge points, and acquire series of edge points which are candidates of the marking. Then, the ECU 10 calculates a degree of existence of feature as a marking for each of the plurality of markings, and detects a candidate having the largest degree of existence of the feature to be the marking. According to the present embodiment, the ECU 10 corresponds to marking detection unit.

The ECU 10 estimates a road curvature of the own lane based on a marking included in a predetermined section among the detected markings using the captured image. According to the present embodiment, the ECU 10 detects the center points between the left and right markings at predetermined intervals, from a front area of the own vehicle to a distance area ahead of the own vehicle. Then, the ECU 10 calculates an approximation formula of a line connecting the detected center points, and estimates the road curvature. The ECU 10 estimates the road curvature based on the marking ahead of the own vehicle at a predetermined period. Then, the ECU 10 performs smoothing processing of the road curvature calculated at the current period, and estimates the smoothed road curvature to be a current estimated value of the road curvature. For example, as the smoothing process, a weighted average or a moving average can be used.

Also, the ECU 10 estimates the road curvature based on a marking of one side (one side marking) in the left and right markings, when detecting only one side marking in the left and right markings from the captured image. For example, the ECU 10 calculates an approximation formula that approximates detected one of the left and right markings, and estimates the road curvature by using the calculated approximation formula. The ECU 10 corresponds to curvature estimation unit.

The ECU 10 sets, based on the estimated road curvature, a target steering amount Ta and a steering change rate R indicating a change rate of the steering amount. According to the present embodiment, the target steering amount Ta and the steering change rate R are set using a road curvature of a lane section from a current location of the own vehicle to a location at which the own vehicle reaches when a predetermined period elapses. Hereinafter, among road curvatures used for setting the target steering amount Ta and the steering change rate R, a road curvature estimated based on both left and right markings is referred to as a first curvature ρ 1 and a road curvature estimated based on only one of the left and right markings is referred to as a second curvature ρ 2 .

FIG. 2 is a timing diagram of a steering amount T in which the vertical line shows the steering amount T. As shown in FIG. 2 , the target steering amount Ta shows a maximum value of the steering amount required for the current steering operation. According to the present embodiment, the target steering amount Ta is set to be a value where a predetermined gain K 1 is added to the road curvature. The steering change rate R shows a change rate of the steering amount T per unit of time. Specifically, the change rate R indicates respective change rates of the steering amount when the steering amount T increases to the target steering amount Ta and when the steering amount T decreases from the target steering amount ta.

Note that the ECU 10 may set the target steering amount Ta such that a value where the gain K 1 is added to the road curvature, and a value where the gain K 2 is added to a horizontal deviation Δy are added to obtain the target steering amount Ta. The horizontal deviation Δy represents a difference of the distance between the center of the own lane in the vehicle width direction and the current location of the own vehicle.

FIG. 3 is a diagram showing a state where the own vehicle travels on a road having a road slope ahead of the own vehicle, which is viewed from a horizontal direction of the own vehicle. In FIG. 3 , a slope change point P is present ahead of the own vehicle and the road slope decreases from the slope change point P to a vehicle distance side A 2 . According to the present embodiment, a case where the road slope from the slope change point P to the vehicle distance side A 2 is inclined downward with respect to the road slope from the slope change point P to a vehicle vicinity side A 1 , is referred to as a decrease in road slope. On the other hand, a case where the road slope from the slope change point P to the vehicle distance side A 2 is inclined upward with respect to the road slope from the slope change point P to a vehicle vicinity side A 1 , is referred to as an increase in road slope. Note that as a case where the road slope decreases, for example, it is expected that state of the road changes from a flat road to a downhill road. As a case where the road slope increases, for example, it is expected that the state of the road changes from a flat road to an uphill road.

When the road slope changes on the road where the own vehicle travels, a distance between the capturing axis B and the road surface in the height direction varies around the slope change point P and may cause a distortion of the marking in the road width direction in the captured image. Also, when the own vehicle changes its direction while travelling on such a road to approach either left or right marking, a degree of distortion differs between respective side markings in the captured image.

FIG. 4A illustrates a captured image when the own vehicle travels on a straight road having no road slope. FIG. 4B illustrates a captured image when the own vehicle travels on a straight road having a road slope shown in FIG. 3 and changes its direction to right direction. In FIGS. 4A and 4B , a travelling direction of the own vehicle is indicated by an arrow. According to the present embodiment, presence of the road slope refers to a change in the road slope being larger than or equal to a predetermined value, and absence of the road slope refers to the road slope being less than the predetermined value.

When the own vehicle travels on a straight road without a change in the road slope, as shown in FIG. 4A , left side markings C 1 C 2 extend linearly towards a vanishing point FOE from a vehicle vicinity side. On the other hand, when the own vehicle changes its direction to a right direction while travelling on the straight road having a road slope, as shown in FIG. 4B , the left right markings C 3 and C 4 extend towards the vanishing point FOE in a region from the slope change point P to the vehicle vicinity side. Note that position of the FOE is omitted for convenience of the explanation. Meanwhile, in the vehicle distance side further than the slope change point P, the left side marking C 3 does not extend towards the vanishing point FOE, but is distorted inside in the vehicle width direction compared to the right side marking C 4 .

In the case where the ECU 10 estimates the road curvature using both sides markings (i.e. left and right markings), due to a difference of the distortion between the left-right markings in the captured image, the road curvature may be set to be a value smaller than the actual road curvature and an unnecessary steering amount may be applied to the own vehicle. For example, when the own vehicle travels on a straight road with a change in the road slope, since the road curvature is estimated to be a value smaller than the actual road curvature, it is possible that the own vehicle is unable to travel along the straight road because of applying a steering amount in either left or right direction. The travelling route indicated by a dotted line shown in FIG. 4B is an expected travelling route of the own vehicle when assuming that the steering control is performed using the road curvature estimated with the marking having no distortion. According to an example of FIG. 4B , a steering amount in the right direction is applied to the own vehicle, whereby the travelling route of the own vehicle is shifted to the right direction with respect to the expected travelling route indicated by the dotted line.

In this respect, the ECU 10 applies a restriction to the steering control during a state where a change in the road slope ahead of the own vehicle has been detected and a change in the direction of the own vehicle has been detected. Specifically, the ECU 10 sets a steering change rate R when increasing the steering amount to be a value smaller than a reference value, thereby restricting the steering control.

As a determination whether a change in the road slope is present, a known optical flow method is used for the determination according to the present embodiment. The optical flow indicates a movement vector of a pixel that constitutes an object in the captured image. In a flat road in which the road slope is not changed, in the captured image, a stationary object appears from the vanishing point FOE and the optical flow of the stationary object is recognized as a line segment extending in the vehicle width direction when approaching the vehicle vicinity side from the vehicle distance side. On the other hand, when the road slope changes ahead of the own vehicle, the stationary object does not appear from the vanishing point so that the optical flow of the stationary object is not linear. For example, when the road slope decreases more in the vehicle distance side than in the slope change point P, the stationary object appears from lower side than the FOE point in the captured image. Also, when the road slope increases further away than the slope change point P, the stationary object appears from the upper side than the FOE point. Hence, the ECU 10 detects, in the captured image, stationary objects such as electric poles, signs, signals and street trees in accordance with a known pattern matching method using dictionary information, and calculates a change in the optical flow around the FOE point in the detected stationary object. Then, the ECU 10 determines whether a change in the road slope is present based on a change in the optical flow.

Next, with reference to the flowchart shown in FIG. 5 , a procedure for executing the steering control will be described. The flowchart shown in FIG. 5 is repeatedly executed by the ECU 10 at predetermined periods.

At step S 10 , the process acquires a yaw angle φ of the own vehicle detected by the yaw angle sensor 14 . According to the present embodiment, step S 10 corresponds to a yaw angle acquiring unit. The yaw angle changes depending on the direction of the own vehicle.

At step S 11 , the process determines whether both of the left right markings have been detected. At step 11 , when determined that left right markings have been detected, the process proceeds to step S 12 .

At step S 12 , the process determines that whether a direction of the own vehicle is changed. According to the present embodiment, the process determines that the direction of the own vehicle is changed when the yaw angle φ detected by the yaw angle sensor 14 is larger than or equal to a threshold TH 1 . Step S 12 corresponds to a change determination unit.

At step S 12 , when it is determined that the direction of the own vehicle is not changed, the process proceeds to step S 15 and determines whether a predetermined period has elapsed from a time when the steering control is executed using each steering control values Ta and R 3 shown in step S 21 . Here, assuming that the predetermined period has not elapsed from the time when the steering control is executed, the process proceeds to step S 19 .

When the process proceeds to step S 19 , the process sets a target steering amount Ta and a first steering change rate R 1 based on the first curvature ρ 1 estimated using left and right markings. For example, a map which defines a relationship between the target steering amount Ta and the first steering change rate R 1 is prepared and stored. Then, by referring the map, the process sets each of the steering control values Ta and R 1 .

At step S 23 , the process performs a steering control using each of the steering control values Ta and R 1 which have been set at step S 19 .

Referring back to step S 12 , when the process determines that the direction of the own vehicle has changed, the process proceeds to step S 13 and determines whether a change in the road slope is present ahead of the own vehicle. When it is determined that there is no change in the road slope ahead of the own vehicle, the process proceeds to step S 15 . The step S 13 corresponds to slope determination unit.

On the other hand, at step S 12 , when the process determines that a change in the road slope is present ahead of the own vehicle, the process proceeds to step S 14 . The difference of amount of distortion between the left and right markings in the captured image varies depending on a change amount GA of the road slope the direction of the own vehicle. Specifically, as a change in the road slope becomes larger, in the captured image, distortion of the marking in the road width direction becomes larger in the vehicle distance side than the slope change point P. Also, as the yaw angle detected in the own vehicle becomes larger, the difference between the left and right markings becomes larger. Hence, at step S 14 , the change amount GA of the road slope is acquired first.

The change amount GA of the road slope refers to a change amount of a relative slope angle on the road sections between the vehicle vicinity side and the vehicle distance side with respect to the slope change point P. For example, at step S 13 , the process stores a slope change amount map which defines a correspondence between a direction of the optical flow used for determination whether a change in the road slope is present, and the change amount GA of the road slope. Then, the process may acquire, from the slope change amount map, the change amount GA corresponding to the direction of the optical flow used for the determination at step S 13 . Step S 14 corresponds to a change amount acquiring unit.

At step S 17 , the process sets the target steering amount Ta and a third steering change rate R 3 based on the first curvature ρ 1 . At this moment, the process sets the third steering change rate R 3 based on the yaw angle φ and the change amount GA. As shown in FIG. 6 , when the road curvature is the same value, the third steering change rate R 3 is smaller than the first steering change rate R 1 .

According to the present embodiment, the larger the yaw angle φ and the change amount GA, the smaller the third steering change rate R 3 is. For example, a steering amount map is stored in advance, which defines a correspondence between a combination of the first curvature ρ 1 , the yaw angle φ and the change amount GA, and a combination of the target steering amount Ta and the third steering change rate R 3 . Then, by referring to the steering amount map, the process may set the target steering amount Ta and the third steering change rate R 3 . Note that the maximum value of the third steering change rate R 3 which is set depending on the yaw angle φ and the change amount GA is smaller than the first steering change rate R 1 .

Referring back to FIG. 5 , at step S 21 , the process performs a steering control using each of the steering control values Ta and R 3 which have been set at step S 17 . Hence, in the steering control at step S 21 , the steering change rate is more restricted than a case where the steering control is performed at step S 23 . According to the present embodiment, performing the steering control using each of the steering control values Ta and R 3 corresponds to a first restriction.

Referring back to step S 15 , when the process determines that it is in a continuous period DT from the steering control at step S 21 , the process proceeds to step S 18 . At step S 18 , the process sets the target steering amount Ta and the second steering change rate R 2 based on the first curvature ρ 1 .

A reason for setting the second steering change rate R 2 at step S 18 will be described. FIGS. 8A to 8D are diagrams showing a change in the position of the own vehicle when the own vehicle travels on a curved road including a slope change point P. Changing from FIGS. 8A to 8D , time elapses from t 1 to t 4 .

At time t 1 shown in FIG. 8A , the road curvature is estimated with both left and right markings in the section D. After that, at time t 2 , when the own vehicle travels in the section D, steering control using the road curvature estimated at time t 1 is performed. Similarly, at time t 2 , the road curvature in the section D is estimated using both of the left and right markings. Then, at time t 3 , steering control using the road curvature estimated at time t 1 is performed. Similarly, at time t 2 , the road curvature in the section D is estimated using the left and right markings. Thereafter, at time t 3 , when the own vehicle travels on the section D, steering control using the road curvature estimated at time t 2 is performed.

The ECU 10 performs an averaging process of the road curvature calculated at a predetermined period, thereby estimating the current value of the road curvature. Hence, as shown in FIG. 8D , immediately after the own vehicle passes the slope change point P, the direction of the travelling route of the own vehicle may be influenced by the road curvature estimated using both of the left and right markings having different degrees of distortion

In this respect, according to the present embodiment, the steering control is continuously restricted at a travelling section in the vehicle vicinity side and a travelling section in the vehicle distance side with respect to the slope change point. For example, in FIGS. 8A to 8D , the steering control is restricted in the traveling section KB which is a distance side of the own vehicle with respect to the slope change point P, in addition to the travelling section KA which is a vicinity side own vehicle with respect to the slope change point P. According to the present embodiment, respective travelling sections KA and KB are set as sections different from the sections shown in FIGS. 8A to 8D , but may be set in the same sections. Also, in FIGS. 8A to 8D , the travelling section KB is set to be longer than the travelling section KA. However, the lengths of respective sections KA and KB may be appropriately set depending on the restriction applied to the steering control. The travelling section KA corresponds to a first traveling section and the travelling section KB corresponds to the second travelling section KB.

The continuous period DT determined at step S 15 refers to a required period from a time when the own vehicle passes through the slope change point P to a time when the own vehicle passes through the travelling section KB. For example, the continuous period DT may be changed depending on the traveling speed of the own vehicle. According to the present embodiment, as shown in FIG. 6 , the second steering change rate R 2 which is set at step S 18 is larger than or equal to the third steering change rate R 3 and smaller than the first steering change rate R 1 .

At step S 22 , the process executes steering control using the target steering amount Ta and the second steering change rate R 2 which are set at step S 18 . Hence, during the continuous period DT after completing the steering control at step S 21 , the steering control is continuously restricted. According to the present embodiment, execution of the steering control using each of the steering control values Ta and R 2 corresponds to a second limit.

Meanwhile, at step S 11 , when the process determines that both of the left and right markings have not been detected, the process proceeds to step S 16 . At step S 16 , the process determines whether either one of the left and right markings has been detected.

When the process determines that one side marking in the left and right markings has been detected at step S 16 , at step S 20 , the process sets the target steering amount Ta and the fourth steering change rate R 4 based on the second curvature ρ 2 estimated using the one side marking in the left and right markings. For example, a map which defines a relationship between the target steering amount Ta and the fourth steering change rate R 4 in accordance with the second curvature ρ 2 is prepared and stored. Then, by referring to the map, the process sets the target steering amount Ta and the fourth steering change rate R 4 corresponding to the second curvature ρ 2 .

According to the present embodiment, as shown in FIG. 6 , the fourth steering change rate R 4 is set to be lower than the first to third steering change rates R 1 to R 3 . This is because the first curvature ρ 1 estimated using both of the left and right markings is larger than the second curvature ρ 2 estimated using one side marking in the left and right markings.

At step S 24 , the process performs a steering control using the steering control values Ta and R 4 which have been set at step S 20 . It should be noted that when the process determines that onside marking in both left and right markings have not been detected, the process temporarily terminated the process shown in FIG. 5 .

According to the present embodiment, steps S 17 to S 24 correspond to a control unit. When processes of steps S 21 to S 24 are completed, the process temporarily terminates the process shown in FIG. 5 .

According to the present embodiment, the following effects and advantages can be obtained.

The ECU 10 determines whether the direction of the own vehicle has changed with respect to a direction where the own lane extends, and determines whether the road slope ahead of the own vehicle has changed. Then, the steering control is restricted (restriction is applied to the steering control) based on the first curvature ρ 1 , when the process determines that the direction of the own vehicle changes and the road slope ahead of the own vehicle changes. In this case, the own vehicle can be prevented from being applied with an unnecessary steering amount depending on a difference of degree of distortion between the left and right markings.

The difference of degree of distortion between the left and right markings, which may influence an estimation error of the road curvature, becomes a value corresponding to a change amount GA of the road slope and a yaw angle φ. In this respect, the ECU 10 sets a degree of restriction of the steering control to be variable. In this case, the steering control can be prevented from being applied with unnecessary restriction by setting the restriction to be variable depending on the difference of degree of distortions.

The ECU 10 continuously applies restriction to the steering control in traveling sections of the vehicle vicinity side and the vehicle distance side with respect to the slope change point P when determining that the direction of the own vehicle changes and the road slope changes. In this case, the steering control is prevented from being influenced by the difference of the distortion between the left and right markings in the captured image even after the own vehicle passes through the slope change point P, and the direction of the own vehicle can be prevented from being excessively shifted to either left or right marking.

The ECU 10 applies a first restriction to the steering control when the own vehicle travels in a vehicle vicinity side section with respect to the slope change point P, and applies a second restriction of which the degree of restriction is weaker than that of the first restriction when the own vehicle travels in a vehicle distance side with respect to the slope change point P. In this case, the steering control can be prevented from being applied with unnecessary restriction after the own vehicle passes through the slope change point P.

Second Embodiment

In the second embodiment, configurations which differ from the first embodiment will be described. Note that portions having the same reference numbers represent the same portion and explanation thereof is not repeated.

As the change in the road slope according to the second embodiment, a case of increasing road slope and a case of decreasing road slope are distinguished, and the steering change rate in the case of decreasing road slope is set to be lower than the steering change rate of the case of increasing road slope. An example of decreasing road slope is a case where the road changes from the flat road to the down slope.

FIG. 9A illustrates a captured image in which the road slope ahead of the own vehicle decreases on a straight road, and FIG. 9B illustrates a captured image in which the road slope ahead of the own vehicle increases on a straight road.

When steering control such as LKA (i.e. lane keeping assist) control is performed, the steering amount is controlled such that the own vehicle travels along the marking. Here, as shown in FIG. 9A , when the road slope decreases, in the captured image, both of the left and right markings C 11 and C 11 are distorted/deformed inward in the distance side with respect to the slope change point P, whereby the left and right markings C 11 and C 11 may be disappeared. On the other hand, as shown in FIG. 9B , when the road slope increases, in the captured image, both of the left and right markings C 11 and C 11 are distorted/deformed outward in the distance side with respect to the slope change point P, however, the both markings are not disappeared. Hence, comparing a case where the road slope decreases and a case where the road slope increases, in the former case, the markings used for estimating the road curvature becomes excessively small so that the accuracy for estimating the road curvature decreases. As a result, steering control may be affected by these excessively small markings.

In this regard, according to the present embodiment, when it is determined that a change in the road slope decreases, the ECU 10 strengthens the restriction applied to the steering control more than a case where a change in the road slope increases.

A process of the steering control according to the second embodiment will be described with reference to the flowchart shown in FIG. 10 . The flowchart shown in FIG. 10 is repeatedly executed at a predetermined period.

At step S 13 , when the process determines that a change in the road slope is present, the process proceeds to step S 14 and acquires a change amount GA of the road slope.

At step S 31 , the process determines whether the road slope is increasing or decreasing (i.e. increase/decrease determination). The increase/decrease determination of the road slope may be performed using the optical flow used for the determination whether a change in the road slope is present. In this case, when the optical flow is formed such that the stationary object appears from an upper side with respect to the vanishing point FOE in the captured image, the process can determine that the road slope ahead of the own vehicle increases. On the other hand, when the optical flow is formed such that the stationary object appears from the lower side with respect to the vanishing point FOE in the captured image, the process can determine that the road slope ahead of the own vehicle decreases. Step 31 corresponds to increase/decrease determination unit.

On the other hand, at step S 32 , when the process determines that the road slope changes in the increase/decrease determination, the process proceeds to step S 34 , and acquires the target steering amount Ta and the fifth steering changer rate R 5 based on the first curvature ρ 1 . At step S 36 , the process performs a steering control based on the target steering amount Ta and the fifth steering change rate R 5 .

At step S 32 , when the increase/decrease determination determines that the road slope decreases, the process proceeds to step S 33 , and sets the target steering amount Ta and sixth steering change rate R 6 . Since the sixth steering change rate R 6 is a value which is set when the process determines that the road slope decreases, the sixth steering change rate R 6 is set to be lower than the fifth steering change rate R 5 while the same road curvature and the same change amount GA are maintained.

At step S 35 , the steering control is performed based on the target steering mount Ta and the sixth steering change rate R 6 .

When the processes of steps S 22 to 24 , S 35 and S 36 are completed, the process in FIG. 10 is temporarily terminated.

According to the present embodiment as described above, the ECU 10 determines the road slope whether increases or decreases, when a change in the road slope is determined. When the ECU 10 determines that the road slope decreases, the ECU 10 strengthens the restriction applied to the steering control more than a case where a change in the road slope increases. In this case, the steering control can be restricted to safer side for a direction of a change in the road slope which worsen the estimation accuracy of the road curvature among the roads in which a slope change is present.

Third Embodiment

In the third embodiment, configurations which differ from the first embodiment will be described. Note that portions having the same reference numbers represent the same portion and explanation thereof is not repeated.

FIG. 11 is a diagram showing a theory of technique in the third embodiment. When the own vehicle travels closely to either left or right marking with respect to the center of the own lane, in the captured image, one side marking C 21 in the distance side of the own vehicle shows larger distortion than that of one side marking C 22 in the vicinity side of the own vehicle. The difference of a degree of distortion between the left and tight markings C 21 and C 22 appears such that the farther the own vehicle position M 2 from the center of the own lane in the vehicle width direction, the larger the difference of degree of the distortion.

In this respect, according to the present embodiment, unlike the first embodiment, a deviation ΔW defined as a deviation of distance between the center M of the own lane and the own vehicle position M 2 in the vehicle width direction is calculated and the restriction applied to the steering control is determined such that the larger the deviation ΔW, the more strengthen the degree of restriction. In this case, during a setting of the third steering change rate R 3 at step S 17 , the center M 1 of the own lane is calculated using both of the left and right markings for example. Then, a distance between the calculated center M 1 of the own lane and the own vehicle position M 2 is calculated as the deviation ΔW.

For example, in the captured image, the center of the vehicle width direction indicating the imaging axis may be used as the own vehicle position M 2 . Also, a steering amount map may be stored in advance, which defines a correspondence between a combination of the first curvature ρ 1 , the yaw angle φ, the change amount GA and the deviation ΔW, and the third steering change rate R 3 . Then, by referring to the steering map, the third steering change rate R 3 may be set. The ECU 10 corresponds to a deviation calculation unit.

According to the present embodiment as described above, the ECU 10 calculates the deviation ΔW, and sets the degree of restriction applied to the steering control such that the larger the calculated deviation ΔW, the stronger the degree of the restriction. In this case, unnecessary steering amount caused by the own vehicle position can be avoided.

Fourth Embodiment

When a change in the road slope is determined, the target steering angle Ta may be restricted instead of the steering change rate R. FIG. 12 is a diagram showing a target steering amount set by ECU 10 according to the fourth embodiment.

In this case, at steps S 17 and S 18 , depending on the first curvature ρ 1 and the change amount GA of the road slope, the target steering amount Ta is set. Specifically, the target steering amount Ta set at step S 17 is set such that the larger the change amount GA of the road slope, the smaller the target steering amount Ta is as long as the road curvature is the same value. Also, the upper limit value of the target steering amount Ta set at the step S 17 may be determined to be less than or equal to the target steering amount Ta set at step S 19 .

Modification 1 of Fourth Embodiment

When a change in the road slope is determined, the ECU 10 may change a restriction value of the steering angle to add the restriction to the steering control. In this case, at steps S 17 and S 18 , the ECU 10 may set the target steering angle Ta and the steering change rate R, together with the restriction value of the steering angle. Further, the restriction value of the steering angle set at step S 17 is set such that the larger the change amount GA of the road slope, the smaller the upper limit value of the steering angle is.

Modification 2 of Fourth Embodiment

The ECU 10 may apply the restriction to the steering control by changing each of t the restriction value of the target steering amount Ta, the steering change rate R, and of the steering angle. For example, the ECU 10 may set respective restriction values of the target steering amount Ta, the steering change rate R and the steering angle so as to strengthen the restriction of the steering control.

Other Embodiments

When a change in the road slope is determined, the ECU 10 may set each of the steering control values Ta and R 3 to be a fixed value, instead of changing the steering control values Ta and R 3 depending on the change amount GA of the road slope. In this case, when a change in the road slope is determined at step S 13 shown in FIG. 5 , the process proceeds to step S 17 and sets each of the steering control values Ta and R 3 .

The ECU 10 may perform no steering control when the change amount GA of the road slope acquired at step S 14 is larger than a predetermined controllable threshold at which the steering control can be performed.

In the determination at step S 15 , the process may proceed to step S 18 while the own vehicle travels for a predetermined travel distance after applying the restriction to the steering control at step 21 .

The ECU 10 may perform, instead of using LKA control, a lane departure prevention control that issues an alert to the driver when the own vehicle is departing from the own lane across the marking. Even in this case, when the ECU 10 detects a change in the direction of the own vehicle and a change in the road slope, the ECU 10 may add a restriction to the steering control.

In the case where the steering control system 100 is provided with a navigation system storing map information, the ECU 10 may determine a change in the road slope based on the absolute coordinate on the road and a slope angle of each section on the road which constitute the map information. In this case, at step S 13 , the map information may be used to detect a location at which a change in the slope angle is present on the road, thereby detecting a change in the road slope.

When the steering control system 100 includes a navigation system, by using the map information, the change amount GA of the road slope may be acquired at step S 13 , and an increase/decrease determination of the road slope may be performed at step S 31 .