METHOD FOR STEERING A VEHICLE

Abstract

A method for controlling a vehicle including an actuator along a trajectory, in which the trajectory is planned within a search space, and considers a projection of a manipulated variable of the actuator. The method includes creating an actuator model of the actuator on the basis of the manipulated variable of the actuator; defining time increments of the projection; determining the change in the manipulated variable of the actuator along the time increments on the basis of the actuator model and a limit value for the manipulated variable; limiting the search space on the basis of the limit value of the manipulated variable of the actuator; determining an acceleration value and/or a deceleration value of the vehicle by converting the manipulated variable using the vehicle mass and the wheel radius; and outputting the acceleration value and the deceleration value to limit the search space within which the trajectory is planned.

Claims

1. A method for controlling a vehicle comprising at least one actuator along a trajectory, in which the trajectory is planned within a search space, taking into account a projection of at least one manipulated variable of the actuator, the method comprising: creating an actuator model of the actuator on the basis of the at least one manipulated variable of the actuator, defining time increments of the projection, determining a change in the manipulated variable of the actuator along the time increments on the basis of the actuator model and a limit value for the manipulated variable, limiting the search space on the basis of the limit value of the manipulated variable of the actuator, determining at least one of an acceleration value or a deceleration value of the vehicle by converting the at least one manipulated variable using vehicle mass and wheel radius, and outputting the at least one of the acceleration value or the deceleration value to limit the search space within which the trajectory is planned.

2. The method according to claim 1, wherein the actuator is an engine and/or a brake of the vehicle.

3. The method according to claim 2, wherein the manipulated variable is a torque, in particular an engine torque of the engine or a braking torque of the brake.

4. The method according to claim 1, wherein the limit value is a maximum possible change in the manipulated variable in at least one of a positive or negative direction.

5. The method according to claim 1, wherein the actuator model is based on a function of the manipulated variable and includes a positive gradient of the manipulated variable for manipulated variable build-up and a negative gradient of the manipulated variable for manipulated variable reduction with respect to time t.

6. The method according to claim 1, wherein the acceleration value is a maximum possible acceleration of the vehicle, and the deceleration value is a maximum possible deceleration of the vehicle.

7. The method according to claim 1, wherein driving resistance is determined, in particular from the time increments of the projection.

8. The method according to claim 7, wherein the driving resistance is additionally taken into account when determining the at least one of the acceleration value or the deceleration value.

9. The method according to claim 1, further comprising providing at least one sensor for detecting the surroundings.

10. The method according to claim 9, wherein the detected surroundings are used to define at least one of the search space or trajectory planning.

11. A computer program comprising program code for carrying out the method according to claim 1, wherein the computer program is executed on a computer.

12. A computer-readable storage medium comprising instructions that cause a computer on which the instructions are executed to carry out a method according to claim 1.

13. A control device for controlling a vehicle along a trajectory, wherein the vehicle is controlled by means of a method according to claim 1.

14. The method according to claim 9, wherein the at least one sensor comprises at least one of a camera, a Lidar sensor, a radar sensor or an ultrasonic sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The invention is described in more detail below with reference to expedient exemplary embodiments. In the drawings:

[0035] FIG. 1 is a simplified schematic view of a vehicle in which a maximum manipulated variable is predicted using the method according to the invention, and

[0036] FIG. 2 is a simplified schematic view of a sequence of the method according to the invention.

DETAILED DESCRIPTION

[0037] Reference sign 1 in FIG. 1 refers to a vehicle having various actuators (steering system 3, engine 4, brake 5), the vehicle having a control device 2 (ECU, Electronic Control Unit) by means of which trajectory planning may be performed with respect to the actuator dynamics. The trajectory is calculated on the basis of a trajectory planner, wherein a prediction of a maximum manipulated variable of the particular actuator is made, in particular in the longitudinal direction, to limit the search space of the trajectory planner and is used for trajectory planning. The trajectory planner may be configured as a hardware module of the control device 2 or merely as a software module. Furthermore, the vehicle 1 has sensors for detecting the environment (camera 6, lidar sensor 7, radar sensor 8 and ultrasonic sensors 9a, 9b), the sensor data from which is used for detecting the environment and objects such that various assistance functions may be implemented, such as an emergency brake assistance system (EBA, Electronic Brake Assist), distance following control (ACC, Automatic Cruise Control), lane-keeping control or a lane keep assistance system (LKA, Lane Keep Assist), or the like. In a practical manner, the assistance functions may also be carried out by means of the control device 2 or a separate control device.

[0038] The method according to the present disclosure uses the input signals of vehicle acceleration a, vehicle speed v, braking torque T.sub.B, engine torque T.sub.M, engine torque minimum T.sub.M,min, engine torque maximum T.sub.M,max and the currently engaged gear and provides the two output vectors of maximum acceleration and maximum deceleration, each having a variable projection. The vehicle parameters of transmission ratio i.sub.g, vehicle mass m, wheel radius r, front area A, drag coefficient c.sub.W (with decreasing accuracy requirements in this order) and air density ρ.sub.L (in kg/m.sup.3) are known. A simplified structure of a flow chart and of the data flow of the method is shown in FIG. 2.

[0039] In FIG. 2, as examples, the actuators are the brake and the engine, which are represented by respective associated actuator models (engine model 10 and brake model 11), each of which each exhibits a positive gradient of the torque T for torque build-up (engine torque build-up 10a and braking torque build-up 11a) and a negative gradient of the torque T for torque reduction (engine torque reduction 10b and braking torque reduction 11b) with respect to time t. In FIG. 2, the torque T is indicated in Newton meters (Nm) and the time is indicated in seconds (s). The brake is represented by a linear function with dead time and saturation; the dead time to be optionally included having the first slope section and the saturation includes the second slope section of the function. The engine in the engine model 10 is represented as a piecewise-defined linear function with optional dead time and saturation, since, for example, internal combustion engines and electric engines, due to their design, provide a lower torque gradient above a gear-dependent engine torque limit value than below the engine torque limit value. By contrast, for an electric engine with a single-gear transmission, modeling may be selected as in the brake model 11.

[0040] As part of the projection 12, the maximum rising and falling gradients of the actuators are each multiplied by the vector of the projection in order to determine the maximum positive and negative change of the torque T in the time increments (time t in seconds s) indicated by the vector. According to FIG. 2, the following time increments were selected: 0 s, 0.5 s, 1 s and 2 s.

[0041] Furthermore, the maximum torque change plus the current torque T cannot exceed the absolute limit of the particular actuator (i.e., for example, engine torque maximum T.sub.M,max) and is therefore limited to the possible operating range of the actuator, as shown by the saturation 13.

[0042] Subsequently, a conversion 14 is expediently carried out, in which the (four) torque changes are converted into (four) vehicle accelerations on the basis of

a=T.Math.(m.Math.r)

using the vehicle mass m and the wheel radius r. The converted sum of engine torque build-up and braking torque reduction then gives the maximum vehicle acceleration. Accordingly, the converted sum of engine torque reduction and braking torque build-up gives the maximum vehicle deceleration.

[0043] In addition, the driving resistance is taken into account for the determined vehicle deceleration. The calculated vehicle acceleration is applied to produce a change in driving resistance over the duration of the projection. This also causes a change in the acceleration. The change in driving resistance 15a, 15b may be taken into account by applying the following:

[00001]$a_{\mathrm{res}}=\frac{1}{2}.Math.c_w.Math.A.Math.{\rho }_L.Math.v_{\mathrm{diff}}^2$

[0044] At the output (right arrow), the acceleration and deceleration limits corrected by the influence of the change in driving resistance are then both displayed or outputted with the projection, e.g., 0 s, 0.5 s, 1 s, 2 s or the like (variable), and transmitted to the planner.

[0045] In summary, the example embodiments are able to provide a prediction method for estimating the current and future actuator limits, in particular in the longitudinal direction. These actuator limits are to be made available to the planner in order to calculate trajectories that may be driven. In particular, the available dynamics and the absolute limits of the engine and brake as actuators are to be estimated. In addition, driving resistance is also to be taken into account. The estimated actuator limits may be calculated for the current point in time and for a temporal projection which is based on the planner. Furthermore, the estimated actuator limits may be transmitted to the planner in the form of longitudinal vehicle accelerations in order to achieve compatibility with optimization-based and non-optimization-based planning approaches. Furthermore, the present invention may also be adapted to over-actuated systems, e.g., vehicles with a front and rear axle steering system or all-wheel drive vehicles, i.e., may be extended to include additional longitudinal actuators. In addition, an application to redundant actuators is possible, e.g. a “brake-by-wire brake” with a conventional brake as a fallback path. Furthermore, the method is not limited to control in the longitudinal direction, but may also be applied to “steer-by-braking” methods. Moreover, the method may be applied both to planner concepts and controller approaches and to combined approaches such as model predictive control (MPC).

LIST OF REFERENCE NUMERALS

[0046] 1 Vehicle [0047] 2 Control device [0048] 3 Steering system [0049] 4 Engine [0050] 5 Brake [0051] 6 Camera [0052] 7 Lidar sensor [0053] 8 Radar sensor [0054] 9a Ultrasonic sensor [0055] 9b Ultrasonic sensor [0056] 10 Engine model [0057] 10a Engine torque build-up [0058] 10b Engine torque reduction [0059] 11 Brake model [0060] 11a Braking torque build-up [0061] 11b Braking torque reduction [0062] 12 Projection [0063] 13 Saturation [0064] 14 Conversion [0065] 15a Driving resistance [0066] 15b Driving resistance [0067] A Front area [0068] a Vehicle acceleration [0069] c.sub.W Drag coefficient [0070] i.sub.G Transmission ratios [0071] m Vehicle mass [0072] r Wheel radius [0073] T Torque [0074] t Time [0075] v Vehicle speed [0076] ρ.sub.L Air density