阅读说明：本技术 电子液压-电子机械的混合式汽车线控制动控制系统 (Electronic hydraulic-electronic mechanical hybrid automobile brake-by-wire control system ) 是由 孙骏 张世斌 张宸维 白先旭 于 2021-08-30 设计创作，主要内容包括：本发明公开了一种电子液压-电子机械的混合式汽车线控制动控制系统,包括：传感器子系统、EHB、EMB、上层控制器和下层控制器；其中,上层控制器根据传感器子系统反馈的系统状态信息,获取车辆的运动姿态,识别驾驶员的制动意图,对四个车轮的制动力进行单独分配；下层控制器控制调节EHB的输入目标轮缸压力和EMB的输入目标夹紧力,实现单独对四个车轮的制动力的精准控制。本发明能单独地对四个车轮进行制动力的控制,最大程度上利用路面附着系数,以获取最高的制动效率。(The invention discloses an electronic hydraulic-electronic mechanical hybrid automobile brake-by-wire control system, which comprises: the system comprises a sensor subsystem, an EHB, an EMB, an upper controller and a lower controller; the upper layer controller acquires the motion attitude of the vehicle according to the system state information fed back by the sensor subsystem, identifies the braking intention of a driver and independently distributes the braking force of the four wheels; and the lower layer controller controls and adjusts the input target wheel cylinder pressure of the EHB and the input target clamping force of the EMB, so that the independent accurate control of the braking force of the four wheels is realized. The invention can independently control the braking force of the four wheels, and utilizes the road adhesion coefficient to the maximum extent to obtain the highest braking efficiency.)

1. An electro-hydraulic-electro-mechanical hybrid automotive brake-by-wire control system, comprising: the system comprises a sensor subsystem, an EHB, an EMB, an upper controller and a lower controller;

the sensor subsystem includes: the device comprises a steering wheel corner sensor, a front wheel corner sensor, a brake pedal displacement sensor, a vehicle speed sensor, a rotating speed sensor, a pressure sensor and a clamping force sensor;

the EHB includes: a hydraulic pump, a linear electromagnetic valve and a brake wheel cylinder;

the EMB includes: the device comprises a motor, a transmission speed reducing mechanism and an actuating mechanism;

the upper layer controller includes: the system comprises a target braking force calculation module, an additional yaw moment calculation module and a braking force distribution subsystem; wherein the braking force distribution subsystem comprises: the left and right braking force distribution modules and the front and rear wheel braking force distribution modules;

the lower layer controller includes: the system comprises a front and rear axle braking force coordination controller, an EHB pressure following PID controller and an EMB pressure following PID controller;

when the driver steps on the brake pedal to perform deceleration braking, the brake pedal displacement sensor acquires the displacement of the brake pedal and transmits the displacement to the target braking force calculation module for judgment, and if the displacement is detected, the target braking force calculation module performs judgmentThe displacement of the movable pedal is within a preset time t₀Up to the maximum displacement s of the brake pedal_maxIf the braking intention is judged to be emergency braking by the target braking force calculation module, and the target braking force F of the whole vehicle is calculated_XbSetting the ideal maximum braking force which can be provided for the vehicle on the ground; if the displacement of the brake pedal is within the preset time t₀Failure to reach the maximum displacement s of the brake pedal_maxIf the braking intention is normal braking, the target braking force calculation module judges that the braking intention is normal braking, obtains the braking intensity expected by the driver, and obtains the required braking force according to the braking intensity to be used as the target braking force F of the whole vehicle_Xb；

The additional yaw moment calculation module identifies a braking path expected by a driver through a steering wheel angle acquired by the steering wheel angle sensor and a vehicle speed acquired by the vehicle speed sensor, and calculates an additional yaw moment delta T required for enabling the vehicle to reach a target driving direction of the driver: when the steering wheel angle acquired by the steering wheel angle sensor is 0 degrees, the braking intention of the driver is straight braking, and delta T is set to be zero; when the steering wheel angle is not 0 degrees, the braking intention is curve braking, and delta T is calculated according to the steering wheel angle and the vehicle speed;

the braking force distribution subsystem distributes left and right braking forces by using the left and right braking force distribution modules according to target braking force and additional yaw moment delta T of the whole vehicle to obtain left and right braking force distribution results, distributes front and rear wheel braking forces by using the front and rear wheel braking force distribution modules according to the left and right braking force distribution results to obtain distribution results of front and rear four single-wheel braking forces in the left and right sides, and converts the single-wheel braking forces into corresponding target pressure p of a brake wheel cylinder in the EHB by using the relation between ground braking force and brake clamping force_tarAnd target clamping force F of actuator in EMB_tar；

The front and rear axle braking force coordination controller receives the target pressure p of the brake wheel cylinder in the EHB from the upper layer controller_tarAnd target clamping force F of actuator in EMB_tarCalculating and adjusting the front axle target braking force and the rear axle target braking force:

for the front axle, the front axle actual braking force P is judged_{f_act}Whether or not the front axle target braking force P is reached_{f_tar}If P is_{f_act}＜P_{f_tar}Then let P_{f_ref}＝P_{f_max}(ii) a If P_{f_act}≥P_{f_tar}Then let P_{f_ref}＝P_{f_tar}(ii) a Wherein, P_{f_ref}Indicating front axle reference brake force, P_{f_max}Represents the maximum pressure that the front axle brake can provide;

for the rear axle, the actual rear axle braking force P is determined_{r_act}Whether or not the rear axle target braking force P is to be achieved_{r_tar}If P is_{r_act}＜P_{r_tar}-x_rThen let P_{r_ref1}＝P_{r_max}(ii) a If P_{r_act}≥P_{r_tar}-x_rThen let P_{r_ref1}＝P_{r_act}(ii) a Wherein x is_rIndicates a preset value, P_{r_ref1}Indicating the rear axle reference braking force, P, of the intermediate stage_{r_max}Indicating the maximum pressure that the rear axle brake can provide; then, the actual braking force P of the front axle is judged_{f_act}Whether or not the front axle target braking force P is to be achieved_{f_tar}If P is_{f_act}＜P_{f_tar}-x_fThen let P_{r_ref2}＝P_{r_ref1}(ii) a If P_{f_act}≥P_{f_tar}-x_fThen let P_{r_ref2}＝P_{r_tar}(ii) a Wherein x is_fIndicates another preset value, P_{r_ref2}Indicating the final rear axle reference brake force; finally P is added_{f_ref}、P_{r_ref2}The front axle brake and the rear axle brake are respectively input.

2. The electro-hydraulic-electro-mechanical hybrid vehicle brake-by-wire control system according to claim 1, wherein the target braking force calculation module calculates the target braking force of the entire vehicle as follows:

if the braking intention of the driver is recognized as emergency braking, the target braking force F of the whole vehicle_XbThe maximum longitudinal braking force which can be acted on the vehicle by the ground under the condition that the vehicle is not unstable;

if regular braking is identified, thenRecording the longitudinal braking strength as z, and obtaining the target braking force F of the whole vehicle_XbMzg, where m is the total mass of the vehicle and g is the acceleration of gravity.

3. The electro-hydraulic-electro-mechanical hybrid vehicle brake-by-wire control system according to claim 2, wherein the brake force distribution subsystem distributes the four front and rear single-wheel brake forces on the left and right sides as follows:

when the driver's braking intention is straight braking:

step a1, calculating the maximum braking force which can be provided by the ground to each wheel;

the peak adhesion coefficients of the four wheels of the left front wheel, the left rear wheel, the right front wheel and the right rear wheel are respectively set asThe vertical loads of the four wheels are respectively F_{Z_lf}、F_{Z_lr}、F_{Z_rf}、F_{Z_rr}So as to obtain the maximum ground braking force which can be formed by a single wheel ofi＝lf、lr、rf、rr；

Step a2, calculating the target braking force of the left side and the right side;

let the sum of the left braking forces be F_lThe sum of the right braking forces is F_r；

Under emergency braking, let F_l＝F_r＝min{F_{μ_lf}+F_{μ_lr},F_{μ_rf}+F_{μ_rr}}；

Under normal braking, let

Step a3, calculating the target braking force of a single wheel;

under emergency braking, if F_{μ_lf}+F_{μ_lr}≤F_{μ_rf}+F_{μ_rr}Obtaining F_l＝F_r＝F_{μ_lf}+F_{μ_lr}The target braking forces of the four wheels of the left front wheel, the left rear wheel, the right front wheel and the right rear wheel are respectively F_lf＝F_{μ_lf}、F_lr＝F_{μ_lr}、If F_{μ_lf}+F_{μ_lr}＞F_{μ_rf}+F_{μ_rr}Obtaining F_l＝F_r＝F_{μ_rf}+F_{μ_rr}The target braking forces of the four wheels of the left front wheel, the left rear wheel, the right front wheel and the right rear wheel are respectivelyF_rf＝F_{μ_rf}、F_rr＝F_{μ_rr}；

Under the conventional braking, the single-wheel target braking forces of the four wheels of the left front wheel, the left rear wheel, the right front wheel and the right rear wheel are respectively

When the driver's braking intention is curve braking:

step b1, calculating the extra longitudinal braking force Δ F required to create the additional yaw moment Δ T and determining the object to be applied: when the vehicle brakes on a curve, if excessive steering occurs, extra longitudinal braking force delta F is applied to the outer front wheel, and if understeer occurs, extra longitudinal braking force delta F is applied to the inner rear wheel;

step b2, calculating the maximum braking force which can be provided by the ground to each wheel;

the peak adhesion coefficients of four wheels of an inner front wheel, an inner rear wheel, an outer front wheel and an outer rear wheel are respectively set asThe vertical loads of the four wheels are respectively F_{Z_if}、F_{Z_ir}、F_{Z_of}、F_{Z_or}Thereby obtaining the maximum ground that a single wheel can formThe flour power isj＝if、ir、of、or；

Step b3, calculating the inner and outer target braking force;

let the sum of the longitudinal braking forces on the inside be F_iThe sum of the outside longitudinal braking forces is F_oAnd F is_i、F_oThe front wheel rotation angle collected by the front wheel rotation angle sensor is delta without delta F;

if excessive steering occurs, under emergency braking, let F_i＝F_o＝min{F_{μ_if} cosδ+F_{μ_ir},F_{μ_of} cosδ+F_{μ_or}- Δ F }; under normal braking, let

If understeer occurs, under emergency braking, let F_i＝F_o＝min{F_{μ_if} cosδ+F_{μ_ir}-ΔF,F_{μ_of} cosδ+F_{μ_or}}; under normal braking, let

Step b4, calculating the target braking force of the single wheel;

if excessive steering occurs, under emergency braking, if F_{μ_if} cosδ+F_{μ_ir}≥F_{μ_of} cosδ+F_{μ_or}Δ F, target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively set to F_of＝F_{μ_of}、F_or＝F_{μ_or}(ii) a If F_{μ_if} cosδ+F_{μ_ir}＜F_{μ_of} cosδ+F_{μ_or}Δ F, the target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively made to be F_if＝F_{μ_if}、F_ir＝F_{μ_ir}、

Under the conventional braking, the single-wheel target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively set as

If understeer occurs, under emergency braking, if F_{μ_if} cosδ+F_{μ_ir}-ΔF≤F_{μ_of} cosδ+F_{μ_or}Respectively setting the target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel to F_if＝F_{μ_if}、F_ir＝F_{μ_ir}、If F_{μ_if}cosδ+F_{μ_ir}-ΔF＞F_{μ_of} cosδ+F_{μ_or}The target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively set toF_of＝F_{μ_of}、F_or＝F_{μ_or}；

Under the conventional braking, the single-wheel target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively set as

4. The electro-hydraulic-electro-mechanical hybrid vehicle brake-by-wire control system according to claim 1,

the EHB pressure follows the target pressure p of the brake wheel cylinder by the PID controller_tarAnd the actual pressure p acquired by the pressure sensor_actComparing, performing pressure ring PID control on the obtained deviation, and outputting the target current I of the linear solenoid valve_tarThen the target current I is set_tarWith the actual current I_actComparing, and after carrying out current PID control on the obtained deviation of the two, outputting a PWM value and inputting the PWM value into a linear electromagnetic valve so as to control the opening of the linear electromagnetic valve, and further controlling the flow of brake fluid provided by the hydraulic pump entering and exiting a brake wheel cylinder, thereby realizing pressure following;

the EMB pressure follows the PID controller to set the target clamping force F of the actuator_tarActual clamping force F collected by clamping force sensor_actComparing the two values, and performing PID control on the obtained deviation of the two values to output the target rotation speed theta of the motor_tarThen the target rotation speed theta is set_tarAnd the actual rotating speed theta acquired by the rotating speed sensor_actComparing, and performing PID control on the obtained deviation of the two, and outputting a target current i_tarThen the target current i_tarAnd the actual current i_actAnd comparing, performing current loop PID control on the obtained deviation of the two, and outputting a target torque to the EMB executing mechanism through the transmission speed reducing mechanism so as to realize pressure following.

Technical Field

The invention belongs to the technical field of vehicle brake-by-wire control, and particularly relates to an electronic hydraulic-electronic mechanical hybrid automobile brake-by-wire control system which utilizes respective road adhesion coefficients of four wheels to the maximum extent to coordinate and control the braking force of an electronic hydraulic brake and an electronic mechanical brake so as to obtain the highest braking efficiency.

Background

In recent years, "motorization, intellectualization, networking and sharing" of automobiles has attracted wide attention worldwide, and the technology thereof is rapidly developed and is regarded as an important strategic opportunity for the development of the automobile industry in China. Automatic driving is becoming the main development direction of intellectualization and networking in the current automobile field. The brake-by-wire system is one of key core systems of an intelligent automobile, can complete the accurate and rapid control of active braking and braking pressure which cannot be realized by a traditional braking system, and the maturity of the brake-by-wire technology influences the final landing and mass production of automatic driving to a great extent.

The brake-by-wire system mainly comprises two different braking modes, namely an electro-hydraulic brake (EHB) and an electro-mechanical brake (EMB), wherein the two different braking modes have advantages and disadvantages respectively. In a hybrid braking system based on EHB-EMB, considering that load transfer of front and rear axles occurs during braking of an automobile, braking force requirements of the front and rear axles are different, EHB is adopted for front wheels, and EMB is adopted for rear wheels (ZL201711268000.X, ZL201611241247.8 and ZL 202121711099.8). The front wheel adopts an EHB system, so that the braking force of a single wheel of the front wheel can be accurately adjusted, and the requirement of brake failure backup can be met; the rear wheel adopts the EMB, so that a brake pipeline on an automobile chassis can be simplified, the brake response speed and the control precision are improved, and meanwhile, the electronic parking brake is favorably realized.

The conventional braking force distribution curve is a beta straight line with a fixed ratio of the braking force of the front axle and the braking force of the rear axle, and the ground adhesion coefficient cannot be well utilized. In order to avoid the locking of the rear wheel, various hydraulic regulating valves, such as a proportional valve, a pressure limiting valve and the like, are provided, but the effect is still not ideal.

In the brake-by-wire system, the electric drive element replaces the traditional hydraulic brake or air brake actuating element, and the brake actuators of the four wheels can realize independent braking and control. The distribution of braking force is particularly important, and an unreasonable distribution strategy can cause dangerous working conditions such as tail flicking, sideslip and loss of directional stability.

The braking force distribution strategy based on the slip ratio is a better distribution method, most of the existing braking force distribution strategies are directed at a hydraulic braking system, the braking force control strategy facing a brake-by-wire system is still in a starting stage, and the optimal braking force is not obtained so as to obtain the highest braking efficiency.

Disclosure of Invention

The invention provides an electronic hydraulic-electronic mechanical hybrid automobile brake-by-wire control system for overcoming the defects in the prior art, aiming at the characteristics of EHB and EMB and combining the respective vertical loads and road surface conditions of four wheels, the four wheels can be independently controlled in braking force, and therefore the highest braking efficiency can be obtained by utilizing the braking force to the maximum extent.

In order to solve the technical problems, the invention adopts the following technical scheme:

the invention relates to an electronic hydraulic-electronic mechanical hybrid automobile brake-by-wire control system which is characterized by comprising the following components: the system comprises a sensor subsystem, an EHB, an EMB, an upper controller and a lower controller;

the sensor subsystem includes: the device comprises a steering wheel corner sensor, a front wheel corner sensor, a brake pedal displacement sensor, a vehicle speed sensor, a rotating speed sensor, a pressure sensor and a clamping force sensor;

the EHB includes: a hydraulic pump, a linear electromagnetic valve and a brake wheel cylinder;

the EMB includes: the device comprises a motor, a transmission speed reducing mechanism and an actuating mechanism;

the upper layer controller includes: the system comprises a target braking force calculation module, an additional yaw moment calculation module and a braking force distribution subsystem; wherein the braking force distribution subsystem comprises: the left and right braking force distribution modules and the front and rear wheel braking force distribution modules;

the lower layer controller includes: the system comprises a front and rear axle braking force coordination controller, an EHB pressure following PID controller and an EMB pressure following PID controller;

when a driver steps on a brake pedal to perform deceleration braking, the brake pedal displacement sensor collects the displacement of the brake pedal and transmits the displacement to the target braking force calculation module for judgment, and if the displacement of the brake pedal is within a preset time t₀Up to the maximum displacement s of the brake pedal_maxIf the braking intention is judged to be emergency braking by the target braking force calculation module, and the target braking force F of the whole vehicle is calculated_XbSetting the ideal maximum braking force which can be provided for the vehicle on the ground; if the displacement of the brake pedal is within the preset time t₀Failure to reach the maximum displacement s of the brake pedal_maxIf the braking intention is normal braking, the target braking force calculation module judges that the braking intention is normal braking, obtains the braking intensity expected by the driver, and obtains the required braking force according to the braking intensity to be used as the target braking force F of the whole vehicle_Xb；

The additional yaw moment calculation module identifies a braking path expected by a driver through a steering wheel angle acquired by the steering wheel angle sensor and a vehicle speed acquired by the vehicle speed sensor, and calculates an additional yaw moment delta T required for enabling the vehicle to reach a target driving direction of the driver: when the steering wheel angle acquired by the steering wheel angle sensor is 0 degrees, the braking intention of the driver is straight braking, and delta T is set to be zero; when the steering wheel angle is not 0 degrees, the braking intention is curve braking, and delta T is calculated according to the steering wheel angle and the vehicle speed;

the braking force distribution subsystem distributes left and right braking forces by using the left and right braking force distribution modules according to target braking force and additional yaw moment delta T of the whole vehicle to obtain left and right braking force distribution results, distributes front and rear wheel braking forces by using the front and rear wheel braking force distribution modules according to the left and right braking force distribution results to obtain distribution results of front and rear four single-wheel braking forces in the left and right sides, and converts the single-wheel braking forces into corresponding target pressure p of a brake wheel cylinder in the EHB by using the relation between ground braking force and brake clamping force_tarAnd target clamping force F of actuator in EMB_tar；

The front and rear axle braking force coordination controller receivesTarget pressure p of brake wheel cylinder in EHB from upper controller_tarAnd target clamping force F of actuator in EMB_tarCalculating and adjusting the front axle target braking force and the rear axle target braking force:

for the front axle, the front axle actual braking force P is judged_{f_act}Whether or not the front axle target braking force P is reached_{f_tar}If P is_{f_act}＜P_{f_tar}Then let P_{f_ref}＝P_{f_max}(ii) a If P_{f_act}≥P_{f_tar}Then let P_{f_ref}＝P_{f_tar}(ii) a Wherein, P_{f_ref}Indicating front axle reference brake force, P_{f_max}Represents the maximum pressure that the front axle brake can provide;

for the rear axle, the actual rear axle braking force P is determined_{r_act}Whether or not the rear axle target braking force P is to be achieved_{r_tar}If P is_{r_act}＜P_{r_tar}-x_rThen let P_{r_ref1}＝P_{r_max}(ii) a If P_{r_act}≥P_{r_tar}-x_rThen let P_{r_ref1}＝P_{r_act}(ii) a Wherein x is_rIndicates a preset value, P_{r_ref1}Indicating the rear axle reference braking force, P, of the intermediate stage_{r_max}Indicating the maximum pressure that the rear axle brake can provide; then, the actual braking force P of the front axle is judged_{f_act}Whether or not the front axle target braking force P is to be achieved_{f_tar}If P is_{f_act}＜P_{f_tar}-x_fThen let P_{r_ref2}＝P_{r_ref1}(ii) a If P_{f_act}≥P_{f_tar}-x_fThen let P_{r_ref2}＝P_{r_tar}(ii) a Wherein x is_fIndicates another preset value, P_{r_ref2}Indicating the final rear axle reference brake force; finally P is added_{f_ref}、P_{r_ref2}The front axle brake and the rear axle brake are respectively input.

The electronic hydraulic-electronic mechanical hybrid automobile brake-by-wire control system is also characterized in that the target braking force calculation module calculates the target braking force of the whole automobile according to the following process:

if the braking intention of the driver is recognized as emergency braking, the target braking force F of the whole vehicle_XbThe maximum longitudinal braking force which can be acted on the vehicle by the ground under the condition that the vehicle is not unstable;

if the conventional braking is identified, the longitudinal braking strength is recorded as z, and the target braking force F of the whole vehicle is obtained_XbMzg, where m is the total mass of the vehicle and g is the acceleration of gravity.

The braking force distribution subsystem distributes the braking force of four front and rear single wheels on the left and right sides according to the following processes:

when the driver's braking intention is straight braking:

step a1, calculating the maximum braking force which can be provided by the ground to each wheel;

the peak adhesion coefficients of the four wheels of the left front wheel, the left rear wheel, the right front wheel and the right rear wheel are respectively set asThe vertical loads of the four wheels are respectively F_{Z_lf}、F_{Z_lr}、F_{Z_rf}、F_{Z_rr}So as to obtain the maximum ground braking force which can be formed by a single wheel ofi＝lf、lr、rf、rr；

Step a2, calculating the target braking force of the left side and the right side;

let the sum of the left braking forces be F_lThe sum of the right braking forces is F_r；

Under emergency braking, let F_l＝F_r＝min{F_{μ_lf}+F_{μ_lr},F_{μ_rf}+F_{μ_rr}}；

Under normal braking, let

Step a3, calculating the target braking force of a single wheel;

under emergency braking, if F_{μ_lf}+F_{μ_lr}≤F_{μ_rf}+F_{μ_rr}Obtaining F_l＝F_r＝F_{μ_lf}+F_{μ_lr}The target braking forces of the four wheels of the left front wheel, the left rear wheel, the right front wheel and the right rear wheel are respectively F_lf＝F_{μ_lf}、F_lr＝F_{μ_lr}、If F_{μ_lf}+F_{μ_lr}＞F_{μ_rf}+F_{μ_rr}Obtaining F_l＝F_r＝F_{μ_rf}+F_{μ_rr}The target braking forces of the four wheels of the left front wheel, the left rear wheel, the right front wheel and the right rear wheel are respectivelyF_rf＝F_{μ_rf}、F_rr＝F_{μ_rr}；

Under the conventional braking, the single-wheel target braking forces of the four wheels of the left front wheel, the left rear wheel, the right front wheel and the right rear wheel are respectively

When the driver's braking intention is curve braking:

step b1, calculating the extra longitudinal braking force Δ F required to create the additional yaw moment Δ T and determining the object to be applied: when the vehicle brakes on a curve, if excessive steering occurs, extra longitudinal braking force delta F is applied to the outer front wheel, and if understeer occurs, extra longitudinal braking force delta F is applied to the inner rear wheel;

step b2, calculating the maximum braking force which can be provided by the ground to each wheel;

the peak adhesion coefficients of four wheels of an inner front wheel, an inner rear wheel, an outer front wheel and an outer rear wheel are respectively set asThe vertical loads of the four wheels are respectively F_{Z_if}、F_{Z_ir}、F_{Z_of}、F_{Z_or}So as to obtain the maximum ground braking force which can be formed by a single wheel ofj＝if、ir、of、or；

Step b3, calculating the inner and outer target braking force;

let the sum of the longitudinal braking forces on the inside be F_iThe sum of the outside longitudinal braking forces is F_oAnd F is_i、F_oThe front wheel rotation angle collected by the front wheel rotation angle sensor is delta without delta F;

if excessive steering occurs, under emergency braking, let F_i＝F_o＝min{F_{μ_if} cosδ+F_{μ_ir},F_{μ_of} cosδ+F_{μ_or}- Δ F }; under normal braking, let

If understeer occurs, under emergency braking, let F_i＝F_o＝min{F_{μ_if} cosδ+F_{μ_ir}-ΔF,F_{μ_of} cosδ+F_{μ_or}}; under normal braking, let

Step b4, calculating the target braking force of the single wheel;

if excessive steering occurs, under emergency braking, if F_{μ_if} cosδ+F_{μ_ir}≥F_{μ_of} cosδ+F_{μ_or}Δ F, target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively set to F_of＝F_{μ_of}、F_or＝F_{μ_or}(ii) a If F_{μ_if} cosδ+F_{μ_ir}＜F_{μ_of} cosδ+F_{μ_or}Δ F, the target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively made to be F_if＝F_{μ_if}、F_ir＝F_{μ_ir}、

Under the conventional braking, the single-wheel target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively set as

If understeer occurs, under emergency braking, if F_{μ_if} cosδ+F_{μ_ir}-ΔF≤F_{μ_of} cosδ+F_{μ_or}Respectively setting the target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel to F_if＝F_{μ_if}、F_ir＝F_{μ_ir}、If F_{μ_if}cosδ+F_{μ_ir}-ΔF＞F_{μ_of} cosδ+F_{μ_or}The target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively set toF_of＝F_{μ_}of、F_or＝F_{μ_or}；

Under the conventional braking, the single-wheel target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively set as

The EHB pressure follows the target pressure p of the brake wheel cylinder by the PID controller_tarAnd the actual pressure p acquired by the pressure sensor_actComparing, performing pressure ring PID control on the obtained deviation, and outputting the target current I of the linear solenoid valve_tarThen the target current I is set_tarWith the actual current I_actComparing, and after carrying out current PID control on the obtained deviation of the two, outputting a PWM value and inputting the PWM value into a linear electromagnetic valve so as to control the opening of the linear electromagnetic valve, and further controlling the flow of brake fluid provided by the hydraulic pump entering and exiting a brake wheel cylinder, thereby realizing pressure following;

the EMB pressure follows the PID controller to set the target clamping force F of the actuator_tarActual clamping force F collected by clamping force sensor_actComparing the two values, and performing PID control on the obtained deviation of the two values to output the target rotation speed theta of the motor_tarThen the target rotation speed theta is set_tarAnd the actual rotating speed theta acquired by the rotating speed sensor_actComparing, and performing PID control on the obtained deviation of the two, and outputting a target current i_tarThen the target current i_tarAnd the actual current i_actAnd comparing, performing current loop PID control on the obtained deviation of the two, and outputting a target torque to the EMB executing mechanism through the transmission speed reducing mechanism so as to realize pressure following.

Compared with the prior art, the invention has the beneficial effects that:

1. the invention fully considers the difference of response time of the EHB and the EMB, and adjusts the braking force of the front axle and the rear axle in real time through the front axle and rear axle braking force coordination controller, so that the braking force of the whole automobile is always kept at a higher level in the pressure building process, and meanwhile, the braking force of the rear axle is close to the maximum braking force provided by the ground when the wheels of the front axle are not locked, but does not reach the locking degree, thereby preventing the rear wheel from being locked before the front wheel, and being beneficial to avoiding dangerous working conditions such as tail flicking and the like caused by the locking of the rear wheel first;

2. the electronic hydraulic-electronic mechanical hybrid automobile brake-by-wire control system provided by the invention considers the difference of respective vertical loads of four wheels and the adhesion condition with the ground, fully utilizes the road adhesion coefficient, is beneficial to shortening the braking distance and improving the braking efficiency;

3. the invention fully considers the lateral stability of the vehicle, and when the vehicle is steered and braked, extra braking force is applied to a certain wheel to form an additional yaw moment couple so as to maintain the stability of the vehicle body, thereby being beneficial to improving the stability and the safety of the vehicle during the steering and braking.

Drawings

FIG. 1 is a flow chart of the operation of the present invention;

FIG. 2 is a schematic diagram of the operation of the underlying controller of the present invention;

FIG. 3 is a graph of the pressure buildup time of the EHB and EMB of the present invention (F-t graph);

FIG. 4 is a schematic diagram of the front and rear axle braking force coordination controller of the present invention.

Detailed Description

In this embodiment, an electronic hydraulic-electronic mechanical hybrid automobile brake-by-wire control system is characterized by including: the system comprises a sensor subsystem, an EHB, an EMB, an upper controller and a lower controller;

the sensor subsystem includes: the device comprises a steering wheel corner sensor, a front wheel corner sensor, a brake pedal displacement sensor, a vehicle speed sensor, a current sensor, a rotating speed sensor, a pressure sensor and a clamping force sensor;

the EHB includes: a hydraulic pump, a linear electromagnetic valve and a brake wheel cylinder;

the EMB includes: the device comprises a motor, a transmission speed reducing mechanism and an actuating mechanism;

the upper layer controller includes: the system comprises a target braking force calculation module, an additional yaw moment calculation module and a braking force distribution subsystem; wherein the braking force distribution subsystem comprises: the left and right braking force distribution modules and the front and rear wheel braking force distribution modules;

the lower layer controller includes: the system comprises a front and rear axle braking force coordination controller, an EHB pressure following PID controller and an EMB pressure following PID controller;

referring to fig. 1, when a driver steps on a brake pedal to perform deceleration braking, the brake pedal displacement sensor collects displacement of the brake pedal and transmits the displacement to the target braking force calculation module for judgment, and if the displacement of the brake pedal is within a preset time t₀Up to the maximum displacement s of the brake pedal_maxIf the target braking force calculation module judges that the braking intention is emergency braking, the target braking force F of the whole vehicle is calculated_XbSetting a maximum longitudinal braking force which can be acted on the vehicle by the ground under the condition that the vehicle is not unstable; if the displacement of the brake pedal is within the preset time t₀Failure to reach the maximum displacement s of the brake pedal_maxIf the target braking force calculation module judges that the braking intention is conventional braking, obtains the braking intensity expected by the driver, and records the longitudinal braking intensity as z, so that the required braking force is obtained according to the braking intensity and is used as the target braking force F of the whole vehicle_Xb，F_XbMzg, wherein m is the total mass of the whole vehicle, and g is the gravity acceleration;

the additional yaw moment calculation module identifies a braking path expected by a driver through a steering wheel angle acquired by the steering wheel angle sensor and a vehicle speed acquired by the vehicle speed sensor, and calculates an additional yaw moment delta T required for enabling the vehicle to reach a target driving direction of the driver: when the steering wheel angle acquired by the steering wheel angle sensor is 0 degrees, the braking intention of the driver is straight braking, and delta T is set to be zero; when the steering wheel angle is not 0 degrees, the braking intention is curve braking, and delta T is calculated according to the steering wheel angle and the vehicle speed;

the braking force distribution subsystem distributes the braking force of four front and rear single wheels on the left and right sides according to the following processes:

when the driver's braking intention is straight braking:

step a1, calculating the maximum braking force which can be provided by the ground to each wheel;

wheel braking force is proportional to the vertical load of the wheelThe vertical load of each wheel consists of three parts: normal reaction of static axle load, load transfer of front and rear axles during braking, and load transfer of inner and outer sides during steering. The peak adhesion coefficients of the four wheels of the left front wheel, the left rear wheel, the right front wheel and the right rear wheel are respectively set asThe vertical loads of the four wheels are respectively F_{Z_lf}、F_{Z_lr}、F_{Z_rf}、F_{Z_rr}So as to obtain the maximum ground braking force which can be formed by a single wheel ofi＝lf、lr、rf、rr；

Step a2, calculating the target braking force of the left side and the right side;

the maximum ground braking force which can be formed by the left wheel and the right wheel is not always equal, and the sum of the left braking force is F_lThe sum of the right braking forces is F_r；

Under emergency braking, let F_l＝F_r＝min{F_{μ_lf}+F_{μ_lr},F_{μ_rf}+F_{μ_rr}}；

Under normal braking, let

Step a3, calculating the target braking force of a single wheel;

under emergency braking, the maximum ground braking force generated by the front and rear wheels on the side with smaller maximum ground braking force sum is distributed to the front and rear wheels on the other side according to the ratio of the target ground braking force to the maximum ground braking force generated by the side, if F_{μ_lf}+F_{μ_lr}≤F_{μ_rf}+F_{μ_rr}Obtaining F_l＝F_r＝F_{μ_lf}+F_{μ_lr}The target braking forces of the four wheels of the left front wheel, the left rear wheel, the right front wheel and the right rear wheel are respectively F_lf＝F_{μ_lf}、F_lr＝F_{μ_lr}、If F_{μ_lf}+F_{μ_lr}＞F_{μ_rf}+F_{μ_rr}Obtaining F_l＝F_r＝F_{μ_rf}+F_{μ_rr}The target braking forces of the four wheels of the left front wheel, the left rear wheel, the right front wheel and the right rear wheel are respectivelyF_rf＝F_{μ_rf}、F_rr＝F_{μ_rr}；

Under the normal braking, the four wheels are distributed according to the ratio of the target braking force on one side to the maximum ground braking force which can be generated on one side, and the target braking forces on the single wheels of the four wheels on the left front wheel, the left rear wheel, the right front wheel and the right rear wheel are respectively

When the driver's braking intention is curve braking:

step b1, calculating the extra longitudinal braking force Δ F required to create the additional yaw moment Δ T and determining the object to be applied: when the vehicle brakes on a curve, if excessive steering occurs, extra longitudinal braking force delta F is applied to the outer front wheel, and if understeer occurs, extra longitudinal braking force delta F is applied to the inner rear wheel;

step b2, calculating the maximum braking force which can be provided by the ground to each wheel;

the peak adhesion coefficients of four wheels of an inner front wheel, an inner rear wheel, an outer front wheel and an outer rear wheel are respectively set asThe vertical loads of the four wheels are respectively F_{Z_if}、F_{Z_ir}、F_{Z_of}、F_{Z_or}So as to obtain the maximum ground braking force which can be formed by a single wheel ofj＝if、ir、of、or；

Step b3, calculating the inner and outer target braking force;

let the sum of the longitudinal braking forces on the inside be F_iThe sum of the outside longitudinal braking forces is F_oAnd F is_i、F_oThe front wheel rotation angle collected by the front wheel rotation angle sensor is delta without delta F;

if excessive steering occurs, under emergency braking, let F_i＝F_o＝min{F_{μ_if} cosδ+F_{μ_ir},F_{μ_of} cosδ+F_{μ_or}- Δ F }; under normal braking, let

If understeer occurs, under emergency braking, let F_i＝F_o＝min{F_{μ_if} cosδ+F_{μ_ir}-ΔF,F_{μ_of} cosδ+F_{μ_or}}; under normal braking, let

Step b4, calculating the target braking force of the single wheel;

if excessive steering occurs, under emergency braking, if F_{μ_if} cosδ+F_{μ_ir}≥F_{μ_of} cosδ+F_{μ_or}Δ F, target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively set to F_of＝F_{μ_of}、F_or＝F_{μ_or}(ii) a If F_{μ_if} cosδ+F_{μ_ir}＜F_{μ_of} cosδ+F_{μ_or}Δ F, the target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively made to be F_if＝F_{μ_if}、F_ir＝F_{μ_ir}、

Under the conventional braking, the single-wheel target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively set as

If understeer occurs, under emergency braking, if F_{μ_if} cosδ+F_{μ_ir}-ΔF≤F_{μ_of} cosδ+F_{μ_or}Respectively setting the target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel to F_if＝F_{μ_if}、F_ir＝F_{μ_ir}、If F_{μ_if}cosδ+F_{μ_ir}-ΔF＞F_{μ_of} cosδ+F_{μ_or}The target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively set toF_of＝F_{μ_of}、F_or＝F_{μ_or}；

Under the conventional braking, the single-wheel target braking forces of the inner front wheel, the inner rear wheel, the outer front wheel and the outer rear wheel are respectively set as

Then, the braking force distribution subsystem converts the single-wheel braking force into the target pressure p of the brake wheel cylinder in the corresponding EHB_tarAnd target clamping force F of actuator in EMB_tar；

The front and rear axle braking force coordination controller receives the target pressure p of the brake wheel cylinder in the EHB from the upper layer controller_tarAnd target clamping force F of actuator in EMB_tarCalculating and adjusting the front axle target braking force and the rear axle target braking force:

for the front axle, the front axle actual braking force P is judged_{f_act}Whether or not the front axle target braking force P is reached_{f_tar}If P is_{f_act}＜P_{f_tar}Then let P_{f_ref}＝P_{f_max}Effectively reducing the response time of the braking force and increasing the actual braking force P in the pressure build-up process_{f_act}The size of (d); if P_{f_act}≥P_{f_tar}Then let P_{f_ref}＝P_{f_tar}The braking force enters a pressure maintaining stage; wherein, P_{f_ref}Indicating front axle reference brake force, P_{f_max}Represents the maximum pressure that the front axle brake can provide;

for the rear axle, the actual rear axle braking force P is determined_{r_act}Whether or not the rear axle target braking force P is to be achieved_{r_tar}If P is_{r_act}＜P_{r_tar}-x_rThen let P_{r_ref1}＝P_{r_max}(ii) a If P_{r_act}≥P_{r_tar}-x_rThen let P_{r_ref1}＝P_{r_act}(ii) a Wherein x is_rIndicates a preset value, P_{r_ref1}Indicating the rear axle reference braking force, P, of the intermediate stage_{r_max}Indicating the maximum pressure that the rear axle brake can provide; then, the actual braking force P of the front axle is judged_{f_act}Whether or not the front axle target braking force P is to be achieved_{f_tar}If P is_{f_act}＜P_{f_tar}-x_fThen let P_{r_ref2}＝P_{r_ref1}(ii) a If P_{f_act}≥P_{f_tar}-x_fThen let P_{r_ref2}＝P_{r_tar}To actually brake the front wheelsThe force reaches the target braking force before the actual braking force of the rear wheel, so that dangerous working conditions such as drifting and the like caused by locking of the rear wheel before the front wheel are avoided; wherein x is_fIndicates another preset value, P_{r_ref2}Indicating the final rear axle reference brake force;

finally P is added_{f_ref}、P_{r_ref2}The brake of the front axle and the brake of the rear axle are respectively input to realize deceleration braking, so that the automobile reaches an expected state.

Referring to fig. 2, the EHB pressure follows the target pressure p of the brake cylinder by the PID controller_tarAnd the actual pressure p acquired by the pressure sensor_actComparing, performing pressure ring PID control on the obtained deviation, and outputting the target current I of the linear solenoid valve_tarThen the target current I is set_tarWith the actual current I_actComparing, and after carrying out current PID control on the obtained deviation of the two, outputting a PWM value and inputting the PWM value into a linear electromagnetic valve so as to control the opening of the linear electromagnetic valve, and further controlling the flow of brake fluid provided by the hydraulic pump entering and exiting a brake wheel cylinder, thereby realizing pressure following;

the EMB pressure follows the PID controller to set the target clamping force F of the actuator_tarActual clamping force F collected by clamping force sensor_actComparing the two values, and performing PID control on the obtained deviation of the two values to output the target rotation speed theta of the motor_tarThen the target rotation speed theta is set_tarAnd the actual rotating speed theta acquired by the rotating speed sensor_actComparing, and performing PID control on the obtained deviation of the two, and outputting a target current i_tarThen the target current i_tarAnd the actual current i_actAnd comparing, performing current loop PID control on the obtained deviation of the two, and outputting a target torque to the EMB executing mechanism through the transmission speed reducing mechanism so as to realize pressure following.

Referring to fig. 3, when EHB takes its maximum braking force EHB _ max that can be provided as an input value, the braking force F generated by the system rises along a curve OAB with time t; the system generates the braking force when the EMB takes the maximum braking force EMB _ max which can be provided by the EMB as an input valueThe power F rises along the curve OCD with time t. It can be seen that EHB _ max > EMB _ max, and the response time t for the EHB braking force to reach the maximum value_HLonger than the response time t for the EMB braking force to reach the maximum value_M；

Taking EHB as an example, when the system takes a certain target value EHB _ tar as an input value, the braking force F generated by the system rises along the curve OEF with time t, and at time t₂The target value EHB _ tar is reached. If the target value is not changed and the input value of the system is changed to EHB _ max, the generated braking force will rise along the OA curve, and when t is₁When the braking force reaches the target value EHB _ tar at the moment, the input value is changed to the target value, and the braking force changes along the curve OGEF in the whole process. Compared with the method that the target value is always used as the input, the braking force (0 to t) of the system in the response process is improved₁OG curve significantly higher than OE curve over time), and the response time of the target value is taken from t₂To reduce to t₁The brake system is beneficial to increasing the braking force in the pressure building process of the whole vehicle brake system and shortening the pressure building time, thereby improving the braking efficiency.

Referring to fig. 4, the front and rear axle braking force cooperative controller receives a target pressure p of a brake wheel cylinder in an EHB from an upper controller_tarAnd target clamping force F of actuator in EMB_tarCalculating and adjusting the front axle target braking force and the rear axle target braking force:

for the front axle, the front axle actual braking force P is judged_{f_act}Whether or not the front axle target braking force P is reached_{f_tar}If P is_{f_act}＜P_{f_tar}Then let P_{f_ref}＝P_{f_max}(ii) a If P_{f_act}≥P_{f_tar}Then let P_{f_ref}＝P_{f_tar}(ii) a Wherein, P_{f_ref}Indicating front axle reference brake force, P_{f_max}Represents the maximum pressure that the front axle brake can provide;

for the rear axle, the actual rear axle braking force P is determined_{r_act}Whether or not the rear axle target braking force P is to be achieved_{r_tar}If P is_{r_act}＜P_{r_tar}-x_rThen let P_{r_ref1}＝P_{r_max}(ii) a If P_{r_act}≥P_{r_tar}-x_rThen let P_{r_ref1}＝P_{r_act}(ii) a Wherein x is_rIndicates a preset value, P_{r_ref1}Indicating the rear axle reference braking force, P, of the intermediate stage_{r_max}Indicating the maximum pressure that the rear axle brake can provide; then, the actual braking force P of the front axle is judged_{f_act}Whether or not the front axle target braking force P is to be achieved_{f_tar}If P is_{f_act}＜P_{f_tar}-x_fThen let P_{r_ref2}＝P_{r_ref1}(ii) a If P_{f_act}≥P_{f_tar}-x_fThen let P_{r_ref2}＝P_{r_tar}(ii) a Wherein x is_fIndicates another preset value, P_{r_ref2}Indicating the final rear axle reference brake force; finally P is added_{f_ref}、P_{r_ref2}The front axle brake and the rear axle brake are respectively input.