CN105751919B - A kind of four-wheel wheel hub electric vehicle anti-skid control method - Google Patents

Abstract

The invention discloses a kind of four-wheel wheel hub electric vehicle anti-skid control methods, calculate the optimal slip ratio of wheel in real time by road surface recognizer, and the expectation rotating speed of wheel is calculated by the optimal slip ratio of wheel.Then, according to the state of wheel, the compensation torque of wheel is calculated；Wherein, if wheel-slip, wheel speed target in order to control it is expected with wheel, compensation torque is calculated by the PID controller of wheel wheel speed, if wheel is non-slip, compensation torque is zero；Meanwhile speed control calculates the command torque of motor according to speed controller with desired speed target in order to control；Finally, foregoing compensation torque and command torque phase adduction input motor are realized that the Anti-slip regulation of four-wheel wheel hub electric vehicle controls.

Description

Anti-skid control method for four-wheel hub electric automobile

Technical Field

The invention belongs to the technical field of electric automobiles, and particularly relates to an anti-skid control method for a four-wheel hub electric automobile.

Background

The four-wheel hub motor electric vehicle has become one of the development hotspots of the electric vehicle by virtue of the characteristics that the four-wheel driving torque is independently controllable and the torque and the rotating speed are easy to measure. When the four-wheel hub motor electric vehicle runs on a low-adhesion road surface, particularly runs at an accelerated speed, the output torque of the motor of the four-wheel hub motor electric vehicle may exceed the torque corresponding to the maximum adhesion force which can be provided by the road surface. When the situation occurs, the difference value between the wheel speed and the vehicle speed can be rapidly increased, the wheel slips, the slip rate enters an unstable area from the stable area, the adhesive force between the electric automobile and the road surface is reduced, and the safety accident is caused. In recent years, research on four-wheel hub motor electric vehicles focuses on implementation of basic control functions, and intensive research on driving anti-skid control methods of four-wheel hub motor electric vehicles is rarely carried out.

At present, the method for driving the anti-skid control mainly comprises methods such as a logic threshold, PID control, fuzzy control and the like, wherein the PID control method is widely applied. However, in the above methods, the optimum slip ratio of the wheel is regarded as a constant value, but the optimum slip ratio of the wheel changes with a change in road surface conditions during actual running of the vehicle. In order to improve the control effect of the drive slip control method, a road surface identification algorithm is introduced into the drive slip control method, and the optimal slip ratio of the wheel is calculated according to the result of road surface identification. Meanwhile, a PID control parameter setting method is provided for solving the problem that control parameters are difficult to determine in a driving antiskid method based on PID control.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides an anti-skid control method for a four-wheel hub electric automobile, which utilizes the optimal slip rate of wheels to enhance the stability and safety of the electric automobile so as to achieve the anti-skid control of driving.

In order to achieve the aim, the invention discloses an anti-skid control method for an electric automobile with four wheel hubs, which is characterized by comprising the following steps of:

(1) obtaining the optimal slip rate s of the wheel_{opt_ij}

(1.1) calculating the real-time wheel slip rate s in the driving process of the electric automobile_ij；

Wherein, ω is_ijThe wheel rotation speed, r, v, vehicle speed, ij ═ fl, fr, rl, rr, respectively representing the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel;

(1.2) calculating the coefficient of utilization adhesion u of each wheel according to the principle of wheel driving torque balance_ij；

Wherein, T_ijIs the driving force of the wheel, J is the moment of inertia of the wheel,angular acceleration of wheel, F_{z_ij}Is a wheel load, and satisfies:

wherein m is the full load mass of the vehicle, g is the acceleration of gravity, l_f、l_rThe distances from the center of mass of the vehicle to the front and rear axles respectively;

(1.3) according to the real-time slip rate s of the wheel_ijCalculating the adhesion coefficient u under the standard road surface by using the relation between the adhesion coefficient of the standard road surface and the wheel slip ratio_{t_ij}；

Wherein t ═ 1,2,3,4,5,6 represents 6 standard road surfaces, C_{1_t}、C_{2_t}、C_{3_t}Is a parameter related to a standard road surface;

(1.4) calculating the weight coefficient x under the standard road surface_t；

Wherein ε is a positive number with infinity close to 0;

(1.5) calculating the optimal wheel slip ratio s_{opt_ij}；

Wherein s is_{opt_t}The optimal slip ratio of the wheels under the standard road surface is obtained;

(2) calculating the expected wheel speed omega_{ref_ij}

(3) And compensation torque T output by using PID controller_{e_ij}Performing wheel speed control

The current wheel rotation speed omega is measured_ijDesired wheel speed omega from the wheel_{ref_ij}By comparison, if the wheel speed ω is_ijGreater than desired wheel speed ω_{ref_ij}I.e. omega_ij＞ω_{ref_ij}If the wheel slips, the PID controller is used to control the rotation speed omega of the wheel_ijDesired wheel speed omega from the wheel_{ref_ij}Difference e of_ijControl is carried out to obtain the compensation torque T_{e_ij}；

Wherein k is_{p_ij}Is the proportionality coefficient, k, of a PID controller_{i_ij}Is the integral coefficient, k, of a PID controller_{d_ij}Is the integral coefficient of the controller;

if the wheel speed is less than or equal to the desired wheel speed, i.e. ω_ij≤ω_{ref_ij}If the wheel does not slip, the PID controller outputs the compensation torque T_{e_ij}＝0；

(4) Calculating the command torque T of each motor_{com_ij}

(4.1) calculating the Total command Torque T_com；

Where e is the deviation between the desired vehicle speed and the actual vehicle speed, k_{p_v}、k_{i_v}、k_{d_v}Respectively are proportional, integral and differential constants in vehicle speed control;

(4.2) total command torque T_comEvenly distributed to each motor to obtain the command torque T of each motor_{com_ij}；

(5) Calculating the drive torque T_{d_ij}

In the motor of the electric automobile, the compensation torque T is firstly_{e_ij}And the command torque T_{com_ij}Summing to obtain input torque of amplitude limiting moduleThen by clippingThe module carries out amplitude limiting processing to obtain the driving torque T of the motor_{d_ij}；

Wherein, T_maxThe maximum output torque of the hub motor is obtained;

finally, the driving torque T is adjusted_{d_ij}The anti-skid control is carried out by controlling the speed of the electric automobile through inputting the anti-skid control signals to each motor.

Further, the transfer function c(s) of the PID controller is:

where s is the frequency domain operator, k_{p_ij}Is the proportionality coefficient, k, of a PID controller_{i_ij}Is the integral coefficient of the PID controller;

in the wheel speed control, the transfer function g(s) of the hub motor of the controlled object can be expressed as:

wherein T is a motor time constant, and J is the rotational inertia of the wheel;

from equations (12) and (13), the closed loop transfer function for wheel speed control is:

from equation (14), the system characteristic equation for wheel speed control is:

JTs³+Js²+k_{p_ij}s+k_{i_ij}＝0 (15)

in order to ensure the stability of the wheel speed control, the following criteria are obtained:

proportional parameter k of PID controller in wheel rotating speed control_{p_ij}And an integral parameter k_{i_ij}The values of (a) should satisfy:

the invention aims to realize the following steps:

the invention relates to an anti-skid control method for an electric vehicle with four wheel hubs, which is characterized in that the optimal slip rate of wheels is calculated in real time through a road surface recognition algorithm, and the expected rotating speed of the wheels is calculated according to the optimal slip rate of the wheels. Then, calculating the compensation torque of the wheel according to the state of the wheel; if the wheel slips, the expected wheel speed of the wheel is taken as a control target, the compensation torque is calculated through a PID controller of the wheel speed, and if the wheel does not slip, the compensation torque is zero; meanwhile, the vehicle speed control takes the expected vehicle speed as a control target, and calculates the command torque of the motor according to a vehicle speed controller; finally, adding the compensation torque and the command torque and inputting the sum into a motor to realize the driving antiskid control of the four-wheel hub electric automobile; therefore, the invention can ensure that the wheels run in a stable region in the running process of the vehicle, thereby improving the stability and the safety of the vehicle; secondly, the invention also adopts a parameter setting method of the PID controller, and solves the problem that the parameters of the controller in the driving antiskid control system need to be repeatedly debugged in the actual engineering.

Drawings

FIG. 1 is a schematic diagram of the antiskid control of a four-wheel hub electric vehicle according to the present invention;

FIG. 2 is a flow chart of the anti-skid control of the four-wheel hub electric vehicle according to the present invention;

FIG. 3 is a flow chart of road surface identification;

FIG. 4 is a block diagram of an electric vehicle motor control algorithm based on PID control;

FIG. 5 is a graph comparing simulation results with and without antiskid control;

FIG. 6 is a comparison of wheel slip ratio simulation results with and without anti-skid control;

FIG. 7 is a diagram of simulation results of the driving trajectory of an electric vehicle with and without antiskid control.

Detailed Description

The following description of the embodiments of the present invention is provided in order to better understand the present invention for those skilled in the art with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention.

Examples

FIG. 1 is a schematic diagram of the antiskid control of the four-wheel hub electric vehicle of the present invention.

In the present embodiment, as shown in fig. 1, a four-wheel hub electric vehicle drive antiskid control system includes: the device comprises a road surface identification module, an expected wheel speed calculation module, a wheel driving antiskid control module, a vehicle speed control module and an amplitude limiting module.

The road surface identification module carries out real-time estimation on the road surface on which the electric automobile runs to obtain the optimal wheel slip rate s_{opt_ij}。

An expected wheel speed calculation module for obtaining the optimal wheel slip rate s according to road surface identification_{opt_ij}The vehicle speed v and the wheel radius r, and calculating the expected wheel speed omega of the wheel_{ref_ij}。

The wheel driving antiskid control module obtains the compensation torque T of the wheel according to the state of the wheel_{e_ij}. If the wheel speed omega_ijGreater than the desired speed omega of the wheel_{ref_ij}I.e. omega_ij＞ω_{ref_ij}If the wheel slips, the PID controller is used to control the rotation speed omega of the wheel_ijDesired wheel speed omega from the wheel_{ref_ij}Difference e of_ijControl is carried out to obtain the compensation torque T_{e_ij}(ii) a If the wheel speed is less than or equal to the desired wheel speed, i.e. ω_ij≤ω_{ref_ij}The wheel does not slip, and the antiskid control module is driven to output the compensation torque T_{e_ij}＝0。

A vehicle speed control module for controlling the vehicle speed v according to the wheel expected vehicle speed v_refCalculating the total command torque T of the wheels from the difference between the actual vehicle speed v and the vehicle speed v_comThen, the total command torque is distributed to each wheel through an average distribution control algorithm to obtain the command torque T of each wheel_{com_ij}。

Amplitude limiting module for compensating torque T_{e_ij}And a command torque T_{com_ij}Sum T_{d_ij}Limiting, i.e. at maximum output torque T of the motor_maxIn contrast, when T is_{d_ij}Greater than T_maxIf the output is not the same as the output of the amplitude limiting module, otherwise, T is output_{d_ij}。

FIG. 2 is a flow chart of the anti-skid control of the four-wheel hub electric vehicle according to the present invention.

In this embodiment, as shown in fig. 2, the antiskid control method for an electric vehicle with four wheel hubs according to the present invention includes the following steps:

s1, obtaining the optimal slip rate S of the wheel_{opt_ij}

S1.1, calculating the real-time wheel slip rate S in the driving process of the electric automobile_ij；

Wherein, ω is_ijThe wheel rotation speed, r, v, vehicle speed, ij ═ fl, fr, rl, rr, respectively representing the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel;

s1.2, calculating the utilization adhesion coefficient u of each wheel according to the driving moment balance principle of the wheels_ij；

Wherein, T_ijIs the driving force of the wheel, J is the moment of inertia of the wheel,angular acceleration of wheel, F_{z_ij}Is a wheel load, and satisfies:

wherein m is the full load mass of the vehicle, g is the acceleration of gravity, l_f、l_rThe distances from the center of mass of the vehicle to the front and rear axles respectively;

in this embodiment, m is 2150kg, the gravitational acceleration is 9.8, and the wheel radius is 0.3262m, l_fAnd l_rAll values of (A) are 1.35 m.

S1.3, the functional curve expression provided by Burckhardt can well describe the relationship between the road adhesion coefficient u and the wheel slip S rate, and the functional relationship is as follows:

real-time wheel slip rate s_ijBy substituting the formula (4) into the flow shown in FIG. 3, the adhesion coefficient u under the standard road surface can be calculated_{t_ij}；

Where t ═ 1,2,3,4,5,6, represents 6 standard road surfaces, namely: 6 standard pavements of ice, snow, wet cobblestones, wet asphalt, dry cement and dry asphalt; c_{1_t}、C_{2_t}、C_{3_t}As a parameter related to a standard road surface, in the present embodiment, as shown in table 1;

table 1 is standard road surface related parameters;

road surface	C1	C2	C3	sopt
					Ice	0.05	306.39	0.001	0.03
Snow (snow)	0.1946	94.129	0.0646	0.06
					Wet cobble	0.4004	33.7080	0.1204	0.14
Wet asphalt	0.8570	33.822	0.3470	0.13
					Dry cement	1.1973	25.168	0.5373	0.16
Dry asphalt	1.2801	23.99	0.52	0.17

TABLE 1

6 standard pavement u-s curves can be obtained according to the formula (5) and the table 1;

s1.4, calculation standardWeight coefficient x under road surface_t；

Wherein ε is a positive number with infinity close to 0;

in this embodiment, ε is 0.00001.

S1.5, calculating the optimal wheel slip rate S_{opt_ij}；

Wherein s is_{opt_t}The optimal slip ratio of the lower wheel on the standard road surface can be found through the table 1; s2, calculating the expected wheel speed omega_{ref_ij}

S3 compensation torque T output by PID controller_{e_ij}Performing wheel speed control

The current wheel rotation speed omega is measured_ijDesired wheel speed omega from the wheel_{ref_ij}By comparison, if the wheel speed ω is_ijGreater than desired wheel speed ω_{ref_ij}I.e. omega_ij＞ω_{ref_ij}If the wheel slips, the PID controller is used to control the rotation speed omega of the wheel_ijDesired wheel speed omega from the wheel_{ref_ij}Difference e of_ijControl is carried out to obtain the compensation torque T_{e_ij}；

Wherein k is_{p_ij}Is the proportionality coefficient, k, of a PID controller_{i_ij}Is an integral system of a PID controllerNumber, k_{d_ij}Is the integral coefficient of the controller;

if the wheel speed is less than or equal to the desired wheel speed, i.e. ω_ij≤ω_{ref_ij}If the wheel does not slip, the PID controller outputs the compensation torque T_{e_ij}＝0；

In this embodiment, for a four-wheel hub motor electric vehicle, the wheel rotation speed control may be equivalent to motor rotation speed control, and a transfer function block diagram of a motor vector control algorithm based on a PID control algorithm is shown in fig. 4.

Wherein, the transfer function C(s) of the PID controller is:

where s is the frequency domain operator, k_{p_ij}Is the proportionality coefficient, k, of a PID controller_{i_ij}Is the integral coefficient of the PID controller;

in the wheel speed control, the transfer function g(s) of the hub motor of the controlled object can be expressed as:

wherein T is a motor time constant, and J is the rotational inertia of the wheel;

from equations (11) and (12), the closed loop transfer function for wheel speed control is:

from equation (13), the system characteristic equation for wheel speed control is:

JTs³+Js²+k_{p_ij}s+k_{i_ij}＝0 (14)

in order to ensure the stability of the wheel speed control, the following criteria are obtained:

proportional parameter k of PID controller in wheel rotating speed control_{p_ij}And an integral parameter k_{i_ij}The values of (a) should satisfy:

in this embodiment, the torque motor time constant T of the motor is 0.7, k_{p_ij}Has a value of 200, k_{i_ij}The value is 50.

S4, calculating the command torque T of each motor_{com_ij}

S4.1, calculating total command torque T_com；

Where e is the deviation between the desired vehicle speed and the actual vehicle speed, k_{p_v}、k_{i_v}、k_{d_v}Respectively are proportional, integral and differential constants in vehicle speed control;

s4.2, converting the total command torque T_comEvenly distributed to each motor to obtain the command torque T of each motor_{com_ij}；

S5, calculating the driving torque T_{d_ij}

In the motor of the electric automobile, the compensation torque is firstlyT_{e_ij}And the command torque T_{com_ij}Summing to obtain input torque of amplitude limiting moduleThen, amplitude limiting processing is carried out through an amplitude limiting module to obtain the driving torque T of the motor_{d_ij}；

Wherein, T_maxThe maximum output torque of the hub motor is obtained;

in this embodiment, the maximum output torque of the in-wheel motor is 320 Nm.

Finally, the driving torque T is adjusted_{d_ij}The anti-skid control is carried out by controlling the speed of the electric automobile through inputting the anti-skid control signals to each motor.

In the embodiment, by using Carsim and simulink combined simulation, the initial speed of the four-wheel hub electric automobile is set to be 5km/h, the expected speed is 60km/h, the road adhesion coefficient is 0.1, the simulation is respectively carried out by adopting the vehicle speed control without driving an antiskid method and the vehicle speed control with driving the antiskid method, the vehicle speed simulation result is shown in figure 5, in the vehicle speed control without driving the antiskid method, the vehicle speed gradually rises from 5km to the expected vehicle speed of 60km/h, the vehicle speed reaches the expected vehicle speed for about 82s and is kept stable, and the vehicle speed overshoot in the control process is 36.6%; in the vehicle speed control including the driving antiskid method, the vehicle speed reaches the expected vehicle speed within 20s and is kept stable in the process of gradually increasing the vehicle speed from 5km to the expected vehicle speed of 60km/h, and the vehicle speed overshoot in the control process is 0%.

In the present embodiment, as shown in fig. 6, (a), (b), (c), (d) represent the slip ratio simulation results of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel of the electric vehicle, respectively, and it can be seen from the four images that in the vehicle speed control without the driving anti-skid method, the slip ratio of the four wheels within 1s rapidly increases and exceeds 0.9, the wheels are severely slipped, and as time increases, the wheel slip ratio cannot converge to the optimal slip ratio, that is, the wheels are always in an out-of-control state; in the vehicle speed control including the drive anti-skid method, the wheel slip rate is increased to 0.2 at the beginning, but under the intervention of drive anti-skid, the wheel slip rate in 2s is converged to the optimal slip rate of 0.05, and the wheel slip state is well controlled.

In this embodiment, the driving trajectory of the electric vehicle is also simulated, and the simulation result is shown in fig. 7, in the vehicle speed control without the antiskid driving method, the longitudinal displacement of the vehicle gradually increases along with the movement of the vehicle, and meanwhile, the vehicle generates a transverse movement, and finally, when the longitudinal displacement of the vehicle is 1000m, the transverse displacement of the vehicle is 3m, which means that the vehicle has a lateral deviation phenomenon; in the vehicle speed control including the driving antiskid method, the transverse displacement of the vehicle is 0m along with the increase of the longitudinal displacement of the vehicle in the vehicle moving process, the vehicle does not deviate, the vehicle can well track an expected track, and the driving antiskid control can improve the stability and the safety of the vehicle as can be seen from simulation.

Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.

Claims (2)

1. The anti-skid control method of the four-wheel hub electric automobile is characterized by comprising the following steps of:

(1) obtaining the optimal slip rate s of the wheel_{opt_ij}

(1.1) calculating the real-time wheel slip rate s in the driving process of the electric automobile_ij；

Wherein, ω is_ijAs the rotational speed of the wheelR is a wheel radius, v is a vehicle speed, ij ═ fl, fr, rl, rr respectively represent a left front wheel, a right front wheel, a left rear wheel, and a right rear wheel;

(1.2) calculating the coefficient of utilization adhesion u of each wheel according to the principle of wheel driving torque balance_ij；

Wherein, T_ijIs the driving force of the wheel, J is the moment of inertia of the wheel,angular acceleration of wheel, F_{z_ij}Is a wheel load, and satisfies:

wherein m is the full load mass of the vehicle, g is the acceleration of gravity, l_f、l_rThe distances from the center of mass of the vehicle to the front and rear axles respectively;

(1.3) according to the real-time slip rate s of the wheel_ijCalculating the adhesion coefficient u under the standard road surface by using the relation between the adhesion coefficient of the standard road surface and the wheel slip ratio_{t_ij}；

Wherein t ═ 1,2,3,4,5,6 represents 6 standard road surfaces, C_{1_t}、C_{2_t}、C_{3_t}Is a parameter related to a standard road surface;

(1.4) calculating the weight coefficient x under the standard road surface_t；

Wherein ε is a positive number with infinity close to 0;

(1.5) calculating wheel optimaSlip ratio s_{opt_ij}；

Wherein s is_{opt_t}The optimal slip ratio of the wheels under the standard road surface is obtained;

(2) calculating the expected wheel speed omega_{ref_ij}

(3) And compensation torque T output by using PID controller_{e_ij}Performing wheel speed control

The current wheel rotation speed omega is measured_ijDesired wheel speed omega from the wheel_{ref_ij}By comparison, if the wheel speed ω is_ijGreater than desired wheel speed ω_{ref_ij}I.e. omega_ij＞ω_{ref_ij}If the wheel slips, the PID controller is used to control the rotation speed omega of the wheel_ijDesired wheel speed omega from the wheel_{ref_ij}Difference e of_ijControl is carried out to obtain the compensation torque T_{e_ij}；

Wherein k is_{p_ij}Is the proportionality coefficient, k, of a PID controller_{i_ij}Is the integral coefficient, k, of a PID controller_{d_ij}Is the integral coefficient of the controller;

if the wheel speed is less than or equal to the desired wheel speed, i.e. ω_ij≤ω_{ref_ij}If the wheel does not slip, the PID controller outputs the compensation torque T_{e_ij}＝0；

(4) Calculating the command torque T of each motor_{com_ij}

(4.1) calculating the Total command Torque T_com；

Wherein,e is the deviation between the desired vehicle speed and the actual vehicle speed, k_{p_v}、k_{i_v}、k_{d_v}Respectively are proportional, integral and differential constants in vehicle speed control;

(4.2) total command torque T_comEvenly distributed to each motor to obtain the command torque T of each motor_{com_ij}；

(5) Calculating the drive torque T_{d_ij}

In the motor of the electric automobile, the compensation torque T is firstly_{e_ij}And the command torque T_{com_ij}Summing to obtain input torque of amplitude limiting moduleThen, amplitude limiting processing is carried out through an amplitude limiting module to obtain the driving torque T of the motor_{d_ij}；

Wherein, T_maxThe maximum output torque of the hub motor is obtained;

finally, the driving torque T is adjusted_{d_ij}The anti-skid control is carried out by controlling the speed of the electric automobile through inputting the anti-skid control signals to each motor.

2. The anti-skid control method for the four-wheel hub electric vehicle as claimed in claim 1, wherein in the step (3), the transfer function C(s) of the PID controller during the wheel speed control is as follows:

where s is the frequency domain operator, k_{p_ij}Is the proportionality coefficient, k, of a PID controller_{i_ij}Is the integral coefficient of the PID controller;

in the wheel speed control, the transfer function g(s) of the hub motor of the controlled object can be expressed as:

wherein T is a motor time constant, and J is the rotational inertia of the wheel;

from equations (12) and (13), the closed loop transfer function for wheel speed control is:

from equation (14), the system characteristic equation for wheel speed control is:

JTs³+Js²+k_{p_ij}s+k_{i_ij}＝0 (15)

in order to ensure the stability of the wheel speed control, the following criteria are obtained:

proportional parameter k of PID controller in wheel rotating speed control_{p_ij}And an integral parameter k_{i_ij}The values of (a) should satisfy: