CN110001630A - A differential correction system and method for automatic parking and driving trajectory of a distributed drive electric vehicle - Google Patents

Abstract

The invention discloses a differential correction system and method for a track of an automatic parking vehicle of a distributed driving electric automobile, which comprises the following steps that firstly, a detection module automatically detects a parking position and sends parking environment information to a control module; and secondly, a track planning module of the control module VCU plans a reference parking track, and controls a steering motor to steer autonomously according to the actual track of the vehicle so as to drive the vehicle to track the reference parking track. In the tracking process, when the deviation e between the actual parking track of the vehicle and the reference parking track is large, the differential compensation module of the VCU takes the e as a control target, the torque difference of the left hub motor and the right hub motor is taken as control output, the vehicle is driven to perform differential steering, and the track deviation caused by poor steering precision when the steering system is at low speed is reduced. The invention can reduce the parking error of the autonomous steering of the vehicle and improve the parking track precision and the parking reliability of the automatic parking by using the differential steering to assist the vehicle to carry out parking control in the automatic parking process.

Description

A distributed driving electric vehicle automatic parking driving trajectory differential correction system and method

technical field

The invention relates to the technical field of intelligent vehicle control, in particular to a system and a method for correcting the automatic parking and driving trajectory of a distributed driving electric vehicle.

Background technique

The automatic parking system can help the inexperienced driver to park conveniently, freeing the driver from the tedious parking process. One of the difficulties of the automatic parking system is that due to the low vehicle speed during parking, the steering torque of the steering motor is large, the steering response is relatively sluggish, and the steering accuracy is low, resulting in a large deviation between the parking trajectory and the reference parking trajectory. Because the torque of each in-wheel motor can be independently controlled, the distributed drive electric vehicle has high maneuverability, flexibility and reliability. By giving different torque control signals to the left and right wheel hub motors, the left and right wheels can generate a torque difference and a speed difference, which drives the vehicle to slide and steer. At present, the existing automatic parking technology of traditional vehicles or distributed driving electric vehicles mainly uses various additional sensors to improve the accuracy of parking environment perception, and pays less attention to the tracking deviation caused by the execution error of the actuator.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the problem of low parking precision and large trajectory deviation due to the relatively sluggish steering response of the steering motor and low steering precision when the distributed driving electric vehicle is automatically parked, using the power of the distributed driving vehicle It can make the left and right wheel hub motors generate torque difference and speed difference, drive the vehicle to slide and turn and improve the steering flexibility of the vehicle, so as to make up for the trajectory deviation caused by the autonomous steering of the steering motor.

In order to achieve the above purpose of the invention, the following technical solutions are adopted:

When the vehicle is controlled by the steering motor for autonomous steering, based on the three-degree-of-freedom model of the vehicle, the deviation e between the actual parking trajectory of the vehicle and the reference parking trajectory is used as the input of the PID controller, and the torque of the left and right in-wheel motors is used as the output. , so that the torque difference and speed difference between the left and right wheels of the vehicle are generated, and the vehicle is driven to perform differential steering, eliminating the deviation e, thereby making up for the steering error of the steering execution motor.

A differential correction system for the automatic parking and driving trajectory of a distributed driving electric vehicle of the present invention comprises a detection module, a control module and an execution module;

The detection module includes a position detection sensor, as well as several rotational speed sensors and current sensors, which are respectively used to detect the rotational speed and current of the four in-wheel motors of the electric vehicle; the position detection sensor is used to detect the parking space environmental location information; the detection module sends the detected location information to the control module, and sends the detected speed signal and current signal to the execution module;

The control module is a vehicle-mounted VCU, and the VCU includes three modules: a path planning module, an autonomous steering module, and a differential compensation module; the path planning module performs parking trajectory planning according to the environmental information of the parking space detected by the detection module. , and determine the reference parking trajectory; the autonomous steering module uses the automatic parking steering algorithm to obtain the steering angle according to the deviation e between the reference parking trajectory output by the path planning module and the actual parking trajectory detected by the detection module δ; the differential compensation module judges whether differential compensation is required according to the magnitude of the deviation e between the reference parking trajectory and the actual parking trajectory;

The control module sends the calculated steering wheel angle command to each in-wheel motor torque command to the execution module; the execution module includes a steering motor controller and a steering motor, an in-wheel motor controller and an in-wheel motor.

Further, the steering motor controller is used to receive the steering wheel angle δ of the autonomous steering module of the VCU, and control the steering motor to perform steering.

Further, the rotational speed sensor includes a rotational speed sensor a, a rotational speed sensor b, a rotational speed sensor c, and a rotational speed sensor d, and the current sensor includes a current sensor a, a current sensor b, a current sensor c, and a current sensor d; the rotational speed sensor a is used for Detect the rotational speed of the in-wheel motor a; the rotational speed sensor b is used to detect the rotational speed of the in-wheel motor b; the rotational speed sensor c is used to detect the rotational speed of the in-wheel motor c; the rotational speed sensor d is used to detect the rotational speed of the in-wheel motor d; The current sensor b is used to detect the current of the in-wheel motor a; the current sensor b is used to detect the current of the in-wheel motor b; the current sensor c is used to detect the current of the in-wheel motor c; the current sensor d is used to detect the in-wheel motor d. the current.

The technical scheme of the method of the present invention is: a method for a distributed driving electric vehicle automatic parking driving trajectory differential correction system, comprising the following steps:

After the driver arrives near the parking space, press the start button of the automatic parking system, at this time, the system starts to work;

First, the detection module detects the parking position information, and sends the parking environment position information to the control module VCU;

Secondly, the path planning module of the VCU plans the reference parking trajectory according to the parking position information. At the same time, the autonomous steering module calculates the steering wheel angle δ according to the deviation e between the reference parking trajectory and the actual parking trajectory, and the differential compensation The module judges whether differential compensation is required according to the deviation e between the reference parking trajectory and the actual parking trajectory, and if necessary, calculates the torque of each in-wheel motor and sends it to the execution module;

Then, the steering motor controller of the execution module controls the steering motor to rotate to reach the corresponding steering wheel angle, and the in-wheel motor controller controls the in-wheel motor to achieve the corresponding torque until the parking ends.

Further, determine whether differential compensation is required. If |e|>e ₀ , the trajectory deviation is relatively large, and differential compensation needs to be performed at this time. If |e _| , when it is judged that differential compensation is required, based on the three-degree-of-freedom model of the vehicle, a simple and effective PID algorithm is used to calculate the torque of the left in-wheel motor a and in-wheel motor b Torque of right hub motor c and hub motor d When the deviation e is positive, M is positive, and when the deviation e is negative, M is negative.

Further, the specific process for the path planning module to realize the determination of the location information of the vehicle body and the environment is as follows:

Using the position detection sensor, the rough position information of the environment and the vehicle is obtained. Considering the rotation angle of the front wheel, the speed of the four in-wheel motors is integrated with time to obtain the motion trajectory of the vehicle:

where s is the displacement of the wheel, w is the rotational speed of the wheel, and R is the radius of the wheel;

When calculating the trajectory of the vehicle, the current i of the in-wheel motor is taken into account to calculate the driving force T of the driving wheel:

T=CΦiR

Among them, C is the motor constant, Φ is the motor magnetic flux, and R is the wheel radius. After the driving torque T of each in-wheel motor is obtained, the yaw moment M of the whole vehicle is calculated:

M=T _fr -T _fl +T _rl -T _rr

in are the driving torques of the left front, right front, left rear, and right rear in-wheel motors, respectively. After obtaining the vehicle yaw moment, its influence on the vehicle state is considered. Based on the vehicle three-degree-of-freedom dynamic model, the system state equation is:

Where x=[β γ] ^T , w=δ, u=M are the state variables of the system (center of mass slip angle and yaw angular velocity), front wheel rotation angle and yaw moment, respectively. The declination angle β is integrated to obtain the displacement of the vehicle during the driving process of rotation and sideslip, which is taken into account during the movement of the vehicle body to further determine the trajectory and specific position of the vehicle.

beneficial effect

(1) Equivalent to its own parking system, no additional devices and sensors are added, which saves costs.

(2) Since the wheel torque can be obtained, the dynamic information of the vehicle body can be grasped more accurately, and the vehicle position information can be determined more accurately.

(3) The differential steering is used to compensate the parking trajectory deviation caused by the poor autonomous steering effect, which improves the steering flexibility of the vehicle and the accuracy of the parking trajectory.

(4) Differential steering is realized by controlling the torque of the in-wheel motor, and the automatic parking function can also be realized independently when the steering motor fails, which improves the robustness and fault tolerance of the parking system.

(5) It can reduce the torque output pressure of the steering motor and reduce the jitter and yaw instability during the parking process.

Description of drawings

Fig. 1 is the system structure diagram of the present invention

Figure 2 is a flow chart of the system work

Detailed ways

The specific implementation of the present invention will be further described below with reference to the accompanying drawings.

As shown in FIG. 1 , the system of the present invention can be divided into three modules: a detection module, a control module, and an execution module. The detection module includes a rotational speed sensor a, a current sensor a, a rotational speed sensor b, a current sensor b, a rotational speed sensor c, a current sensor c, a rotational speed sensor d, a current sensor d, and a position detection sensor. The rotational speed sensor a is used to detect the rotational speed of the in-wheel motor a; the rotational speed sensor b is used to detect the rotational speed of the in-wheel motor b; the rotational speed sensor c is used to detect the rotational speed of the in-wheel motor c; the rotational speed sensor d is used to detect the rotational speed of the in-wheel motor d The current sensor a is used to detect the current of the in-wheel motor a; the current sensor b is used to detect the current of the in-wheel motor b; the current sensor c is used to detect the current of the in-wheel motor c; the current The sensor d is used to detect the current of the in-wheel motor d; the position detection sensor is a commonly used sensor for automatic parking, which can be an ultrasonic sensor or a radar sensor, and is used to detect the environmental location information of the parking space. The detection mechanism sends the detected position information to the control module, and sends the detected rotational speed signal and current signal to the execution module. The control module is a vehicle-mounted VCU, and the VCU includes three modules: a path planning module, an autonomous steering module, and a differential compensation module. The main functions of the path planning module are two: the first is to determine the position information of the vehicle body and the environment. Using the position detection sensor, the rough position information of the environment and the vehicle is obtained. Considering the front wheel angle, the four in-wheel motor speeds are integrated with time to obtain the motion trajectory of the vehicle, as shown in formula (1):

where s is the displacement of the wheel, w is the rotational speed of the wheel, and R is the radius of the wheel.

When calculating the motion trajectory of the vehicle, the current i of the in-wheel motor is taken into account to calculate the driving force T of the driving wheel. The formula is shown in (2):

T=CΦiR (2)

Where C is the motor constant, Φ is the motor magnetic flux, and R is the wheel radius. After the driving torque T of each in-wheel motor is obtained, the yaw moment M of the vehicle is calculated, as shown in formula (3):

M=T _fr -T _fl +T _rl -T _rr (3)

in are the driving torques of the left front, right front, left rear, and right rear wheel hub motors, respectively. After obtaining the vehicle yaw moment, considering its influence on the vehicle state, based on the vehicle three-degree-of-freedom dynamic model, the system state equation is shown in formula (3):

Where x=[β γ] ^T , w=δ, u=M are the state variables of the system (center of mass slip angle and yaw rate), front wheel rotation angle and yaw moment, respectively. It can be seen that the yaw moment affects both the yaw and yaw motion of the vehicle. The yaw angular velocity γ and the center of mass sideslip angle β are respectively integrated to obtain the displacement of the vehicle during the driving process of rotation and sideslip, which is taken into account during the movement of the vehicle body to further determine the trajectory and specific position of the vehicle. The second function is to plan the parking trajectory according to the surrounding environment and body position information, and determine the reference parking trajectory; the autonomous steering module is based on the reference parking trajectory output by the path planning module and the actual parking detected by the detection module. The deviation e between the trajectories, the steering algorithm commonly used in automatic parking such as PID, fuzzy control, etc. is used to calculate the steering angle δ; the differential compensation module is based on the deviation e between the reference parking trajectory and the actual parking trajectory If |e|>e ₀ (e ₀ is a positive value set according to experience), the trajectory deviation is large, and differential compensation is required at this time, if |e|≤e ₀ , it means that the deviation is small and no differential compensation is required. When it is judged that differential compensation is required, the torque of the left in-wheel motor a and in-wheel motor b is calculated based on the three-degree-of-freedom model of the vehicle using a simple and effective PID algorithm. Torque of right hub motor c and hub motor d When the deviation e is positive, M is positive, and when the deviation e is negative, M is negative. The control module sends the calculated steering wheel angle command to each in-wheel motor torque command to the execution module. The execution module includes steering motor controller and steering motor, hub motor controller a, hub motor controller b, hub motor controller c, hub motor controller d, hub motor a, hub motor b, hub motor c , In-wheel motor d. The steering motor controller is used to receive the steering wheel angle δ of the autonomous steering module of the VCU, and control the steering motor to perform steering. The in-wheel motor controller a and in-wheel motor b are used to receive the torque command of the differential compensation module The hub motor c and hub motor d are used to receive the torque command from the differential compensation module And according to the corresponding speed sensor a, current sensor a, speed sensor b, current sensor b, speed sensor c, current sensor c, speed sensor d, current sensor d The current signal and the speed signal detected by the current sensor d control the corresponding hub motor a, In-wheel motor b, in-wheel motor c, and in-wheel motor d achieve corresponding torque.

Below in conjunction with Fig. 2, the system workflow of the present invention is described in detail:

After the driver drives to the vicinity of the parking space, presses the start button of the automatic parking system, at this time, the system starts to work. First, the detection module detects the parking position information, and sends the parking environment position information to the control module VCU. Secondly, the path planning module of the VCU plans the reference parking trajectory according to the parking position information. At the same time, the autonomous steering module calculates the steering wheel angle δ according to the deviation e between the reference parking trajectory and the actual parking trajectory, and the differential compensation The module judges whether differential compensation is required according to the deviation e between the reference parking trajectory and the actual parking trajectory, and if necessary, calculates the torque of each in-wheel motor and sends it to the execution module. Then, the steering motor controller of the execution module controls the steering motor to rotate to reach the corresponding steering wheel angle, and the in-wheel motor controller controls the in-wheel motor to achieve the corresponding torque until the parking ends.

In conclusion, the present invention provides a system and method for differential correction of driving trajectory of distributed driving electric vehicle automatic parking, and proposes a driving trajectory correction system and method for the automatic parking system of distributed driving electric vehicle. First, the detection module automatically detects the parking space and sends the parking environment information to the control module; secondly, the trajectory planning module of the control module VCU plans the reference parking trajectory, and controls the steering motor to perform autonomous steering according to the actual trajectory of the vehicle, driving the vehicle to track the reference Parking track. During the tracking process, when the deviation e between the actual parking trajectory of the vehicle and the reference parking trajectory is large, the differential compensation module of the VCU takes e as the control target, and the torque difference between the left and right wheel hub motors is the control output to drive the differential steering of the vehicle. , to reduce the trajectory deviation caused by poor steering precision at low speed of the steering system. The present invention uses differential steering to assist the vehicle to perform parking control during the automatic parking process, thereby reducing the parking error of the vehicle's autonomous steering and improving the parking trajectory accuracy and parking reliability of the automatic parking.

In the description of this specification, reference to the terms "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples", etc., is meant to incorporate the embodiments A particular feature, structure, material, or characteristic described by an example or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, The scope of the invention is defined by the claims and their equivalents.

Claims (6)

1. a distributed driving electric vehicle automatic parking driving track differential correction system, is characterized in that, comprises detection module, control module, execution module; The detection module includes a position detection sensor, as well as several rotational speed sensors and current sensors, which are respectively used to detect the rotational speed and current of the four in-wheel motors of the electric vehicle; the position detection sensor is used to detect the parking space environmental location information; the detection module sends the detected location information to the control module, and sends the detected speed signal and current signal to the execution module; The control module is a vehicle-mounted VCU, and the VCU includes three modules: a path planning module, an autonomous steering module, and a differential compensation module; the path planning module performs parking trajectory planning according to the environmental information of the parking space detected by the detection module. , and determine the reference parking trajectory; the autonomous steering module uses the automatic parking steering algorithm to obtain the steering angle according to the deviation e between the reference parking trajectory output by the path planning module and the actual parking trajectory detected by the detection module δ; the differential compensation module judges whether differential compensation is required according to the magnitude of the deviation e between the reference parking trajectory and the actual parking trajectory; The control module sends the calculated steering wheel angle command to each in-wheel motor torque command to the execution module; the execution module includes a steering motor controller and a steering motor, an in-wheel motor controller and an in-wheel motor. 2. a kind of distributed drive electric vehicle automatic parking driving track differential correction system according to claim 1, is characterized in that, described steering motor controller receives the steering wheel angle δ of the autonomous steering module of VCU, and controls Steer the motor to steer. 3. A kind of distributed driving electric vehicle automatic parking driving trajectory differential correction system according to claim 1, is characterized in that, described rotational speed sensor comprises rotational speed sensor a, rotational speed sensor b, rotational speed sensor c, rotational speed sensor d , the current sensor includes a current sensor a, a current sensor b, a current sensor c, and a current sensor d; the rotational speed sensor a is used to detect the rotational speed of the in-wheel motor a; the rotational speed sensor b is used to detect the rotational speed of the in-wheel motor b; the rotational speed sensor c Used to detect the rotational speed of the hub motor c; the rotational speed sensor d is used to detect the rotational speed of the hub motor d; the current sensor a is used to detect the current of the hub motor a; the current sensor b is used to detect the current of the hub motor b ; The current sensor c is used to detect the current of the in-wheel motor c; the current sensor d is used to detect the current of the in-wheel motor d. 4. A method for a distributed driving electric vehicle automatic parking driving trajectory differential correction system according to claim 3, characterized in that, comprising the following steps: After the driver arrives near the parking space, press the start button of the automatic parking system, at this time, the system starts to work; First, the detection module detects the parking position information, and sends the parking environment position information to the control module VCU; Secondly, the path planning module of the VCU plans the reference parking trajectory according to the parking position information. At the same time, the autonomous steering module calculates the steering wheel angle δ according to the deviation e between the reference parking trajectory and the actual parking trajectory, and the differential compensation The module judges whether differential compensation is required according to the deviation e between the reference parking trajectory and the actual parking trajectory, and if necessary, calculates the torque of each in-wheel motor and sends it to the execution module; Then, the steering motor controller of the execution module controls the steering motor to rotate to reach the corresponding steering wheel angle, and the in-wheel motor controller controls the in-wheel motor to achieve the corresponding torque until the parking ends. 5 . The method for the differential correction system for automatic parking of distributed driving electric vehicles according to claim 4 , wherein the specific process for judging whether differential compensation is required is: if |e|>e ₀ , If the trajectory deviation is large, differential compensation needs to be performed at this time. If |e|≤e ₀ , it means that the deviation is small and no differential compensation is required. When it is judged that differential compensation is required, based on the vehicle three degrees of freedom model, use PID The algorithm calculates the torque of the left hub motor a and the hub motor b Torque of right hub motor c and hub motor d When the deviation e is positive, M is positive, and when the deviation e is negative, M is negative. 6 . The method for the differential correction system for automatic parking and driving trajectory of distributed driving electric vehicles according to claim 4 , wherein the path planning module comprises the step of realizing the determination of the position information of the vehicle body and the environment; 7 . The specific process is: Using the position detection sensor, the rough position information of the environment and the vehicle is obtained. Considering the rotation angle of the front wheel, the speed of the four in-wheel motors is integrated with time to obtain the motion trajectory of the vehicle: where s is the displacement of the wheel, w is the rotational speed of the wheel, and R is the radius of the wheel; When calculating the trajectory of the vehicle, the current i of the in-wheel motor is taken into account to calculate the driving force T of the driving wheel: T=CΦiR Among them, C is the motor constant, Φ is the motor magnetic flux, and R is the wheel radius. After the driving torque T of each in-wheel motor is obtained, the yaw moment M of the whole vehicle is calculated: M=T _fr -T _fl +T _rl -T _rr Among them, T _fl , T _fr , T _rl , and T _rr are the driving torques of the left front, right front, left rear, and right rear in-wheel motors, respectively. After the yaw moment of the whole vehicle is obtained, its influence on the state of the whole vehicle is considered. Based on the three degrees of freedom of the vehicle The dynamic model, the state equation of the system is: Where x=[β γ] ^T , w=δ, u=M are the state variables of the system (center of mass slip angle and yaw angular velocity), front wheel rotation angle and yaw moment, respectively. The declination angle β is integrated to obtain the displacement of the vehicle during the driving process of rotation and sideslip, which is taken into account during the movement of the vehicle body to further determine the trajectory and specific position of the vehicle.