CN118876976A - Vehicle automatic lane changing control method - Google Patents

Abstract

The present invention relates to the field of vehicle automatic driving technology, and in particular to a vehicle automatic lane change control method. A vehicle automatic lane change control method, through environmental perception equipment and combined inertial navigation to perceive the driving environment and current movement conditions around the vehicle, the decision control unit integrates environmental information and driving information to determine whether the vehicle meets the lane change conditions, if the lane change conditions are met, then the torque control command is output, and the operation execution unit is operated to make the vehicle stably drive along the planned target trajectory, automatically complete the lane change action, so as to improve driving safety and reduce the driver's operating burden. The automatic lane change control method of the present invention plans the optimal lane change trajectory and the reasonable time required to complete the lane change when the surrounding environment of the vehicle permits. At the same time, the lateral and longitudinal stability of the vehicle is considered to ensure that the vehicle implements lane changes under different road conditions, prevent the vehicle from deviating from the target trajectory, and meet the comfort of the automatic lane change experience.

Description

Vehicle automatic lane changing control method

Technical Field

The present invention relates to the technical field of vehicle automatic driving, and in particular to a vehicle automatic lane changing control method.

Background Art

At present, the vehicle automatic lane change control method is generally as follows: first, using the lane line information of the vehicle, multiple cubic spline curves (or Bezier curves) are fitted as a family of feasible motion trajectories for automatic lane change; then, according to the boundary conditions, a specific optimization algorithm (such as A* algorithm, Lattice algorithm, etc.) is used to calculate an optimal target motion trajectory; then, the sensors of the autonomous vehicle are used to collect the lateral position of the vehicle, the yaw angle of the vehicle, and other information; then, based on the above target trajectory and the position information of the autonomous vehicle, the lateral position deviation and the yaw angle deviation of the autonomous vehicle are calculated; finally, the desired EPS steering angle or EPS torque is calculated for the lateral position deviation and yaw angle deviation of the autonomous vehicle through a specific algorithm (PID control, LQR control, etc.).

The above-mentioned vehicle automatic lane change control method is only applicable to ideal road conditions. In rainy and snowy weather, when the road is slippery, the vehicle is prone to instability and deviates from the target trajectory during the automatic lane change process, so the lateral and longitudinal stability of the vehicle needs to be considered. Therefore, the vehicle needs to change lanes when driving autonomously. When the surrounding environment of the vehicle allows, choosing an optimal lane change trajectory and designing a reasonable lane change completion time have become the key to a comfortable automatic lane change experience.

Summary of the invention

The technical problem to be solved by the present invention is: in order to solve the problems existing in the prior art in the above-mentioned background technology, a vehicle automatic lane change control method is provided.

The technical solution adopted by the present invention to solve the technical problem is: a vehicle automatic lane change control method, which senses the driving environment and current motion situation around the vehicle through an environmental sensing device and a combined inertial navigation system, and a decision control unit combines environmental information and driving information to determine whether the vehicle meets the lane change conditions. If the lane change conditions are met, a torque control command is output to make the vehicle stably drive along the planned target trajectory and automatically complete the lane change action;

The specific steps include:

S1. Lane recognition: The left lane line y _l , the right lane line y _r , and the right outer lane line y _rr on the right adjacent lane of the vehicle are recognized through the environment perception device;

S2. Lane line confidence judgment: Calculate the lane line type, confidence, validity and effective distance to judge the lane line quality and further evaluate whether it can be used for control decision-making;

S3, target trajectory extraction: obtaining actual lane line information through step S1, processing the actual lane line information, and then extracting the target trajectory of the vehicle traveling in the lane according to the road environment;

S4, judging the driver's intention: The automatic lane change system judges whether the driver is in the active driving state. If the driver is in the active driving state, the lane change will not be performed. In other cases, the lane change will be performed from the left or right lane according to the surrounding environment;

S5, target path planning: Assuming that the current lane of the ego vehicle is located at point A which is ALC _AO away from point O, start planning the lane change trajectory. The lane change path is divided into two sections. First, plan the first driving curve section OO', calculate the lateral offset ALC _AO of the planned lane change trajectory and the ordinate x and abscissa y of the planned path; then plan the second driving curve section O'O'', calculate the lateral offset ALC _AO ' of the ego vehicle relative to the center line of the lane at this time;

S6. Optimize the planned path: first calculate the lateral velocity v _y of the planned path and the lateral acceleration a _y of the uniformly moving vehicle, then calculate the upper limit a _{y max} of the lateral acceleration during turning, the lower limit a _xLim of the longitudinal acceleration and the acceleration limit a _Lim , and finally calculate the shortest time T _sLim to complete the lane change;

S7, collision detection: Use sensors to detect whether there are obstacles around. If yes, return to step S5 to re-plan the target path. If no, start lane change action;

S8, lane change control: first calculate the torque Torq _LatErr implemented by the lateral deviation control on the EPS steering gear, then calculate the torque Torq _HdAngle implemented by the yaw angle deviation control on the EPS steering gear, then calculate the feedforward compensation torque Torq _fwd , and finally add the above three to obtain the final steering torque Torq _total .

Furthermore, the calculation formula of the left lane line y _l in step S1 is: (i),

The calculation formula for the right lane line y _r is: (ii),

The calculation formula for the right outer lane line y _rr is: (iii);

In formula (i), l0 is the lateral distance of the left lane _line relative to the vehicle, l1 is the yaw _angle of the left lane line, _l2 is the curvature of the left lane line, _and l3 is the rate of change of the curvature of the left lane line _; in formula (ii), r0 is the lateral distance of _the right lane line relative to the vehicle, l1 is the yaw angle of the right lane line _, r2 is the curvature of the right lane line, _and r3 is the rate of change of the curvature of the right lane line; in formula (iii ) , rr0 is the lateral distance of the right outer lane line relative to the vehicle, _rr1 is the yaw angle of the right lane line, rr2 is the curvature of the right lane line, _{and rr3} is the rate of change of the curvature of _the right lane line.

Furthermore, the calculation formula of the lateral offset ALC _AO of the lane change trajectory planned in step S5 is:

(1),

In formula (1), A _O is the distance that the vehicle deviates from the center line of the lane at point O, and its calculation formula is:

(2),

Lane _width is the lane width, which is calculated as:

(3),

T _delta is the timer from the start of the lane change to the end of the lane change, and its calculation formula is:

(4),

In formula (4), ΔT is the operation cycle of the controller calling the automatic lane change algorithm software, k is a natural number, which means that k operation cycles have been experienced from the start of the lane change to the end of the lane change, _and Ts is the time required to complete the lane change;

Assuming that the speed of the vehicle when planning to change lanes is V _O , and assuming that the vehicle maintains a uniform speed during the entire lane change process, the calculation formula for the ordinate x of the planned path is:

(5),

The calculation formula of the horizontal coordinate y of the planned path is:

(6);

The calculation formula of the lateral offset ALC _AO ′ of the vehicle relative to the lane centerline is:

(7).

Furthermore, the calculation formula of the lateral speed v _y of the path planned in step S6 is:

(8),

Substituting formula (1) into formula (8), we get:

(9),

The calculation formula for the lateral acceleration ay of a uniformly moving vehicle is _:

(10),

Considering that the longitudinal speed v _o of a vehicle is generally large during high-speed driving, while the lateral speed v _{y <<} v _o , equation (10) is simplified to:

(11),

In formula (11), R is the turning radius. When a vehicle changes lanes on a curved road, the actual turning curvature of the vehicle is calculated as:

(12),

(13),

_In equations (12) and (13), A2 is the curvature of the road on which the vehicle is located. For a road where both left and right lane lines are equally credible, the calculation formula for _the curvature A2 is:

(14),

ρ is the road curvature of the planned cosine curve, and its calculation formula is:

(15),

From equations (5) and (6), we can get:

(16),

Taking the first-order derivative of y in equation (16), we get:

(17),

Taking the second-order derivative of y in equation (16), we get:

(18),

Considering that the longitudinal speed v _o is generally large during high-speed driving, while the lateral speed v _{y <<} v _o , equation (17) is simplified to:

(19),

According to formula (18) and formula (15), we can get:

(20),

Substituting formula (20) into formula (13), we get:

(twenty one),

Substituting equation (21) into equation (11), we get:

(twenty two),

Formula (22) can be simplified to:

(twenty three),

If the curvature of the lane change is large, it is necessary to consider the effect of A2 on _the lateral acceleration and then calculate the limit of the lateral acceleration during the turn, specifically:

when When , a _y reaches an extreme value, so when A ₂ > 0 and When the vehicle is turning, the calculation formula for the limit value of the lateral acceleration a _{y max} is:

(twenty four),

or A ₂ < 0 and When , the lateral acceleration reaches the extreme value, and the calculation formula is:

(25),

In formula (25), the positive and negative signs only indicate whether the direction of acceleration is to the left or to the right.

Furthermore, when calculating the acceleration limit value a _Lim in step S6, the road adhesion system μ and the gravity acceleration ɡ need to be considered.

For low adhesion road surfaces μ＜0.3, the calculation formula for the acceleration limit a _Lim is:

(26),

For the road surface with adhesion coefficient μ>=0.3, the calculation formula of acceleration limit value a _Lim is:

(27),

During the lane change process, the acceleration is ≤ the acceleration limit a _Lim , which is:

(28),

In formula (28), a _x is the longitudinal acceleration. Under the condition of uniform vehicle speed, a _x ≈ 0.

The lateral acceleration limit a _{y Lim} is not greater than the acceleration limit a _Lim , from which it can be concluded that:

(28').

Furthermore, when calculating the shortest time T _sLim to complete the lane change in step S6, whether the lane change condition is met is first considered, specifically:

like , indicating that the road curvature is too large at this time, and the lane change condition is not met, so the lane change is not performed;

like , and then calculate the minimum time required to complete the lane change;

Further judgment:

When A ₂ > 0, that is, the road itself curves to the right:

if , that is, the road curvature satisfies At this time, the vehicle can maintain a constant speed to complete the lane change. The minimum time T _S required to complete the lane change is calculated using the following formula:

(29),

In this case, the minimum time to complete the lane change T _sLim is calculated as:

(30),

When A ₂ < 0, that is, the road itself is curved to the left:

if , that is, the road curvature satisfies At this time, the vehicle can maintain a constant speed to complete the lane change, and the minimum time T _S required to complete the lane change is calculated. The calculation formula is:

(31),

In this case, the minimum time to complete the lane change T _sLim is calculated as:

(32),

In the actual lane changing process, a certain safety margin needs to be taken into account, and the time required to complete the lane change should be appropriately extended. Taking the safety factor η>1.0, we get:

(33),

Considering that the vehicle usually does not change lanes at a constant speed but at a variable speed, assuming that the limit of the longitudinal acceleration during the variable speed movement is a _{x Lim} , then:

(34),

(34′),

Substituting equation (34) into equation (24) or equation (25), we can obtain the minimum time T _sLim for the speed change motion to complete the lane change.

Furthermore, in step S8, the torque Torq _LatErr implemented by the lateral deviation control on the EPS steering gear is calculated as follows:

(a) Calculate the expected lateral displacement value ALC _AO ,

(b) Measure the actual lateral displacement value: The offset of the vehicle in the lane is measured by the environmental perception device and calculated using the following formula:

(35),

(c) Calculate the lateral deviation error value. The calculation formula is:

(36),

(d) Control of lateral deviation: The torque of the EPS steering gear applied by the lateral deviation control is calculated using the control algorithm. The calculation formula is:

(37).

Furthermore, the torque Torq _HdAngle implemented by the yaw angle deviation control on the EPS steering gear is calculated in step S8, specifically:

(I) Calculate the desired yaw angle ALC _A1 using the following formula:

(38),

Among them, the longitudinal velocity v _x = v _O , and the lateral velocity v _y is obtained according to formula (4):

(39),

(II) Calculate the actual yaw angle: The actual yaw angle of the vehicle in the lane measured by the environment perception device is calculated using the following formula:

(40),

(III) calculating the yaw angle error value;

(41),

(IV) Control of lateral deviation: The torque applied to the EPS steering gear by yaw angle deviation control is calculated using a control algorithm. The calculation formula is:

(42),

Furthermore, the feedforward compensation torque Torq _fwd is calculated in step S8, specifically:

(A) Calculate the road curvature of the planned path: According to the planned path curvature ρ calculated by equation (13), when the vehicle changes lanes on a curved road, the actual turning curvature of the vehicle is calculated to obtain ALC _A2 ;

(B) Calculate the feedforward compensation torque using the following formula:

(43),

In formula (43), ɡ(ALC _A2 ) is a function of the curvature of the target trajectory,

(C) Calculate the final steering torque Torq _total using the following formula:

(44).

Furthermore, the environmental perception device in step S1 includes a front-view camera, a side-view camera, a rear-view camera, a forward millimeter-wave radar, a corner millimeter-wave radar and a GPS; the control algorithm in step S8 includes a pid control algorithm, an LQR control algorithm and an MPC control algorithm.

Beneficial effects of the present invention: The automatic lane change control method of the present invention plans the optimal lane change trajectory and the reasonable time required to complete the lane change when the vehicle's surrounding environment permits. At the same time, it takes into account the lateral and longitudinal stability of the vehicle to ensure that the vehicle can change lanes under different road conditions, prevent the vehicle from deviating from the target trajectory, and meet the comfort of the automatic lane change experience.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described below in conjunction with the accompanying drawings and embodiments.

FIG. 1 is a control principle diagram for realizing the vehicle automatic lane changing control method of the present invention.

FIG. 2 is a schematic diagram of target path planning in the vehicle automatic lane change control method of the present invention.

DETAILED DESCRIPTION

The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

As shown in Figure 1, the method for realizing the automatic lane change control of a vehicle requires a vehicle instrument, ESP (vehicle stability program), an integrated machine (ADAS function controller), sensors, EMS (engine control system), BCM (body controller), EPS (power steering), CGW (vehicle gateway) and IMU sensor (inertial sensor). The vehicle instrument displays the ADAS function (such as ALC (automatic lane change function)/LKA (lane keeping assist)/ACC (adaptive cruise control)) request, opening status and set vehicle speed and other information; ESP is used to control the acceleration and deceleration of the vehicle; the integrated machine is used to realize the lateral and longitudinal fusion control of the vehicle (such as lane keeping function); the sensor recognizes the external environment information and sends the external environment information to the ADAS controller; EMS is used to provide power; BCM transmits the body status to the ACC function controller; EPS is used to realize the vehicle's lane keeping and lane changing functions; CGW is used to realize the communication function between CAN and vehicle Ethernet; IMU sensor includes measuring longitudinal acceleration, lateral acceleration, yaw rate, etc.

There is no specific requirement for the sensor used in the vehicle automatic lane change control method of this embodiment, as long as it can collect vehicle information in the external environment. For example, some systems only have forward radar installed but no corner radar, and the lateral control function is implemented in the ADAS function controller.

The vehicle automatic lane changing control method of this embodiment senses the driving environment and current motion conditions around the vehicle through environmental sensing equipment and combined inertial navigation. The decision control unit combines environmental information with driving information to determine whether the vehicle meets the lane changing conditions. If the lane changing conditions are met, a torque control command is output to allow the vehicle to stably travel along the planned target trajectory and automatically complete the lane changing action.

The specific steps include:

S1. Lane recognition: Lane recognition is one of the key technologies of the automatic lane change system (ALC). Lane recognition is responsible for detecting and outputting the control parameters required by the automatic lane change system (ALC), including lane curvature, vehicle position relative to the lane, and heading relative to the lane. Since road scenes are easily affected by many factors such as weather, lighting, and road traffic environment, lane recognition requires both accuracy, real-time performance, and robustness.

As shown in FIG2 , the environment perception device recognizes the left lane line y _l , the right lane line y _r , and the right outer lane line y _rr on the right adjacent lane of the vehicle.

The calculation formula for the left lane line y _l is: (i),

The calculation formula for the right lane line y _r is: (ii),

_{The calculation formula for the right outer lane line yrr} is : (iii);

The left lane line information is obtained through the vehicle's camera: in formula (i), l0 is the _lateral distance of _the left lane line relative to the vehicle (the right side is positive here), l1 is the yaw angle of the left lane line, l2 is the curvature of the left lane line (the right side is positive here ), and l3 _is the rate of change of the curvature of the left lane line; in formula (ii), _r0 is the lateral distance of _the right lane line relative to the vehicle, r1 is the yaw angle of the right lane line, r2 is the curvature of _{the right} lane line, and r3 _is the rate of change of the curvature of the right lane line; in formula (iii), rr0 is the lateral distance of the right outer lane line relative to the vehicle, _rr1 is the yaw angle _{of the right lane line, rr2} is the curvature of the right lane line, and _rr3 is the rate of change of the curvature _of the right lane line.

S2. Confidence judgment of lane lines: Calculate the lane line type, confidence, validity and effective distance to judge the quality of the lane line and further evaluate whether it can be used for control decision-making. When the confidence of the lane line recognition is low or the effective distance of the lane line is short, the automatic lane change function is suppressed.

S3, target trajectory extraction: obtain the actual lane line information through step S1, process the actual lane line information, and then extract the target trajectory of the vehicle in the lane according to the road environment. After the ALC control is completed, the vehicle should be on the target trajectory, which is generally the center line of the lane. Appropriate offsets can be made for curves, single-sided approach to guardrails and other road conditions. As shown in Figure 2, the target trajectory when the lane change is completed is the center line of the right lane.

S4. Determine the driver's intention: In order to avoid excessive interference of the system with the driver's operation and cause trouble to the driver during driving, the automatic lane change system (ALC) needs to determine whether the driver is in an active driving state through the turn signal lever, steering wheel torque, corner signal, accelerator pedal signal, brake pedal signal, gear position signal, etc., so as to determine whether the system function needs to be suppressed. In the decision-making process of the autonomous driving vehicle, if the vehicle speed is less than the cruise setting speed for more than a certain time (this time can be calibrated, the variable is ALC_LowSpd _Time), it means that the lane is crowded and the front vehicle is blocking the vehicle's travel. At the same time, according to the surrounding environment of the vehicle, it can be judged that the lane can be changed to overtake from the left or right lane.

S5. Target path planning: In order to make the planned path feasible and ensure that the vehicle can stably track the target trajectory, it is necessary to consider the vehicle's dynamic factors during path planning to ensure the real-time nature of path planning and the comfort of vehicle driving. The ALC system activates the lane change function at least 500m before the latest lane change point and waits for an opportunity to complete the lane change action; the lane change point should be within the interval of the dotted lane line (lane change is prohibited on the solid line); the lane change scene should meet the lane change conditions and should comply with the requirements of traffic regulations.

There are potential risks in changing lanes. The system should change lanes safely when the lane change conditions are met. If the traffic scenario cannot support safe lane changes and the lane change waiting time ALC_Holdon_Time is exceeded, the system should abandon the lane change, re-update the navigation route and plan the driving route or prompt the driver to take over.

When the ego vehicle is at point A, which is ALC _AO away from point O, it starts planning the lane change trajectory. The lane change path planning is divided into two steps. First, the ego vehicle is planned to drive from point O to point O'. Before changing lanes (i.e. ), plan the first driving curve segment OO', calculate the lateral offset ALC _AO of the planned lane change trajectory and the ordinate x and abscissa y of the planned path;

(1),

In formula (1), A _O is the distance that the vehicle deviates from the center line of the lane at point O, and its calculation formula is:

(2),

Lane _width is the lane width, which is calculated as:

(3),

T _delta is the timer from the start of the lane change to the end of the lane change, and its calculation formula is:

(4),

In formula (4), ΔT is the operation cycle of the controller calling the automatic lane change algorithm software, k is a natural number, which means that k operation cycles have been experienced from the start of the lane change to the end of the lane change, _and Ts is the time required to complete the lane change;

Assuming that the speed of the vehicle when planning to change lanes is V _O , and assuming that the vehicle maintains a uniform speed during the entire lane change process, the calculation formula for the ordinate x of the planned path is:

(5),

The calculation formula of the horizontal coordinate y of the planned path is:

(6);

Secondly, the plan is to drive from point O' to point O", after the vehicle changes to the right lane (corresponding to time ), plan the second driving curve segment O'O''. When the vehicle passes the O' point, the left and right lane line equations perceived by the camera installed on the vehicle will change. Relatively speaking, the new left lane line perceived by the camera is transformed into yr, and the new right lane line perceived by the camera is transformed into yrr. Relative to the object perceived by the camera at the time of point O, both are translated by a lane line width. Therefore, this time corresponds to the lateral offset ALC _AO ' relative to the vehicle. The calculation formula is as follows:

(7).

S6. Optimize the planned path: There is a parameter T _s in the planned path above, that is, the time required for the transformation to be completed. Here, the optimal value of T _s is calculated. First, the lateral speed v _y of the planned path is calculated. The calculation formula is:

(8),

Substituting formula (1) into formula (8), we get:

(9),

The calculation formula for the lateral acceleration ay of a uniformly moving vehicle is _:

(10),

Considering that the longitudinal speed v _o of a vehicle is generally large during high-speed driving, while the lateral speed v _{y <<} v _o , equation (10) is simplified to:

(11),

In formula (11), R is the turning radius. When a vehicle changes lanes on a curved road, the actual turning curvature of the vehicle is calculated as:

(12),

(13),

_In equations (12) and (13), A2 is the curvature of the road on which the vehicle is located. For a road where both left and right lane lines are equally credible, the calculation formula for _the curvature A2 is:

(14),

ρ is the road curvature of the planned cosine curve, and its calculation formula is:

(15),

From equations (5) and (6), we can get:

(16),

Taking the first-order derivative of y in equation (16), we get:

(17),

Taking the second-order derivative of y in equation (16), we get:

(18),

Considering that the longitudinal speed v _o is generally large during high-speed driving, while the lateral speed v _{y <<} v _o , equation (17) is simplified to:

(19),

According to formula (18) and formula (15), we can get:

(20),

Substituting formula (20) into formula (13), we get:

(twenty one),

Substituting equation (21) into equation (11), we get:

(twenty two),

Formula (22) can be simplified to:

(twenty three),

If the curvature of the lane change is large, it is necessary to consider the effect of A2 on _the lateral acceleration and then calculate the limit of the lateral acceleration during the turn, specifically:

when When , a _y reaches an extreme value, so when A ₂ > 0 and When the vehicle is turning, the calculation formula for the limit value of the lateral acceleration a _{y max} is:

(twenty four),

or A ₂ ＜0 and When , the lateral acceleration reaches the extreme value, and the calculation formula is:

(25),

In formula (25), the positive and negative signs only indicate whether the direction of acceleration is to the left or to the right.

To calculate the acceleration limit a _Lim , we need to consider the road adhesion system μ and the gravity acceleration ɡ .

For low adhesion road surfaces μ＜0.3, the calculation formula for the acceleration limit a _Lim is:

(26),

For the road surface with adhesion coefficient μ>=0.3, for lane change path planning, the lateral and longitudinal acceleration and deceleration of the vehicle should not be too large. Excessive acceleration and deceleration will reduce the comfort of the passengers. Here, the acceleration limit value is set to 0.3g (g refers to the acceleration of gravity, generally 9.8 m/s ² ), and the calculation formula of the acceleration limit value a _Lim is:

(27),

During the lane change process, the acceleration is ≤ the acceleration limit a _Lim , which is:

(28),

Based on this, the minimum time required for lane change is solved. In formula (28), a _x is the longitudinal acceleration. Under the condition of uniform vehicle speed, a _x ≈ 0;

The lateral acceleration limit a _{y Lim} should not be greater than the acceleration limit a _Lim , from which it can be concluded that:

(28'),

Then, determine whether the current road conditions meet the lane change conditions. , indicating that the road curvature is too large at this time, and the lane change condition is not met, so the lane change is not performed;

like , and then calculate the minimum time required to complete the lane change;

Further judgment:

When A ₂ > 0, that is, the road itself curves to the right:

if , that is, the road curvature satisfies At this time, the vehicle can maintain a constant speed to complete the lane change. The minimum time T _S required to complete the lane change is calculated using the following formula:

(29),

In this case, the minimum time to complete the lane change T _sLim is calculated as:

(30),

When A ₂ < 0, that is, the road itself is curved to the left:

if , that is, the road curvature satisfies At this time, the vehicle can maintain a constant speed to complete the lane change, and the minimum time T _S required to complete the lane change is calculated. The calculation formula is:

(31),

In this case, the minimum time to complete the lane change T _sLim is calculated as:

(32),

In the actual lane changing process, a certain safety margin needs to be taken into account, and the time required to complete the lane change should be appropriately extended. Taking the safety factor η>1.0, we get:

(33),

Finally, calculate the shortest time T _sLim to complete the lane change when the vehicle changes speed. Considering that the vehicle usually does not change speed at a constant speed during the lane change, but uses variable speed motion, assuming that the limit value of the longitudinal acceleration during the variable speed motion is a _{x Lim} , then:

(34),

and (34′),

Substituting equation (34) into equation (24) or equation (25), we can obtain the minimum time T _sLim for the speed change motion to complete the lane change.

S7, collision detection: Based on the longitudinal and lateral accelerations and road adhesion conditions, _{the TS} required to complete the lane change is calculated, so that when the vehicle is at point O, a lane change path as shown in Figure 2 can be planned. If there are no obstacles on this planned route through the detection of sensors such as cameras and radars, the path planning is successful and the lane change can be performed.

S8, Lane Change Control: First calculate the torque Torq _LatErr implemented by the lateral deviation control on the EPS steering gear, specifically:

(a) Calculate the expected lateral displacement value ALC _AO ,

(b) Measure the actual lateral displacement value: The offset of the vehicle in the lane is measured by the environmental perception device and calculated using the following formula:

(35),

(c) Calculate the lateral deviation error value. The calculation formula is:

(36),

(d) Control of lateral deviation: The torque of the EPS steering gear applied by the lateral deviation control is calculated using the control algorithm. The calculation formula is:

(37).

Then calculate the torque Torq _HdAngle implemented by the yaw angle deviation control on the EPS steering gear, specifically:

(I) Calculate the desired yaw angle ALC _A1 using the following formula:

(38),

Among them, the longitudinal velocity v _x = v _O , and the lateral velocity v _y is obtained according to formula (4):

(39),

(II) Calculate the actual yaw angle: The actual yaw angle of the vehicle in the lane measured by the environment perception device is calculated using the following formula:

(40),

(III) calculating the yaw angle error value;

(41),

(IV) Control of lateral deviation: The torque applied to the EPS steering gear by yaw angle deviation control is calculated using a control algorithm. The calculation formula is:

(42),

Then the feedforward compensation torque Torq _fwd is calculated as follows:

(A) Calculate the road curvature of the planned path: According to the planned path curvature ρ calculated by equation (13), when the vehicle changes lanes on a curved road, the actual turning curvature of the vehicle is calculated to obtain ALC _A2 ;

(B) Calculate the feedforward compensation torque using the following formula:

(43),

In formula (43), ɡ(ALC _A2 ) is a function of the curvature of the target trajectory,

(C) Calculate the final steering torque Torq _total using the following formula:

(44).

Finally, the practical EPS assist torque also requires the calculation of the upper and lower limits of the EPS execution torque, as well as filtering and rising and falling rate limits to eliminate sudden changes. These sudden changes may be caused by the perceived lateral deviation of the lane line and the sudden change of the yaw angle. Since the output EPS execution torque part includes the difference in yaw angle multiplied by a specific constant, for example, if the yaw angle suddenly changes from -1 degree to +1 degree, the output EPS execution torque is bound to change suddenly.

Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims (10)

1. An automatic lane change control method for a vehicle is characterized in that: the environment sensing equipment and the combined inertial navigation sense the driving environment and the current movement condition around the vehicle, and the decision control unit synthesizes the environment information and the driving information to judge whether the vehicle meets the lane changing condition, if the vehicle meets the lane changing condition, a torque control command is output to ensure that the vehicle stably runs along a planned target track and automatically completes lane changing action;

The method specifically comprises the following steps:

S1, lane identification: identifying a left lane line y _l, a right lane line y _r and a right outer lane line y _rr on a right adjacent lane of the vehicle by the environment sensing device;

S2, judging the confidence degree of the lane line: calculating the type, confidence, effectiveness and effective distance of the lane lines, judging the quality of the lane lines, and further evaluating whether the lane lines can be used for control decision;

s3, extracting a target track: s1, acquiring actual lane line information, processing the actual lane line information, and extracting a target track of a vehicle running in a lane according to a road environment;

S4, judging the intention of a driver: the automatic lane change system judges whether a driver is in an active driving state, if the driver is in the active driving state, lane change overtaking is not carried out, and other conditions judge that lane change overtaking is carried out from a left lane or a right lane according to surrounding environments;

S5, planning a target path: assuming that a current driving lane of the own vehicle is positioned at a point A which is distant from an O point by ALC _AO, planning a lane changing track, dividing a lane changing path into two sections, firstly planning a first driving curve section OO', and calculating to obtain a lateral offset ALC _AO of the planned lane changing track and an ordinate x and an abscissa y of the planned path; secondly, planning a second section of running curve section O 'O' ', and calculating to obtain the transverse offset ALC _AO' of the own vehicle relative to the center line of the lane at the moment;

S6, optimizing the path obtained through planning: firstly, calculating the transverse speed v _y of the planned path and the transverse acceleration a _y of the uniform motion vehicle, then calculating the limit value a _{y max} of the transverse acceleration, the limit value a _xLim of the longitudinal acceleration and the limit value a _Lim of the acceleration during steering, and finally calculating the shortest time T _sLim for finishing lane change;

S7, collision detection: detecting whether the surrounding is provided with an obstacle or not through a sensor, if so, returning to the step S5 to plan the target path again, and if not, starting the lane changing action;

S8, lane change control: the torque Torq _LatErr of the lateral deviation control on the EPS steering gear is calculated, the torque Torq _HdAngle of the yaw deviation control on the EPS steering gear is calculated, the feedforward compensation torque Torq _fwd is calculated, and finally the final steering torque Torq _total is obtained by adding the above three.

2. The automatic lane-changing control method for a vehicle according to claim 1, wherein: the calculation formula of the left lane line y _l in the step S1 is as follows:（i），

The calculation formula of the right lane line y _r is: （ii），

The calculation formula of the right outer lane line y _rr is: （iii）；

In the formula (i), l ₀ is the transverse distance of the left lane line relative to the vehicle, l ₁ is the yaw angle of the left lane line, l ₂ is the curvature of the left lane line, and l ₃ is the curvature change rate of the left lane line; in the formula (ii), r ₀ is the lateral distance of the right lane line relative to the vehicle, r ₁ is the right lane line yaw angle, r ₂ is the right lane line curvature, and r ₃ is the right lane line curvature change rate; in the formula (iii), r _r0 is the lateral distance of the right outer lane line from the vehicle, r _r1 is the right lane line yaw angle, r _r2 is the right lane line curvature, and r _r3 is the right lane line curvature change rate.

3. The automatic lane-changing control method for a vehicle according to claim 1, wherein: the calculation formula of the lateral offset ALC _AO of the lane-changing track planned in step S5 is as follows:

（1），

in the formula (1), A _O is the distance from the vehicle to the lane center line at the point O, and the calculation formula is as follows:

（2），

Lane _width is the Lane width, and its calculation formula is:

（3），

t _delta is a timer from the start of implementing the lane change to the end of the lane change, and the calculation formula is as follows:

（4），

In the formula (4), delta T is the running period of the controller calling the automatic lane changing algorithm software, k is a natural number, and refers to the time required for finishing lane changing after k operation periods from the start of lane changing to the end of lane changing;

Assuming that the vehicle speed is V _O when the vehicle plans the lane change and assuming that the whole lane change process of the vehicle keeps constant motion, the calculation formula of the ordinate x of the planned path is:

（5），

The calculation formula of the abscissa y of the planned path is as follows:

（6）；

The calculation formula of the lateral offset ALC _AO' of the own vehicle relative to the lane center line is as follows:

（7）。

4. The automatic lane-changing control method for a vehicle according to claim 3, wherein: the calculation formula of the lateral velocity v _y of the path planned in step S6 is as follows:

（8），

Substituting formula (1) into formula (8) to obtain:

（9），

the calculation formula of the lateral acceleration a _y of the uniform motion vehicle is as follows:

（10），

Considering that the longitudinal vehicle speed v _o of a general vehicle motion is relatively large and the lateral speed v _y＜＜v_o during high-speed traveling, equation (10) is simplified to:

（11），

In the formula (11), R is a turning radius, and when the vehicle runs on a curved road to change the road, a curvature calculation formula of the actual turning of the vehicle is:

（12），

（13），

In the formulas (12) and (13), a ₂ is the curvature of the road where the vehicle is located, and the calculation formula of the curvature a ₂ is as follows for the road where both the left and right lane lines are equally trusted:

（14），

ρ is the road curvature of the planned cosine curve, and its calculation formula is:

（15），

from the formula (5) and the formula (6):

（16），

taking the first derivative of y in equation (16) yields:

（17），

obtaining a second derivative of y in the formula (16):

（18），

Considering that the general longitudinal vehicle speed v _o is relatively large and the lateral speed v _y＜＜v_o is relatively large during high-speed traveling, equation (17) is simplified as:

（19），

And then according to the formula (18) and the formula (15):

（20），

substituting formula (20) into formula (13) to obtain:

（21），

Then, formula (21) is substituted into formula (11), to obtain:

（22），

The simplification of formula (22) yields:

（23），

if the curvature of the lane change is large, the influence of a ₂ on the lateral acceleration needs to be considered, and then the limit value of the lateral acceleration during steering is calculated, specifically:

When (when) At a _y, so when A ₂ > 0 andThe calculation formula of the limit value a _{y max} of the lateral acceleration during steering is as follows:

（24），

Or A ₂ < 0 and And when the lateral acceleration obtains an extreme value, the calculation formula is as follows:

（25），

in the expression (25), the sign merely indicates whether the direction of the acceleration is directed to the left or the right.

5. The automatic lane-changing control method for a vehicle according to claim 4, wherein: the calculation of the acceleration limit a _Lim in step S6 requires consideration of the road surface adhesion system mu and the gravitational acceleration g,

For low adhesion road surfaces μ < 0.3, the calculation formula for the acceleration limit a _Lim is:

（26），

For the adhesion coefficient μ > =0.3 road surface, the calculation formula of the acceleration limit a _Lim is:

（27），

In the course of changing the track, the acceleration is less than or equal to the acceleration limit value a _Lim, namely:

（28），

in the formula (28), a _x is longitudinal acceleration, a _x is approximately equal to 0 under the condition of uniform speed of the vehicle,

The lateral acceleration limit a _{y Lim} is not greater than the acceleration limit a _Lim, from which:

（28’）。

6. The automatic lane-changing control method for a vehicle according to claim 5, wherein: in the step S6, when the shortest time T _sLim for completing the lane change is calculated, whether the lane change condition is satisfied is considered, specifically:

If it is The road curvature is too large at the moment, the road changing condition is not met, and the road changing is not carried out;

If it is Calculating the minimum time required for finishing the lane change;

And judging:

when A ₂ > 0, i.e. the road itself is curved to the right:

If it is I.e. road curvature is metAt this time, the vehicle can complete lane changing at a constant speed, and the minimum time T _S required for lane changing completion is calculated according to the following calculation formula:

（29），

In this case, the calculation formula of the minimum time T _sLim to complete the lane change is:

（30），

When A ₂ < 0, i.e. the road itself is curved to the left:

If it is I.e. road curvature is metAt this time, the vehicle can complete lane changing at a constant speed, and the minimum time T _S required for lane changing is calculated, and the calculation formula is as follows:

（31），

In this case, the calculation formula of the minimum time T _sLim to complete the lane change is:

（32），

in the actual lane changing process, a certain safety margin is also required to be considered, the time required for the lane changing to be completed is moderately prolonged, and the safety coefficient eta is more than 1.0, so that the following is obtained:

（33），

considering that the vehicle is not generally at a constant speed in the course of changing the road, but a variable speed motion is adopted, and assuming that the limit value of the longitudinal acceleration is a _{x Lim} in the variable speed motion, then:

（34），

While （34′），

Substituting equation (34) into equation (24) or equation (25) yields the minimum time T _sLim for the shift motion to complete the lane change.

7. The automatic lane-changing control method for a vehicle according to claim 4, wherein: in the step S8, the torque Torq _LatErr applied to the EPS steering device by the lateral deviation control is calculated, specifically:

(a) The desired lateral displacement value ALC _AO is calculated,

(B) Measuring the actual lateral displacement value: according to the offset of the self-vehicle in the lane measured by the environment sensing equipment, the calculation formula is as follows:

（35），

(c) Calculating the transverse deviation error value, wherein the calculation formula is

（36），

(D) Control the lateral deviation: the torque applied to the EPS steering gear by the lateral deviation control is calculated by adopting a control algorithm, and the calculation formula is as follows:

（37）。

8. The automatic lane-changing control method for a vehicle according to claim 7, wherein: in the step S8, the torque Torq _HdAngle applied to the EPS steering device by the yaw angle deviation control is calculated specifically as follows:

(I) The desired yaw angle ALC _A1 is calculated as:

（38），

Wherein the longitudinal velocity v _x=v_O and the transverse velocity v _y are according to equation (4), the following equation is obtained:

（39），

(II) calculating an actual yaw angle: according to the actual yaw angle of the vehicle in the lane measured by the environment sensing equipment, the calculation formula is as follows:

（40），

(III) calculating a yaw angle error value;

（41），

(IV) controlling the lateral deviation: the torque applied to the EPS steering gear by yaw angle deviation control is calculated by adopting a control algorithm, and the calculation formula is as follows:

（42）。

9. The automatic lane-changing control method for a vehicle according to claim 8, wherein: in the step S8, the feedforward compensation torque Torq _fwd is calculated, specifically:

(A) Calculating the road curvature of the planned path: calculating the curvature of the actual turning of the vehicle to obtain ALC _A2 when the vehicle runs on a curved road and changes lanes according to the planned path curvature rho calculated in the formula (13);

(B) The feedforward compensation torque is calculated, and the calculation formula is as follows:

（43），

In equation (43), the sample (ALC _A2) is a function of the curvature of the target trajectory,

(C) The final steering torque Torq _total is calculated by the following formula:

（44）。

10. The automatic lane-changing control method for a vehicle according to claim 8, wherein: the environment sensing equipment in the step S1 comprises a front-view camera, a side-view camera, a rear-view camera, a forward millimeter wave radar, an angle millimeter wave radar and a GPS; the control algorithm in the step S8 includes a pid control algorithm, an LQR control algorithm, and an MPC control algorithm.