CN113844535A - Active steering control method based on steering wheel torque - Google Patents
Active steering control method based on steering wheel torque Download PDFInfo
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Abstract
The invention discloses an active steering control method based on steering wheel torque, which comprises the following steps: determining a pre-aiming distance and a pre-aiming point based on a planned track of the vehicle; determining the road turning curvature according to the pre-aiming point; and obtaining the steering wheel torque of the vehicle according to the road turning curvature, the current vehicle speed of the vehicle and a pre-established vehicle transverse rotation model, wherein the vehicle transverse rotation model is used for representing the corresponding relation between the steering wheel torque and the vehicle speed of the vehicle under the preset road turning curvature. According to the active steering control method based on the steering wheel torque, the road turning curvature calculated based on the preview point is utilized, the corresponding vehicle steering wheel torque is obtained through a vehicle transverse rotation model in combination with the current vehicle speed of the vehicle, road shape characteristic information and the vehicle steering wheel torque can be organically combined, the vehicle steering wheel torque is obtained according to the planned track, and accurate driving along the planned path can be achieved under the automatic driving working conditions of low speed and large curvature, such as turning around, steering and the like.
Description
Technical Field
The invention relates to the technical field of automatic driving, in particular to an active steering control method based on steering wheel torque.
Background
When the degree of curvature of a road changes during the driving process of an automatic driving vehicle, the driving direction (head) of the automatic driving vehicle is necessarily required to be changed continuously so as to adapt to the change of the degree of curvature of the road, and therefore the essence of the transverse control system of the automatic driving vehicle is to control the driving direction of the vehicle.
Currently, two active steering control methods are mainly used for automatically driving a vehicle, one is that a controller calculates an expected turning angle through road curvature, and the expected turning angle is output and sent to an actuating mechanism to control a steering wheel to rotate so as to realize automatic steering of the automatically driven vehicle, which is called as an active steering control method based on the turning angle for short; the other method is an active steering control method based on torque for short, which controls the steering wheel to rotate by outputting the torque of the steering wheel to realize the automatic steering of the automatic driving vehicle. Generally, a control method based on torque mainly calculates expected torque by a PID control algorithm through a road curvature. The method can well drive along the route on a straight road surface with small curvature, but the method cannot accurately drive along the route for road conditions with large curvature, such as intersection turning and turning around, so the method is mainly applied to the development of lane keeping functions.
Therefore, an active steering control method based on steering wheel torque is needed.
Disclosure of Invention
The invention aims to provide an active steering control method based on steering wheel torque, which aims to solve the problems in the prior art and can accurately track a route to run on a road with large curvature.
The invention provides an active steering control method based on steering wheel torque, which comprises the following steps:
determining a pre-aiming distance and a pre-aiming point based on a planned track of the vehicle;
determining the road turning curvature according to the pre-aiming point;
and obtaining the steering wheel torque of the vehicle according to the road turning curvature, the current vehicle speed of the vehicle and a pre-established vehicle transverse rotation model, wherein the vehicle transverse rotation model is used for representing the corresponding relation between the steering wheel torque and the vehicle speed of the vehicle under the preset road turning curvature.
The active steering control method based on steering wheel torque as described above, wherein preferably, the determining a pre-aiming distance and a pre-aiming point based on a planned trajectory of the vehicle specifically includes:
determining a pre-aiming distance according to the real-time speed of the vehicle based on the planned track of the vehicle;
and determining a preview point according to the preview distance.
The active steering control method based on the steering wheel torque as described above, wherein preferably, the determining a pre-aiming distance according to the real-time vehicle speed of the vehicle based on the planned trajectory of the vehicle specifically includes:
in the planned track, calibrating the corresponding shortest pre-aiming distance of the vehicle at the typical vehicle speed to obtain a relation table of the shortest pre-aiming distance and the typical vehicle speed;
calculating the corresponding shortest pre-aiming distance under the atypical vehicle speed through a linear interpolation method to obtain a relation table of the shortest pre-aiming distance and the atypical vehicle speed;
according to the real-time vehicle speed of the vehicle, the pre-aiming distance corresponding to the real-time vehicle speed of the vehicle is determined by table look-up in the relation table of the shortest pre-aiming distance and the typical vehicle speed or the relation table of the shortest pre-aiming distance and the atypical vehicle speed.
The active steering control method based on steering wheel torque as described above, wherein preferably, the step of calibrating the shortest preview distance corresponding to the vehicle at the typical vehicle speed to obtain the relation table of the shortest preview distance and the typical vehicle speed specifically includes:
step A1, controlling the vehicle to run at a constant speed under the minimum typical speed, and setting an initial pre-aiming distance;
step A2, observing the running state of the vehicle, if the snake shape does not appear, reducing the pre-aiming distance, carrying out the experiment again until the snake shape appears in the running state of the vehicle, and taking the pre-aiming distance before the snake shape appears as the pre-aiming distance under the preset constant vehicle speed;
and step A3, controlling the vehicle to increase the vehicle speed in the sequence from low to high according to the typical vehicle speed to drive at a preset constant vehicle speed, and executing steps A1 and A2 to finish the calibration of the pre-aiming distance under all the typical vehicle speeds.
The active steering control method based on steering wheel torque as described above, wherein preferably, the determining a preview point according to the preview distance specifically includes:
and continuously taking a plurality of waypoints forward along the planned trajectory at preset distance intervals from the pre-aiming distance as pre-aiming points.
The active steering control method based on steering wheel torque as described above, wherein preferably, the determining the road turning curvature according to the preview point specifically includes:
an optimal curvature objective function is calculated,
wherein J represents an optimal curvature objective function, AiThe ith pre-aiming point is shown, C is the circle center of the optimal turning circular arc, y is the vertical coordinate of the circle center of the optimal turning circular arc, the radius of the circular arc is also equal to y, the optimal turning circular arc takes the original point as the starting point and takes the x axis as the tangent, then C is always on the y axis,
indicating the preview point aiDistance to arc of circle, which is equal to AiDistance to C minus radius y, n representing the number of preview points, J being equal to AiThe sum of squares of the differences between the squares of the distances to the circular arcs and the squares of the radii:
calculating an optimal turning radius according to the optimal curvature objective function,
order to
The optimal turning radius y, mark A can be obtainediThe coordinate is (x)i,yi) Then, then
Obtaining an optimal turning curvature rho according to the optimal turning radius y,
and taking the optimal turning curvature rho as the road turning curvature.
The active steering control method based on the steering wheel torque as described above, wherein preferably the method of establishing the vehicle lateral rotation model includes:
collecting model calibration data;
and carrying out data processing on the collected model calibration data to establish a vehicle transverse rotation model.
The active steering control method based on steering wheel torque as described above, wherein preferably, the collecting model calibration data specifically includes:
the method comprises the steps of sequentially collecting model calibration data according to the sequence that the angle of a steering wheel increases from small to large and the sequence that the angle decreases from small to large, fixing the steering wheel at a preset angle, enabling a vehicle to start to accelerate from a static state until the rollover risk is about to occur, and collecting longitude information x, latitude coordinate information y, speed information v, a steering wheel corner Tn and steering wheel torque Tq at the same moment in a sampling period.
The active steering control method based on steering wheel torque as described above, wherein preferably, the performing data processing on the collected model calibration data to establish a vehicle lateral rotation model specifically includes:
fitting the vehicle longitude information x and the vehicle latitude coordinate information y to obtain a road curvature Q;
according to the sequence that the vehicle speed increases from small to large, the steering wheel torque Tq corresponding to the vehicle speed is calculated by averaging the steering wheel torques corresponding to a plurality of steering wheel rotation angles Tn under the same vehicle speed vi in a sampling periodi；
Under the working condition of the road curvature Q, the steering wheel torque Tq and the vehicle speed v are fitted into a polynomial Tq-F (v) form, so that corresponding relational expressions of the steering wheel torque and the vehicle speed under different road curvatures are obtained.
The active steering control method based on steering wheel torque as described above, wherein preferably, the obtaining of the steering wheel torque of the vehicle according to the road curvature, the current vehicle speed of the vehicle and a vehicle lateral rotation model established in advance includes:
comparing the road turning curvature Q with each road curvature in the vehicle transverse rotation model by adopting a table look-up method so as to find out a curvature section Qn < Q < Qn +1 corresponding to the road turning curvature Q;
according to a corresponding relation formula Tq ═ F (v) of the steering wheel torque and the vehicle speed under the road turning curvature Q in the vehicle transverse rotation model, respectively calculating the torque Tqn corresponding to the Qn under the current vehicle speed and the torque Tqn +1 corresponding to the Qn + 1;
obtaining the torque Tq under the road turning curvature Q by adopting an interpolation method according to the torque Tqn corresponding to the Qn at the current vehicle speed and the torque Tqn +1 corresponding to the Qn +1,
Tq＝(Q-Qn/Qn+1-Qn)*(Tqn+1-Tqn)+Tqn。
the invention provides an active steering control method based on steering wheel torque, which utilizes road turning curvature calculated based on a preview point, combines the current speed of a vehicle and then obtains the corresponding vehicle steering wheel torque through a vehicle transverse rotation model, can fully and organically combine road shape characteristic information with the vehicle steering wheel torque, thereby obtaining the vehicle steering wheel torque according to a planned track, and can realize accurate driving along the planned path under the automatic driving working conditions of low speed and large curvature, such as turning around, steering and the like.
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In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described with reference to the accompanying drawings, in which:
FIG. 1 is a flow chart of an embodiment of a steering wheel torque based active steering control method provided by the present invention;
FIG. 2 is a schematic diagram of the determination of the preview point provided by the present invention;
fig. 3 is a schematic diagram of the preview point and the optimal turning arc in the vehicle coordinate system provided by the invention.
Detailed Description
Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. The description of the exemplary embodiments is merely illustrative and is in no way intended to limit the disclosure, its application, or uses. The present disclosure may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. It should be noted that: the relative arrangement of parts and steps, the composition of materials, numerical expressions and numerical values set forth in these embodiments are to be construed as merely illustrative, and not as limitative, unless specifically stated otherwise.
As used in this disclosure, "first", "second": and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The word "comprising" or "comprises", and the like, means that the element preceding the word covers the element listed after the word, and does not exclude the possibility that other elements are also covered. "upper", "lower", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships may also be changed accordingly.
In the present disclosure, when a specific component is described as being located between a first component and a second component, there may or may not be intervening components between the specific component and the first component or the second component. When it is described that a specific component is connected to other components, the specific component may be directly connected to the other components without having an intervening component, or may be directly connected to the other components without having an intervening component.
All terms (including technical or scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs unless specifically defined otherwise. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail, but are intended to be part of the specification where appropriate.
The existing active steering control method adopted by the automatic driving vehicle mainly comprises two methods, one is an active steering control method based on a corner, and the method is based on a pure path tracking algorithm and firstly calculates the road curvature Q according to the pre-aiming distance; then, calculating an expected rotation angle according to a two-degree-of-freedom kinematic model of the vehicle; and then, a PID control mode and other modes are adopted to input an expected rotation angle and output an execution torque. The other is an active steering control method based on torque, firstly, a pre-aiming point is obtained according to a pre-aiming distance, and then an included angle between the current vehicle course and the pre-aiming point is calculated; and then, controlling the included angle between the vehicle course and the pre-aiming point to be 0 by adopting modes of PID control and the like, namely inputting the current included angle and outputting execution torque.
In order to solve the above-mentioned disadvantages, the present invention provides an active steering control method based on steering wheel torque. As shown in fig. 1, the active steering control method based on steering wheel torque provided in this embodiment specifically includes the following steps in an actual implementation process:
and step S1, determining the pre-aiming distance and the pre-aiming point based on the planned track of the vehicle.
In an embodiment of the steering wheel torque-based active steering control method of the present invention, the step S1 may specifically include:
and step S11, determining the pre-aiming distance according to the real-time speed of the vehicle based on the planned track of the vehicle.
In order to simulate the behavior of a human-driven vehicle, the autonomous vehicle needs to acquire road information from a forward path at each control cycle, and how far to acquire the road information depends on the length of the pre-aiming distance, which is similar to how far the driver looks forward.
The inventor continuously analyzes the driving behaviors of the human vehicles to find that the human vehicles usually run faster on a flat road, and can ensure the smooth running of the vehicles only by projecting the eyes to a farther place; when the vehicle runs to a road with larger curvature, the vehicle speed is usually reduced, and meanwhile, the sight is concentrated at a place which is close to the vehicle in the front, so that a driver can know the road condition in the front in time, and the steering of the vehicle is accurately adjusted.
Since the speed of the vehicle is determined by the decision end, when the vehicle passes through roads with different bending degrees, the corresponding speed is set, so that the speed becomes an important certificate for selecting the pre-aiming distance for the control system. Therefore, the invention can design a control strategy of changing the pre-aiming distance based on the real-time speed of the vehicle by referring to the driving experience of human beings, and establishes the relative relation between the pre-aiming distance and the real-time speed of the vehicle, thereby ensuring the stability and the accuracy of the vehicle when the vehicle runs on roads with different bending degrees.
In an embodiment of the steering wheel torque-based active steering control method of the present invention, the step S11 may specifically include:
and S111, calibrating the shortest pre-aiming distance corresponding to the vehicle at the typical vehicle speed in the planned track to obtain a relation table of the shortest pre-aiming distance and the typical vehicle speed.
In the specific implementation, the shortest pre-aiming distance corresponding to the automatically-driven vehicle at the typical vehicle speed is obtained through a calibration experiment, and a series of two-dimensional discrete points are obtained, as shown in table 1, wherein v represents the actual vehicle speed and has a unit of km/h, and s represents the pre-aiming distance and has a unit of m. It should be noted that, before the calibration, the debugging of the longitudinal motion control algorithm of the autonomous vehicle needs to be completed first, and the specific debugging method may refer to the prior art and is not described herein again.
TABLE 1 corresponding Preview distance at typical vehicle speeds
In an embodiment of the steering wheel torque-based active steering control method of the present invention, the step S111 may specifically include:
and step A1, controlling the vehicle to run at a constant vehicle speed under the minimum typical vehicle speed, and setting an initial preview distance.
Wherein the minimum typical vehicle speed is, for example, 8km/h, and the initial pre-aiming distance is typically 20 m.
And A2, observing the running state of the vehicle, reducing the pre-aiming distance if the snake shape does not occur, and performing the experiment again until the snake shape occurs in the running state of the vehicle, wherein the pre-aiming distance before the snake shape occurs is taken as the pre-aiming distance at the preset constant vehicle speed.
In this case, each reduced preview distance is 0.5m, for example, when the preview distance is reduced.
And step A3, controlling the vehicle to increase the vehicle speed in the order of the typical vehicle speed from low to high (for example, increasing the vehicle speed in the order of the left to the right in the table 1), driving at a preset constant vehicle speed, and executing the steps A1 and A2 to finish the calibration of the preview distance under all the typical vehicle speeds.
And step S112, calculating the corresponding shortest pre-aiming distance under the atypical vehicle speed through a linear interpolation method to obtain a relation table of the shortest pre-aiming distance and the atypical vehicle speed.
By performing linear interpolation based on step S111, the corresponding preview distance at any vehicle speed can be calculated in real time.
And S113, according to the real-time vehicle speed of the vehicle, looking up a table in the relation table of the shortest preview distance and the typical vehicle speed or the relation table of the shortest preview distance and the atypical vehicle speed to determine the preview distance corresponding to the real-time vehicle speed of the vehicle.
Therefore, with the support of the shortest preview distance-typical vehicle speed relation table and the shortest preview distance-atypical vehicle speed relation table, the transverse motion control algorithm can select a determined preview distance in the beginning stage of each motion control period.
And step S12, determining a preview point according to the preview distance.
The pre-aiming point is important information reflecting road characteristics at the pre-aiming distance, and a traditional PID transverse control method usually takes a single point at the pre-aiming distance on a planning track as the pre-aiming point to participate in later-stage calculation; however, when observing the road surface, a person cannot observe the road condition by looking at a place with a very small range on the road, and must make an accurate judgment on the overall characteristics of the road ahead, which is particularly important when the vehicle passes through a curved road surface. It can be seen that the single preview point can also drive the vehicle, but obviously the working principle of the method is not very consistent with the characteristics of human driving. In view of this, in the present invention, the preview point is a point set formed by a plurality of GPS waypoints located on the planned trajectory at the preview distance, and may also be simply regarded as a small path intercepted from the preview distance, so that the selected preview point can reflect the road characteristics in a distance ahead, and a route with a large straight line, arc line and curvature should be reflected more accurately from the preview point. Specifically, starting from the pre-aiming distance, a plurality of waypoints are continuously taken forward along the planned trajectory at preset distance intervals as pre-aiming points. In the embodiment of the invention, a series of preview points are selected on the basis of the preview distance to describe the road characteristics, and as shown in fig. 2, three waypoints are continuously taken as the preview points at intervals of 0.5m forward (i.e. in the direction of the vehicle head) along the planned trajectory from the preview distance. It should be noted that, in a specific implementation, a first point having a distance from the vehicle body greater than or equal to the pre-aiming distance may be selected as the pre-aiming point, considering that there is not necessarily exactly one GPS waypoint at the pre-aiming distance.
And step S2, determining the road turning curvature according to the preview point.
In the invention, the degree of curvature of the road is expressed by curvature, and the curvature of a segment of circular arc is inversely proportional to the corresponding radius of the segment of circular arc, namely R is 1/Q, wherein R represents the radius, and Q represents the curvature. In the invention, it can be assumed that in each control period, a series of collected pre-aiming points are all positioned on a section of standard circular arc, so that the turning curvature (radius) corresponding to the section of circular arc can be conveniently fitted by a least square method. In an embodiment of the steering wheel torque-based active steering control method of the present invention, the step S2 may specifically include:
step S21, calculating the optimal curvature objective function,
wherein J represents the optimal curvature objective function, as shown in FIG. 3, AiThe ith pre-aiming point is shown, C is the circle center of the optimal turning circular arc, y is the vertical coordinate of the circle center of the optimal turning circular arc, the radius of the circular arc is also equal to y, the optimal turning circular arc takes the original point as the starting point and takes the x axis as the tangent, then C is always on the y axis,
indicating the preview point aiDistance to arc of circle, which is equal to AiDistance to C minus radius y, n representing the number of preview points, J being equal to AiThe sum of the squares of the differences between the squares of the distances to the circular arcs and the squares of the radii.
Step S22, calculating the optimal turning radius according to the optimal curvature objective function,
order to
The optimal turning radius y, mark A can be obtainediThe coordinate is (x)i,yi) Then, then
Step S23, obtaining the optimal turning curvature rho according to the optimal turning radius y,
And step S24, taking the optimal turning curvature p as the road turning curvature.
In the invention, the estimation of the shape of the road ahead by the driver is simulated through the optimal turning curvature, and more road information is utilized due to the adoption of a plurality of preview points, so that the estimated average shape of the road can better reflect the shape characteristics of the road, and meanwhile, the influence of single-point noise on the control quantity is greatly reduced, and the smooth rotation of a steering wheel is facilitated.
And step S3, obtaining the steering wheel torque of the vehicle according to the road turning curvature, the current vehicle speed of the vehicle and a pre-established vehicle transverse rotation model, wherein the vehicle transverse rotation model is used for representing the corresponding relation between the steering wheel torque and the vehicle speed of the vehicle under the preset road turning curvature.
It can be known from the basic dynamics principle of vehicles that when a steering wheel of a vehicle runs at a certain fixed turning angle and a fixed vehicle speed, the running path of the vehicle is generally a section of arc with a fixed turning radius (curvature) (currently, the understeer coefficient is not considered for the moment), and then through a series of calibration experiments, the corresponding relation between the steering wheel torque and the corresponding turning radius (curvature) of a certain vehicle at a certain vehicle speed can be obtained, which is called as a vehicle transverse rotation model in the invention.
In an embodiment of the steering wheel torque-based active steering control method according to the present invention, the method for establishing the vehicle lateral rotation model may specifically include:
and step B1, collecting model calibration data.
Specifically, model calibration data are sequentially collected according to the ascending order and the descending order of the steering wheel angle from small to large respectively, the steering wheel is fixed at a preset angle, the vehicle starts to run from a static state in an accelerated mode until the rollover risk is not added, and in a sampling period, vehicle longitude information x, vehicle latitude coordinate information y, vehicle speed information v, a steering wheel turning angle Tn and steering wheel torque Tq at the same moment are collected.
Specifically, a high-precision positioning device is installed on the central point of the rear axle of the vehicle, and longitude and latitude coordinate information (x, y) of the vehicle output by the high-precision positioning device, vehicle speed information v and steering wheel corner Tn and torque Tq information output by a vehicle body CAN CAN be synchronously received through an industrial personal computer.
Because the angle of the steering wheel is fixed, the vehicle can run along a fixed curvature route at the moment, and because the speed is increased, the torque fed back by the steering wheel can be synchronously changed. The sampling period of the industrial personal computer is 100ms, for example, and x, y, v, Tn and Tq at the same time in the sampling period are recorded, so that the acquisition of a group of data is completed. In the specific implementation, starting from a steering wheel angle of 5 degrees, a group of data is collected every 5 degrees at the first 100 degrees, a group of data is collected every 10 degrees after 100 degrees until 450 degrees (the maximum steering wheel angle) is reached, 55 groups of data are collected, and then 55 groups of data are collected in the reverse direction by adopting the same method, and 110 groups of data are collected in total. One steering wheel angle corresponds to one road turning curvature, corresponding to one set of sampled data.
And step B2, performing data processing on the collected model calibration data to establish a vehicle transverse rotation model.
In an embodiment of the steering wheel torque-based active steering control method of the present invention, the step B2 may specifically include:
and B21, fitting the vehicle longitude information x and the vehicle latitude coordinate information y to obtain the road curvature Q.
Step B22, according to the increasing sequence of the vehicle speed from small to big, calculating the steering wheel torque Tq corresponding to the vehicle speed by averaging the steering wheel torques corresponding to a plurality of steering wheel rotation angles Tn under the same vehicle speed vi in a sampling periodi。
Illustratively, the vehicle speed is calculated by averaging from 1m/s to 1m/s as the magnitude of steering wheel torque Tq1, once every 1m/s, up to TqN.
And step B23, fitting the steering wheel torque Tq and the vehicle speed v to a polynomial Tq ═ f (v) under the working condition of the road curvature Q, so as to obtain corresponding relational expressions of the steering wheel torque and the vehicle speed under different road curvatures.
Through the steps B21-B23, the vehicle speed and torque model at the 110 road curvature Q is completed. The invention relates to a method for correlating road curvature with steering wheel control torque when building a vehicle transverse rotation model, which is different from the prior technical route that a steering model of curvature and corner is built firstly and then the corner is converted into torque through modes of PID control and the like.
In an embodiment of the steering wheel torque-based active steering control method of the present invention, the step S3 may specifically include:
and step S31, comparing the road turning curvature Q with each road curvature in the vehicle transverse rotation model by adopting a table look-up method so as to look up a curvature section Qn < Q < Qn +1 corresponding to the road turning curvature Q.
And comparing the curvature with the 110 curvature by adopting a table lookup method, and searching the curvature interval corresponding to Q.
Step S32 is to calculate torque Tqn corresponding to Qn at the current vehicle speed and torque Tqn +1 corresponding to Qn +1, from a correspondence expression Tq ═ f (v) between the steering wheel torque and the vehicle speed at the road turning curvature Q in the vehicle lateral rotation model.
Step S33, obtaining the torque Tq under the road turning curvature Q by adopting an interpolation method according to the torque Tqn corresponding to the Qn at the current vehicle speed and the torque Tqn +1 corresponding to the Qn +1,
Tq＝(Q-Qn/Qn+1-Qn)*(Tqn+1-Tqn)+Tqn。
according to the active steering control method based on the steering wheel torque, the road turning curvature calculated based on the preview point is utilized, the corresponding vehicle steering wheel torque is obtained through the vehicle transverse rotation model in combination with the current vehicle speed of the vehicle, the road shape characteristic information and the vehicle steering wheel torque can be organically combined fully, the vehicle steering wheel torque is obtained according to the planned track, and accurate driving along the planned path can be achieved under the automatic driving working conditions of low-speed and large-curvature, such as turning around and steering.
Thus, various embodiments of the present disclosure have been described in detail. Some details that are well known in the art have not been described in order to avoid obscuring the concepts of the present disclosure. It will be fully apparent to those skilled in the art from the foregoing description how to practice the presently disclosed embodiments.
Although some specific embodiments of the present disclosure have been described in detail by way of example, it should be understood by those skilled in the art that the foregoing examples are for purposes of illustration only and are not intended to limit the scope of the present disclosure. It will be understood by those skilled in the art that various changes may be made in the above embodiments or equivalents may be substituted for elements thereof without departing from the scope and spirit of the present disclosure. The scope of the present disclosure is defined by the appended claims.
Claims (10)
1. An active steering control method based on a steering wheel torque, characterized by comprising:
determining a pre-aiming distance and a pre-aiming point based on a planned track of the vehicle;
determining the road turning curvature according to the pre-aiming point;
and obtaining the steering wheel torque of the vehicle according to the road turning curvature, the current vehicle speed of the vehicle and a pre-established vehicle transverse rotation model, wherein the vehicle transverse rotation model is used for representing the corresponding relation between the steering wheel torque and the vehicle speed of the vehicle under the preset road turning curvature.
2. The steering wheel torque-based active steering control method according to claim 1, wherein the determining a pre-aiming distance and a pre-aiming point based on the planned trajectory of the vehicle specifically comprises:
determining a pre-aiming distance according to the real-time speed of the vehicle based on the planned track of the vehicle;
and determining a preview point according to the preview distance.
3. The active steering control method based on the steering wheel torque according to claim 2, wherein the step of determining the pre-aiming distance according to the real-time vehicle speed of the vehicle based on the planned trajectory of the vehicle specifically comprises:
in the planned track, calibrating the corresponding shortest pre-aiming distance of the vehicle at the typical vehicle speed to obtain a relation table of the shortest pre-aiming distance and the typical vehicle speed;
calculating the corresponding shortest pre-aiming distance under the atypical vehicle speed through a linear interpolation method to obtain a relation table of the shortest pre-aiming distance and the atypical vehicle speed;
according to the real-time vehicle speed of the vehicle, the pre-aiming distance corresponding to the real-time vehicle speed of the vehicle is determined by table look-up in the relation table of the shortest pre-aiming distance and the typical vehicle speed or the relation table of the shortest pre-aiming distance and the atypical vehicle speed.
4. The active steering control method based on the steering wheel torque according to claim 3, wherein the step of calibrating the shortest preview distance corresponding to the vehicle at the typical vehicle speed to obtain the relation table of the shortest preview distance and the typical vehicle speed specifically comprises the following steps:
step A1, controlling the vehicle to run at a constant speed under the minimum typical speed, and setting an initial pre-aiming distance;
step A2, observing the running state of the vehicle, if the snake shape does not appear, reducing the pre-aiming distance, carrying out the experiment again until the snake shape appears in the running state of the vehicle, and taking the pre-aiming distance before the snake shape appears as the pre-aiming distance under the preset constant vehicle speed;
and step A3, controlling the vehicle to increase the vehicle speed in the sequence from low to high according to the typical vehicle speed to drive at a preset constant vehicle speed, and executing steps A1 and A2 to finish the calibration of the pre-aiming distance under all the typical vehicle speeds.
5. The steering wheel torque-based active steering control method according to claim 2, wherein the determining a preview point according to the preview distance specifically comprises:
and continuously taking a plurality of waypoints forward along the planned trajectory at preset distance intervals from the pre-aiming distance as pre-aiming points.
6. The steering wheel torque-based active steering control method according to claim 5, wherein the determining a road turning curvature from the preview point specifically comprises:
an optimal curvature objective function is calculated,
wherein J represents an optimal curvature objective function, AiThe ith pre-aiming point is shown, C is the circle center of the optimal turning circular arc, y is the vertical coordinate of the circle center of the optimal turning circular arc, the radius of the circular arc is also equal to y, the optimal turning circular arc takes the original point as the starting point and takes the x axis as the tangent, then C is always on the y axis,
indicating the preview point aiDistance to arc of circle, which is equal to AiDistance to C minus radius y, n representing the number of preview points, J being equal to AiThe sum of squares of the differences between the squares of the distances to the circular arcs and the squares of the radii:
calculating an optimal turning radius according to the optimal curvature objective function,
order to
The optimal turning radius y, mark A can be obtainediThe coordinate is (x)i,yi) Then, then
Obtaining an optimal turning curvature rho according to the optimal turning radius y,
and taking the optimal turning curvature rho as the road turning curvature.
7. The steering wheel torque-based active steering control method according to claim 1, characterized in that the vehicle lateral turning model establishing method includes:
collecting model calibration data;
and carrying out data processing on the collected model calibration data to establish a vehicle transverse rotation model.
8. The active steering control method based on steering wheel torque according to claim 7, wherein the collecting model calibration data specifically comprises:
the method comprises the steps of sequentially collecting model calibration data according to the sequence that the angle of a steering wheel increases from small to large and the sequence that the angle decreases from small to large, fixing the steering wheel at a preset angle, enabling a vehicle to start to accelerate from a static state until the rollover risk is about to occur, and collecting longitude information x, latitude coordinate information y, speed information v, a steering wheel corner Tn and steering wheel torque Tq at the same moment in a sampling period.
9. The active steering control method based on steering wheel torque according to claim 8, wherein the data processing of the collected model calibration data to establish a vehicle lateral rotation model specifically comprises:
fitting the vehicle longitude information x and the vehicle latitude coordinate information y to obtain a road curvature Q;
according to the sequence that the vehicle speed increases from small to large, the steering wheel torque Tq corresponding to the vehicle speed is calculated by averaging the steering wheel torques corresponding to a plurality of steering wheel rotation angles Tn under the same vehicle speed vi in a sampling periodi；
Under the working condition of the road curvature Q, the steering wheel torque Tq and the vehicle speed v are fitted into a polynomial Tq-F (v) form, so that corresponding relational expressions of the steering wheel torque and the vehicle speed under different road curvatures are obtained.
10. The active steering control method based on steering wheel torque according to claim 9, wherein the obtaining of the steering wheel torque of the vehicle according to the road turning curvature, the current vehicle speed of the vehicle and a vehicle lateral rotation model established in advance specifically comprises:
comparing the road turning curvature Q with each road curvature in the vehicle transverse rotation model by adopting a table look-up method so as to find out a curvature section Qn < Q < Qn +1 corresponding to the road turning curvature Q;
according to a corresponding relation formula Tq ═ F (v) of the steering wheel torque and the vehicle speed under the road turning curvature Q in the vehicle transverse rotation model, respectively calculating the torque Tqn corresponding to the Qn under the current vehicle speed and the torque Tqn +1 corresponding to the Qn + 1;
obtaining the torque Tq under the road turning curvature Q by adopting an interpolation method according to the torque Tqn corresponding to the Qn at the current vehicle speed and the torque Tqn +1 corresponding to the Qn +1,
Tq＝(Q-Qn/Qn+1-Qn)*(Tqn+1-Tqn)+Tqn。
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