Lane keeping assist device

Abstract

To provide a lane keeping assist device that is able to accurately control lateral acceleration so as not to exceed the maximum lateral acceleration, while preventing influence by vehicle characteristics or peripheral environment.SOLUTION: A lane keeping assist device 1 includes: a lane recognition unit 31 configured to recognize a lane in which a vehicle is traveling; a target steering angle calculation unit 32 configured to calculate a target steering angle θa for following a target path in the lane; a lane keeping control unit 33 configured to perform steering control on the basis of the target steering angle θa, so as to maintain traveling of the vehicle in the lane and so as not to exceed a preset maximum lateral acceleration; a lateral acceleration acquisition unit 34 configured to acquire, as a first lateral acceleration Ayy, a lateral acceleration generated in the vehicle; a lateral acceleration calculation unit 35 configured to calculate a lateral acceleration based on a steering angle input from a steering angle sensor 24 as a second lateral acceleration Ays; and a control adjustment unit 36 configured to compare the first lateral acceleration Ayy with the second lateral acceleration Ays and adjust the steering control on the basis of an index I indicating a comparison result.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a lane keeping assist system. [Background technology]

[0002] There is known a lane keeping assist device that assists a vehicle in driving near the center of a lane. For example, Patent Document 1 discloses a driving assist device that assists a driver in steering by changing a steering angle so that the vehicle drives along a target driving line that is the center position of the left and right white lines. The device described in Patent Document 1 is configured to control the steering angle so that the lateral acceleration of the vehicle does not exceed a maximum lateral acceleration during lane keeping control, estimates the lateral acceleration that occurs when lane keeping control is performed based on the curvature of the target driving line and the current speed of the vehicle, and generates an alarm when it is predicted that the lateral acceleration of the vehicle will exceed the maximum lateral acceleration. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6686873 Summary of the Invention [Problem to be solved by the invention]

[0004] When performing lane keeping control, it is required that a maximum lateral acceleration is set in advance in accordance with international standards, and that the lateral acceleration generated during turning is controlled so as not to exceed the maximum lateral acceleration. Since the lateral acceleration generated in a vehicle is affected by vehicle characteristics including, for example, vehicle weight and tire air pressure, and the surrounding environment, it is desired to precisely control the lateral acceleration during lane keeping control without being affected by the vehicle characteristics or the surrounding environment.

[0005] The present invention has been made in consideration of the above-described circumstances, and its object is to provide a lane keeping assist device that can precisely control lateral acceleration so as not to exceed maximum lateral acceleration, while suppressing the influence of vehicle characteristics or the surrounding environment in lane keeping control. [Means for solving the problem]

[0006] According to one aspect of the present invention, a lane keeping assist device includes a lane recognition unit that recognizes the lane in which a vehicle is traveling, a target steering angle calculation unit that calculates a target steering angle for following a target route within the lane, a lane keeping control unit that performs steering control based on the target steering angle so as to maintain the vehicle's traveling within the lane and not exceed a predetermined maximum lateral acceleration, a lateral acceleration acquisition unit that acquires lateral acceleration occurring in the vehicle as a first lateral acceleration, a lateral acceleration calculation unit that calculates lateral acceleration based on a steering angle input from a steering angle sensor as a second lateral acceleration, and a control adjustment unit that compares the first lateral acceleration with the second lateral acceleration and adjusts the steering control based on an index representing the comparison result. Effect of the Invention

[0007] The lane keeping assist system according to the present invention can precisely control the lateral acceleration during lane keeping control so that the maximum lateral acceleration is not exceeded. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of a lane keeping assist device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a flowchart showing the flow of lane keeping control in one embodiment. [Diagram 3] FIG. 3 is a flowchart illustrating the setting of the weighting coefficients. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A lane keeping assist device according to a first embodiment of the present invention will be described in detail below with reference to the drawings. Fig. 1 is a block diagram showing a schematic configuration of the lane keeping assist device in this embodiment. The lane keeping assist device is mounted on a vehicle to assist the driver's driving operation, and is configured to perform steering control so that the vehicle runs while maintaining the vehicle near the center of the lane.

[0010] 1, the lane keeping assist device 1 includes a camera 21 as forward detection means for detecting the area ahead of the vehicle, a yaw rate sensor 22 for detecting a yaw rate γ of the vehicle, a vehicle speed sensor 23 for detecting a speed (vehicle speed) V of the vehicle, and a steering angle sensor 24 for detecting a steering angle (front wheel steering angle) δ of the vehicle. The lane keeping assist device 1 further includes a control device 30, an EPS (electric power steering) controller 40, and the like.

[0011] The camera 21 is configured to capture an image of the area in front of the vehicle using an imaging element and input the image data to the control device 30. The camera 21 is configured to detect the positions of dividing lines on the road that define the lane in which the vehicle is traveling and adjacent lanes, and the presence and relative distances of obstacles such as other vehicles and people around the vehicle.

[0012] The signals of the yaw rate γ detected by the yaw rate sensor 22, the vehicle speed V detected by the vehicle speed sensor 23, and the steering angle δ detected by the steering angle sensor 24 are input to the control device 30. The signals of the vehicle speed V detected by the vehicle speed sensor 23 and the steering angle δ detected by the steering angle sensor 24 are also input to the EPS controller 40.

[0013] The control device 30 is configured, for example, by a computer including a ROM that stores programs and data, a CPU that performs arithmetic processing, a RAM that stores dynamic data and arithmetic processing results, an input / output interface, etc. The control device 30 is configured to execute the functions of a lane recognition unit 31, a target steering angle calculation unit 32, a lane keeping control unit 33, a lateral acceleration acquisition unit 34, a lateral acceleration calculation unit 35, and a control adjustment unit 36, and to control the lane keeping assist device 1 as a whole.

[0014] The lane recognition unit 31 is configured to recognize the lane (driving lane) in which the vehicle is traveling. For example, the lane recognition unit 31 performs image processing based on image data of the forward area input from the camera 21, and recognizes the left and right dividing lines (white lines) that define the lane in which the vehicle is traveling. The dividing lines include dividing lines of the own lane and adjacent lanes, and dividing lines at the lateral ends of the own lane. In addition, the lane recognition unit 31 calculates the width of the lane and the center line of the lane that passes through the center position between the left and right dividing lines from the positions of the left and right dividing lines, and calculates the radius of curvature or curvature (= the reciprocal of the radius of curvature) of the road based on the center line of the lane.

[0015] The target steering angle calculation unit 32 is configured to calculate a target steering angle θa for the vehicle to follow a target route within the lane. For example, the target steering angle calculation unit 32 sets a center line passing through the center position of the lane calculated by the lane recognition unit 31 as the target route, and calculates the position and attitude of the vehicle relative to the center line of the lane. The position of the vehicle is, for example, the distance (lateral displacement) y in the vehicle width direction from the center line of the lane to the position of the center of gravity of the vehicle, and the attitude of the vehicle is, for example, the angle (yaw angle) θy between the tangent direction of the center line of the lane and the central axis of the vehicle in the longitudinal direction. The yaw angle θy can also be calculated by integrating the yaw rate γ input from the yaw rate sensor 22. The target steering angle calculation unit 32 calculates the target steering angle θa for following the target route based on the position and attitude of the vehicle.

[0016] The lane keeping control unit 33 executes lane keeping control. Specifically, the lane keeping control unit 33 is configured to perform steering control based on a target steering angle θa so as to keep the vehicle traveling within the lane and not to exceed a preset maximum lateral acceleration. For example, the lane keeping control unit 33 calculates the yaw rate γ and lateral acceleration (d 2 y / dt 2 ) based on the relationship between the vehicle attitude and lateral displacement after Δt seconds that will not exceed the maximum lateral acceleration. Lane keeping control unit 33 calculates a steering angle command that will result in a lateral displacement of yt after Δt seconds, and outputs the command to EPS controller 40.

[0017] The lateral acceleration acquisition unit 34 is configured to acquire a lateral acceleration (first lateral acceleration) Ayy occurring in the vehicle. For example, the lateral acceleration acquisition unit 34 can calculate the first lateral acceleration Ayy based on the vehicle speed V detected by the vehicle speed sensor 23 and the yaw rate γ detected by the yaw rate sensor 22, based on the following (Equation 1). Ayy = V × γ (Equation 1)

[0018] The first lateral acceleration Ayy is calculated based on the yaw rate γ that is actually occurring in the vehicle, and can be said to represent the lateral acceleration that is actually occurring in the vehicle. The yaw rate γ is a positive value when the vehicle is turning left, and a negative value when the vehicle is turning right. Similarly, the lateral acceleration is a positive value when the vehicle is turning left and acceleration is acting in the right direction of the vehicle, and a negative value when the vehicle is turning right and acceleration is acting in the left direction of the vehicle.

[0019] The lateral acceleration calculation unit 35 is configured to calculate a lateral acceleration (second lateral acceleration) Ays based on the steering angle δ input from the steering angle sensor 24. For example, the lateral acceleration calculation unit 35 can calculate the second lateral acceleration Ays based on the following (Equation 2). Ays = (δ × V 2 ) / {(1+A×V2 )×l} (Formula 2) In (Equation 2), V is the vehicle speed detected by the vehicle speed sensor 23, A is the stability factor, and l is the wheelbase.

[0020] The stability factor A is a characteristic value that represents the steering characteristics of a vehicle during steady circular turning with a constant steering wheel rotation angle, and is a design value that is defined based on the vehicle's wheelbase, front axle load, front cornering power, rear axle load, and rear cornering power. The second lateral acceleration Ays is calculated using the stability factor A, which is a design value of the vehicle, and can be said to represent the designed ideal lateral acceleration that is expected to occur in the vehicle at a certain steering angle δ.

[0021] The control adjustment unit 36 ​​is configured to adjust the steering control executed by the lane keeping control unit 33 based on a comparison result between the first lateral acceleration Ayy acquired by the lateral acceleration acquisition unit 34 and the second lateral acceleration Ays calculated by the lateral acceleration calculation unit 35. The adjustment of the steering control in the control adjustment unit 36 ​​will be described later.

[0022] The EPS controller 40 is configured by a computer including, for example, a ROM that stores programs and data, a CPU that performs arithmetic processing, a RAM that stores dynamic data and arithmetic processing results, an input / output interface, etc. The EPS controller 40 is configured to control the steering mechanism 41 based on a steering angle command input from the lane keeping control unit 33 or a steering angle command corresponding to manual steering 34 of the steering wheel.

[0023] Since the steering reaction force changes depending on the vehicle speed, the EPS controller 40 refers to a steering angle-steering torque map for each vehicle speed stored in a memory (not shown), acquires a steering torque based on a steering angle command, and outputs a torque command to the steering mechanism 41. The steering mechanism 41 drives an actuator (EPS motor) (not shown) in response to the torque command, thereby controlling the front wheel steering angle δ so that the vehicle follows the target route.

[0024] As described above, the lane keeping assist device 1 according to the present embodiment is configured to perform so-called hands-on lane keeping control, which assists the driver in driving so that the vehicle keeps the vehicle in the center of the lane. When the hands-on lane keeping control is performed, the maximum lateral acceleration permitted to occur in the vehicle is set in advance in accordance with the international standard. That is, the maximum lateral acceleration is a value of lateral acceleration that guarantees that the vehicle will not deviate from the lane when lateral acceleration occurs in a vehicle that is turning within a predetermined vehicle speed range. Therefore, during the execution of the lane keeping control, the control device 30 must monitor the lateral acceleration occurring in the vehicle, and must control the lateral acceleration occurring when the vehicle is turning so as not to exceed the maximum lateral acceleration.

[0025] The lateral acceleration that actually occurs in a vehicle is affected by vehicle characteristics including vehicle weight, tire air pressure, etc., and the surrounding environment, etc. In other words, a difference may occur between the ideal lateral acceleration that is expected to occur in the vehicle based on its design and the lateral acceleration that actually occurs in the vehicle, depending on the vehicle characteristics and the surrounding environment, etc. In addition, for example, the yaw response of the vehicle when turning left or right may differ depending on the vehicle characteristics and the surrounding environment, etc., and the lateral acceleration that occurs in the vehicle when turning left or right may differ even when traveling at the same vehicle speed around a curve with the same curvature.

[0026] Therefore, during execution of lane keeping control, it is required to precisely control the lateral acceleration acting on the vehicle so as not to exceed the maximum lateral acceleration while suppressing the effects of vehicle characteristics or the surrounding environment.

[0027] Therefore, in this embodiment, the first lateral acceleration Ayy that is actually generated during execution of lane keeping control is compared with an ideal second lateral acceleration Ays calculated from a design value of the vehicle, and the control adjustment unit 36 ​​adjusts the steering control by the lane keeping control unit 33 based on the comparison result. The adjustment of the steering control by the control adjustment unit 36 ​​will be described in detail below.

[0028] The control adjustment unit 36 ​​compares the first lateral acceleration Ayy acquired by the lateral acceleration acquisition unit 34 with the second lateral acceleration Ays calculated by the lateral acceleration calculation unit 35, and calculates the comparison result as an index I. The index I is the ratio of the ideal second lateral acceleration Ays to the actual first lateral acceleration Ayy, and can be expressed by the following (Equation 3). I = Ays / Ayy (Equation 3)

[0029] The indicator I allows the vehicle condition to be understood as follows: When index I=1 This indicates that the first lateral acceleration Ayy and the second lateral acceleration Ays are equal, and that a lateral acceleration equal to the ideal second lateral acceleration Ays that is expected to occur for a certain steering angle δ is occurring in the vehicle. If index I>1 This indicates that the first lateral acceleration Ayy is smaller than the second lateral acceleration Ays, and that a lateral acceleration smaller than the ideal second lateral acceleration Ays is occurring in the vehicle. When index I<1 This indicates a state in which the first lateral acceleration Ayy is greater than the second lateral acceleration Ays, and a lateral acceleration greater than the ideal second lateral acceleration Ays is occurring in the vehicle.

[0030] The control adjustment unit 36 ​​adjusts the steering control so that the index I approaches 1. Specifically, the control adjustment unit 36 ​​adjusts the target steering angle θa calculated by the target steering angle calculation unit 32 so that the index I approaches 1. By performing the steering control based on the adjusted target steering angle θa, the vehicle behavior changes and the lateral acceleration generated in the vehicle is adjusted to approach the ideal second lateral acceleration Ays.

[0031] Considering that the yaw response of the vehicle may differ when turning left or right as described above, the control adjustment unit 36 ​​distinguishes between the index I when the vehicle is turning left as a left turning index Il and the index I when the vehicle is turning right as a right turning index Ir. Whether the vehicle is turning left or right can be determined based on, for example, the front wheel steering angle of the vehicle, the yaw rate occurring in the vehicle, the lateral acceleration occurring in the vehicle, etc. Alternatively, whether the vehicle is turning left or right can also be determined based on the curvature of the road calculated by the lane recognition unit 31 or information on the road shape acquired from a map information database (not shown).

[0032] The control adjustment unit 36 ​​adjusts the target steering angle θal during a left turn based on a left turn index Il when the vehicle is turning left, and adjusts the target steering angle θar during a right turn based on a right turn index Ir when the vehicle is turning right.

[0033] The adjustment of steering control in this embodiment will be described in detail below with reference to the flowchart in Fig. 2. The flowchart in Fig. 2 shows the flow of lane keeping control in which steering control is performed so that the vehicle runs near the center of the lane. The control device 30 repeatedly executes the process shown in Fig. 2 at a predetermined cycle while the lane keeping control is being performed, and adjusts (corrects) the target steering angle θa based on the index I so that the vehicle runs near the center of the lane without exceeding the maximum lateral acceleration during turning. Note that the adjustment method of the target steering angle θa is the same for left turning and right turning, so in the following, for convenience of explanation, the turning direction will not be distinguished, and the index I and the target steering angle θa will be used as representative values ​​for left and right turning.

[0034] In step S101, the control device 30 acquires image data of the area in front of the vehicle input from the camera 21, and also acquires vehicle state data input from the yaw rate sensor 22, the vehicle speed sensor 23, and the steering angle sensor 24. The vehicle state data includes the vehicle speed V, the yaw rate γ, and the steering angle δ.

[0035] In step S102, the lane recognition unit 31 recognizes the lane in which the vehicle is traveling based on the image data input in step S101, and calculates the center line of the lane and the curvature radius of the road.

[0036] In step S103, the target steering angle calculation unit 32 sets the center line of the lane calculated in step as a target route, and calculates a target steering angle θa for following the target route based on the position and attitude of the vehicle with respect to the target route.

[0037] In step S104, it is determined whether the vehicle is turning, and if so, whether it is turning right or left. If the vehicle is turning, the process proceeds to step S105. If the vehicle is not turning, the process proceeds to step S111, where steering control is performed based on the target steering angle θa calculated in step S103. Note that, even if the vehicle is not turning, the process from step S105 onwards may be performed; however, by limiting the process from S105 onwards to when the vehicle is turning, the calculation load on the control device 30 can be reduced.

[0038] In step S105, the lateral acceleration acquisition unit 34 calculates the first lateral acceleration Ayy actually occurring in the vehicle, using the above-mentioned (Equation 1), based on the vehicle speed V and yaw rate γ acquired in step S101.

[0039] In step S106, the lateral acceleration calculation unit 35 uses the steering angle δ acquired in step S101 to calculate the second lateral acceleration Ays that is expected to occur with respect to the steering angle δ from the above-mentioned (Equation 2).

[0040] In step S107, the control adjustment unit 36 ​​calculates the ratio of the second lateral acceleration Ays to the first lateral acceleration Ayy. The ratio calculated here is a value that newly represents the comparison result between the first lateral acceleration Ayy and the second lateral acceleration Ays obtained in the current cycle, and is therefore set as the index Inew.

[0041] In step S108, the index I is updated using the index Inew calculated in step S107. To this end, the index I calculated in the previous cycle is first set as the index Iold, and an average value of the indexes is calculated using the index Iold in the previous cycle and the index Inew newly calculated in step S107. The calculated average value of the indexes is set as the index I representing the comparison result between the first lateral acceleration Ayy and the second lateral acceleration Ays.

[0042] Specifically, the index I is updated using the following (Equation 4). I = (n × Iold + Inew) / (n + 1) (Equation 4) In (Equation 4), n is the number of past periods including the previous period, and an appropriate value is set in advance (for example, n=10). That is, the index I calculated from (Equation 4) represents a moving average of the indexes for (n+1) periods. By using the moving average as the index I, it is expected that noise can be suppressed and robustness can be improved. When the index I is calculated for the first time in the current period, it can be treated as, for example, the index Iold for the previous period=1. When the vehicle is turning left, a left turning index Il is calculated, and when the vehicle is turning right, a right turning index Ir is calculated.

[0043] In step S109, it is determined whether the index I calculated in step S108 is 1. If the index I is 1, the vehicle is experiencing a lateral acceleration equal to the second lateral acceleration Ays expected to occur for the steering angle δ, so the target steering angle θa is not corrected and the process proceeds to step S111. If the index I is not 1, the first lateral acceleration Ayy actually occurring in the vehicle is smaller or larger than the second lateral acceleration Ays, and the first lateral acceleration Ayy is insufficient or excessive with respect to the second lateral acceleration Ays, so the process proceeds to step S110 and the target steering angle θa is adjusted (corrected).

[0044] In step S110, the control adjustment unit 36 ​​adjusts the target steering angle θa calculated in step S103 so as to bring the index I closer to 1. Specifically, the control adjustment unit 36 ​​calculates a correction value θc of the target steering angle θa using the index I from the following (Equation 5). θc=θa+(θa×(I-1)×η) (Formula 5) In equation (5), η is a variable coefficient for weighting the correction of the target steering angle θa. The coefficient η will be described later.

[0045] When the index I>1, the first lateral acceleration Ayy that is actually generated is smaller than the second lateral acceleration Ays. In this case, the correction value θc is increased by (θa×(I-1)×η) more than the target steering angle θa. As a result, the first lateral acceleration Ayy generated in the vehicle increases and approaches the ideal second lateral acceleration Ays.

[0046] When the index I<1, the first lateral acceleration Ayy that is actually generated is greater than the second lateral acceleration Ays. In this case, the correction value θc is reduced from the target steering angle θa by (θa×(I-1)×η), and as a result, the first lateral acceleration Ayy generated in the vehicle is reduced and approaches the ideal second lateral acceleration Ays. The control adjustment unit 36 ​​sets the correction value θc calculated here as the target steering angle θa.

[0047] In step S111, the lane keeping control unit 33 performs steering control based on the target steering angle θa calculated in step S103 or the target steering angle θa corrected in step S110. Specifically, the lane keeping control unit 33 outputs a steering angle command corresponding to the target steering angle θa to the EPS controller 40 as described above, and controls the steering mechanism 41.

[0048] Next, the variable coefficient η for weighting will be described. The coefficient η is used to adjust the degree of correction of the target steering angle θa based on the change tendency of the index I due to the correction of the target steering angle θa. For example, if the index I changes suddenly due to the correction of the target steering angle θa, the steering angle δ may change significantly, which may deteriorate the ride comfort of the passengers. However, if emphasis is placed only on the ride comfort, there is a possibility that the index I will not approach 1 easily even if the target steering angle θa is corrected.

[0049] Therefore, by setting a coefficient η based on the change tendency of the index I when calculating the correction value θc of the target steering angle θa, the target steering angle θa is adjusted to suppress deterioration of the ride comfort while improving the tracking ability so as to quickly approach the index I = 1. Note that the coefficient η is multiplied by the difference (I-1) between the index I and 1 as shown in the above (Equation 5), and can also be said to be a coefficient for weighting the index I.

[0050] The setting of the coefficient η will be described in detail below with reference to the flowchart in Fig. 3. The coefficient η is set separately as a coefficient ηl for the left turning index Il and a coefficient ηr for the right turning index Ir. However, since the method of setting the coefficient η for left turning and right turning is the same, for the sake of convenience, the following description will be given using the coefficient η as a representative value for left and right turning without distinguishing between the turning directions.

[0051] In step S201, the change trend of the index I is calculated. For example, the change speed B of the index I is calculated as the change trend of the index I. In step S202, it is determined whether the absolute value of the change speed B calculated in step S201 is smaller than a predetermined value B1. The predetermined value B1 is set to an appropriate value in advance in order to determine whether the change of the index I is slow. If the absolute value of the change speed B is smaller than the predetermined value B1 and the change of the index I is slow, the process proceeds to step S203.

[0052] In step S203, the coefficient η is increased, taking into consideration that the change in the steering angle δ is slow and the effect of the correction of the target steering angle θa is not very apparent. The increase rate or amount of increase of the coefficient η is set to an appropriate value in advance. For example, the coefficient η is updated by increasing the coefficient η set in the previous cycle at a predetermined increase rate. Note that, when updating the coefficient η for the first time in the current cycle, an initial value (for example, initial value = 1) can be used as the coefficient η of the previous cycle. By increasing the coefficient η, the correction amount (θa × (I-1) × η) of the target steering angle θa becomes large, and the degree of correction of the target steering angle θa increases. This makes it possible to improve the tracking ability to the index I = 1. The coefficient η can be said to be a weighting coefficient for the correction amount (adjustment amount) of the target steering angle θa.

[0053] If it is determined in step S202 that the absolute value of the rate of change B is equal to or greater than the predetermined value B1, the process proceeds to step S204, where it is determined whether or not the absolute value of the rate of change B is greater than a predetermined value B2. The predetermined value B2 is greater than the predetermined value B1, and is set to an appropriate value in advance in order to determine whether or not the index I is changing rapidly. If the absolute value of the rate of change B is greater than the predetermined value B2 and the index I is changing rapidly, the process proceeds to step S205.

[0054] In step S205, the coefficient η is decreased, taking into consideration the possibility that the correction of the target steering angle θa may cause the steering angle δ to change rapidly, resulting in a deterioration in ride comfort. The decrease rate or amount of decrease of the coefficient η is set to an appropriate value in advance. For example, the coefficient η is updated by increasing the coefficient η set in the previous cycle at a predetermined decrease rate. By decreasing the coefficient η, the correction amount (θa×(I-1)×η) of the target steering angle θa becomes smaller, and the degree of correction of the target steering angle θa can be suppressed.

[0055] In step S204, if it is determined that the absolute value of the rate of change B is equal to or greater than a predetermined value B1 and equal to or less than a predetermined value B2, and the index I is changing at an appropriate rate, the process proceeds to step S206. In step S206, it is determined that the steering angle δ is changing smoothly due to the correction of the target steering angle θa, and the coefficient η is maintained.

[0056] The lane keeping assist system 1 according to the present embodiment described above can achieve the following advantageous effects.

[0057] (1) The lane keeping assist device 1 includes a lane recognition unit 31 that recognizes the lane in which the vehicle is traveling, a target steering angle calculation unit 32 that calculates a target steering angle θa for following a target route within the lane, a lane keeping control unit 33 that performs steering control based on the target steering angle θa so as to maintain the vehicle's traveling within the lane and not exceed a predetermined maximum lateral acceleration, a lateral acceleration acquisition unit 34 that acquires the lateral acceleration occurring in the vehicle as a first lateral acceleration Ayy, a lateral acceleration calculation unit 35 that calculates the lateral acceleration based on the steering angle δ input from the steering angle sensor 24 as a second lateral acceleration Ays, and a control adjustment unit 36 ​​that compares the first lateral acceleration Ayy with the second lateral acceleration Ays and adjusts the steering control based on an index I that represents the comparison result.

[0058] Since the lateral acceleration actually generated in the vehicle is affected by vehicle characteristics including vehicle weight and tire air pressure, as well as the surrounding environment, by adjusting the steering control based on index I, which represents the comparison result between the first lateral acceleration Ayy actually generated in the vehicle and the second lateral acceleration Ays that is expected to occur by design based on the steering angle δ, it is possible to precisely control the lateral acceleration so as not to exceed the maximum lateral acceleration while suppressing the influence of vehicle characteristics and the surrounding environment.

[0059] (2) The control adjuster 36 calculates the ratio of the second lateral acceleration Ays to the first lateral acceleration Ayy as an index I representing the comparison result. This makes it possible to represent the comparison result as a dimensionless index I, and to easily grasp the state of the lateral acceleration.

[0060] (3) The control adjustment unit 36 ​​is configured to adjust the target steering angle θa so as to bring the index I closer to 1 when the index I is not 1, and corrects the target steering angle θa when the index I is not 1 and the first lateral acceleration Ayy actually occurring in the vehicle is insufficient or excessive with respect to the ideal second lateral acceleration Ays. The EPS controller 40 controls the torque of the steering mechanism 41 so as to realize the corrected target steering angle θa.

[0061] (4) The control adjustment unit 36 ​​is configured to set a variable coefficient η for weighting the adjustment amount of the target steering angle θa. By weighting the adjustment amount (correction amount) of the target steering angle θa using the variable coefficient η, it is possible to improve the tracking ability to make the index I=1 and suppress excessive changes in vehicle behavior due to changes in the target steering angle θa.

[0062] (5) The control adjustment unit 36 ​​calculates the change speed B of the index I and changes the coefficient η according to the change speed B of the index I. Since the weighting of the adjustment amount (correction amount) of the target steering angle θa is changed according to the change speed B of the index I, i.e., the change tendency, it is possible to adjust the correction amount of the target steering angle θa so as to improve the tracking ability of the index I to 1 when the index I is difficult to approach 1, for example, in a situation where the radius of curvature of the road is not constant. Also, when the index I changes suddenly, it is possible to adjust the correction amount of the target steering angle θa so as to suppress deterioration of the passenger's feeling due to a change in the vehicle behavior.

[0063] (6) The index I calculated by the control adjustment unit 36 ​​includes a left turning index Il, which is the ratio of the second lateral acceleration Ays to the first lateral acceleration Ayy when the vehicle is turning left, and a right turning index Ir, which is the ratio of the second lateral acceleration Ays to the first lateral acceleration Ayy when the vehicle is turning right. The control adjustment unit 36 ​​sets, as the coefficient η, a left turning coefficient ηl corresponding to the rate of change of the left turning index Il, and a right turning coefficient ηr corresponding to the rate of change of the right turning index Ir. By calculating the left turning index Il and the right turning index Ir, and the left turning coefficient ηl and the right turning coefficient ηr, respectively, the lateral acceleration generated in the vehicle can be controlled with high accuracy even when the yaw response of the vehicle during left and right turning differs depending on the vehicle characteristics or the surrounding environment, etc.

[0064] (7) The control adjustment unit 36 ​​is configured to adjust the steering control when the vehicle is turning, making it possible to precisely control the lateral acceleration so that it does not exceed the maximum lateral acceleration during turning.

[0065] -Variations- (1) In the above-described embodiment, the lateral acceleration acquisition unit 34 calculates the first lateral acceleration Ayy occurring in the vehicle from the vehicle speed V and the yaw rate γ. However, this is not limited to this, and the lateral acceleration acquisition unit 34 may be configured to directly acquire the first lateral acceleration Ayy occurring in the vehicle using a lateral acceleration sensor.

[0066] (2) In the above-described embodiment, the ratio of the second lateral acceleration Ays to the first lateral acceleration Ayy is calculated as the index I representing the comparison result between the first lateral acceleration Ayy and the second lateral acceleration Ays. However, the present invention is not limited to this, and the index I of the comparison result may be, for example, the difference between the first lateral acceleration Ayy and the second lateral acceleration Ays.

[0067] (3) In the above embodiment, the average value of the calculated indices is set as the index I. However, this is not limited to this, and the calculated index Inew may be used as the index I as it is.

[0068] (4) In step S109 of the flowchart in Fig. 2, it is determined whether the index I = 1, but it may be determined whether the index I is within a predetermined range including 1. In particular, when the calculated index Inew is used as the index I as is, the effect of suppressing noise, etc. can be expected by correcting the target steering angle θa depending on whether the index I is within the predetermined range.

[0069] Although several embodiments of the present invention have been described above, it should be noted that the present invention is not limited to the above-described embodiments, and various modifications and variations are possible within the scope of the present invention. [Explanation of symbols]

[0070] 1 Lane keeping assist device 24 Steering angle sensor 31 Lane Recognition Unit 32 Target steering angle calculation unit 33 Lane keeping control unit 34 Lateral acceleration acquisition section 35 Lateral acceleration calculation section 36 Control and adjustment section

Claims

1. a lane recognition unit that recognizes the lane in which the vehicle is traveling; a target steering angle calculation unit that calculates a target steering angle for following a target route within the lane; a lane keeping control unit that performs steering control based on the target steering angle so as to maintain the vehicle traveling within the lane and not to exceed a preset maximum lateral acceleration; a lateral acceleration acquisition unit that acquires a lateral acceleration occurring in the vehicle as a first lateral acceleration; a lateral acceleration calculation unit that calculates a lateral acceleration based on a steering angle input from a steering angle sensor as a second lateral acceleration; a control adjustment unit that compares the first lateral acceleration with the second lateral acceleration and adjusts the steering control based on an index that indicates a comparison result; A lane keeping assist device comprising:

2. The lane keeping assist device according to claim 1 , wherein the control adjuster calculates a ratio of the second lateral acceleration to the first lateral acceleration as the index representing the comparison result.

3. The lane keeping assist device according to claim 2 , wherein the control adjustment unit is configured to adjust the target steering angle so as to bring the index closer to 1 when the index is not 1.

4. 4. The lane keeping assist device according to claim 3, wherein the control adjustment unit is configured to set a variable coefficient for weighting an adjustment amount of the target steering angle.

5. The control adjustment unit is Calculating the rate of change of the index; The lane keeping assist device according to claim 4 , wherein the coefficient is changed in accordance with a rate of change of the index.

6. The indexes calculated by the control adjustment unit include a left turn index that is a ratio of the second lateral acceleration to the first lateral acceleration while the vehicle is turning left, and a right turn index that is a ratio of the second lateral acceleration to the first lateral acceleration while the vehicle is turning right, The lane keeping assist device according to claim 5 , wherein the control adjustment unit sets, as the coefficients, a left turning coefficient corresponding to a rate of change of the left turning indicator and a right turning coefficient corresponding to a rate of change of the right turning indicator.

7. The lane keeping assist device according to claim 1 , wherein the control adjustment unit is configured to adjust the steering control when the vehicle is turning.

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