CN113442907B - A method and device for controlling vehicle speed under low-speed conditions - Google Patents

Abstract

The invention discloses a method and device for controlling vehicle speed under low-speed conditions, which includes: step S1, calculating the output torque of the PID controller according to the target vehicle speed and the current vehicle speed; step S2, calculating the starting compensation torque according to the target vehicle speed and the current vehicle speed; S3, obtain the dynamic compensation torque according to the target vehicle speed look-up table; Step S4, obtain the steering torque compensation coefficient according to the target vehicle speed and steering wheel angle look-up table; Step S5, obtain the steering torque compensation coefficient according to the output torque, starting compensation torque, and dynamic compensation torque of the PID controller and steering torque compensation coefficient to output control torque. On the basis of PID speed control, the present invention introduces torque compensation, namely starting torque compensation, dynamic torque compensation and steering torque compensation, which improves the control accuracy of autonomous vehicles under low-speed conditions such as starting, traveling straight at a constant speed, and large turns. .

Description

A method and device for controlling vehicle speed under low-speed conditions

Technical field

The invention belongs to the field of intelligent driving technology, and specifically relates to a method and device for controlling vehicle speed under low-speed conditions.

Background technique

During the vehicle's automatic parking process, the vehicle speed is at a low speed, generally below 5km/h. At low speeds, vehicle speed control is more sensitive to various resistance forces. For example, if the steering wheel is turned to the limit, the vehicle speed will be significantly reduced.

In some existing technologies, the base part of the creep torque is obtained based on the current vehicle speed lookup table, and then the slope of the vehicle is calculated based on the vehicle's longitudinal acceleration and driving acceleration, and the slope resistance compensation part is obtained. The sum of the two is the total creep torque. line torque. However, this solution does not consider starting factors and steering factors. The vehicle speed factor considered is the current vehicle speed rather than the target vehicle speed, resulting in poor speed control accuracy in low-speed conditions such as starting and large turns.

Contents of the invention

The technical problem to be solved by the embodiments of the present invention is to provide a method and device for controlling vehicle speed under low-speed operating conditions, so as to improve the accuracy of vehicle speed control under low-speed operating conditions such as starting and making large turns.

In order to solve the above technical problems, the present invention provides a method for controlling vehicle speed under low speed conditions, including:

Step S1, calculate the output torque of the PID controller based on the target vehicle speed and the current vehicle speed;

Step S2: Calculate the starting compensation torque according to the target vehicle speed and the current vehicle speed;

Step S3, obtain the dynamic compensation torque according to the target vehicle speed lookup table;

Step S4, obtain the steering torque compensation coefficient according to the target vehicle speed and steering wheel angle lookup table;

Step S5: Output the control torque according to the output torque, starting compensation torque, dynamic compensation torque and steering torque compensation coefficient of the PID controller.

Further, step S2 specifically includes:

Step S21, determine whether the current vehicle speed is 0 and whether the target vehicle speed is not 0; if both are satisfied at the same time, execute step S22; otherwise, execute step S23;

Step S22, the output starting compensation torque is a preset value;

Step S23, the output starting compensation torque is 0.

Further, the table looked up in step S3 is a one-dimensional table of target vehicle speed and dynamic compensation torque.

Further, the table looked up in step S4 is a two-dimensional table of target vehicle speed and steering wheel angle. The header of the first column is the absolute value of the steering wheel angle, and the header of the first row is the target vehicle speed.

Further, the step S5 specifically includes:

The output torque, starting compensation torque and dynamic compensation torque of the PID controller are summed, and then the sum is multiplied by the steering torque compensation coefficient to obtain the control torque and output it.

Further, the error input of the PID controller is the difference between the target vehicle speed and the current vehicle speed.

The invention also provides a device for controlling vehicle speed under low-speed conditions, including:

The first calculation module is used to calculate the output torque of the PID controller based on the target vehicle speed and the current vehicle speed;

The second calculation module is used to calculate the starting compensation torque according to the target vehicle speed and the current vehicle speed;

The first table lookup module is used to obtain dynamic compensation torque according to the target vehicle speed table;

The second table lookup module is used to look up the steering torque compensation coefficient according to the target vehicle speed and steering wheel angle;

An output module is used to output control torque according to the output torque, starting compensation torque, dynamic compensation torque and steering torque compensation coefficient of the PID controller.

Further, the second calculation module is specifically used to determine whether the current vehicle speed is 0 and whether the target vehicle speed is not 0. If both are satisfied at the same time, the output starting compensation torque is a preset value, otherwise the output starting compensation torque is 0.

Further, the table looked up by the first table lookup module is a one-dimensional table of target vehicle speed and dynamic compensation torque, and the table looked up by the second table lookup module is a two-dimensional table of target vehicle speed and steering wheel angle. The first table The head is the absolute value of the steering wheel angle, and the head of the first line is the target vehicle speed.

Further, the output module is specifically configured to sum the output torque, starting compensation torque and dynamic compensation torque of the PID controller, and then multiply the sum by the steering torque compensation coefficient to obtain the control torque and output it.

Implementing the embodiments of the present invention has the following beneficial effects: on the basis of PID speed control, torque compensation is introduced, namely starting torque compensation, dynamic torque compensation and steering torque compensation, which improves the performance of autonomous vehicles in starting, traveling straight at a constant speed, and driving in large distances. Control accuracy under low-speed conditions such as steering.

Description of the drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is a schematic flowchart of a method of controlling vehicle speed under low-speed conditions according to an embodiment of the present invention.

Figure 2 is a specific flow diagram of step S2 in Embodiment 1 of the present invention.

Detailed ways

The following description of the embodiments refers to the accompanying drawings to illustrate specific embodiments in which the invention may be implemented.

Referring to Figure 2, Embodiment 1 of the present invention provides a method for controlling vehicle speed under low-speed conditions, including:

Step S1, calculate the output torque of the PID controller based on the target vehicle speed and the current vehicle speed;

Step S2: Calculate the starting compensation torque according to the target vehicle speed and the current vehicle speed;

Step S3, obtain the dynamic compensation torque according to the target vehicle speed lookup table;

Step S4, obtain the steering torque compensation coefficient according to the target vehicle speed and steering wheel angle lookup table;

Step S5: Output the control torque according to the output torque, starting compensation torque, dynamic compensation torque and steering torque compensation coefficient of the PID controller.

Specifically, the method of controlling the vehicle speed under low-speed conditions in this embodiment is particularly suitable for the automatic parking control process. Assume that the target vehicle speed is V _set and the current vehicle speed is V _now . In step S1, the output torque of the PID controller is calculated based on the target vehicle speed V _set and the current vehicle speed V _now (set as T1). The error input of the PID controller is the difference between the target vehicle speed V _set and the current vehicle speed V _now . The integral control quantity should be cleared after stopping. In this embodiment, both the target vehicle speed and the current vehicle speed can be obtained in real time. The target vehicle speed can be determined during the parking path tracking before automatic parking is performed, and can be used as an input in the automatic parking control process.

Please refer to Figure 2. Step S2 specifically includes the following steps:

Step S21, determine whether the current vehicle speed V _now is 0 and whether the target vehicle speed V _set is not 0; if both are satisfied at the same time, execute step S22; otherwise, execute step S23.

Step S22, the output starting compensation torque (set to T2) is the preset value T _orq2 ; considering that on a flat cement floor, the starting torque of the electric vehicle requires approximately 150Nm, the PID controller provides approximately 50Nm at the starting moment, therefore, as a As an example, in this embodiment, T _orq2 may be 100Nm.

Step S23, the output starting compensation torque T2 is 0.

It should be noted that the reason why the starting torque compensation is set in step S2 in this embodiment is that the vehicle needs to overcome static friction resistance at the moment of starting, and the torque required at the moment of starting will be greater than when driving. The target vehicle speed V _set and the current vehicle speed V _now are used for judgment (step S21). If the judgment result is a starting state, the starting torque compensation is output to a preset value T _orq2 (step S22).

Step S3 obtains the dynamic compensation torque (set as T3) based on the target vehicle speed lookup table. The table looked up is a one-dimensional table, as shown in Table 1 below: the first column is the target vehicle speed V _set and the second column is the dynamic compensation torque.

Table 1: One-dimensional table of dynamic compensation torque

Target vehicle speed V _set /(km/h) Dynamic compensation torque T3/(Nm) 0.1 40 1 60 2 100 3 105 4 110 5 115

It should be noted that on a flat concrete floor, given different constant torques to the electric vehicle, the constant speed maintained by the electric vehicle is the corresponding relationship listed in Table 1. Table 1 can be obtained through calibration. The reason why the dynamic torque compensation is set in step S3 in this embodiment is that when the vehicle is moving at a low speed and at a constant speed, it needs to overcome dynamic friction resistance.

Step S4 obtains the steering torque compensation coefficient (set as K) based on the target vehicle speed V _set and the steering wheel angle SteerAng. The table looked up is a two-dimensional table, as shown in Table 2 below: The first column header is the absolute value of the steering wheel angle SteerAng. The header of the first row is the target vehicle speed V _set .

Table 2: Two-dimensional table of steering compensation coefficients

It should be noted that a certain constant torque _Ta can allow the electric vehicle to maintain a certain constant speed V _set . At this time, increasing the steering wheel angle to S1 requires increasing the torque to T _b to maintain the speed of V _set . Then, the absolute value of the steering wheel angle is S1, and the steering torque compensation coefficient K corresponding to the target vehicle speed V _set is equal to the quotient of T _b and _Ta , that is, K = T _b /T _a . The reason why this embodiment sets the steering torque compensation coefficient through step S4 is that when the vehicle is turning, a centripetal force will be generated, and the tangential traction force will be reduced, resulting in a decrease in vehicle speed. Therefore, the target vehicle speed V _set and the steering wheel angle are used. Perform a two-dimensional lookup table on the absolute value of SteerAng to obtain the value of the steering torque compensation coefficient, which is used to compensate for the steering torque. Table 2 is also available through calibration.

Further, in step S5, according to the output torque, starting compensation torque, dynamic compensation torque and steering torque compensation coefficient of the PID control, the method of outputting the control torque is as follows:

T＝(T1+T2+T3)×K

Among them, T is the control torque, T1 is the output torque of PID control, T2 is the starting compensation torque, T3 is the dynamic compensation torque, and K is the steering torque compensation coefficient.

For example, when automatic parking starts, it is determined that the vehicle is in the starting state through the aforementioned step S21, then the starting compensation torque T2 = T _orq2 , and then the dynamic compensation torque T3 and the steering torque compensation coefficient K are obtained by looking up the tables in steps S3 and S4 respectively. , then the output control torque T = (T1 + T _orq2 + T3) × K; if it is determined that the vehicle is not in the starting state through the aforementioned step S21, then the starting compensation torque T2 = 0, and then the dynamic compensation is obtained by looking up the table in steps S3 and S4 respectively. Torque T3 and steering torque compensation coefficient K, then the output control torque T=(T1+0+T3)×K.

Corresponding to the method for controlling vehicle speed under low-speed working conditions provided in Embodiment 1 of the present invention, Embodiment 2 of the present invention provides a device for controlling vehicle speed under low-speed working conditions, including:

The first calculation module is used to calculate the output torque of the PID controller based on the target vehicle speed and the current vehicle speed;

The second calculation module is used to calculate the starting compensation torque according to the target vehicle speed and the current vehicle speed;

The first table lookup module is used to obtain dynamic compensation torque according to the target vehicle speed table;

The second table lookup module is used to look up the steering torque compensation coefficient according to the target vehicle speed and steering wheel angle;

An output module is used to output control torque according to the output torque, starting compensation torque, dynamic compensation torque and steering torque compensation coefficient of the PID controller.

Further, the second calculation module is specifically used to determine whether the current vehicle speed is 0 and whether the target vehicle speed is not 0. If both are satisfied at the same time, the output starting compensation torque is a preset value, otherwise the output starting compensation torque is 0.

Further, the table looked up by the first table lookup module is a one-dimensional table of target vehicle speed and dynamic compensation torque, and the table looked up by the second table lookup module is a two-dimensional table of target vehicle speed and steering wheel angle. The first table The head is the absolute value of the steering wheel angle, and the head of the first line is the target vehicle speed.

Further, the output module is specifically configured to sum the output torque, starting compensation torque and dynamic compensation torque of the PID controller, and then multiply the sum by the steering torque compensation coefficient to obtain the control torque and output it.

From the above description, it can be seen that compared with the prior art, the beneficial effects of the present invention are: the present invention takes into account that the automatic driving vehicle is very sensitive to resistance when moving at low speed, so on the basis of PID speed control, torque compensation is introduced, respectively. It provides starting torque compensation, dynamic torque compensation and steering torque compensation, so that the control accuracy of autonomous vehicles can be good in low-speed conditions such as starting, traveling straight at a constant speed, and large turns, and the error can be controlled within 0.3km/h.

What is disclosed above is only the preferred embodiment of the present invention. Of course, it cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope of the present invention.

Claims (6)

1. A method of controlling vehicle speed under low-speed conditions, including: Step S1, calculate the output torque of the PID controller based on the target vehicle speed and the current vehicle speed; Step S2: Calculate the starting compensation torque according to the target vehicle speed and the current vehicle speed; Step S3, obtain the dynamic compensation torque according to the target vehicle speed lookup table; Step S4, obtain the steering torque compensation coefficient according to the target vehicle speed and steering wheel angle lookup table; Step S5, output the control torque according to the output torque, starting compensation torque, dynamic compensation torque and steering torque compensation coefficient of the PID controller; The step S2 specifically includes: Step S21, determine whether the current vehicle speed is 0 and whether the target vehicle speed is not 0; if both are satisfied at the same time, execute step S22; otherwise, execute step S23; Step S22, the output starting compensation torque is a preset value; Step S23, the output starting compensation torque is 0; The step S5 specifically includes: The output torque, starting compensation torque and dynamic compensation torque of the PID controller are summed, and then the sum is multiplied by the steering torque compensation coefficient to obtain the control torque and output it. 2. The method according to claim 1, characterized in that the table looked up in step S3 is a one-dimensional table of target vehicle speed and dynamic compensation torque. 3. The method according to claim 1, characterized in that the table looked up in step S4 is a two-dimensional table of target vehicle speed and steering wheel angle, the first column header is the absolute value of the steering wheel angle, and the first row header is the target. Vehicle speed. 4. The method according to claim 1, characterized in that the error input of the PID controller is the difference between the target vehicle speed and the current vehicle speed. 5. A device for controlling vehicle speed under low-speed conditions, which is characterized by including: The first calculation module is used to calculate the output torque of the PID controller based on the target vehicle speed and the current vehicle speed; The second calculation module is used to calculate the starting compensation torque according to the target vehicle speed and the current vehicle speed; The first table lookup module is used to obtain dynamic compensation torque according to the target vehicle speed table; The second table lookup module is used to look up the steering torque compensation coefficient according to the target vehicle speed and steering wheel angle; An output module for outputting control torque according to the output torque, starting compensation torque, dynamic compensation torque and steering torque compensation coefficient of the PID controller; The second calculation module is specifically used to determine whether the current vehicle speed is 0 and whether the target vehicle speed is not 0. If both are satisfied at the same time, the output starting compensation torque is a preset value, otherwise the output starting compensation torque is 0; The output module is specifically used to sum the output torque, starting compensation torque and dynamic compensation torque of the PID controller, and then multiply the sum by the steering torque compensation coefficient to obtain the control torque and output it. 6. The device according to claim 5, wherein the table looked up by the first table lookup module is a one-dimensional table of target vehicle speed and dynamic compensation torque, and the table looked up by the second table lookup module is A two-dimensional table of target vehicle speed and steering wheel angle. The first column header is the absolute value of the steering wheel angle, and the first row header is the target vehicle speed.