Lane keeping control device for a vehicle

Abstract

The present invention relates to and provides a lane keeping control device for a vehicle which suppresses a swing behavior like a snake-like driving due to a steering response which is excessively sensitive to a change with time, and obtains a stable driving which is not changed from a time of shipment. The lane keeping control device for the vehicle sets a target path along which the host vehicle should travel, calculates a control amount for an electric power steering motor (12) based on at least an offset from the target path, controls the host vehicle to travel along the target path, compares a response speed (Vn) of an actual steering angle of the host vehicle with respect to a target steering angle for traveling along the target path and a set response speed (V0), decides a gain of a current value (Icmdn+1) for driving the electric power steering motor (12) in a manner that the response speed (Vn) and the set response speed (V0) are coincident, and updates the decided gain.

Description

Technical Field

[0001] This invention relates to a lane keeping control device for a vehicle that controls electric power steering to travel along a predetermined target path. Background Technology

[0002] In recent years, a vehicle lane keeping control technology has been known as a driving assistance system that uses cameras to identify white lines on the road while the vehicle is in motion, and obtains information such as GPS to control the vehicle's operation, maintain lane centering, and prevent lane departure.

[0003] When such a vehicle's lane-keeping control device intervenes, it designs a driving path, performs feedforward control to track the vehicle, provides feedback control on the amount by which the vehicle's actual driving route deviates from the target path, and makes corrections.

[0004] For example, Patent Document 1 discloses a technique that uses the differential value of the target control angle to change the gain so as to drive accurately regardless of the magnitude of road friction.

[0005] In addition, Patent Document 2 discloses a technique for adjusting the steering force based on the torque output value in order to make the power steering feel consistent with the factory settings.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 5-338548

[0009] Patent Document 2: Japanese Patent Application Publication No. 2008-302900 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] However, the vehicle's control mechanism is equipped with a rack and pinion support mechanism. In order to eliminate the loosening of the gear and rack pair in the gear and rack type steering gearbox, a force is applied to the rack shaft by springs or the like, and a specified frictional load is applied to the pinion shaft.

[0012] The frictional load generated by the rack and pinion support mechanism is reduced due to the wear of the gear and rack pair over the years. If the frictional load of the rack and pinion shaft relative to the pinion shaft is reduced, the handling responsiveness during lane keeping will be improved.

[0013] Therefore, the following problem exists: the steering becomes overly sensitive over time, and the actual steering angle deviates from the indicated steering angle generated by lane keeping control, causing swaying (vibration of the vehicle trajectory) behavior. As a result, the vehicle may swerve, failing to achieve stable vehicle movement.

[0014] Therefore, in view of the above, the object of the present invention is to provide a lane keeping control device for a vehicle that suppresses swaying behavior such as serpentine driving caused by excessive sensitivity to manipulation over time, and achieves stable driving that is unchanged from the factory settings.

[0015] Solution for solving the problem

[0016] One aspect of the present invention provides a lane keeping control device for a vehicle, which sets a target path for the vehicle to travel, calculates a control amount for an electric power steering motor based at least on an offset from the target path, controls the vehicle to travel along the target path, wherein the actual steering angle of the vehicle is compared with a target steering angle for traveling along the target path and a set response speed, and a gain of the current value driving the electric power steering motor is determined in such a way that the response speed and the set response speed are consistent, and the determined gain is updated.

[0017] Invention Effects

[0018] According to the present invention, a lane keeping control device for a vehicle can be provided to suppress swaying behavior such as serpentine driving caused by excessive sensitivity to manipulation over time, thereby achieving stable driving as unchanged as when the vehicle was manufactured. Attached Figure Description

[0019] Figure 1 This is a schematic diagram showing the structure of a vehicle's control system.

[0020] Figure 2 This is a sectional view showing the structure of the rack and pinion support mechanism.

[0021] Figure 3 This is a functional block diagram of the control unit.

[0022] Figure 4 An illustrative diagram showing an example of the characteristic of the operating torque of an electric power steering motor versus the basic current value of the electric motor.

[0023] Figure 5 This is an explanatory diagram of feedforward control.

[0024] Figure 6 This is an explanatory diagram of lateral position feedback control.

[0025] Figure 7 This is an explanatory diagram of yaw angle feedback control.

[0026] Figure 8 It is an illustration of the actual driving trajectory of a vehicle on a straight road relative to the target path as time goes by.

[0027] Figure 9 A flowchart illustrating a control example during lane keeping.

[0028] Figure 10 It is an explanatory diagram of the actual driving trajectory of a vehicle on a straight road relative to the target path during control.

[0029] Figure 11 This is an explanatory diagram showing the actual driving trajectory of a vehicle relative to the target path when entering a curve (when entering a curve) without correcting the feedback gain.

[0030] Figure 12 This is an explanatory diagram showing the actual driving trajectory of a vehicle relative to the target path when entering a curve after correcting the feedback gain.

[0031] Symbol Explanation

[0032] 1…Electric power steering

[0033] 2… Steering Axle

[0034] 3… Steering column

[0035] 4… Steering wheel

[0036] 4a…Manipulation angle sensor

[0037] 5…Pinary gear shaft

[0038] 6… Steering gearbox

[0039] 7… rack and pinion shaft

[0040] 7a… rack

[0041] 7b… Back side of the shaft

[0042] 8…Tie bar

[0043] 9…Front Steering Knuckle

[0044] 10L, 10R... left and right wheels

[0045] 11…Auxiliary transmission mechanism

[0046] 12… Electric power steering motor

[0047] 20… Operation and Control Department

[0048] 20a…Motor Basic Current Setting Section

[0049] 20b…Feedforward Control Unit

[0050] 20c… Lateral Position Feedback Control Unit

[0051] 20d…Yaw Angle Feedback Control Unit

[0052] 20e… Lateral Position Feedback Gain Setting Section

[0053] 20f…Yaw Angle Feedback Gain Setting Section

[0054] 20g… Electric power steering motor current value calculation section

[0055] 21…Motor drive unit

[0056] 31…Forward Identification Device

[0057] 32…vehicle speed sensor

[0058] 33…Maneuver Angle Sensor

[0059] 34…Manipulating torque sensor

[0060] 40…Rack and pinion shaft support mechanism Detailed Implementation

[0061] Hereinafter, an embodiment of one aspect of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, in the drawings used for the following description, the scale of each structural element is different in order to make each structural element identifiable on the drawings. The present invention is not limited to the number of structural elements, the shape of the structural elements, the ratio of the sizes of the structural elements, and the relative positional relationships of the structural elements shown in these drawings.

[0062] Figure 1 The electric power steering system 1 shown, which includes the vehicle's lane keeping control device, is a structure in which the steering angle can be freely set independently of the driver's input. The steering shaft 2 is rotatably supported on the body frame (not shown) via the steering column 3, with one end extending to the driver's seat side and the other end extending to the engine compartment side.

[0063] A steering wheel 4 is fixed to the driver's seat side end of the steering shaft 2, and a steering angle sensor 4a is provided thereon. In addition, a pinion shaft 5 is connected to the end of the steering shaft 2 that extends toward the engine compartment.

[0064] A steering gearbox 6 is provided in the engine compartment. The steering gearbox 6 extends in the vehicle width direction and is provided with a rack and pinion support mechanism 40. The rack and pinion 7 is freely inserted and supported in the steering gearbox 6.

[0065] In addition, the left and right ends of the rack shaft 7 protrude from the ends of the steering gearbox 6, and the front steering knuckle 9 is connected to the ends of the rack shaft 7 via the tie rod 8. The front steering knuckle 9 rotatably supports the left and right wheels 10L and 10R, which serve as the control wheels, and is steered freely on the vehicle frame.

[0066] Therefore, when the steering wheel 4 is operated to rotate the steering shaft 2 and the pinion shaft 5, the rack shaft 7 moves to the left and right through the rotation of the pinion shaft 5. Through this movement, the front steering knuckle 9 rotates around the kingpin shaft (not shown), and the left and right wheels 10L and 10R turn to the left and right.

[0067] The rack and pinion support mechanism 40 is mounted on the steering gearbox 6. The rack and pinion support mechanism 40 has a rack and pinion guide rail 42 (see reference). Figure 2 ).

[0068] The rack shaft guide rail 42 is cylindrical in shape, and a rack shaft sliding surface 42a with a semi-circular cross section is formed at the sliding contact part with the rack shaft 7. The rack shaft sliding surface 42a supports the rack 7a relative to the rack shaft 7, which clamps the shaft core on the opposite side of the shaft back surface 7b, to slide freely in the axial direction.

[0069] Furthermore, a lubricant such as grease is filled between the sliding contact surface 42a of the rack shaft and the surface of the rack shaft 7. A spring receiving recess 42b is formed on the surface of the rack shaft guide 42 opposite to the sliding contact surface 42a of the rack shaft.

[0070] Furthermore, a sealing groove 42c is formed on the circumferential portion of the rack shaft guide 42. An O-ring or other sealing ring (not shown) is installed in this sealing groove 42c to maintain a tight seal between the outer circumference of the rack shaft guide 42 and the inner wall of the steering gearbox 6.

[0071] Additionally, a spring-loaded retainer 43 is screwed onto the steering gearbox 6. The base of the spring-loaded retainer 43 protrudes from the steering gearbox 6 and is screwed with a locking nut 45. By tightening the locking nut 45, the spring-loaded retainer 43 is fixed to the steering gearbox 6.

[0072] Additionally, a spring receiving recess 42b with an open base side is formed on the rack shaft guide rail 42. An adjusting spring 44, which serves as a force-applying component, is housed in this spring receiving recess 42b.

[0073] The base of the adjusting spring 44 abuts against the seat surface of the spring receiving plug 43. Thus, by adjusting the force of the spring 44, the rack shaft sliding contact surface 42a formed on the rack shaft guide rail 42 presses and applies force to the pinion 7 toward the pinion shaft 5.

[0074] like Figure 3 As shown, the control unit 20 mainly consists of a motor basic current setting unit 20a, a feedforward control unit 20b, a lateral position feedback control unit 20c, a yaw angle feedback control unit 20d, a lateral position feedback gain setting unit 20e, a yaw angle feedback gain setting unit 20f, and an electric power steering motor current value calculation unit 20g.

[0075] The electric power steering motor (electric motor) 12 is connected to the pinion shaft 5 via an auxiliary transmission mechanism 11. The electric motor 12 assists in applying the steering torque to the steering wheel 4 and adds steering torque as needed to achieve a set steering angle (target steering angle). The electric motor 12 outputs a target current as a control output value from the control unit 20 (described later) to the motor drive unit 21, and is driven by the motor drive unit 21.

[0076] The control unit 20 is connected to a forward recognition device 31, which recognizes the left and right white lines in front and recognizes the shape of the driving path obtained from the position information of the white lines. In addition, the control unit 20 is also connected to a vehicle speed sensor 32 for detecting vehicle speed, a control angle sensor 33 for detecting control angle (actual control angle), and a control torque sensor 34 for detecting control torque.

[0077] The forward recognition device 31 consists of a set of CCD cameras installed at certain intervals in front of the ceiling inside the vehicle, which take stereoscopic pictures of objects outside the vehicle from different viewpoints, and a stereoscopic image processing device that processes the image data from the CCD cameras.

[0078] The image data from the CCD camera is processed in the stereo image processing unit of the forward recognition device 31 as follows. First, for a pair of stereo images of the vehicle's forward direction captured by the CCD camera, distance information is calculated based on the offset of the corresponding position, and a distance image is generated.

[0079] In the recognition of white line data, based on the insight that the white line is brighter than the road surface, the brightness variation in the width direction of the road is evaluated, and the positions of the left and right white lines on the image plane are determined. The actual spatial position (x, y, z) of the white line is based on its position (i, j) on the image plane and the disparity calculated about that position, that is, calculated using a known coordinate transformation formula based on distance information.

[0080] Regarding the coordinate system of actual space established based on the position of this vehicle, in this embodiment, for example, the road surface directly below the center of the stereo camera is taken as the origin, and the vehicle width direction is set as the x-axis, the vehicle height direction as the y-axis, and the vehicle length direction (distance direction) as the z-axis (refer to...). Figure 5 ).

[0081] At this point, the x-z plane (y=0) coincides with the road surface when the road is flat. The road model is represented by dividing the vehicle's driving lane on the road into multiple intervals in the distance direction, and approximating and connecting the left and right white lines in each interval according to regulations.

[0082] Furthermore, based on the aforementioned input signals, the control unit 20 sets the motor base current Ipsb according to the driver's control torque Td, calculates the feedforward control amount Iff of the electric motor 12 required to travel along the target path (the middle of the left white line and the right white line in this embodiment) based on the shape of the driving path through feedforward control, estimates the vehicle trajectory of the vehicle, and calculates the offset Δx between the estimated vehicle trajectory and the target path position of the preset forward gaze point.

[0083] The control unit 20 calculates the lateral position feedback control quantity Ifb, which controls the vehicle along the target path without offset Δx, and calculates the yaw angle feedback control quantity Ifby, which sets the yaw angle of the vehicle to the yaw angle along the target path.

[0084] Regarding the various control quantities of feedback control, when the travel path width Wr is wide, the control unit 20 sets the lateral position feedback gain of the lateral position feedback control quantity Ifb to be larger than when the travel path width Wr is narrow. On the other hand, when the travel path width Wr is narrow, the control unit 20 sets the yaw angle feedback gain of the yaw angle feedback control quantity Ifby to be larger than when the travel path width Wr is wide.

[0085] The control unit 20 adds up the above values, calculates the electric motor current value Icmd, and outputs it to the motor drive unit 21 to drive the electric motor 12.

[0086] The motor basic current setting unit 20a inputs vehicle speed V from vehicle speed sensor 32 and operating torque Td from operating torque sensor 34.

[0087] Then, for example, referring to a pre-set such as Figure 4 The characteristic mapping (map) of the control torque Td-electric motor basic current value Ipsb is shown. The electric motor basic current value Ipsb is set and output to the electric power steering motor current value calculation unit 20g.

[0088] The feedforward control unit 20b is input with image information recognized from the forward recognition device 31. Then, for example, the feedforward control amount (current value) If of the electric motor 12 required to travel along the target path is calculated by the following formula (1), and output to the electric power steering motor current value calculation unit 20g.

[0089] Iff=Giff·κ…(1)

[0090] Here, κ represents, for example, the lane curvature as shown in equation (2) below.

[0091] κ=(κl+κr) / 2…(2)

[0092] In equation (2), κl is the curvature component of the left white line and κr is the curvature component of the right white line.

[0093] Regarding the curvature components κl and κr of these left and right white lines, specifically, concerning Figure 5 The points that form the left and right white lines are determined by using the coefficients of the quadratic terms calculated by the quadratic least squares method.

[0094] For example, in x = A·z 2 In the case of the quadratic approximation of the white line using +B·z+C, the value of 2·A is used as the curvature component. Alternatively, the curvature components κl and κr of these white lines can also be the curvatures of the individual white lines.

[0095] Furthermore, Giff in equation (1) represents the feedforward gain that has been set in advance through experiments, calculations, etc. Thus, the feedforward control unit 20b is set as a feedforward control unit.

[0096] The lateral position feedback control unit 20c is input with image information recognized by the front recognition device 31, vehicle speed V is input from the vehicle speed sensor 32, and control angle θp is input from the control angle sensor 33.

[0097] Then, the lateral position feedback control quantity (current value) Ifb is calculated by the following equation (3), and the lateral position feedback control quantity Ifb is output to the electric power steering motor current value calculation unit 20g.

[0098] Ifb=Gifb·Δx…(3)

[0099] Here, GIFb is a gain that is pre-set through experiments and calculations. Additionally, as... Figure 6 As shown, Δx is calculated using the following equation (4).

[0100] Δx=(xl+xr) / 2-xv…(4)

[0101] In equation (4), xv is the x-coordinate of the estimated vehicle trajectory in the z-coordinate of the vehicle's forward gaze point (O, zv), and zv, which is the forward gaze distance (z-coordinate) of the forward gaze point (O, zv), is calculated in this embodiment by zv = T·V. Here, T is a pre-set anticipation time, for example, set to 1.2 seconds.

[0102] Therefore, when using vehicle specifications or vehicle-specific stability coefficients As based on the vehicle's driving conditions, for example, xv can be calculated using the following equation (5).

[0103] xv=(1 / 2)·(1 / (1+As·V2))·(θp / Lw)·(T·V) 2 …(5)

[0104] Here, Lw is the wheelbase. In addition, in equation (4), xl is the x-coordinate of the left white line in the z-coordinate of the front gaze point (O, zv), and xr is the x-coordinate of the right white line in the z-coordinate of the front gaze point (O, zv).

[0105] In addition, the above-mentioned xv can also be calculated by the vehicle speed V or yaw rate (dθ / dt) using the following equation (6), or it can be calculated based on image information using the following equation (7).

[0106] xv=(1 / 2)·((dθ / dt) / V)·(V·T) 2 …(6)

[0107] xv=(1 / 2)·κ·(V·T) 2 …(7)

[0108] Thus, the lateral position feedback control unit 20c is configured as a lateral position feedback control unit. The yaw angle feedback control unit 20d is input with image information recognized from the forward recognition device 31.

[0109] Furthermore, for example, the yaw angle feedback control quantity (current value) Ifby that controls the vehicle's yaw angle feedback to the yaw angle along the target path is calculated by the following equation (8), and output to the electric power steering motor current value calculation unit 20g.

[0110] Ifby=Gifby·(θtl+θtr) / 2…(8)

[0111] Here, Gifby is the gain set in advance through experiments and calculations, θtl is the slope of the vehicle relative to the left white line obtained from the image information from the front recognition device 31, and θtr is the slope of the vehicle relative to the right white line obtained from the image information from the front recognition device 31 (see reference). Figure 7 ).

[0112] Furthermore, for each point of the white line obtained in the image information, these θtl and θtr can also be calculated using the coefficients of the first-order term (i.e., the white line is represented by x = A·z) through the quadratic least squares method. 2 The value of B when approximating the formula +B·z+C). Thus, the yaw angle feedback control unit 20d is set as the yaw angle feedback control unit.

[0113] The lateral position feedback gain setting unit 20e receives image information recognized from the forward recognition device 31. Furthermore, based on the image information, for example, the driving road width Wr is calculated according to the interval between the left and right white lines, and the driving road width Wr is compared with a pre-set reference width C.

[0114] The comparison results show that when the driving road width Wr is wider than the reference width C (Wr > C), and it can be determined that the driving road is wider than the highway, the lateral position feedback gain Gfb1 is set to a higher value as the lateral position feedback gain Gfb multiplied by the lateral position feedback control quantity Ifb.

[0115] Conversely, when the driving road width Wr is less than or equal to the reference width C (Wr≤C), and the driving road can be determined to be narrow like a normal road with a relatively narrow driving road width Wr, a small value of the lateral position feedback gain Gfb2 is set as the lateral position feedback gain Gfb multiplied by the lateral position feedback control quantity Ifb.

[0116] That is, when Gfb1 > Gfb2 and the driving road width Wr is wider, the influence of the lateral position feedback control value Ifb is stronger than when the driving road width Wr is narrower. The lateral position feedback gain Gfb set in this way is output to the electric power steering motor current value calculation unit 20g. Thus, the lateral position feedback gain setting unit 20e is set as a lateral position feedback gain setting unit.

[0117] The yaw angle feedback gain setting unit 20f receives image information recognized from the forward recognition device 31. Furthermore, based on the image information, for example, the driving road width Wr is calculated according to the interval between the left and right white lines, and the driving road width Wr is compared with a pre-set reference width C.

[0118] The comparison results show that when the driving road width Wr is wider than the reference width C (Wr > C), and it can be determined that the driving road is wider than the highway, the small yaw angle feedback gain Gfby1 is set as the yaw angle feedback gain Gfby multiplied by the yaw angle feedback control quantity Ifby.

[0119] Conversely, when the driving road width Wr is less than or equal to the reference width C (Wr≤C), and the driving road can be determined to be a narrow driving road like a normal road, a large yaw angle feedback gain Gfby2 is set as the yaw angle feedback gain Gfby multiplied by the yaw angle feedback control quantity Ifby.

[0120] That is, when Gfby1 < Gfby2 and the road width Wr is narrow, the influence of the yaw angle feedback control value Ifby is stronger than when the road width Wr is wide. The yaw angle feedback gain Gfby set in this way is output to the electric power steering motor current value calculation unit 20g. Thus, the yaw angle feedback gain setting unit 20f is set as the yaw angle feedback gain setting unit.

[0121] The electric power steering motor current value calculation unit 20g inputs the electric motor basic current value Ipsb from the motor basic current setting unit 20a, the feedforward control quantity Ifff from the feedforward control unit 20b, the lateral position feedback control quantity Ifb from the lateral position feedback control unit 20c, the yaw angle feedback control quantity Ifby from the yaw angle feedback control unit 20d, the lateral position feedback gain Gfb from the lateral position feedback gain setting unit 20e, and the yaw angle feedback gain Gfby from the yaw angle feedback gain setting unit 20f.

[0122] Furthermore, for example, the electric motor current value Icmd is calculated by the following equation (9) and output to the motor drive unit 21 to drive and control the electric motor 12.

[0123] Icmd=Ipsb+Iff+Gfb·Ifb+Gfby·Ifby…(9)

[0124] Lane keeping control is performed by the steering control unit 20 configured as described above. Furthermore, examples of lane keeping control in the steering control unit 20 are well-known; therefore, details regarding these examples are omitted.

[0125] However, the rack and pinion support mechanism 40 provided in the steering gearbox 6 reduces the loosening of the meshing between the rack of the rack shaft 7 and the pinion of the pinion shaft 5.

[0126] Over time, wear occurs at the sliding contact points of the rack and pinion. Due to reduced friction, the responsiveness of the steering angle relative to the steering angle (target steering angle) improves, leading to errors in the response speed of the vehicle's actual steering angle. Specifically, the actual steering angle during lane keeping is faster than the target steering angle, such as... Figure 8 As shown, the vehicle moves rapidly toward the target path between the left and right white lines, and is controlled to return, thus producing a serpentine driving behavior.

[0127] To improve this phenomenon, the electric power steering device 1 of this embodiment performs lane keeping control... Figure 9 The control example is shown in the flowchart.

[0128] like Figure 9 As shown in the flowchart, firstly, the operation control unit 20 of the electric power steering device 1 determines whether lane keeping is activated (S1).

[0129] With lane keeping assist engaged, the feedback gain mapping of the electric motor current value Icmdn stored in the internal memory is read in (S2). Furthermore, the feedback gain IGkn here is the gain used to calculate the electric motor current value Ik, which is optimized such that the angular velocity of the vehicle's actual steering angle relative to the indicated steering angle (target steering angle), i.e., the response speed Vn, becomes the factory-set response speed V0. Therefore, at the time of vehicle manufacture, a mapping is written in which the feedback gain IGkn for calculating the electric motor current value Ik is zero (IGkn = 0).

[0130] The control unit 20 calculates the electric motor current value Icmdn+1 that applies the feedback gain IGkn read in step S2, and outputs it to the motor drive unit 21 (S3).

[0131] Here, the feedback gain IGkn is multiplied by the electric motor current value Icmdn calculated according to the above equation (9) to determine the electric motor current value Icmdn+1.

[0132] The control unit 20 compares the response speed Vn of the actual control angle detected by the control angle sensor 33 with the indicated control angle (target control angle) and the set response speed V0 when the vehicle leaves the factory, and determines whether the response speed Vn is faster than the set response speed V0 (S4).

[0133] In step S4, if the response speed Vn of the actual control angle relative to the indicated control angle (target control angle) is the same as the factory-set response speed V0 of the vehicle (Vn = V0), the control unit 20 proceeds to step S7.

[0134] On the other hand, if the response speed Vn of the actual control angle relative to the indicated control angle (target control angle) is faster than the factory-set response speed V0 (Vn > V0), the control unit 20 proceeds to step S5. In step S5, the control unit 20 calculates the feedback gain IGkn+1 of the electric motor current value Icmdn+1 to make the response speed Vn of the actual control angle match the factory-set response speed V0 (Vn = V0) (S5).

[0135] Furthermore, the control unit 20 rewrites and updates the mapping of the feedback gain IGkn+1 of the calculated electric motor current value Icmdn+1 in the internal memory (S6).

[0136] Next, the control unit 20 calculates the curvature of the driving path based on the image information input from the forward recognition device 31 (S7), and corrects the feedback gain IGkn+1 of the electric motor current value Icmdn+1 according to the amount of change in the calculated curvature of the driving path (S8).

[0137] Furthermore, the control unit 20 calculates the electric motor current value Icmdn+1 with the modified feedback gain IGkn+1 applied, and outputs it to the motor drive unit 21 (S9).

[0138] The correction amount of the feedback gain IGkn+1 is changed according to the curvature change of the driving road from which the vehicle travels. That is, in the control steps S7 to S9 performed by the steering control unit 20, for example, as Figure 10 As shown, when the driving road is straight, the change in curvature of the driving road is approximately 0 (zero). Therefore, by not changing the correction amount of the feedback gain IGkn+1, the following is suppressed: Figure 8 The vehicle, as shown, performs serpentine driving to achieve stable straight-line driving along the target driving path between the left and right white lines.

[0139] Furthermore, for example, when the driving road is a stable curve, the curvature change of the driving road is approximately 0 (zero). Therefore, the control unit 20 does not change the correction amount of the feedback gain IGkn+1, or reduces the correction amount. As a result, the vehicle can achieve stable cornering performance along the target driving road between the left and right white lines.

[0140] Furthermore, in situations such as entering a curve or other driving road with significant curvature changes, the control unit 20 increases the curvature change of the driving road and reduces the correction amount of the feedback gain IGkn+1 based on this change. As a result, the response speed Vn of the actual control angle relative to the indicated control angle (target control angle) is faster, such as... Figure 11 As shown, this prevents the vehicle from bulging outwards from the curve and deviating from the target path between the left and right white lines due to a delay in handling response. Figure 12 As shown, the vehicle's cornering performance is obtained by stably traveling along the target path when entering a curve.

[0141] Then, the control unit 20 determines whether lane keeping is off (S10). If lane keeping is not off, the control unit 20 will return to step S2 and repeat steps S2 to S9. If lane keeping is off, control will end.

[0142] As described above, when the control unit 20 of this embodiment performs automatic or assisted lane keeping along the target path, the vehicle's behavior may change due to mechanical factors such as wear of gears and racks over time, compared to the vehicle's factory-set handling responsiveness. The control unit determines how fast the response is and accordingly changes the feedback gain of the electric motor current value to maintain the vehicle's factory-set handling responsiveness. In other words, the control unit 20 controls the correction of the deviation between the vehicle's actual steering angle and the target steering angle during lane keeping, returning the vehicle to its factory-set handling responsiveness.

[0143] In addition, the control unit 20 corrects the feedback gain of the electric motor current value based on the curvature change in the driving road with different curvatures, such as when going straight, turning, or entering a curve, and controls the vehicle to drive stably along the target path between the left and right white lines.

[0144] This allows for the maintenance of straight-line stability, while ensuring that the sensation remains unchanged over time, thus preventing driver discomfort.

[0145] Based on the above description, the lane keeping control device of this embodiment can suppress the swaying (vibration of the vehicle trajectory) caused by the excessive sensitivity of the steering response to changes over time and the deviation of the actual steering angle from the indicated steering angle based on lane keeping control. As a result, the vehicle can achieve stable driving as it has remained unchanged since it left the factory.

[0146] In the embodiment described above, an example of recognizing the shape of the driving road based on images from a single set of CCD cameras was used, but it can also be determined based on image information from a single-lens camera, a color camera, etc. Alternatively, a structure can be used to perform steering control based on the detected position of the vehicle detected by a GPS mounted on the vehicle.

[0147] Furthermore, the operating control unit 20 of the electric power steering system 1 includes a central processing unit (CPU) and a processor containing storage devices such as ROM and RAM. Additionally, the structure of all or part of the processor's multiple circuits can be executed by software. For example, the CPU can also read and execute various programs stored in the ROM corresponding to different functions.

[0148] In addition, all or part of the functions of a processor can be composed of logic circuits or analog circuits, or various programs can be processed through electronic circuits such as FPGAs.

[0149] The invention described in the above embodiments is not limited to these methods. Furthermore, various modifications can be implemented during the implementation phase without departing from its spirit. In addition, the above methods encompass inventions at various stages, and a wide variety of inventions can be derived through appropriate combinations of the disclosed constituent elements.

[0150] For example, even if several structural elements are removed from the full structural elements shown in each method, the problem stated can be solved, and the structure in which the constituent element has been removed can be extracted as an invention while achieving the effect stated.

Claims

1. A lane keeping control device for a vehicle, comprising setting a target path for the vehicle to travel, calculating a control quantity for an electric power steering motor based at least on an offset from the target path, and controlling the vehicle to travel along the target path, characterized in that, The lane keeping control device compares the actual steering angle of the vehicle with the target steering angle for driving along the target path and the set response speed, and determines the feedback gain of the current value driving the electric power steering motor in a manner that makes the response speed and the set response speed consistent. The feedback gain mapping of the current value stored in the internal memory is then rewritten and updated to the determined feedback gain mapping.

2. The lane keeping control device for a vehicle according to claim 1, characterized in that, The feedback gain is corrected based on the curvature change of the vehicle's travel path.

3. The lane keeping control device for a vehicle according to claim 2, characterized in that, The greater the curvature change, the smaller the correction to the feedback gain.

4. The lane keeping control device for a vehicle according to any one of claims 1 to 3, characterized in that, The set response speed is the response speed of the actual control angle relative to the target control angle when the vehicle leaves the factory.

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