阅读说明：本技术 商用车分布式线控制动系统及控制方法 (Distributed line control brake system and control method for commercial vehicle ) 是由 杨义勇 魏凌涛 陶兴军 鲁之轩 李亮 于 2020-02-26 设计创作，主要内容包括：本发明提供了一种商用车分布式线控制动系统及控制方法,控制方法包括步骤：先建立滑移率控制器,并根据车辆状态信息确认实际滑移率和目标滑移率；然后为各驱动轮分配目标制动扭矩；接着建立所述车辆的制动成本函数,通过对所述成本函数求极值得到所述预期总再生制动扭矩、各所述驱动轮的预期气压制动扭矩；最后根据所述预期总再生制动扭矩并结合电机能够提供的最大扭矩和最小扭矩确定电机的实际输出制动扭矩,然后控制电机输出实际制动扭矩；同时,根据各所述预期气压制动扭矩控制气压制动系统工作。本发明能够使ABS和再生制动协调工作,确保车辆的稳定性和达到最大能量再生。(The invention provides a distributed line control brake system and a control method for a commercial vehicle, wherein the control method comprises the following steps: firstly, establishing a slip ratio controller, and confirming an actual slip ratio and a target slip ratio according to vehicle state information; then distributing target braking torque for each driving wheel; then, a braking cost function of the vehicle is established, and the expected total regenerative braking torque and the expected air pressure braking torque of each driving wheel are obtained by solving the extreme value of the cost function; finally, determining the actual output braking torque of the motor according to the expected total regenerative braking torque and the combination of the maximum torque and the minimum torque which can be provided by the motor, and then controlling the motor to output the actual braking torque; and simultaneously, controlling the pneumatic braking system to work according to each expected pneumatic braking torque. The invention can lead the ABS and the regenerative braking to work coordinately, ensure the stability of the vehicle and achieve the maximum energy regeneration.)

1. A control method of a distributed brake-by-wire system of a commercial vehicle is characterized by comprising the following steps:

s1: acquiring a brake signal;

s2: acquiring vehicle state information;

s3: establishing a slip rate controller, and confirming an actual slip rate and a target slip rate according to the vehicle state information;

s4: distributing target braking torque for each driving wheel according to the actual slip rate and the target slip rate and combining the slip rate controller

S5: establishing a braking cost function for the vehicle, the braking cost function being an expected total regenerative braking torque T for the vehicle_dExpected air brake torque of each of the drive wheelsThen combining said target braking torque of each of said drive wheelsObtaining the expected total regenerative braking torque T by extremizing the braking cost function_dExpected air brake torque of each of the drive wheels

S6: based on the expected total regenerative braking torque T_dIn combination with the maximum torque that the motor can provideAnd minimum torqueDetermining the actual output brake torque T of the electric machine_eThen controlling the motor to output the actual output braking torque T_e(ii) a At the same time, according to each of the expected air brake torquesAnd controlling the pneumatic braking system to work.

2. The control method according to claim 1, characterized in that the vehicle state information in step S2 includes: the friction coefficient of the road surface on which the vehicle runs, the mass of the vehicle, the longitudinal speed, the angular speed of the driving wheel, the radius of the driving wheel, the moment of inertia of the driving wheel, the longitudinal force of the driving wheel, and the vertical force of the driving wheel in the direction of the rotation axis thereof.

3. The control method according to claim 2, wherein in the step S3, the establishing slip ratio controller includes:

s31: setting a proportional integral model: s_i＝e_i+α_i∫e_idt of, wherein e_i＝λ_i-λ_di；

S33: the slip rate controller is established as follows:

the step S4 includes:

s41: the proportional integral model is subjected to derivation to obtain a reciprocal model

S42: make itObtaining a target braking torque of each of the drive wheels

Wherein λ is_iIs the actual slip ratio, λ, of the vehicle_diTarget slip ratio for the vehicle, α_i、₁、₀、Is a preset coefficient.

4. Control method according to claim 2, characterized in that the actual slip ratio λ_iCalculated according to the following formula:

the target slip ratio lambda_diCalculated according to the following formula:

wherein u is_xIs the longitudinal speed, ω, of the vehicle_iIs the driving wheel angular velocity, R, of the vehicle_iIs a drive wheel radius of the vehicle; k_λIs a preset coefficient; μ is a friction coefficient of a road surface on which the vehicle travels;to utilize the coefficient of friction; m_threIs a yaw moment threshold for yaw control; l is the driving wheel track of the vehicle; f_ziThe vertical force of the driving wheel in the direction of the rotating shaft of the driving wheel; f. of^-1Is a preset friction coefficient table.

5. The control method according to any one of claims 1 to 4, wherein the braking cost function in step S5 is:

wherein the content of the first and second substances,an expected air brake torque for the drive wheel;a target braking torque for the drive wheel; t is_dIs the expected total regenerative braking torque;for optimal regenerative braking torque;is the maximum value of the regenerative braking torque;is a reserve gap.

6. The control method according to claim 5, wherein said step S5 is preceded by the step of:

s0: establishing a brake pressure increasing characteristic curve chart and a brake pressure reducing characteristic curve chart of a pneumatic brake system of each driving wheel, wherein the brake pressure increasing characteristic curve chart comprises a pressure increasing and maintaining period and a plurality of pressure increasing pressure variation quantities of the pneumatic brake systemAnd the shortest time required for increasing each supercharging pressure variation, wherein the brake decompression characteristic curve chart comprises a decompression and pressure maintaining period and a plurality of decompression pressure variations of the pneumatic brake systemAnd reduceThe minimum time required for each of the reduced pressure variations;

the braking cost function in the step S5 is:

wherein m and n are min, 2, 3, … and max respectively; k_rIs a preset coefficient; delta P_aiAs the amount of change in the pressure of the drive wheel,

7. the control method according to claim 6, wherein in the step S6, the air brake torque is controlled according to each of the expected air brake torquesThe method for controlling the work of the air pressure braking system specifically comprises the following steps: performing the following steps for each of the drive wheels:

s81: braking torque according to expected air pressureDetermining a target pressure P_i；

S82: obtaining the actual pressure P of the brake chamber_i0And calculating the pressure difference delta P between the target pressure and the pressure_i＝P_i-P_i0；

S83: determining the pressure difference Δ P_iWhether it is within the preset pressure range, if so, executing S84; otherwise, executing S850;

s84: maintaining the pressure;

s850: and controlling the opening and closing of an air inlet valve and an air outlet valve of the brake air chamber according to the pressure change rule in the brake pressure increasing characteristic curve chart and the brake pressure reducing characteristic curve chart.

Preferably, the step S850 specifically includes:

s85: determining the pressure difference Δ P_iIf greater than 0, execute S86; if less than 0, go to S87;

s86: determining the pressure difference Δ P_iWhether the maximum boost pressure adjustment amount in the brake boost characteristic curve graph is exceeded or not, if yes, opening an air inlet valve of a brake chamber for a first preset time all the time, and then returning to S82; if not, determining the pressure difference delta P according to the brake pressure increasing characteristic curve graph_iThe corresponding shortest time, the air inlet valve of the brake chamber is opened periodically according to the shortest time and the setting mode of the pressurization and pressure maintaining period, then the second preset time is continued, and then the step returns to S82;

s87: determining the pressure difference Δ P_iWhether the maximum decompression pressure adjustment amount in the brake decompression characteristic curve graph is exceeded or not, if yes, opening an exhaust valve of the brake chamber for a third preset time all the time, and then returning to S82; if not, determining the pressure difference delta P according to the brake pressure reduction characteristic curve graph_iAnd (4) opening an exhaust valve of the brake chamber periodically according to the shortest time and the setting mode of the pressure reduction and pressure maintaining period, continuing for a fourth preset time, and returning to the step S82.

8. The control method according to any one of claims 1 to 7, characterized in that in said step S6, the total regenerative braking torque T is expected according to the total regenerative braking torque T_dIn combination with the maximum torque that the motor can provideAnd minimum torqueDetermining the actual output brake torque T of the electric machine_eThen controlling the motor to output the actual braking torque T_eThe method comprises the following steps:

s71: based on the expected total regenerative braking torque T_dDetermining a desired braking torque output by an electric machine

S72: obtaining the maximum torque that the motor can provideAnd minimum torque

S73: determining a desired braking torque output by the motorWith maximum torqueMinimum torqueThe size of (2):

if it isThen

If it isThen

If it isThen

S74: controlling the motor outputActual braking torque T_e。

9. A distributed brake-by-wire system for a commercial vehicle, comprising:

the upper layer module is used for acquiring a brake signal and vehicle state information; establishing a slip rate controller, confirming an actual slip rate and a target slip rate according to the vehicle state information, and distributing target braking torque for each driving wheel according to the actual slip rate and the target slip rate and combining the slip rate controller

A middle module connected with the upper module for establishing a braking cost function of the vehicle, the braking cost function being an expected total regenerative braking torque T_dExpected air brake torque of each of the drive wheelsAnd for combining said target braking torque of each of said drive wheelsObtaining the expected total regenerative braking torque T by extremizing a braking cost function_dExpected air brake torque of each of the drive wheels

A regenerative braking module for varying the total regenerative braking torque T based on the desired total regenerative braking torque_dIn combination with the maximum torque that the motor can provideAnd minimum torqueDetermining the actual output brake torque T of the electric machine_eAnd controlling the motor to output the actual braking torque T_e；

A pneumatic brake module for generating a desired pneumatic brake torque according to each of the desired pneumatic brake torquesAnd controlling the pneumatic braking system to work.

10. The braking system of claim 9, wherein the upper module includes a control unit;

the pneumatic braking system comprises an active braking valve, a double check valve, a relay valve and an ABS (anti-lock brake system) valve, wherein the active braking valve and the ABS valve are electronic valves and are both connected with the control unit, and the double check valve and the relay valve are pneumatic control valves; a first communication end of the active brake valve is communicated with a total air pressure loop of a vehicle, and a second communication end of the active brake valve is communicated with a first control end of the double check valve; the second control end of the double check valve is communicated with an air pressure valve of a brake pedal; and the communication end of the double check valve is communicated with one end of the relay valve, and the other end of the relay valve is communicated with the brake air chamber through the ABS valve.

Technical Field

The invention relates to the field of automobile braking, in particular to a distributed brake-by-wire system and a control method for a commercial vehicle.

Background

An anti-lock braking system (ABS) for a vehicle is one of active safety devices of the vehicle, which adjusts a locking degree of a wheel by controlling a braking torque according to a velocity feedback of the wheel, can sufficiently utilize a road adhesion and ensure a stability of the vehicle in an emergency braking, and is important for improving the stability and the safety of the vehicle. In hybrid electric vehicles (HEV/EV), braking torque is provided by both mechanical braking (i.e., ABS) and regenerative braking, and energy regeneration during braking is a key energy saving technology for hybrid electric vehicles. However, in the prior art, when an anti-lock brake system (ABS) is activated, increasing regenerative braking affects the braking process, resulting in incompatibility of vehicle stability and maximum energy recovery, and it is difficult to coordinate mechanical braking and regenerative braking to ensure vehicle stability and maximum energy regeneration.

Disclosure of Invention

Based on the above situation, the present invention provides a distributed brake-by-wire system and a control method for a commercial vehicle, so as to coordinate mechanical braking and regenerative braking to ensure vehicle stability and maximum energy regeneration.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

the invention provides a control method of a distributed brake-by-wire system of a commercial vehicle, which comprises the following steps:

s1: acquiring a brake signal;

s2: acquiring vehicle state information;

s3: establishing a slip rate controller, and confirming an actual slip rate and a target slip rate according to the vehicle state information;

s4: according to the aboveActual slip ratio and target slip ratio, and combining the slip ratio controller to distribute target brake torque for each driving wheel

S5: establishing a braking cost function for the vehicle, the braking cost function being the total regenerative braking torque T expected for the vehicle_dExpected air brake torque of each of the drive wheelsThen combining said target braking torque of each of said drive wheelsObtaining the expected total regenerative braking torque T by extremizing the braking cost function_dExpected air brake torque of each of the drive wheels

S6: based on the expected total regenerative braking torque T_dIn combination with the maximum torque that the motor can provideAnd minimum torqueDetermining the actual output brake torque T of the electric machine_eThen controlling the motor to output actual output brake torque T_e(ii) a At the same time, according to each of the expected air brake torquesAnd controlling the pneumatic braking system to work.

Preferably, the vehicle state information in step S2 includes: the friction coefficient of the road surface on which the vehicle runs, the mass of the vehicle, the longitudinal speed, the angular speed of the driving wheel, the radius of the driving wheel, the moment of inertia of the driving wheel, the longitudinal force of the driving wheel, and the vertical force of the driving wheel in the direction of the rotation axis thereof.

Preferably, in step S3, the slip ratio establishing controller includes:

s31: setting a proportional integral model: s_i＝e_i+α_i∫e_id_tWherein e is_i＝λ_i-λ_di；

S32: the slip rate controller is established as follows:

the step S4 includes:

s41: the proportional integral model is subjected to derivation to obtain a reciprocal model

S42: make itObtaining a target braking torque of each of the drive wheels

Wherein λ is_iIs the actual slip ratio, λ, of the vehicle_diTarget slip ratio for the vehicle, α_i、₁、₀、Is a preset coefficient.

Preferably, said actual slip ratio λ_iCalculated according to the following formula:

the target slip ratio lambda_diCalculated according to the following formula:

wherein u is_xIs the longitudinal speed, ω, of the vehicle_iIs the driving wheel angular velocity, R, of the vehicle_iIs a drive wheel radius of the vehicle; k_λIs a preset coefficient; μ is a friction coefficient of a road surface on which the vehicle travels;to utilize the coefficient of friction; m_threIs a yaw moment threshold for yaw control; l is the driving wheel track of the vehicle; f_ziThe vertical force of the driving wheel in the direction of the rotating shaft of the driving wheel; f. of^-1Is a preset friction coefficient table.

Preferably, the braking cost function in step S5 is:

wherein the content of the first and second substances,an expected air brake torque for the drive wheel;a target braking torque for the drive wheel; t is_dIs the expected total regenerative braking torque;for optimal regenerative braking torque;for the regenerative brakingThe maximum value of the moment;is a reserve gap.

Preferably, the step S5 is preceded by the step of:

s0: establishing a brake pressure increasing characteristic curve chart and a brake pressure reducing characteristic curve chart of a pneumatic brake system of each driving wheel, wherein the brake pressure increasing characteristic curve chart comprises a pressure increasing and maintaining period and a plurality of pressure increasing pressure variation quantities of the pneumatic brake systemAnd the shortest time required for increasing each supercharging pressure variation, wherein the brake decompression characteristic curve chart comprises a decompression and pressure maintaining period and a plurality of decompression pressure variations of the pneumatic brake systemAnd the minimum time required for reducing each of the decompression pressure variations;

the braking cost function in the step S5 is:

wherein m and n are min, 2, 3, … and max respectively; k_rIs a preset coefficient; delta P_aiAs the amount of change in the pressure of the drive wheel,

preferably, in the step S6, the air brake torque is adjusted according to each of the expected air brake torquesThe method for controlling the work of the air pressure braking system specifically comprises the following steps: performing the following steps for each of the drive wheels:

s81: braking torque according to expected air pressureDetermining a target pressure P_i；

S82: obtaining the actual pressure P of the brake chamber_i0And calculating the pressure difference delta P between the target pressure and the pressure_i＝P_i-P_i0；

S83: determining the pressure difference Δ P_iWhether or not it is larger than the minimum decompression pressure adjustment amount in the brake decompression characteristic mapAnd is less than the minimum boost pressure adjustment in the brake boost characteristic curveIf yes, go to S84; otherwise, go to S85;

s84: maintaining the pressure;

s85: determining the pressure difference Δ P_iIf greater than 0, execute S86; if less than 0, go to S87;

s86: determining the pressure difference Δ P_iWhether the maximum boost pressure adjustment amount in the brake boost characteristic curve graph is exceeded or not, if yes, opening an air inlet valve of a brake chamber for a first preset time all the time, and then returning to S82; if not, determining the pressure difference delta P according to the brake pressure increasing characteristic curve graph_iThe corresponding shortest time, the air inlet valve of the brake chamber is opened periodically according to the shortest time and the setting mode of the pressurization and pressure maintaining period, then the second preset time is continued, and then the step returns to S82;

s87: determining the pressure difference Δ P_iWhether the maximum decompression pressure adjustment amount in the brake decompression characteristic curve graph is exceeded or not, if yes, opening an exhaust valve of the brake chamber for a third preset time all the time, and then returning to S82; if not, determining the pressure difference delta P according to the brake pressure reduction characteristic curve graph_iThe corresponding shortest time, and according to the shortest time and the setting mode of the pressure reducing and maintaining period, the exhaust valve of the brake chamber is periodically opened, and then the fourth time is continuedPreset time, and then returns to S82.

Preferably, in the step S6, the total regenerative braking torque T is predicted according to the expected total regenerative braking torque T_dIn combination with the maximum torque that the motor can provideAnd minimum torqueDetermining the actual output brake torque T of the electric machine_eThen controlling the motor to output the actual braking torque T_eThe method comprises the following steps:

s71: based on the expected total regenerative braking torque T_dDetermining a desired braking torque output by an electric machine

S72: obtaining the maximum torque that the motor can provideAnd minimum torque

S73: determining a desired braking torque output by the motorWith maximum torqueMinimum torqueThe size of (2):

if it isThen

If it isThen

If it isThen

S74: controlling the motor to output an actual braking torque T_e。

The second aspect of the invention provides a distributed brake-by-wire system for a commercial vehicle, which comprises:

the upper layer module is used for acquiring a brake signal and vehicle state information; establishing a slip rate controller, confirming an actual slip rate and a target slip rate according to the vehicle state information, and distributing target braking torque for each driving wheel according to the actual slip rate and the target slip rate and combining the slip rate controller

A middle module connected with the upper module for establishing a braking cost function of the vehicle, the braking cost function being an expected total regenerative braking torque T_dExpected air brake torque of each of the drive wheelsAnd for combining said target braking torque of each of said drive wheelsObtaining the expected total regenerative braking torque T by extremizing a braking cost function_dExpected air brake torque of each of the drive wheels

A regenerative braking module for varying the total regenerative braking torque T based on the desired total regenerative braking torque_dIn combination with the maximum torque that the motor can provideAnd minimum torqueDetermining the actual output brake torque T of the electric machine_eAnd controlling the motor to output the actual braking torque T_e；

A pneumatic brake module for generating a desired pneumatic brake torque according to each of the desired pneumatic brake torquesAnd controlling the pneumatic braking system to work.

Preferably, the upper module includes a control unit;

the pneumatic braking system comprises an active braking valve, a double check valve, a relay valve and an ABS (anti-lock brake system) valve, wherein the active braking valve and the ABS valve are electronic valves and are both connected with the control unit, and the double check valve and the relay valve are pneumatic control valves; a first communication end of the active brake valve is communicated with a total air pressure loop of a vehicle, and a second communication end of the active brake valve is communicated with a first control end of the double check valve; the second control end of the double check valve is communicated with an air pressure valve of a brake pedal; and the communication end of the double check valve is communicated with one end of the relay valve, and the other end of the relay valve is communicated with the brake air chamber through the ABS valve.

According to the control method, the slip rate controller and the brake cost function are established, and a control strategy of layered control is combined, so that the actual slip rate of a vehicle is close to the target slip rate as much as possible through the slip rate controller, then the pneumatic brake torque and the regenerative brake torque are distributed by setting the brake cost function, the utilization of regenerative energy is realized, and the brake torque is distributed in a brake cost function mode, so that the maximum energy regeneration can be achieved; and the regenerative braking and the pneumatic braking work simultaneously in consideration of the delay of the pneumatic braking, and the delay of the pneumatic braking can be compensated by utilizing the regenerative braking, so that the stability and the safety of the vehicle braking are improved, and the problem that the vehicle stability and the maximum energy are incompatible is solved.

Other advantages of the present invention will be described in the detailed description, and those skilled in the art will understand the technical features and technical solutions presented in the description.

Drawings

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the figure:

fig. 1 is a flowchart of a preferred embodiment of a control method of a distributed brake-by-wire system of a commercial vehicle according to the present invention;

FIG. 2 is a brake boosting characteristic curve and a brake pressure reducing characteristic curve in the control method of the distributed brake-by-wire system of the commercial vehicle according to the present invention;

FIG. 3 is a flow chart of another preferred embodiment of the control method of the distributed brake-by-wire system of the commercial vehicle provided by the invention;

FIG. 4 is a system diagram of a preferred embodiment of the distributed brake-by-wire system of a commercial vehicle according to the present invention;

fig. 5 is a system diagram of another preferred embodiment of the distributed brake-by-wire system of the commercial vehicle provided by the invention.

Detailed Description

The present invention will be described below based on examples, but the present invention is not limited to only these examples. In the following detailed description of the present invention, certain specific details are set forth in order to avoid obscuring the nature of the present invention, well-known methods, procedures, and components have not been described in detail.

Further, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, what is meant is "including, but not limited to".

In the description of the present invention, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.

Therein, the textλ_i、λ_di、e_i、S_i、α_i、ω_i、R_i、F_zi、ΔP_i、P_i、P_i0In the above formula, i represents left front F L, right front FR, left rear R L, and right rear RR.

The invention provides a control method of a distributed wire control brake system of a commercial vehicle, which can be used for electric and hybrid vehicles, and particularly, the vehicle can only use a rear wheel as a driving wheel, and also can use four wheels as the driving wheels. As shown in fig. 1, the control method includes the steps of:

s1: acquiring a brake signal;

s2: acquiring vehicle state information;

s3: establishing a slip rate controller, and confirming an actual slip rate and a target slip rate according to vehicle state information;

s4: according to the actual slip rate and the target slip rate and in combination with a slip rate controller, distributing target brake torque for each driving wheelWherein i represents left front F L, right front FR, left rear R L, right rear RR,such asA target braking torque for the right rear wheel;

s5: establishing a braking cost function J for the vehicle, the braking cost function J being an expected total regenerative braking torque T for the vehicle_dExpected air brake torque of each driving wheelThen combining the target braking torque of each driving wheelObtaining the expected total regenerative braking torque T by extremizing the braking cost function J_dExpected air brake torque of each driving wheelUnderstandably, the total regenerative braking torque T is expected_dEqual to the sum of the expected regenerative braking torques of the drive wheels, e.g. total regenerative braking torque T in the embodiment where only two rear wheels are the drive wheels_dEqual to the sum of the expected regenerative braking torque of the right rear wheel and the expected regenerative braking torque of the left rear wheel, that is, by extremizing the braking cost function J, the sum T of the expected regenerative braking torque of the right rear wheel and the expected regenerative braking torque of the left rear wheel can be obtained_dAnd expected air brake torque of the right rear wheelAnd expected air brake torque of the left rear wheel

S6: based on expected total regenerative braking torque T_dIn combination with the maximum torque that the motor can provideAnd minimum torqueDetermining the actual output brake torque T of the electric machine_eAnd controlling the motor to output the actual brake output torque T_e(ii) a At the same time, according to each expected air braking torqueAnd controlling the pneumatic braking system to work.

The invention also provides a distributed brake-by-wire system of a commercial vehicle, which can work by using the control method, and as shown in fig. 4, the brake system comprises: the system comprises an upper layer module 1, a middle layer module 2, a regenerative braking module 3 and an air pressure braking module 4, wherein the upper layer module 1 is used for acquiring braking signals and vehicle state information; establishing a slip rate controller, confirming an actual slip rate and a target slip rate according to vehicle state information, and distributing target braking torque for each driving wheel according to the actual slip rate and the target slip rate and combining the slip rate controllerThe middle module 2 is connected to the upper module 1 for establishing a braking cost function J of the vehicle, which is the expected total regenerative braking torque T_dExpected air brake torque of each driving wheelAnd for combining the target braking torque of each driving wheelObtaining the expected total regenerative braking torque T by extremizing the braking cost function J_dExpected air brake torque of each driving wheelThe regenerative braking module 3 is used for predicting the total regenerative braking torque T according to the expected total regenerative braking torque_dIn combination with the maximum torque that the motor can provideAnd minimum torqueDetermining the actual output brake torque T of the electric machine_eThen controlling the motor to output the actual braking torque T_e(ii) a The pneumatic brake module 4 is used for braking torque according to each expected pneumatic brakeAnd controlling the pneumatic braking system to work.

According to the braking system and the control method, the slip rate controller and the braking cost function J are established, the control strategy of layered control is combined, the actual slip rate of the vehicle is firstly made to be close to the target slip rate as much as possible through the slip rate controller, then the air pressure braking torque and the regenerative braking torque are distributed through the braking cost function J, so that the utilization of regenerative energy is realized, and the braking torque is distributed in the mode of the braking cost function J, so that the maximum energy regeneration can be achieved; meanwhile, the invention takes the delay of the air pressure brake into consideration, so that the regenerative brake and the air pressure brake work simultaneously, and the delay of the air pressure brake can be compensated by utilizing the regenerative brake, thereby improving the stability and the safety of the vehicle brake.

Specifically, the vehicle state information in step S2 includes: coefficient of friction mu of road surface on which vehicle is running, mass m of vehicle, longitudinal velocity u_xAngular velocity omega of driving wheel_iRadius of driving wheel R_iRotational inertia of the drive wheel, longitudinal force F of the drive wheel_xiVertical force F of the driving wheel in the direction of its axis of rotation_ziSome of the state parameters may be provided or obtained by subsequent measurement when the vehicle leaves a factory, and some of the state parameters may be obtained by measurement of instruments such as a sensor in actual use, and the specific obtaining mode is not limited.

In order to make the actual slip ratio as close as possible to the target slip ratio, in one embodiment of the present invention, in step S3, the establishing slip ratio controller includes:

s31: setting a proportional integral model as formula (1):

S_i＝e_i+α_i∫e_idt， (1)

wherein e is_i＝λ_i-λ_di； (2)

S32: the slip rate controller is established as in equation (3):

wherein λ is_iIs the actual slip ratio, λ, of the vehicle_diSat is a saturation function for the target slip ratio of the vehicle, α_i、₁、₀、The coefficient can be preset according to the requirement so as to adjust the slip ratio controller to ensure that the braking effect of the braking system is better.

In this embodiment, step S4 includes:

s41: the integral model of the proportion is derived to obtain a reciprocal model

S42: make itObtaining target braking torque of each driving wheel

That is, i may be set to left front F L, right front FR, left rear R L, and right rear RR, respectively, to obtain the target braking torque of each drive wheelIn the steps, the static error of the slip rate can be eliminated as far as possible by setting the proportional-integral model, and meanwhile, the wheel speed can be reduced by setting the slip rate controller containing the saturation function satAnd the reciprocal of the proportional-integral model is equal to the set slip ratio controller, so that the actual slip ratio is closer to the target slip ratio in the target of the whole control method, and the utilization rate of the regenerated energy is further improved.

Specifically, the actual slip ratio λ_iIt can be calculated as the following equation (4):

target slip ratio lambda_diCalculated according to the following equation (5):

wherein u is_xIs the longitudinal speed, omega, of the vehicle_iIs the driving wheel angular velocity, R, of the vehicle_iIs the radius of the driving wheel of the vehicle; k_λThe coefficient is preset and can be obtained according to experiments; μ is the coefficient of friction of the road surface on which the vehicle is traveling;to utilize the coefficient of friction; m_threIs a yaw moment threshold for yaw control; l is the wheel track of the driving wheels of the vehicle, and if only two rear wheels are the driving wheels, the value is the wheel track of the left rear wheel and the right rear wheel; f_ziThe vertical force of the driving wheel in the direction of the rotating shaft of the driving wheel; f. of^-1The friction coefficient table is a preset friction coefficient table, and can be measured according to experiments; wherein the above-mentioned preset viscosity may be selected to be 0.5.

It is to be noted that, in the brake system and the control method of the invention, the vehicle is regarded as a rigid body, and only the longitudinal motion thereof is considered, and therefore, the kinetic equation of the vehicle is formula (7):

wherein, F_xiThe longitudinal force applied to the wheels is shown, and the right side of the formula is the sum of the longitudinal forces applied to each wheel (including the driving wheel and the non-driving wheel).

For a driving wheel, the rotational movement under the action of the longitudinal force and the braking torque can be expressed as formula (8):

the target braking torque can be obtained according to the formulas (1) to (8)Expression (9):

that is, the target braking torque can be obtained according to the formula (9) in step S4As in the embodiment where only two rear wheels are the drive wheels, the target braking torque of the left rear wheel can be found separatelyAnd target braking torque of the right rear wheelNote that in equation (9), ∑ F in equation (9) is calculated regardless of which drive wheel's target braking torque is calculated_xi(λ_i，F_zi) Is the sum of the longitudinal forces of all wheels, including the driven and non-driven wheels.

In the above embodiments, the braking cost function in step S5 can be specifically expressed as formula (10):

wherein the content of the first and second substances,an expected air brake torque for the drive wheel;a target braking torque for the drive wheel; t is_dIs the expected total regenerative braking torque;to maximize the regenerative efficiency of the braking energy and to ensure that the regenerative braking torque compensates for the lack of the pneumatic braking torque, it is set to be close to but less than the maximum value of the regenerative braking torqueConsidering that in a braking system having an ABS, if the regenerative braking torque is too large, the pneumatic braking system will not provide any torque, resulting in that the wheels will necessarily lock, therefore, the regenerative braking torque cannot be too large to exceed the target braking torqueSpecifically, the method can be selected according to formula (11);a maximum value of the regenerative braking torque, which is determined by the electric machine of the vehicle, generally selected as the rated output torque of the electric machine;for the reserve gap, it can be obtained experimentally, as a constant value.

In embodiments where only two rear wheels are the drive wheels, equation (11) is simplified to equation (12):

accordingly, the braking cost function is expressed as equation (12):

further, considering that a time-delayed response occurs due to a pressure variation amount in a pressure regulation period of each air brake, the above-mentioned brake cost function is expressed as formula (13),

and the pneumatic brake torque can be given in the predicted form according to equation (14):

wherein (K +1) represents the predicted value of the next control period, K represents the value of the current control period, and K_rIs a preset coefficient; delta P_aiIs the pressure variation of the driving wheel.

In a preferred embodiment of the present invention, in order to reduce the calculation load, the expected air brake torque is set within one control cycleExpected total regenerative braking torque T_dOptimal regenerative braking torqueAll are unchanged, so that an optimized braking energy function is obtained, and the expression is as shown in a formula (15):

in this embodiment, the pressure change amount Δ P_aiThe method can be obtained by the following method, specifically, the step S5 is preceded by the following steps:

s0: establishing a brake pressure increasing characteristic curve graph and a brake pressure reducing characteristic curve graph of a pneumatic brake system of each driving wheel, wherein the brake pressure increasing characteristic curve graph comprises a pressure increasing and maintaining period and a plurality of pressure variation of the pneumatic brake systemAnd the shortest time required for increasing each boost pressure variation, wherein the pressure reduction curve database comprises the pressure reduction and pressure maintaining period and a plurality of pressure variations of the pneumatic brake systemAnd the minimum time required to reduce each decompression pressure variation amount;

wherein m and n are min, 2, 3, … and max respectively; k_rIs a preset coefficient; delta P_aiThe amount of change in the pressure of the drive wheel corresponds to Δ P in the pressure increasing/reducing characteristic_a，

Specifically, the brake pressure increasing characteristic map and the brake pressure decreasing characteristic map may be obtained in a preset manner, and in a preferred embodiment, the step S0 includes a brake pressure increasing characteristic map obtaining step and a brake pressure decreasing characteristic map obtaining step, wherein,

the obtaining step of the brake boosting characteristic curve comprises the following steps:

s11: setting a pressurization time t1 and a pressurization and pressure maintaining period t2, wherein t2 is not less than t 1;

s12: periodically controlling the opening and closing of an air inlet valve of the brake air chamber according to a pressurizing and pressure maintaining period t2 until the pressure in the brake air chamber does not rise any more, and recording the pressure change of the brake air chamber in a time period t2 in each pressurizing and pressure maintaining period; in each pressure increasing and maintaining period t2, the air inlet valve is in an open state within the pressure increasing time t1, and the air inlet valve is in a closed state within the time t2-t 1;

s13: performing the steps S11 and S12 in a loop for a plurality of times, wherein each time the supercharging time t1 is longer than the last supercharging time t1, the supercharging and pressure maintaining period t2 is unchanged, that is, in the supercharging and pressure maintaining period t2, the opening time of the intake valve is gradually prolonged, and the closing time is gradually shortened;

s14: selecting a group of pressure data each time and subtracting the group of pressure data at the same time at the last time to obtain the boost pressure adjustment quantityI.e. the boost pressure adjustment amount in two adjacent dataThe pressure value of the first time is subtracted from the pressure value of the second time corresponding to the same moment; a brake boost characteristic map is then created, wherein the brake boost characteristic map is adjusted by the boost pressure in each caseAs ordinate, the actual time of each time is abscissa, as shown in fig. 2;

the brake decompression characteristic curve graph obtaining step comprises the following steps:

s15: setting a decompression time t3 and a decompression and pressure maintaining period t4, wherein t4 is more than or equal to t 3;

s16: the method comprises the steps of periodically controlling an exhaust valve of a brake air chamber to be opened and closed according to a pressure reducing and maintaining period t4 until the pressure in the brake air chamber does not decrease any more, and recording the pressure change of the brake air chamber in each pressure reducing and maintaining period t 4; in each pressure reducing and maintaining period t4, the exhaust valve is in an open state within the pressure reducing time t3, and the exhaust valve is in a closed state within the time t4-t 3;

s17: performing S15 and S16 in a circulating mode for multiple times, wherein the decompression time t3 of each time is longer than the last decompression time t3, namely the opening time of the exhaust valve is gradually prolonged and the closing time is gradually shortened in the decompression and pressure maintaining period t 4;

s18: selectingSubtracting the group of pressure data from the group of pressure data at the same time to obtain the adjustment amount of the reduced pressureI.e. the amount of adjustment of the pressure reduction pressure in two adjacent dataThe pressure value of the second time corresponding to the same time is subtracted by the pressure value of the first time; then, a brake decompression characteristic curve chart is established, wherein the amount of decompression pressure adjustment is carried out on the brake decompression characteristic curve chart according to each decompression pressure adjustment amountAs the ordinate, the actual time of each time is the abscissa, as shown in fig. 2.

The pressure increasing and maintaining period t2 and the pressure reducing and maintaining period t4 can be 30ms, and the pressure increasing time t1 and the pressure reducing time t3 can respectively start from 1ms and increase at intervals of 1 ms.

The boost pressure adjustment amount in the brake boost characteristic curve obtained by the method for obtaining the boost/decompression characteristicMay be exhaustive, and the pressurization time t1 may also be exhaustive, and similarly, the amount of pressure reduction pressure adjustment in the brake pressure reduction characteristic curveAnd decompression time t3 may also be exhaustive, for convenience, the boost time t1 and the decompression time t3 are collectively referred to as durations, and the durations of opening the intake or exhaust valves are taken as examples of j cycles of boost and decompression, respectively Amount of pressure adjustment Therefore, the pressure increasing and reducing characteristics can be expressed as: delta P_a＝f(P_k，u_k，t_a) Wherein P is_kFor braking the pressure in the air chamber u_kFor the pressure regulation state, it is possible to use +1 for pressurization, 0 for pressure holding and-1 for depressurization. In this embodiment, the above Δ P_aiIs namely delta P_aMay be selected from Here, values are taken.

In the step of acquiring the brake pressure reduction map, the intake valve and the exhaust valve are initially closed at each test, and the intake valve and the exhaust valve are initially opened at the start of each cycle.

It is to be understood that, in the step of obtaining the brake boost characteristic map, the pressure in the brake chamber is gradually increased, and therefore, the respective boost pressure adjustment amountsIs greater than zero; in the step of acquiring the brake decompression characteristic map, the pressure in the brake chamber is gradually reduced, and therefore, the respective decompression pressure adjustment amountsIs less than zero.

In fact, for the same vehicle or even the same model of vehicle, the characteristics of the brake chambers of the driving wheels are basically the same, so after the brake pressure increasing characteristic curve and the brake pressure reducing characteristic curve of the brake chamber corresponding to one of the driving wheels are obtained by the method, the other driving wheels can directly adopt the two curves.

Referring to fig. 3, after obtaining the above-described brake pressure increasing characteristic map and brake pressure decreasing characteristic map, in step S6, the braking torque is applied according to each expected air pressureThe method for controlling the work of the air pressure braking system specifically comprises the following steps: performing the following steps for each drive wheel:

s81: braking torque according to expected air pressureDetermining a target pressure P_iThe value may be determined according to the braking demand of the vehicle, may be an active braking demand (such as braking by the vehicle control center detecting the presence of an obstacle in the course of traveling in automatic driving), or may be a demand for the driver to press the brake pedal to request braking, and may specifically be calculated according to equation (16);

wherein, K_iIs a conversion coefficient;

s82: obtaining the actual pressure P of the brake chamber_i0(is the target pressure P in S81_iActual pressure of the corresponding wheel), and specifically, the actual pressure can be obtained by a pressure sensor arranged in a brake chamber of the vehicle, and the pressure difference Δ P between the actual pressure and the target pressure can be calculated_i＝P_i-P_i0；

S83: determining the pressure difference Δ P_iWhether or not it is larger than the minimum decompression pressure adjustment amount in the brake decompression characteristic diagramAnd is less than the minimum boost pressure adjustment in the brake boost characteristic curveIs determined promptlyIf not, if yes, executing S84; otherwise, executing S850;

s84: maintaining the pressure;

s850: and controlling the opening and closing of an air inlet valve and an air outlet valve of the brake air chamber according to the pressure change rule in the brake pressure increasing characteristic curve chart and the brake pressure reducing characteristic curve chart.

Preferably, step S850 specifically includes:

s85: determining the pressure difference Δ P_iIf it is greater than 0, determine Δ P_i>If 0 is true, if greater than 0, it indicates that the brake chamber needs to be pressurized, so the intake valve needs to be opened and the exhaust valve needs to be closed, specifically executed according to S86; if the pressure is less than 0, the pressure in the brake chamber needs to be reduced, so that the exhaust valve needs to be opened and the intake valve needs to be closed, and the operation is specifically executed according to S87;

s86: determining the pressure difference Δ P_iWhether or not the maximum boost pressure adjustment in the brake boost characteristic map is exceededIn thatWhen it is greater than 0, the judgment is madeIf so, it is indicated that the pressure in the brake air chamber is too small and exceeds the maximum pressure adjustment range calibrated in the brake pressure increasing characteristic curve chart, at this time, the pressure in the brake air chamber needs to be adjusted in the whole pressure increasing and maintaining period, so that more air can rapidly enter the brake air chamber, therefore, the air inlet valve of the brake air chamber is opened for the first preset time all the time to obtain rapid pressure response, and then the process returns to S82; if not, the pressure in the brake air chamber needs to be adjusted slightly, and the pressure difference delta P can be determined according to the brake pressure increasing characteristic curve chart_iCorresponding minimum time, i.e. from the brake boost characteristic curveSelecting and delta P_iCorresponding Δ P_aAnd further from and Δ P_aCorresponding multiple supercharging time t_aSelecting the minimum supercharging time t_aAs the minimum time and in accordance with the minimum supercharging time t_a(i.e., t1) and the pressure increasing and maintaining period t2, the method is that the air inlet valve of the brake chamber is opened periodically and then continues for a second preset time so as to enable the brake chamber to reach the target pressure P in the shortest time_iThen returns to S82;

s87: determining the pressure difference Δ P_iWhether or not the maximum decompression pressure adjustment in the brake decompression characteristic diagram is exceededIn thatWhen less than 0, it is judgedIf so, it is indicated that the pressure in the brake air chamber is too large and exceeds the maximum pressure adjustment range calibrated in the brake pressure reduction characteristic curve chart, at this time, the pressure in the brake air chamber needs to be adjusted in the whole pressure reduction and pressure maintaining period, so that the brake air chamber rapidly discharges more air, therefore, the exhaust valve of the brake air chamber is opened for a third preset time all the time to obtain rapid pressure response, and then the process returns to S82; if not, the pressure in the brake air chamber needs to be adjusted slightly, and the pressure difference delta P can be determined according to the brake decompression characteristic curve chart_iCorresponding shortest time, i.e. selecting from the brake pressure reduction characteristic diagram_iCorresponding Δ P_aAnd further from and Δ P_aCorresponding multiple decompression time t_aSelecting the minimum decompression time t_a(i.e., t3) as a minimum time, i.e., an optimum time for continuing to open the exhaust valve, and then according to the minimum decompression time t_a(i.e., t3), the pressure reducing and maintaining period t4 is set such that the exhaust valve of the brake chamber is periodically opened for a fourth preset time, and then returns to S82.

The air pressure in the brake air chamber is adjusted by adopting different control methods according to the situations, so that the pressure response in the brake air chamber is more timely, and the whole brake pressure regulation and control method is more accurate.

The second preset time is greater than or equal to the pressure increasing and maintaining period, and the fourth preset time is greater than or equal to the pressure reducing and maintaining period. Alternatively, the first preset time may be greater than or equal to the pressure increasing and maintaining period, and the third preset time may be greater than or equal to the pressure reducing and maintaining period. When selecting, the first preset time, the second preset time, the third preset time and the fourth preset time may be determined as needed, and the four times may be equal, only two or three of the four times may be equal, or all four times are different.

In the above steps, unless otherwise specified, the exhaust valve is in a closed state when the intake valve is opened for the same brake chamber; when the exhaust valve is opened, the intake valve is in a closed state; in the process of pressurization, the exhaust valve is always in a closed state; during decompression, the inlet valve is used in the closed state.

In addition, in step S6, the air brake torque is adjusted according to each expected air brake torqueControlling the operation of the pneumatic brake system is not limited to the above-described embodiments, and the pneumatic brake system may be controlled in other ways, such as in determining the target pressure P_iAnd obtaining the actual pressure P of the brake chamber_i0Then, the time required to open the intake valve or the exhaust valve can be directly calculated from the difference between the two, and then the intake valve or the exhaust valve is opened for that time.

For expected total regenerative braking torque T_dElectric motors are desirable because regenerative braking of the motor output causes a loss of torque during transmission to the drive wheels, and the torque output by the motor is typically distributed to the drive wheels through a gearbox and differentialDesired braking torque of machine outputEqual to the expected total regenerative braking torque T_dAnd the sum of the loss torque.

Specifically, in a vehicle with a differential, the regenerative braking torque on the axles may be expressed as equation (16):

wherein, J_eIs the moment of inertia of the motor rotor; i.e. i_gThe gear ratio of the gear box on the driving shaft; i.e. i₀Is the gear ratio of the differential; j. the design is a square_gIs the moment of inertia of the gearbox; j. the design is a square₀Is the moment of inertia of the differential case; omega_dη is the transmission efficiency;

thus, the desired braking torque output by the motorCan be expressed as formula (17):

with continued reference to FIG. 3, in step S6, the total regenerative braking torque T is predicted based on the expected total regenerative braking torque T_dIn combination with the maximum torque that the motor can provideAnd minimum torqueDetermining the actual output brake torque T of the electric machine_eAnd controlling the motor to output the actual braking torque T_eThe method comprises the following steps:

s71: based on expected total regenerative braking torque T_dDetermining a desired braking torque output by an electric machineSpecifically, the calculation can be carried out according to the formula (17);

s72: obtaining the maximum torque that the motor can provideAnd minimum torque

S73: determining a desired braking torque output by an electric machineWith maximum torqueMinimum torqueThe size of (2):

if it isThen

If it isThen

If it isThen

Wherein the maximum torqueMinimum torqueAngular velocity omega with the motor_eIn connection with this, it can be expressed as formula (18), and the angular velocity ω of the motor_eCan be expressed as formula (19):

s74: controlling the motor to output the actual braking torque T_e。

Outputting actual braking torque T at motor_eAfter the torque is applied, the torque loss of the transmission shaft is removed, and the torque is distributed to the wheel end of each driving wheel through a differential mechanism and finally transmitted to a vehicle driving axle for braking.

Referring to fig. 5, in the above-described brake system, the upper module 1 includes a control unit 101; the air pressure braking system comprises an active braking valve 5, a double check valve 6, a relay valve 7 and an ABS valve 8, wherein the active braking valve 5 and the ABS valve 8 are electronic valves and are connected with a control unit 101, and the double check valve 6 and the relay valve 7 are air pressure control valves; a first communication end of the active brake valve 5 is communicated with a main air pressure loop 9 of the vehicle, and a second communication end is communicated with a first control end of the double check valve 6; the second control end of the double check valve 6 is communicated with a pneumatic valve of a brake pedal 10; the communication end of the double check valve 6 is communicated with one end of the relay valve 7, and the other end of the relay valve 7 is communicated with the brake air chamber through the ABS valve 8.

In fig. 5, a motor 11 of a vehicle transmits an output torque to a wheel shaft via an AMT transmission 12 and a differential 13, and then to left and right rear wheels. As will be appreciated, the regenerative braking module 3 includes a motor controller 301 for controlling the operation of the motor, which is connected to the control unit 101.

With continued reference to fig. 5, during active braking, when there is a demand for deceleration, the active brake valve 5 is first opened; then, since the pressure (reservoir pressure) on the active brake valve 5 side is greater than the brake pedal 10 side (zero), the gas in the gas tank (gas tank in the vehicle pneumatic brake system) is directly transferred to the relay valve 7 through the double check valve 6. Then, the ABS valve 8 takes a large flow of gas and transmits it to the brake chamber, and the ABS valve 8 switches between pressure rising, lowering, and holding states in accordance with pressure feedback from the pressure sensor to adjust the air pressure in the brake chamber. During driver-operated braking, the driver's deceleration request is measured by means of a displacement sensor. When the brake pedal 10 is depressed, the active brake valve 5 opens and the brake chamber pressure is regulated in response to the deceleration demand in the same manner as the active braking process. Upon failure of any electronic component, the control unit 101 immediately cuts off the control of the ABS valve 8 and the active brake valve 5, and therefore the control gas from the brake pedal 10 is applied to the relay valve 7 because its pressure (non-zero) is greater than that on the active brake valve 5 side (zero). In this case, the deceleration can be achieved by a completely mechanical (i.e., ABS) method.

For regenerative braking, it is a supplement to pneumatic braking during active braking and driver braking. The braking torque in the electric machine is regulated directly by the electric machine controller 301 and transmitted via the AMT gearbox 12 to the differential 13, which differential 13 distributes the regenerative braking torque to the left and right driving wheels, which means that the regenerative braking torque is coupled to each other on both sides of the driving axle.

It will be appreciated by those skilled in the art that the above-described preferred embodiments may be freely combined, superimposed, without conflict.

It will be understood that the embodiments described above are illustrative only and not restrictive, and that various obvious and equivalent modifications and substitutions for details described herein may be made by those skilled in the art without departing from the basic principles of the invention.