CN115923932A

CN115923932A - Steering control method, device, equipment and medium for distributed drive vehicle

Info

Publication number: CN115923932A
Application number: CN202211741050.6A
Authority: CN
Inventors: 赵煜; 李晓萌; 刘益滔; 李鹏飞; 邓宇帆; 胡成帅; 张德旺
Original assignee: Zhejiang Geely Holding Group Co Ltd; Geely Automobile Research Institute Ningbo Co Ltd
Current assignee: Zhejiang Geely Holding Group Co Ltd; Geely Automobile Research Institute Ningbo Co Ltd
Priority date: 2022-12-30
Filing date: 2022-12-30
Publication date: 2023-04-07

Abstract

The application provides a steering control method, a steering control device, steering control equipment and a steering control medium for a distributed driving vehicle. According to the scheme, after the vehicle controller detects that the pivot steering function is started, whether preset pivot steering activation conditions are met or not is judged, after the vehicle meets the pivot steering activation conditions, a target yaw rate is obtained according to the opening degree of an accelerator pedal, then the target yaw torque of each wheel motor is determined according to the target yaw rate, the road surface adhesion coefficient and the target yaw rate, the vehicle is controlled to pivot in a manner of taking a geometric center as a circle center based on the target yaw torque of each wheel motor, the steering radius of the steering mode is greatly reduced to 0 compared with the prior art, and only torque control is adopted without combining a chassis controller, so that the efficiency is higher, the direction is more efficient, and the parasitic loss is reduced.

Description

Steering control method, device, equipment and medium for distributed drive vehicle

Technical Field

The present application relates to the field of vehicle technologies, and in particular, to a method, an apparatus, a device, and a medium for controlling steering of a distributed drive vehicle.

Background

In recent years, pure electric vehicles and hybrid electric vehicles are more and more common in the market, the electric vehicles are powered by a power battery to provide part or all of energy, and a motor is used for providing power to drive an actuator, wherein most of the vehicles adopt a centralized driving mode, namely, a single motor is arranged on a front shaft or a rear shaft of the vehicle, and a mechanical differential is used for realizing differential speed of the left shaft and the right shaft and achieving the purpose of steering the vehicle.

In the prior art, the implementation mode of the pivot steering function mainly focuses on a tracked vehicle or an all-wheel steering vehicle with steering mechanisms additionally arranged on each wheel, but the tracked vehicle is only used for special purposes, the application range is narrow, an additional steering system needs to be additionally arranged on the all-wheel steering vehicle, the vehicle cost and the complexity of a mechanical structure are increased, meanwhile, higher requirements on the control of a driving system and the steering system are provided, and both the tracked vehicle and the all-wheel steering vehicle are not suitable for passenger vehicle types.

Currently, few researches on pivot steering control schemes of distributed drive vehicles are carried out, and a technical scheme for controlling pivot steering of the distributed drive vehicles is lacked.

Disclosure of Invention

The application provides a steering control method, a steering control device, steering control equipment and a steering control medium for a distributed driving vehicle. Provided is a technical scheme for controlling pivot steering of a distributed drive vehicle.

In a first aspect, an embodiment of the present application provides a steering control method for a distributed-drive vehicle, including:

after the pivot steering function is detected to be started, judging whether a preset pivot steering activation condition is met or not according to the state of the vehicle;

if the vehicle meets the pivot steering activation condition, acquiring a target yaw rate according to the opening degree of an accelerator pedal;

determining a target yaw torque of each wheel motor of the vehicle according to the actual yaw velocity, the road surface attachment coefficient and the target yaw velocity of the vehicle;

and controlling the vehicle to perform circular motion for pivot steering by taking a geometric center as a circle center according to the target yaw torque of each wheel motor of the vehicle, wherein the geometric center is a point where axes of four wheels of the vehicle after rotation intersect.

In one embodiment, the method further comprises:

acquiring a current available yaw moment limit value of a motor of each wheel in the pivot steering process of the vehicle;

determining a motor target torque for each wheel based on a maximum speed threshold for the motor for each wheel of the vehicle and a currently available yaw moment limit for each wheel;

and controlling the corresponding motor according to the motor target torque of each wheel.

In one specific embodiment, the obtaining of the currently available yaw moment limit value of the motor of each wheel includes:

and comparing the motor maximum limit and the motor minimum limit of the motor with the motor external characteristics of the motor according to the yaw moment maximum limit and the yaw moment minimum limit of the motor of each wheel to obtain the current available yaw moment limit value of the motor of each wheel.

In one embodiment, the determining the motor target torque for each wheel based on a maximum rotation speed threshold of the motor for each wheel of the vehicle and a currently available yaw moment limit value for each wheel comprises:

acquiring the current rotating speed of a motor of each wheel;

performing table look-up coefficient conversion on a part of the motor of each wheel, of which the current rotating speed exceeds the maximum rotating speed threshold of the motor, so as to obtain target yaw torque limitation of the wheel;

the motor target torque for each wheel is determined based on the target yaw torque limit for each wheel and a currently available yaw torque limit value, wherein the currently available yaw torque limit value includes a maximum limit torque and a minimum limit torque.

In a specific embodiment, the determining whether the preset pivot steering activation condition is met according to the vehicle state includes:

acquiring a no-system fault signal zone bit, a safety condition zone bit and the state of a brake pedal of the vehicle;

and if the no-system fault signal zone bit is 1, the safety condition zone bit is also 1, and the brake pedal is in a released state, determining that the vehicle meets the preset steering activation condition.

In one embodiment, the obtaining the target yaw rate according to the opening degree of the accelerator pedal includes:

and inquiring a preset pedal opening and yaw rate corresponding table, and determining the yaw rate corresponding to the accelerator pedal opening as the target yaw rate.

In one embodiment, the determining a target yaw torque of each wheel motor of the vehicle based on an actual yaw rate, a road attachment coefficient, and the target yaw rate of the vehicle includes:

determining a target feedforward value FF corresponding to the road surface attachment coefficient and the target yaw rate by inquiring a mapping table between a preset yaw rate and an attachment coefficient and a feedforward value;

according to the formula:

and ω Trq = FF + ω dyn, and calculating a target yaw torque ω Trq of each wheel motor;

kp and Ki are calibrated PI parameters, tgt ω r is a target yaw rate, ω r is an actual yaw rate, and ω dyn is a feedback control yaw torque.

In one embodiment, the method further comprises:

the formula is adopted:

calculating to obtain the road adhesion coefficient; wherein it is present>

Represents the coefficient of adhesion; />

Indicating adhesion; f _z Representing a ground normal reaction force; fxmax represents the limit value of the ground tangential reaction force.

In a second aspect, an embodiment of the present application provides a steering control device for a distributed drive vehicle, including:

the first processing module is used for judging whether a preset pivot steering activation condition is met or not according to the self state of the vehicle after the pivot steering function is detected to be started;

the second processing module is used for acquiring a target yaw velocity according to the opening degree of an accelerator pedal if the vehicle meets the pivot steering activation condition;

the third processing module is used for determining a target yaw torque of each wheel motor of the vehicle according to the actual yaw velocity, the road surface attachment coefficient and the target yaw velocity of the vehicle;

and the control module is used for controlling the vehicle to perform circular motion by taking a geometric center as a circle center to perform pivot steering according to the target yaw torque of each wheel motor of the vehicle, wherein the geometric center is a point where axes of four wheels of the vehicle after rotation intersect.

In one embodiment, the apparatus further comprises:

the fourth processing module is used for acquiring the current available yaw moment limit value of the motor of each wheel in the pivot steering process of the vehicle;

the fourth processing module is further used for determining a motor target torque of each wheel according to a maximum rotating speed threshold value of a motor of each wheel of the vehicle and a current available yaw moment limit value of each wheel;

the control module is further configured to control the corresponding motor according to the motor target torque of each wheel.

In a specific embodiment, the fourth processing module is specifically configured to:

and comparing the maximum limit and the minimum limit of the yaw moment of the motor with the external motor characteristics of the motor according to the maximum limit and the minimum limit of the yaw moment of the motor, so as to obtain the current available yaw moment limit value of the motor of each wheel.

In a specific embodiment, the fourth processing module is further specifically configured to:

acquiring the current rotating speed of a motor of each wheel;

performing table look-up coefficient conversion on a part of the current rotating speed of the motor of each wheel, which exceeds the maximum rotating speed threshold of the motor, so as to obtain the target yaw torque limit of the wheel;

In a specific embodiment, the first processing module is specifically configured to:

and if the no-system fault signal flag is 1, the safety condition flag is also 1, and the brake pedal is in a released state, determining that the vehicle meets the preset steering activation condition.

In a specific embodiment, the second processing module is specifically configured to:

In a specific embodiment, the third processing module is specifically configured to:

according to the formula:

kp and Ki are calibrated PI parameters, tgt ω r is a target yaw angular velocity, ω r is an actual yaw angular velocity, and ω dyn is a feedback control yaw torque.

In a specific embodiment, the third processing module is further configured to:

the formula is adopted:

calculating to obtain the road adhesion coefficient; wherein +>

Represents the coefficient of adhesion; />

Indicating adhesion; f _z Representing a ground normal reaction force; fxmax represents the limit for the ground tangential reaction force.

In a third aspect, an embodiment of the present application provides a vehicle, including: a vehicle body, a vehicle controller, a motor for each wheel, a memory, and computer program instructions stored on and executable on the memory, the vehicle controller when executing the computer program instructions for implementing a steering control method of a distributed drive vehicle as set forth in any one of the first aspects.

In a fourth aspect, the present embodiments provide a computer-readable storage medium, in which a computer is stored, and the computer executes instructions, and the computer executes the instructions to implement the steering control method for a distributed drive vehicle according to any one of the first aspect.

The embodiment of the application provides a steering control method, a steering control device, steering control equipment and a steering control medium for a distributed driving vehicle. According to the scheme, after the vehicle controller detects that the pivot steering function is started, whether preset pivot steering activation conditions are met or not is judged, after the vehicle meets the pivot steering activation conditions, a target yaw rate is obtained according to the opening degree of an accelerator pedal, then the target yaw torque of each wheel motor is determined according to the target yaw rate, the road surface adhesion coefficient and the target yaw rate, the vehicle is controlled to pivot in a manner of taking a geometric center as a circle center based on the target yaw torque of each wheel motor, the steering radius of the steering mode is greatly reduced to 0 compared with the prior art, and only torque control is adopted without combining a chassis controller, so that the efficiency is higher, the direction is more efficient, and the parasitic loss is reduced.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and together with the description, serve to explain the principles of the application.

Fig. 1 is a schematic diagram of a distributed drive and a centralized drive provided in an embodiment of the present application;

FIG. 2 is a schematic diagram illustrating a comparison between a distributed drive vehicle in-situ u-turn and an existing u-turn provided by an embodiment of the present application;

fig. 3 is a schematic turning-around diagram of a distributed drive vehicle according to an embodiment of the present application;

fig. 4 is a schematic software structure diagram of a steering control method for a distributed drive vehicle according to an embodiment of the present application;

fig. 5 is a schematic flowchart of a first embodiment of a steering control method for a distributed-drive vehicle according to the present disclosure;

FIG. 6 is a schematic diagram illustrating determination of entry and exit conditions of the pivot steering mode according to an embodiment of the present disclosure;

fig. 7 is a schematic diagram of a direct yaw torque control provided by an embodiment of the present invention;

fig. 8 is a schematic flowchart of a second embodiment of a steering control method for a distributed drive vehicle according to an embodiment of the present application;

FIG. 9 is a schematic diagram illustrating a rotational speed limiting protection of a motor according to an embodiment of the present disclosure;

fig. 10 is a schematic structural diagram of a steering control device of a distributed drive vehicle according to an embodiment of the present application.

With the above figures, there are shown specific embodiments of the present application, which will be described in more detail below. These drawings and written description are not intended to limit the scope of the inventive concepts in any manner, but rather to illustrate the inventive concepts to those skilled in the art by reference to specific embodiments.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Before introducing the embodiments of the present application, an application context of the embodiments of the present application is explained first:

a novel driving mode, namely a distributed driving technology, appears in the current new energy automobile industry, a wheel side motor or a wheel hub motor is adopted as a power driving actuator, a mechanical differential and other complex transmission systems are omitted, the torque of a left motor and a right motor is directly distributed through a distributed controller (also called as a vehicle controller or a power control unit and the like), and further the functions of steering and yaw control and the like are realized. The scheme has the following advantages:

1. the middle transmission parts are reduced, the vehicle weight is reduced, the space in the vehicle is increased, and the arrangement of the whole vehicle is convenient;

2. in the aspect of a passenger car, a 3-motor (front and rear shaft 1+2 motor) or 4-motor distributed driving scheme (front and rear shaft 2+2 motors) is mostly adopted, and the power output and the power performance of the whole car can be greatly improved.

The distributed drive needs to consider several differences relative to a conventional fuel vehicle:

3. because the mechanical energy output is realized by adopting the motor in the distributed driving mode, the speed measuring precision of the motor rotary transformer is higher, and the bandwidth is higher, which cannot be compared with a vehicle speed sensor. This is an advantage of distributed driving; secondly, more than 2 motors are driven in a distributed mode, the motors are related to the wheel speed, and the validity and the confidence coefficient of the speed measurement result can be identified by comparing the speed measurement results of different motors;

4. the distributed driving adopts a 3-motor scheme or a 4-motor scheme, all wheels are driving wheels, and so-called follower wheels are not provided. When the vehicle speed is estimated, 4 wheel speed fluctuations are large, and the estimation difficulty is improved.

Fig. 1 is a schematic diagram of distributed drive and centralized drive provided by the embodiment of the present application, as shown in fig. 1, compared to the centralized drive with only one electric drive system for driving four wheels, the distributed drive can provide separate electric drive systems for each wheel, in the case of three electric motor drives, the rear wheels are respectively provided with separate electric drive systems, and the two front wheels are driven by the electric drive systems and the mechanical differential.

Fig. 2 is a schematic diagram illustrating a comparison between an in-situ u-turn mode and an existing u-turn mode of a distributed drive vehicle provided in an embodiment of the present application, where as shown in fig. 2, the u-turn of the existing vehicle can be implemented only by rotating the entire vehicle for a large circle, and a specific radius of the u-turn is affected by a wheelbase of the vehicle, and the larger the radius of the u-turn of the large vehicle is. Due to the fact that single-wheel independent power control (single-wheel independent torque/speed control) exists in distributed driving, special functions which are difficult to complete through centralized driving can be achieved better, for example, a turning function shown in the drawing is achieved, a vehicle can turn around in situ along a geometric center, the function is characterized in that even if the vehicle is a front-wheel steering vehicle, the turning around in situ can be achieved, and the radius of the whole turning around reaches 0.

Fig. 2 shows that for a distributed drive vehicle, the u-turn function can be achieved by distributing the torque of four wheels individually, without the need for anti-lock brake system (ABS) calipers or four-wheel steering. When the tank turns around, can turn to along the vehicle barycenter, can satisfy special application demands such as obstacle avoidance in situ.

The existing centralized driving vehicle generally cannot realize the function of steering along the mass center of the vehicle, in the scheme, a scheme for realizing the 0-radius pivot steering by respectively controlling motors based on a distributed driving vehicle is provided, and the scheme can be specifically explained through the following embodiments.

The core of the technical scheme of the application is as follows: based on the opening degree of an accelerator pedal, independent torque distribution can be realized for each wheel at the same time by using a distributed multi-motor scheme, and even the torques in different directions can be realized. Thus, the original turning function can be realized. The specific scheme is as follows: fig. 3 is a schematic view of a u-turn of the distributed drive vehicle according to the embodiment of the present application, as shown in fig. 3, the four wheels rotate until the wheel axes intersect at a geometric center cog of the vehicle, and then perform a circular motion with the geometric center of the vehicle as a center cog. An additional yaw moment is generated through four-wheel differential torque, and the torque of a wheel end motor is adjusted, so that the lateral force of the tire is controlled. The combination force direction of the lateral force and the longitudinal force of the tire realizes the control of the yaw torque of the vehicle, and further realizes the in-situ turning function.

Fig. 4 is a schematic software structure diagram of a steering control method for a distributed drive vehicle according to an embodiment of the present application, and as shown in fig. 4, the implementation of the u-turn function software for the distributed drive vehicle mainly includes three software structures:

after the pivot steering function is turned on, a pivot steering activation condition determination (also referred to as pivot vehicle turn around entry and exit condition):

the determination of the pivot steering activation condition is used for the driver to correctly activate the pivot steering function (pivot turning function) of the enabled vehicle and close the pivot steering function (pivot turning function). And simultaneously monitoring whether stable control can be performed in the process of executing the turning around. And if the control deviation is overlarge, the original turning function is quitted.

Direct yaw torque control: direct yaw torque control, torque control for vehicle turning around is achieved by closed-loop control based on a target yaw rate and an actual yaw rate.

And (3) rotating speed limiting protection of the motor: and the rotation speed of the motor is limited and protected. Yaw torque limit to prevent motor speed from flying (closed loop control based on absolute value of actual motor speed and maximum speed threshold).

The function of turning around of the distributed driving vehicle is realized through the three parts.

Fig. 5 is a schematic flowchart of a first embodiment of a steering control method for a distributed-drive vehicle according to an embodiment of the present disclosure, and as shown in fig. 5, the steering control method for a distributed-drive vehicle is applied to a controller (also referred to as a vehicle control unit, a vehicle controller, or the like) of a vehicle, and the method includes:

s101: and after the pivot steering function is detected to be started, judging whether a preset pivot steering activation condition is met or not according to the state of the vehicle.

In this scheme, when a vehicle driven by a user needs to be steered in place, the user needs to perform manual operation to start the steering function of the vehicle in place (some vehicles are also called as the turning-around function, and the scheme is not limited). When the vehicle detects that the pivot steering function is started by a user, relevant states such as safety conditions and fault conditions of the vehicle are required to be acquired to determine whether the current state of the vehicle meets the pivot steering activation conditions, and pivot steering is performed only when the pivot steering activation conditions of the vehicle are met.

In a specific implementation, fig. 6 is a schematic diagram illustrating a determination of entry and exit conditions of a pivot steering mode according to an embodiment of the present disclosure, as shown in fig. 6, after a switch of a pivot steering function (i.e., a switch of the pivot steering function) is turned on, that is, set from 0 to 1, it is determined whether a safety condition is satisfied, and in the case that a non-associated fault flag is 1, and the safety condition flag is 1 and the pivot steering switch is also 1, a state of the vehicle is determined, a pivot steering activation condition is satisfied, a driver determines that the pivot steering function of the vehicle is activated after releasing a brake pedal, and then pivot steering control is performed according to a subsequent process. When the safety condition is not met, or the driver actively steps on the brake pedal, or the driver does not release the brake pedal, or the driver turns off the switch with the pivot turning function, namely the pivot turning is turned on Guan Zhiwei 0, or a correlation fault exists, the conditions that the pivot turning activation condition is not met are met, and the turning-off needs to be waited.

In a specific implementation mode, a vehicle controller acquires a system fault signal-free zone bit, a safety condition zone bit and the state of a brake pedal of the vehicle; and determining that the flag bit of the no-system fault signal is 1, the flag bit of the safety condition is also 1, and the brake pedal is in a released state, and determining that the vehicle meets the preset steering activation condition.

In the specific implementation of the step, the method mainly comprises the following implementation stages:

waiting for activation:

triggering a rising edge of a turning request signal switch of the vehicle; the switch is operable by the mechanical switch by drivability. The driver depresses the brake pedal.

Some conditions (such as vehicle speed, lateral acceleration, longitudinal acceleration, yaw rate, etc.) that are not requested by the system fault signal and are considered safely are determined.

The safety condition flag bit comprises: the signals of the vehicle sensors are all in logical relation with an and gate (and), and only the safety condition flag =1 can be output.

The vehicle speed u is within the range of A being not more than u being not more than B, and A and B are set values; the output of the satisfaction range is 1.

The range of the longitudinal acceleration Ax is not less than C and not more than Ax and not more than D, and C and D are set values; the output of the satisfaction range is 1.

The range of the transverse acceleration Ay is equal to or less than E and equal to or less than F, and E and F are set values; the output of the satisfaction range is 1.

The range of the steering wheel corner delta sw is that G is not more than delta sw and not more than H, and G and H are set values; the output of the satisfaction range is 1. (this solution is a turn around solution-the steering wheel angle needs to be limited around the 0 deg. range, controlled within + -7 deg. at the H and G settings, unlike other turn around solutions in place).

The no-system fault signal comprises: the motor has no motor fault request, and the motor fault request is sent through a CAN network. The reliability of the transverse acceleration quality signal, the longitudinal acceleration quality signal, the vehicle speed quality signal and the actual yaw velocity quality signal is obtained by sending through a chassis stability controller through a CAN network. When the signal no-fault state and the signal reliability are satisfied, an uncorrelated fault flag =1 (also referred to as a no-system fault signal = 1) is obtained.

Confirming activation: in the pivot steering activation condition, when a safety condition flag =1, and a uncorrelated fault signal =1, and a pivot U-turn switch flag =1, determining that the activation condition is met, waiting for activating the pivot U-turn function, and when a driver releases a brake pedal, starting to activate the pivot U-turn function.

Waiting for closing:

some conditions based on safety considerations are not met (e.g., vehicle speed, lateral acceleration, longitudinal acceleration, yaw rate, etc.).

Or the driver actively steps on the brake pedal;

or the driver actively turns off the switch of the in-place turning function.

If at least one of the above situations occurs, the function is waited to be turned off if the in-situ turning-around condition is not met.

And (3) closing state:

the actual yaw rate absolute value is smaller than a threshold value H, which is a set value.

Namely: abs (ω r) < H

The vehicle controller determines that the current state of the vehicle is a state which meets the activation condition and waits for the pivot steering process to be activated or waits for the pivot steering function to be turned off through the judgment mode.

S102: and if the vehicle meets the pivot steering activation condition, acquiring the target yaw rate according to the opening degree of an accelerator pedal.

In this step, if the vehicle controller determines that the vehicle satisfies the pivot steering activation condition and the driver releases the brake pedal, the control process of the pivot steering of the vehicle may be performed. First, it is necessary to acquire a target yaw rate from the accelerator pedal opening degree.

In a specific implementation, a table may be looked up according to an accelerator pedal opening, a corresponding table of the pedal opening and the yaw rate may be configured in advance in a vehicle control system, the corresponding table may be obtained according to actual tests and experiments, when a target yaw rate needs to be obtained in a vehicle control process, the preset corresponding table of the pedal opening and the yaw rate is queried, and the yaw rate corresponding to the accelerator pedal opening is determined as the target yaw rate.

S103: and determining the target yaw torque of each wheel motor of the vehicle according to the actual yaw rate, the road adhesion coefficient and the target yaw rate of the vehicle.

In this step, the vehicle controller needs to control the vehicle based on the target yaw rate after obtaining the target yaw rate, specifically needs to control each wheel by the yaw torque, and thus needs to acquire the target yaw torque of each wheel of the vehicle first.

In a specific implementation manner, fig. 7 is a schematic diagram of direct yaw torque control provided by the embodiment of the invention, and as shown in fig. 7, the control of the target yaw torque includes three parts, target yaw rate calculation, feed-forward control and feedback control.

The target yaw rate is obtained by looking up a table in the previous step. For example: a table can be looked up: tgt ω r = {0.0,0.2,0.4,0.6,0.8,1.0,1.2,1.4,1.6,1.8,2.0}.

In the feedforward control process, the control is required to be carried out based on the road adhesion coefficient and the target yaw velocity, and in the process, a two-dimensional table look-up is firstly carried out based on the road adhesion coefficient and the expected target yaw velocity. And obtaining a feedforward value FF based on the target yaw angular velocity and different attachment road surfaces.

That is, the target feedforward value FF corresponding to the road surface adhesion coefficient and the target yaw rate can be determined by referring to a map between a preset yaw rate, an adhesion coefficient, and a feedforward value.

The road adhesion coefficient can be expressed by the following formula:

and (4) calculating. Wherein +>

Represents the coefficient of adhesion; />

And a feedback control part for outputting a target yaw torque of each motor by using a PI control method in order to ensure that the actual yaw rate follows the response target yaw rate. Specifically, the calculation can be performed by the following formula:

according to the formula:

The actual yaw rate is obtained by an Electronic Stability Program (ESP) of the chassis through a CAN network. The feed-forward control torque FF (i.e., the feed-forward value FF) and the feedback control yaw torque ω dyn are added to obtain a final target yaw torque ω Trq.

S104: and controlling the vehicle to perform circular motion for pivot steering by taking a geometric center as a circle center according to the target yaw torque of each wheel motor of the vehicle, wherein the geometric center is a point where axes of four wheels of the vehicle after rotation intersect.

In this step, after the target yaw torque of each wheel motor is obtained, the corresponding wheel can be controlled according to the target yaw torque of each wheel, and the scheme of vehicle pivot steering is realized. The difference between this solution and other solutions is that the vehicle is controlled to turn around along the center of mass, also called geometric center, which is the point where the axes of the four wheels of the vehicle intersect, as schematically shown on the right side in fig. 2.

The application provides a steering control method of a distributed driving vehicle, in the whole steering control process, after a vehicle controller detects that an in-place steering function is started, whether a preset in-place steering activation condition is met or not is judged, after the in-place steering activation condition is met, a target yaw rate is obtained according to the opening degree of an accelerator pedal, then the target yaw rate is based on the actual yaw rate, a road surface adhesion coefficient and the target yaw rate determine the target yaw torque of each wheel motor, the vehicle is controlled to steer in place by taking a geometric center as a circle center based on the target yaw torque of each wheel motor, the steering radius of the steering mode is greatly reduced compared with that of the prior art and is reduced to 0, and a chassis controller is not required to be combined, only torque control is adopted, the steering control is more efficient and direct, and parasitic loss is reduced.

In the steering process of the vehicle, in order to ensure stability and safety, the rotating speed of the motor needs to be limited and protected, and the safety problem is avoided.

Fig. 8 is a schematic flow chart of a second embodiment of a steering control method for a distributed-drive vehicle according to an embodiment of the present application, and as shown in fig. 8, on the basis of the foregoing embodiment, the steering control method for a distributed-drive vehicle further includes the following steps:

s105: during the pivot steering of the vehicle, the current available yaw moment limit value of the motor of each wheel is obtained.

Fig. 9 is a schematic view illustrating the rotational speed limiting protection of the motor according to the embodiment of the present application, and as shown in fig. 9, the rotational speed limiting protection process of the motor includes three parts: yaw moment limit calculation, top speed protection and maximum minimum torque limit.

In this step, during the steering of the vehicle, it is necessary to calculate the yaw moment limit, i.e. the yaw torque limit, of the steering function. The calculation of the yaw torque limit can be made according to the maximum minimum limit achieved by the motor. And acquiring the maximum limit and the minimum limit of the yaw torque of the motor for each motor, and then comparing the maximum limit and the minimum limit of the yaw torque of the motor with the external characteristics of the motor to obtain the limit value of the current available yaw torque of the motor of the wheel.

In a specific implementation, the maximum limit M of four motors _TMAX Minimum limit M _TMIN The value is obtained by a Motor Control Unit (MCU) through CAN network transmission, and the current available yaw moment limit torque is obtained by comparing with the external Motor characteristic, wherein the external Motor characteristic is a set value.

S106: the motor target torque for each wheel is determined based on a maximum speed threshold for the motor for each wheel of the vehicle and a currently available yaw moment limit for each wheel.

In this step, in order to determine the motor target torque of each wheel, it is necessary to obtain the current rotation speed of the motor of each wheel, and then perform table lookup coefficient conversion on the portion where the current rotation speed of the motor of each wheel exceeds the maximum rotation speed threshold of the motor, so as to obtain the target yaw torque limit of the wheel. Finally, a motor target torque for each wheel is determined based on the target yaw torque limit for each wheel and a currently available yaw torque limit value, wherein the currently available yaw torque limit value comprises a maximum limit torque and a minimum limit torque.

In a specific implementation mode, when the maximum value of the absolute values of the rotating speeds of the four motors of the vehicle wheels exceeds the maximum rotating speed threshold, table look-up coefficient conversion is carried out on a deviation part exceeding the maximum rotating speed threshold, and the table look-up is carried out in a matching value range of 0-1.

The target yaw torque limit protection can be obtained using the following equation:

MAX{abs(MnFL),abs(MnFR),abs(MnRL),abs(MnRR)}–a＝a Err；

ωTrq*aErr_fac＝ωTrq2；

in the above two formulas, mnFL is the wheel speed of the front left wheel, mnFR is the wheel speed of the front right wheel, mnRL is the wheel speed of the rear left wheel, mnRR is the wheel speed of the rear right wheel, a is the maximum limit rotation speed, aErr is the over-limit wheel speed deviation. aErr _ fac is the matching value converted by the table lookup coefficient.

Then, the final yaw torque is subjected to maximum/minimum torque limitation, and the target motor torque is output.

Taking the left front wheel as an example, the following formula can be adopted to calculate the motor target torque of the left front wheel:

M _Treq ＝MIN[M _TMIN FL,MAX(M _TMAX FL,ωTrq2)]；

in the above formula, M _TMAX FL is the maximum limit torque of the left front wheel motor, omega Trq2 is obtained by rotation speed limit protection, M _TMIN FL is the minimum limiting torque of the left front wheel motor. M _Treq The motor target torque.

For the other wheels of the vehicle, the corresponding motor target torque can be calculated in a similar manner to the left front wheel.

S107: and controlling the corresponding motor according to the motor target torque of each wheel.

In this step, after the vehicle controller obtains the target torque of the motor of each wheel, the motor is controlled according to the target torque of the motor of each wheel, and the vehicle is controlled to run stably and safely in the steering process.

The steering control method of the distributed driving vehicle provided by the embodiment of the application is based on the accelerator pedal and utilizes a distributed multi-motor scheme, independent torque distribution can be realized for each wheel, even torques in different directions can be realized, and therefore in-situ steering of the vehicle is realized, the vehicle rotates along a geometric center in the whole steering process, and the turning radius is greatly reduced to zero. And the chassis controller does not need to be combined in the whole steering process. The torque control is more efficient and direct, and the parasitic loss can be reduced.

The following are embodiments of the apparatus of the present application that may be used to perform embodiments of the method of the present application. For details which are not disclosed in the embodiments of the apparatus of the present application, reference is made to the embodiments of the method of the present application.

Fig. 10 is a schematic structural diagram of a steering control device of a distributed drive vehicle according to an embodiment of the present application. As shown in fig. 10, the steering control device 10 of the distributed drive vehicle includes:

the first processing module 11 is configured to, after it is detected that the pivot steering function is started, determine whether a preset pivot steering activation condition is satisfied according to a vehicle state;

the second processing module 12 is configured to, if the vehicle meets the pivot steering activation condition, obtain a target yaw rate according to an opening degree of an accelerator pedal;

the third processing module 13 is configured to determine a target yaw torque of each wheel motor of the vehicle according to an actual yaw rate, a road surface adhesion coefficient, and the target yaw rate of the vehicle;

and the control module 14 is configured to control the vehicle to perform circular motion to perform pivot steering around a geometric center as a circle center according to the target yaw torque of each wheel motor of the vehicle, where the geometric center is a point where axes of four wheels of the vehicle after rotation intersect.

Optionally, the steering control device 10 of the distributed drive vehicle further includes:

the fourth processing module 15 is used for acquiring a current available yaw moment limiting value of a motor of each wheel during pivot steering of the vehicle;

the fourth processing module 15 is further configured to determine a motor target torque for each wheel according to a maximum rotation speed threshold value of the motor for each wheel of the vehicle and a currently available yaw moment limit value for each wheel;

the control module 14 is further configured to control the corresponding motor based on the motor target torque for each wheel.

Optionally, the fourth processing module 15 is specifically configured to:

Optionally, the fourth processing module 15 is further specifically configured to:

acquiring the current rotating speed of a motor of each wheel;

Optionally, the first processing module 11 is specifically configured to:

acquiring a no-system-fault signal zone bit, a safety condition zone bit and the state of a brake pedal of the vehicle;

Optionally, the second processing module 12 is specifically configured to:

Optionally, the third processing module 13 is specifically configured to:

according to the formula:

Optionally, the third processing module 13 is further configured to:

the formula is adopted:

calculating to obtain the road adhesion coefficient; wherein it is present>

Represents the coefficient of adhesion; />

The steering control device of the distributed driving vehicle is used for executing the technical scheme in any method embodiment, and the implementation principle and the technical effect are similar, and are not described again here.

It should be noted that the division of the modules of the above apparatus is only a logical division, and the actual implementation may be wholly or partially integrated into one physical entity, or may be physically separated. And these modules can be realized in the form of software called by processing element; or may be implemented entirely in hardware; and part of the modules can be realized in the form of calling software by the processing element, and part of the modules can be realized in the form of hardware. In addition, all or part of the modules can be integrated together or can be independently realized. The processing element described herein may be an integrated circuit having signal processing capabilities. In implementation, each step of the above method or each module above may be implemented by an integrated logic circuit of hardware in a processor element or an instruction in the form of software.

In addition, the present application also provides a vehicle, which includes a vehicle main body, a vehicle controller, a motor for each wheel, a memory, and computer program instructions stored on the memory and operable on the vehicle controller, wherein the vehicle controller, when executing the computer program instructions, is configured to implement the technical solution of the steering control method for a distributed drive vehicle in any one of the method embodiments.

Optionally, the above devices in the vehicle may be connected by a system bus.

The memory may be a separate memory unit or a memory unit integrated in the vehicle controller.

Optionally, the vehicle may also include interfaces for interacting with other devices, a display for displaying information by the user, and the like.

It should be understood that the vehicle controller may be a Central Processing Unit (CPU), other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), etc. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like. The steps of a method disclosed in connection with the present application may be embodied directly in a hardware processor, or in a combination of the hardware and software modules in the processor.

The system bus may be a Peripheral Component Interconnect (PCI) bus, an Extended Industry Standard Architecture (EISA) bus, or the like. The system bus may be divided into an address bus, a data bus, a control bus, and the like. For ease of illustration, only one thick line is shown, but this does not mean that there is only one bus or one type of bus. The memory may include Random Access Memory (RAM) and may also include non-volatile memory (NVM), such as at least one disk memory.

All or a portion of the steps of implementing the above-described method embodiments may be performed by hardware associated with program instructions. The aforementioned program may be stored in a readable memory. When executed, the program performs steps comprising the method embodiments described above; and the aforementioned memory (storage medium) includes: read-only memory (ROM), RAM, flash memory, hard disk, solid state disk, magnetic tape (magnetic tape), floppy disk (optical disk), and any combination thereof.

The vehicle provided by the embodiment of the application is used for executing the technical scheme provided by any method embodiment, the implementation principle and the technical effect are similar, and the detailed description is omitted.

The embodiment of the application provides a computer-readable storage medium, wherein a computer executing instruction is stored in the computer-readable storage medium, and when the computer executing instruction runs on a controller of a vehicle, the vehicle is enabled to execute the technical scheme of the steering control method of the distributed driving vehicle.

The computer-readable storage medium may be any type of volatile or non-volatile storage device or combination thereof, such as static random access memory, electrically erasable programmable read only memory, magnetic memory, flash memory, magnetic or optical disk. Readable storage media can be any available media that can be accessed by a general purpose or special purpose computer.

Alternatively, a readable storage medium may be coupled to the processor such that the processor can read information from, and write information to, the readable storage medium. Of course, the readable storage medium may also be an integral part of the processor. The processor and the readable storage medium may reside in an Application Specific Integrated Circuits (ASIC). Of course, the processor and the readable storage medium may also reside as discrete components in the apparatus.

It will be understood that the present application is not limited to the precise arrangements that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the application is limited only by the appended claims.

Claims

1. A steering control method for a distributed drive vehicle, characterized by comprising:

and controlling the vehicle to perform circular motion by taking a geometric center as a circle center to perform pivot steering according to the target yaw torque of each wheel motor of the vehicle, wherein the geometric center is a point where axes of four wheels of the vehicle after rotation intersect.

2. The method of claim 1, further comprising:

determining a motor target torque of each wheel according to a maximum rotation speed threshold value of a motor of each wheel of the vehicle and a current available yaw moment limit value of each wheel;

3. The method of claim 2, wherein said obtaining a current available yaw moment limit value for the motor of each wheel comprises:

4. The method of claim 2, wherein determining the motor target torque for each wheel based on a maximum speed threshold for the motor for each wheel of the vehicle and a currently available yaw moment limit for each wheel comprises:

acquiring the current rotating speed of a motor of each wheel;

the motor target torque for each wheel is determined based on the target yaw torque limit for each wheel, and a currently available yaw torque limit value, wherein the currently available yaw torque limit value includes a maximum limit torque and a minimum limit torque.

5. The method according to any one of claims 1 to 4, wherein the judging whether the preset pivot steering activation condition is met according to the state of the vehicle comprises the following steps:

6. The method according to any one of claims 1 to 4, wherein the obtaining a target yaw rate according to the accelerator pedal opening degree includes:

and inquiring a preset corresponding table of the pedal opening and the yaw angular velocity, and determining the yaw angular velocity corresponding to the accelerator pedal opening as the target yaw angular velocity.

7. The method according to any one of claims 1 to 4, wherein determining a target yaw torque of each wheel motor of the vehicle from an actual yaw rate, a road attachment coefficient, and the target yaw rate of the vehicle comprises:

according to the formula:

8. The method of claim 7, further comprising:

the formula is adopted:

calculating to obtain the road adhesion coefficient; wherein it is present>

Represents the coefficient of adhesion; />

9. A steering control apparatus for a distributed drive vehicle, comprising:

10. The apparatus of claim 9, further comprising:

the fourth processing module is used for acquiring the current available yaw moment limiting value of the motor of each wheel in the pivot steering process of the vehicle;

the control module is further configured to control the corresponding motor based on the motor target torque for each wheel.

11. The apparatus according to claim 10, wherein the fourth processing module is specifically configured to:

12. The apparatus of claim 10, wherein the fourth processing module is further specifically configured to:

acquiring the current rotating speed of a motor of each wheel;

13. The apparatus according to any one of claims 9 to 12, wherein the first processing module is specifically configured to:

14. The apparatus according to any one of claims 9 to 12, wherein the second processing module is specifically configured to:

inquiring a preset corresponding table of the pedal opening and the yaw angular velocity, inquiring the yaw angular velocity corresponding to the acquired accelerator pedal opening and determining the yaw angular velocity as the target yaw angular velocity.

15. The apparatus according to any one of claims 9 to 12, wherein the third processing module is specifically configured to:

according to the formula:

16. The apparatus of claim 15, wherein the third processing module is further configured to:

the formula is adopted:

calculating to obtain the road adhesion coefficient; wherein it is present>

Represents the coefficient of adhesion; />

17. A vehicle, characterized by comprising: a vehicle body, a vehicle controller, a motor for each wheel, a memory, and computer program instructions stored on and executable on the memory, the vehicle controller when executing the computer program instructions for implementing a steering control method for a distributed drive vehicle as claimed in any one of claims 1 to 8.

18. A computer-readable storage medium, characterized in that a computer-executable instruction for implementing a steering control method of a distributed drive vehicle according to any one of claims 1 to 8 is stored in the computer-readable storage medium.