Vehicle control apparatus

This application is based on and claims the benefit of priority from earlier Japanese Patent Application No. 2017-240896 filed Dec. 15, 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 an example of the vehicle control apparatus, an apparatus is known in which a shape of the own lane is estimated by using left and right markings in a captured image in which an area ahead of the own vehicle is captured and steering control of the own vehicle is executed based on the estimated shape of the own vehicle. In such an apparatus, in the case where only one side, i.e. either of the left and right markings is detected, the apparatus estimates the shape of the own lane based on the detected marking of the left and right markings. For example, Japanese Patent Application Laid-Open Publication Number 2017-37473 discloses an apparatus that sets a virtual marking on one side, where no marking is detected, of both left and right markings, and determines a vehicle width in the own lane by using the virtual marking and the detected marking.

According to the above-mentioned patent literature, when the own vehicle travels on a straight road, if single side marking of the left and right markings is detected, the other side marking can be estimated, so that the curvature of the travelling road can be estimated based on the left and right markings including the estimated marking. However, it is hard to estimate the other side marking when the own vehicle travels on a curved road. In this case, it is considered that the curvature is estimated based on single side marking.

Here, when only single side marking is detected, the curvature cannot be estimated correctly depending on a road situation and may cause a negative influence on a steering control. For example, when only single side marking is detected and a down slope is present halfway ahead of the own vehicle, the marking in the captured image is distorted. In this case, when estimating the shape of the own lane which changes in road slope, by using only single side marking of the left and right markings, due to the distortion of the marking, the apparatus possibly applies unnecessary steering to the own vehicle.

The present disclosure is achieved in light of the above-described circumstances, and provides a vehicle control apparatus that avoids applying an unnecessary steering amount to the own vehicle when the shape of the own lane is estimated using only single side marking in the left and right markings.

The present disclosure provides a vehicle control apparatus including a marking detection unit that detects a marking defining an own lane based on an image 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 the marking detected by the marking detection unit;

a control unit that performs a steering control of the own vehicle based on the curvature of the own lane estimated by the curvature estimation unit;

a single side determination unit that determines whether the marking detected by the marking detection unit is only a marking on a single side, among both left side and right side markings, as a single side marking; and

a slope determination unit that determines whether a change in the road slope is present ahead of the own vehicle. The control unit is configured to apply restriction to the steering control during a change road determination state where only the single side marking is detected and a change in the road slope is detected.

In the case where a road slope changes, due to the change in the road slope, the detected marking in the captured image is likely to be distorted in the vehicle width direction. Hence, the distorted marking influences the curvature of the own lane estimated from single side marking to generate an erroneous curvature value compared to the actual curvature value. Then, an unnecessary amount of steering of the own vehicle may be applied. In this regard, according to the present disclosure configured as described above, during a change road determination state where only the single side marking has been detected and a change in the road slope has been detected, restriction is applied to the steering control performed based on the curvature of the own lane. In this case, when estimating the shape of the own lane based on the single side marking on the road having a slope, unnecessary restriction can be prevented from being applied to the own vehicle.

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 graph showing a steering amount set by the ECU;

FIGS. 7A and 7B are diagrams showing a difference between captured images when the road slope is changed to increase and decrease;

FIG. 8 is a flowchart showing a process of setting a steering amount according to a second embodiment; and

FIG. 9 is a graph showing a steering amount set by the ECU according to a third 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 , and a steering apparatus 13 . 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 a 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 the detected marking 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.

Also, the ECU 10 estimates the road curvature based on a marking on one side (single side marking) from the left and right markings, when detecting only single side marking in the left and right markings from the captured image. For example, the ECU 10 calculates an approximation formula that approximates the detected single side marking of the left and right markings, and estimates the road curvature by using the calculated approximation formula. The ECU 10 corresponds to a 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 has elapsed. 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 a single side marking 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 axis 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 either the first curvature ρ 1 or the second curvature ρ 2 . 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 either the first curvature ρ 1 or the second curvature ρ 2 , 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 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. 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 . In FIGS. 4A and 4B , a travelling route of the own vehicle set in the steering control based on the road curvature is shown with an arrow. According to the present embodiment, a presence of a change in the road slope is defined as a case where a change in the road slope is larger than or equal to a predetermined value, and an absence of a change in the road slope is defined as a case where a change in the road slope is 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 , a left side marking C 1 extends linearly towards a vanishing point FOE from a vehicle vicinity side. On the other hand, when the own vehicle travels on a straight road with a change in the road slope, as shown in FIG. 4B , the left side marking C 2 extends linearly towards the vanishing point FOE in a region from the slope change point P to the vehicle vicinity side A 1 . Further, in the vehicle distance side A 2 farther than the slope change point P, the left side marking C 2 does not extend towards the vanishing point FOE, and is distorted inward with respect to the road width direction.

In the case where the ECU 10 estimates the second curvature ρ 2 using single side marking in the left right markings, due to an influence by the distortion of the marking in the captured image, the second curvature ρ 2 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 second curvature ρ 2 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 the steering amount being applied in either the left or right direction. According to an example of FIG. 4B , compared to a case shown in FIG. 4A , 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.

In this respect, the ECU 10 restricts the steering control during a change road determination state where only single side marking in the left right markings has been detected and a change in the road slope 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 method 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 going towards 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, the stationary object appears from lower side of the FOE point in the captured image. Also, when the road slope increases in the vehicle distance side than in the slope change point, the stationary object appears from the upper side of 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 11 , the process determines whether only single side marking has been detected in the captured image. Step S 11 corresponds to a single side determination unit.

At step S 11 , when the process determines that both left and right markings have been detected, processing proceeds to step S 16 . At step S 16 , the process sets the target steering amount Ta and the first steering change rate R 1 based on the first curvature ρ 1 which has been estimated using both left and right markings. For example, a map is stored in advance, which defines a relationship between the target steering amount Ta and the first steering change rate R 1 in accordance with the first curvature ρ 1 . Then, the process refers to the map, thereby setting the target steering amount Ta and the first steering change rate R 1 corresponding to the first curvature ρ 1 .

At step S 11 , when the process determines that only single side marking of the left and right markings has been detected, the process proceeds to step S 12 . At step S 12 , the process determines whether a change in the road slope is present ahead of the own vehicle. When the process determines that there is no change in the road slope ahead of the own vehicle, the process proceeds to step S 15 . Step S 12 corresponds to slope determination unit.

At step S 15 , the process sets the target steering amount Ta and the second steering change rate R 2 based on the second curvature ρ 2 which has been estimated using both left and right markings. In FIG. 6 , the horizontal axis is defined as the road curvature and the vertical axis is defined as the steering change rate. According to the present embodiment, the second steering change rate R 2 is set to be smaller than or equal to the first steering change rate R 1 . This is because the first curvature ρ 1 which has been estimated using the left and right markings has higher estimation accuracy of the road curvature than the second curvature ρ 2 which has been estimated using single side marking in the left and right markings.

Referring back to FIG. 5 , 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 13 . 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 beyond the slope change point. Hence, at step S 13 , the process acquires a change amount GA of the road slope. The change amount GA of the road slope refers to a relative change amount of the road surface between the vehicle vicinity side and the vehicle distance side with respect to the slope change point. For example, at step S 12 , 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 12 . Step S 13 corresponds to a change amount acquiring unit.

At step S 14 , the process sets the target steering amount Ta and a third steering change rate R 3 based on the second curvature ρ 2 . At this moment, the process sets the third steering change rate R 3 based on the change amount GA. As shown in FIG. 6 , when the road curvature (ρ 2 ) is the same value, the third steering change rate R 3 is smaller than the second steering change rate R 2 .

According to the present embodiment, the larger the change amount GA, the smaller the third steering change rate R 3 . For example, a steering amount map is stored in advance, which defines a correspondence between a combination of the second curvature ρ 2 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 2 which is set depending on the change amount GA is smaller than the second steering change rate R 2 .

At step S 17 , the process performs a steering control based on the target steering amount Ta and steering change rates R 1 to R 2 which have been set in any of steps S 14 to S 16 . At this moment, when the steering control is performed based on the third steering change rate R 3 which has been set at step S 14 , the steering change rate is restricted compared to a case where the steering control is performed based on the first steering change rate R 1 which has been set at step S 16 .

Steps S 14 to S 17 corresponds to a control unit. When the process at step S 17 ends, the process temporarily terminates the process shown in FIG. 5 .

According to the above-described embodiment, the following effects and advantages are obtained.

The ECU 10 restricts the steering control performed based on the second curvature ρ 2 during a change road determination state where only single side marking has been detected using the captured image and a change in the road slope has been detected. Hence, even when the road shape is estimated based on the single side marking, the own vehicle can be prevented from being applied with an unnecessary steering amount due to the influence of a distortion in the marking caused by a change in the road slope.

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 beyond the slope change point. In this regard, the ECU 10 acquires a change amount GA of the road slope of the own vehicle when determining a change in road slope. Then, based on the change amount GA, the ECU 10 variably sets restriction of the steering control. In this case, depending on an amount of distortion of the marking, the ECU 10 is able to change the restriction applied to the steering control so that unnecessary restriction can be prevented from being applied to the steering control.

When comparing a case where the second curvature ρ 2 is estimated from single side marking of the left and right markings and a case where the first curvature ρ 1 is estimated from both of the left and right markings, since the former case has lower estimation accuracy of the road curvature than that of the latter case, the steering control may preferably be restricted for the former case. However, even in the case where only single side marking is detected but a change in the road slope is not detected, distortion of the marking in the road width direction in the captured image becomes small compared to a case where a change in the road slope is detected. In this respect, the ECU 10 strengthens the restriction of the steering control in the change road determination state, compared to restriction of the steering control in the flat road determination state. In other words, the ECU 10 weakens the restriction of the steering control in the flat road determination state, compared to restriction of the steering control in the change road determination state. In this case, when estimating the road shape using single side marking, the restriction of the steering control can be prevented from being unnecessarily strengthened.

Second Embodiment

According to the second embodiment, configuration differing from the first embodiment will be mainly described. Note that portions applied with the same reference numbers represent the same portion and repetitive description will be avoided.

In the second embodiment, as a change in the road slope, a case where the road slope increases and a case where the road slope decreases are distinguished, and the steering change rate when the road slope decreases is lowered compared to a case where the steering change rate when the road slope decreases. An example of decreasing road slope is that the state of the road changes from a float road to a down slope road.

FIG. 7A shows a captured image when the road slope ahead of the own vehicle decreases on a straight road, and FIG. 7B shows, on the same straight road, a captured image when the road slope ahead of the vehicle increases.

In the case where the steering control is performed by LKA control or the like, a steering amount is controlled to have the own vehicle travel parallel to the marking. As shown in FIG. 7A , when the road slope decreases, in the captured image, the single side marking C 11 is possibly distorted and deformed inward in the distance side farther than the slope change point P and may be disappeared. On the other hand, as shown in FIG. 7B , when the road slope decreases, in the captured image, the single side marking C 12 is distorted and deformed outward in the distance side farther than the slope change point P, but is still present. Hence, for example, when comparing a case where the road slope decreases and a case where the road slope increases, in the former case, the marking used for estimation of the road curvature becomes excessively small so that estimation accuracy is lowered. As a result, the steering control may be influenced by this lower estimation accuracy of the road curvature.

In this respect, according to the present embodiment, when determining that the road slope decreases, the ECU 10 strengthens the restriction of the steering control, compared to a case where the road slope increases.

With respect to FIG. 8 , a process for setting the target steering amount Ta and the steering change rate R according to the second embodiment will be described. The flowchart shown in FIG. 8 is repeatedly executed by the ECU 10 at predetermined periods.

At step S 12 , when the process determines that a change in the road is present, the process proceeds to step S 13 and acquires a change amount GA of the road slope.

At step S 31 , the process performs an increase/decrease determination of the road slope. The increase/decrease determination of the road slope may be performed using the optical flow used for determining a change in the road slope. In this case, when the optical flow is formed such that a stationary object appears from the upper side of the vanishing point FOE in the captured image, the process is able to determine that the road slope increases ahead of the own vehicle. On the other hand, when the optical flow is formed such that the stationary object appears from the lower side of the vanishing point FOE, the process is able to determine that the road slope decreases ahead of the own vehicle. Step S 31 corresponds to increase/decrease determination unit.

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 the steering change rate R 4 based on the second curvature ρ 2 . On the other hand, when the increase/decrease determination determines that the road slope increases, the process proceeds to step S 34 and acquires the target steering amount Ta and the steering change rate R 5 based on the second curvature ρ 2 . The steering change rate R 4 is set to be smaller than the steering change rate R 5 when the road curvature (ρ 2 ) and the change amount GA are the same as those of the steering change rate R 5 since the steering change rate R 4 is set when determined that the road slope decreases. Note that the steering change rate R 4 and the steering change rate R 5 are changed depending on respective change amounts GA.

When processes of the steps S 33 and S 34 are ended, the process temporarily terminates the process shown in FIG. 8

According to the second embodiment described above, the ECU 10 determines whether the road slope increases or decreases, when determining that the road slope changes. Then, when determined that the road slope decreases, restriction applied to the steering control is strengthened more than a case where the road slope is determined as increase. In this case, the steering control can be restricted to be a safer side with respect to a change direction of the road slope which deteriorates the estimation accuracy of the road curvature.

Third Embodiment

According to the third embodiment, when determining that a change in the road slope is present, instead of using the steering change rate R, the target steering amount Ta may be restricted. FIG. 9 is a diagram showing a steering amount set by the ECU 10 according to the third embodiment.

In this case, at step S 14 , the process sets the target steering amount Ta 2 depending on the second curvature ρ 2 and the change amount GA of the road slope. Specifically, at step S 14 , the target steering amount Ta 2 is set such that the larger the change amount GA of the road slope, the smaller the value of the target steering amount Ta 2 in the same road curvature. The upper limit value of the target steering amount Ta 2 may be defined as a value lower than or equal to the target steering amount Ta 1 which is set at step S 15 depending on the second curvature ρ 2 .

According to the present embodiment described above, similar effects and advantages can be obtained.

First Modification of Third Embodiment

In the case where it is determined that a change in the road slope is present, the ECU 10 may change the limit value of the steering angle as restriction of the steering control. In this case, the process may set, at steps S 14 and S 15 , the limit value of the steering angle together with the target steering amount Ta and the steering change rate R. Also, the limit value of the steering angle to be set at step S 14 is set such that the larger the change amount GA of the road slope, the smaller the upper limit of the steering angle.

Second Modification of Third Embodiment

The ECU 10 may change each of the target steering amount Ta, the steering change rate R and the limit value of the steering angle so as to restrict the steering control. For example, the ECU 10 may set, when determining that the road slope changes, the target steering amount Ta, the steering change rate R and the steering angle such that the restriction applied to the steering control is strengthened more than the case where a change in the road slope is not present.

Other Embodiments

Instead of changing the third steering change rate R 2 or the target steering amount Ta depending on the change amount GA of the road slope, the change amount may be a fixed value. In this case, when the process determines that the road slope is present at step S 12 in FIG. 5 , the process proceeds to step S 14 and sets the third steering change rate R 3 .

When the ECU 10 estimates the second curvature ρ 2 using only single side marking, and determines that no slope change is present, the ECU 10 may set the second steering change rate R 2 to be a value the same as the first steering change rate R 1

The ECU 10 may optionally not perform the steering control when the change amount GA of the road slope acquired at step S 13 is larger than a predetermined controllable threshold which defines a controllable steering control.

The ECU 10 may perform, instead of LKA (lane keeping assist) control, a lane departure avoidance control that notifies the driver with an alert when the own vehicle departs from the marking. Also in this case, the ECU 10 may apply restriction to the steering control when only single side marking has been detected and determines that a change in the road slope is present.

In the case where the steering control system 100 is provided with a navigation apparatus which stores map information, the ECU 100 may use the absolute coordinate on the road and a slope angle of each section of the road which constitute the map information to determine a change in the road slope. In this case, at step S 12 , the map information may be utilized to detect a region on the road where the slope angle changes, thereby determining whether a change in the road slope is present.

When the steering control system 100 includes a navigation apparatus, the apparatus may acquire the change amount GA of the road slope at step S 12 and perform an increase/decrease determination of the road slope at step S 32 using the map information.