CN112141079A - A hydraulic control method and storage medium for following vehicle braking - Google Patents

Abstract

The invention relates to the technical field of vehicle control, in particular to a hydraulic control method and a storage medium during follow-up braking. After receiving a braking deceleration command, the target braking pressure P is set_targetCalculating; the hydraulic pressure regulating unit is based on the target brake pressure P_targetEstablishing a reference hydraulic pressure; when the reference hydraulic pressure reaches the target brake pressure P_targetThen, the hydraulic pressure adjusting unit performs first pressure-maintaining control; monitoring the vehicle speed and the longitudinal pose of the vehicle in real time, and when the vehicle speed is in a set vehicle speed range of v 1-v 2 and the longitudinal pose of the vehicle exceeds a calibrated pose threshold, performing pressure relief control; if the vehicle speed decreases to be not greater than the set vehicle speed threshold value v0, the second pressure holding control is performed. The dynamic vertical load of the front shaft and the rear shaft is promoted to be more uniform while the nod feeling is restrained, so that the brake hydraulic pressure is optimizedMeanwhile, the utilization rate of the adhesion coefficient between the road surface and the tire is improved, the service life of the ESC controller is prolonged, and the loss of the brake is reduced.

Description

A hydraulic control method and storage medium for following vehicle braking

technical field

The present invention relates to the technical field of vehicle control, in particular to a hydraulic control method and a storage medium when a vehicle is braked and stopped.

Background technique

With the rapid progress of Internet technology and the increasing demand for safety and ease of operation of automobiles, the degree of intelligence of automobiles is getting higher and higher. The full-speed ACC start and stop function has been applied in more and more cars. When the ACC is following the car, when the front car suddenly brakes and stops, the own car also brakes to stop. The main control system of a vehicle equipped with full-speed ACC start and follow-stop functions is divided into three parts: (1) target detection; (2) logic processing control; (3) action execution. Target detection is mainly to detect the target in front of the vehicle through millimeter-wave radar, camera or a fusion scheme of the two. The processing control unit is the ADAS function controller, which mainly analyzes and judges the control target and the state of the vehicle, and sends control commands, such as acceleration, deceleration, and parking, according to the calibrated strategy. Actions are executed in response to commands from the ADAS controller. The execution module is divided into two parts, one is the power control execution part, that is, the VCU controller, which is responsible for acceleration; the other is the braking control execution part, that is, the ESC module, which is responsible for deceleration and braking.

The logic of the existing brake control execution part is to directly let the ESC establish a hydraulic constant value of about 100 bar when the ACC follow-stop braking needs to be performed, so as to directly achieve a braking force that can be locked. This control logic does not take into account actual driving conditions and real-time braking torque requirements; sudden braking will cause the vehicle to have a large pitch, especially in the second half of the braking period before the vehicle stops. There is a clear nodding, and the driver and passengers will feel a strong sense of discomfort. On the other hand, at a lower vehicle speed in the second half of braking, the braking system still gives a large braking force, which damages the carrying capacity of the braking system.

SUMMARY OF THE INVENTION

The purpose of the present invention is to aim at the defects of the prior art, to provide a hydraulic control method and a storage medium for braking when following a vehicle, so as to obtain a reasonable braking hydraulic curve, and to prevent the braking pitch generated in the second half of the braking. Effectively suppress, so that the vehicle has a better braking posture, and the driver and passengers also have a better comfortable experience.

The technical scheme of the present invention is: after receiving the braking deceleration command, calculate the target braking pressure P _target ;

The hydraulic adjustment unit establishes a reference hydraulic pressure according to the target braking pressure P _target ;

After the reference hydraulic pressure reaches the target braking pressure P _target , the hydraulic pressure adjustment unit performs the first pressure maintaining control;

Real-time monitoring of the vehicle speed and the vehicle's longitudinal posture, when the vehicle speed is within the set vehicle speed range v1 ~ v2, and the vehicle's longitudinal posture exceeds the calibrated posture threshold, the pressure relief control is performed;

If the vehicle speed is reduced to not greater than the set vehicle speed threshold v0, the second pressure maintaining control is performed.

Preferably, the target braking pressure P _target is obtained based on a front caliper braking force-rear caliper braking force-pipe pressure curve obtained by pre-calibration.

More preferably, the calculation of the target braking pressure P _target includes:

计算出卡钳总制动力F_xbtotal；Request value based on deceleration command

Calculate the total caliper braking force F _xbtotal ;

Based on the front caliper braking force-rear caliper braking force-pipe pressure curve, when the total caliper braking force F _xbtotal is satisfied, the pipeline hydraulic pressure P _max corresponding to the front caliper braking force and the rear caliper braking force is obtained;

The line hydraulic pressure P _max is taken as the target brake pressure P _target .

More preferably, the method further includes correcting the pipeline hydraulic pressure P _max , and using the corrected pipeline hydraulic pressure as the target braking pressure P _target , the target braking pressure P _target =P _max +a, where a is a setting parameter.

More preferably, the longitudinal pose of the vehicle is judged by the pitch angle θ and the vertical bouncing displacement z of the front of the vehicle.

More preferably, when the pitch angle θ is greater than the set pitch angle threshold, and the vertical bouncing displacement z of the head is greater than the set vertical bouncing displacement threshold, it is determined that the longitudinal pose of the vehicle exceeds the calibrated pose threshold.

More preferably, the pressure relief control includes:

Close the inlet valve and open the outlet valve intermittently.

Preferably, the second pressure maintaining control includes:

The liquid outlet valve LRAV is closed, the liquid inlet valve LREV is opened, and the DC motor M drives the hydraulic pump to work until the pressure rises to the set pressure, and the liquid inlet valve LREV is closed.

More preferably, the liquid outlet valve is a linear switch valve, and the liquid outlet valve is controlled by pulses.

The beneficial effects of the present invention are: when the vehicle is braked and stopped, the ESC hydraulic adjustment unit performs coordinated control of three operations of boosting, decompressing and maintaining pressure. When the ESC responds to the deceleration command of the ACC, it first establishes a large brake hydraulic pressure to realize the deceleration in the first half stage; of course, when the vehicle speed is reduced to between 20-30km/h, through the longitudinal pose estimation of the vehicle, when When the posture exceeds the calibration threshold of the vehicle, the brake hydraulic pressure is lowered; at this time, the main inlet valve is closed, and the outlet valve is opened intermittently to relieve pressure; finally, when the vehicle speed is lower than 1km/h, the ESC The hydraulic adjustment unit builds up a pressure of about 15 bar and stops the vehicle in place. The hydraulic control of this solution makes the dynamic vertical load of the front and rear axles more uniform while suppressing the nodding feeling, so as to optimize the brake hydraulic pressure, improve the utilization rate of the adhesion coefficient between the road surface and the tire, and improve the use of the ESC controller. life and reduce brake wear.

Description of drawings

Fig. 1 is a kind of hydraulic control method schematic flow chart of the present invention when braking and stopping;

2 is a schematic diagram of a front caliper braking force-rear caliper braking force-pipe pressure curve of the present invention;

3 is a schematic diagram of the hydraulic circuit of the ESC hydraulic adjustment unit of the present invention;

4 is a schematic diagram of a hydraulic adjustment curve of the present invention;

5 is a schematic diagram of the pulse control principle of the intermittent adjustment of the liquid outlet valve of the present invention;

6 is a schematic diagram of a vehicle attitude estimation model of the present invention;

FIG. 7 is a schematic diagram of a braking control flow diagram applying the present invention.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, so as to facilitate a clear understanding of the present invention, but they do not limit the present invention.

As shown in FIG. 1 , the present invention provides a hydraulic control method when the vehicle is braked and stopped, which includes:

S1: Calculate the target braking pressure P _target . It includes:

计算出卡钳总制动力F_xbtotal。其计算方法如下：S101: When the ESC receives the deceleration command, it requests the value according to the deceleration command

Calculate the total caliper braking force F _xbtotal . Its calculation method is as follows:

其中，G为车辆的重量。

where G is the weight of the vehicle.

基于前卡钳制动力-后卡钳制动力-管压曲线，得到满足卡钳总制动力F_xbtotal时，前卡钳制动力和后卡钳制动力对应的管路液压P_max，i为1或2，F_xb1为前卡钳制动力；F_xb2为后卡钳制动力。S102: Combining formulas

Based on the front caliper braking force-rear caliper braking force-pipe pressure curve, when the total caliper braking force F _xbtotal is satisfied, the pipeline hydraulic pressure P _max corresponding to the front caliper braking force and the rear caliper braking force, i is 1 or 2, F _xb1 For the front caliper braking force; F _xb2 for the rear caliper braking force.

As shown in Figure 2, in the front caliper braking force-rear caliper braking force-pipe pressure curve, on the premise that the sum of the current caliper braking force and the rear caliper braking force has been determined, the only front caliper braking force F _xb1 and The rear caliper braking force F _xb2 , so that the only line pressure, that is, the line hydraulic pressure P _max , is obtained through this curve.

S103: Calculate the target brake pressure P _target based on the line hydraulic pressure P _max . For safety reasons, a margin of 10 bar needs to be added to the line hydraulic pressure P _max ; therefore, the target braking pressure P _target =P _max +10 bar.

The traditional target braking pressure P _target is obtained by inversely calculating the required caliper braking force through deceleration, and then according to the caliper braking force, it is solved by parameters such as caliper structure and friction coefficient. The pipe pressure-braking force curve used in this scheme is obtained directly through the bench test. The influence of environmental factors and brake disc temperature on the friction coefficient is comprehensively considered, and the result is more accurate.

S2: Hydraulic control is performed according to the target braking pressure P _target . The hydraulic circuit of the ESC hydraulic adjustment unit is shown in Figure 3. In the figure, MC2 is the hydraulic master cylinder, HSR2 is the high pressure valve, USV2 is the reversing valve, LREV is the liquid inlet valve, LRAV is the liquid outlet valve, and LR and RF are respectively Caliper wheel cylinder. As shown in Figure 4, the hydraulic control process mainly includes four stages:

S201: The hydraulic pressure adjusting unit establishes a reference hydraulic pressure according to the target braking pressure P _target . Taking the LR caliper wheel cylinder as an example, when the active pressurization is performed, USV2 and LRAV are closed; HSR2 and LREV are opened; at the same time, the DC motor M drives the hydraulic pump to work, and the brake fluid is continuously pressed into the wheel cylinder to realize the pressure rise. The hydraulic pressure in the caliper at this time is estimated by calculating the amount of hydraulic pressure entering the wheel cylinder.

S202 : When the target hydraulic pressure P _target is reached, the liquid inlet valve and the liquid outlet valve are closed to keep the pressure unchanged (ie, the first pressure-holding control), and finally a vigorous boosting operation in the initial stage of deceleration is realized.

S203: The ACC controller continuously monitors the vehicle speed and the longitudinal posture of the vehicle. When the vehicle speed is within the set vehicle speed range v1-v2 (20-30 km/h in this embodiment), and the longitudinal posture of the vehicle exceeds the calibrated posture threshold , the pressure relief control is performed. Wherein, when the pitch angle θ is greater than the set pitch angle threshold, and the vertical bouncing displacement z of the front of the vehicle is greater than the set vertical bouncing displacement threshold, it is determined that the longitudinal pose of the vehicle exceeds the calibrated pose threshold.

Pressure relief controls include:

Close the HSR2 and LREV valves; the LRAV outlet valve opens and closes intermittently, so that the wheel cylinder pressure is reduced in an orderly manner; at this stage, with the continuous reduction of the vehicle speed, the hydraulic pressure gradually decreases; at this stage, due to the caliper control The power is reduced so that the longitudinal pitch of the vehicle is continuously optimized.

The operation of hydraulic pressure reduction can be realized by intermittent adjustment of the LRAV outlet valve; the LRAV outlet valve is a linear switch valve, and its control method is controlled by pulses; as shown in Figure 5, when the control pulse is When it is 0, the liquid outlet valve is closed; when the control pulse is -1, the brake hydraulic pressure is slightly reduced, so as to appropriately reduce the braking force at the wheel end of the vehicle, thereby adjusting the pitch angle.

S204: When the vehicle speed is reduced to 1km/h, the solenoid valves USV2 and LRAV are closed; HSR2 and LREV are opened; at the same time, the DC motor M drives the hydraulic pump to work, and the brake fluid is continuously pressed into the wheel cylinder to realize the pressure rise. When the wheel cylinder When the pressure reaches 15bar, brake to maintain the pressure. When the brake is stopped to maintain the pressure, close the LREV inlet valve and keep the pressure at 15bar to prevent slippage caused by road slope and other reasons, so that the vehicle can safely stop in place.

Preferably, the estimation algorithm for the pitch attitude of the vehicle needs to build an estimation model based on the vehicle dynamics model; the input signals include vehicle speed, wheel speed, and the corresponding vehicle deceleration signal. This pitch attitude estimation algorithm needs to be calibrated and tested in the early stage of function design. The vehicle dynamics model mainly involves the vehicle's chassis dynamics parameters, including the vehicle's tires, suspension, wheelbase, center of mass, and vehicle weight. Based on the above information, a vehicle pitching attitude calculation model is established; this model can dynamically estimate the pitching state of the vehicle according to the input information on the CAN bus. This estimation algorithm, stored in the ACC controller, needs to be calibrated and tested during the vehicle development stage. Among them, wheel speed, vehicle speed and vehicle deceleration are acquired by wheel speed sensors arranged at four wheels, and transmitted to CAN bus through ESC, and then acquired by ACC controller.

When the design parameters of the vehicle have been determined, the dynamic body pitch is mainly determined by the initial speed and dynamic deceleration of the vehicle. Based on the above situation, when the attitude estimation algorithm finds that the attitude of the whole vehicle changes greatly, that is, when the changes of θ and z are large, the pitch moment caused by the deceleration of the vehicle is affected by appropriately adjusting the wheel cylinder pressure of the brake. M _y , and finally achieve the purpose of suppressing the pitch change. Among them, θ-pitch angle; z-vertical bouncing displacement of the head. Its calculation algorithm is integrated in the vehicle ACC controller, and the required parameters mainly include two parts: vehicle configuration parameters and dynamic changes.

Among the above parameters, the vehicle configuration parameters mainly refer to the vehicle's wheelbase, suspension damping, front and rear axle loads, etc. These parameters are integrated in the ADAS controller as known variables during the vehicle development stage. The dynamic change mainly refers to the deceleration caused by braking and the changing force of the front and rear suspension. According to the dynamic analysis of the above parameters, the real-time longitudinal pose changes of the vehicle can be dynamically estimated.

The two monitoring parameters of the dynamic pitch of the vehicle, θ-pitch angle; z-the vertical bouncing displacement of the front of the vehicle, as shown in Figure 6, the estimation model is as follows:

F _front , F _rear are the forces acting on the front and rear suspension; K _f , K _r are the front and rear suspension stiffness; C _f , C _r are the front and rear suspension damping; L _font , L _ront are the front and rear axle center distances;

θ is the pitch angle; z is the vertical bouncing displacement of the front of the vehicle; M _front and M _rear are the front and rear suspension moments;

M _front = -L _front F _front

M _rear =L _r F _rear

为车头垂向弹跳位移二阶加速度；

为俯仰角二阶加速度。m _b is the sprung mass of the body; M _y is the pitching moment caused by deceleration; I _yy is the inertia of the body; g is the constant of gravitational acceleration;

is the second-order acceleration of the vertical bouncing displacement of the front of the vehicle;

is the second-order acceleration of the pitch angle.

Through the above estimation strategy, two parameters representing the longitudinal pose of the vehicle can be estimated: θ-pitch angle; z-vertical bouncing displacement of the front of the vehicle. When the two are greater than the set threshold, the wheel cylinder hydraulic adjustment strategy is triggered. Regarding the threshold setting of the pose parameters, the design method is mainly based on the subjective dynamic calibration by the trained testers. For a sporty vehicle, it can be set higher; for a more comfortable vehicle, it can be set lower and adjusted in advance.

其中，D_rel为两车相对距离，V_rel为两车相对速度。另外，要求刹停时，与目标车的安全距离d₀。那么基于沥青的AEB控制系统，当两车相对距离达到危险距离Dbr时，应立即发生全力刹车指令。其中Dbr计算方法为：Dbr＝TTC·V_rel+d₀。当ESC收到减速指令后，ESC通过对其自身的阀、泵等协调控制来实现快速增压。ESC对ACC控制器发出的刹车跟停指令进行响应时，ESC执行器会对指令的减速度请求值进行计算，通过ESC的液压泵对制动液压回路进行加压。More preferably, the calculation of the deceleration command is based on the calculation of the safe time distance value according to the working conditions of the vehicle for judgment. If the TTC is less than 0.8 seconds, the ACC controller needs to issue a brake braking command. The calculation method of the safety time distance TTC corresponding to the hydraulic start command is as follows:

Among them, D _rel is the relative distance between the two vehicles, and V _rel is the relative speed of the two vehicles. In addition, when braking is required, the safety distance d ₀ from the target vehicle is required. Then, for the asphalt-based AEB control system, when the relative distance between the two vehicles reaches the dangerous distance Dbr, the full braking command should be issued immediately. The calculation method of Dbr is: Dbr=TTC·V _rel +d ₀ . When the ESC receives a deceleration command, the ESC achieves rapid boosting by coordinating control of its own valves and pumps. When the ESC responds to the brake follow-stop command issued by the ACC controller, the ESC actuator will calculate the commanded deceleration request value, and pressurize the brake hydraulic circuit through the ESC hydraulic pump.

Preferably, the design structure of the ACC function is mainly divided into four parts, the front vehicle detection module, the ACC controller unit, the VCU acceleration control unit and the ESC brake execution unit. As shown in Figure 7, the detection module of the ACC function detects the target vehicle ahead in real time, obtains the relative distance and relative speed between the two vehicles, and obtains the true vehicle degree of the preceding vehicle through calculation; Input to the ACC controller unit, the controller unit combines the basic information such as its own vehicle speed and gear position obtained from the CAN bus, and combines with the TTC-collision time distance algorithm to make a comprehensive judgment and issue corresponding commands (acceleration/braking). If it is an acceleration command, the vehicle VCU controller will respond; if it is a braking command, the ESC controller will respond. After the ESC controller receives the deceleration information, it will establish a reference hydraulic pressure according to the received reference deceleration value. While establishing the reference hydraulic pressure, the pitch attitude of the whole vehicle is estimated, and then the hydraulic pressure is dynamically adjusted through the attitude adjustment algorithm designed in this patent, so as to complete the pitch attitude control.

The content not described in detail in this specification belongs to the prior art known to those skilled in the art. The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. It will be understood that each process and/or block in the flowchart illustrations and/or block diagrams, and combinations of processes and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to the processor of a general purpose computer, special purpose computer, embedded processor or other programmable data processing device to produce a machine such that the instructions executed by the processor of the computer or other programmable data processing device produce Means for implementing the functions specified in a flow or flow of a flowchart and/or a block or blocks of a block diagram.

These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory result in an article of manufacture comprising instruction means, the instructions The apparatus implements the functions specified in the flow or flow of the flowcharts and/or the block or blocks of the block diagrams.

These computer program instructions can also be loaded on a computer or other programmable data processing device to cause a series of operational steps to be performed on the computer or other programmable device to produce a computer-implemented process such that The instructions provide steps for implementing the functions specified in the flow or blocks of the flowcharts and/or the block or blocks of the block diagrams.

The above are only examples of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are included in the application for pending approval of the present invention. within the scope of the claims.

Claims (10)

1. a hydraulic control method when braking with a car, it is characterized in that: After receiving the braking deceleration command, calculate the target braking pressure P _target ; The hydraulic adjustment unit establishes a reference hydraulic pressure according to the target braking pressure P _target ; After the reference hydraulic pressure reaches the target braking pressure P _target , the hydraulic pressure adjustment unit performs the first pressure maintaining control; Real-time monitoring of the vehicle speed and the vehicle's longitudinal posture, when the vehicle speed is within the set vehicle speed range v1 ~ v2, and the vehicle's longitudinal posture exceeds the calibrated posture threshold, the pressure relief control is performed; If the vehicle speed is reduced to not greater than the set vehicle speed threshold v0, the second pressure maintaining control is performed. 2 . The hydraulic control method according to claim 1 , wherein the target braking pressure P _target is obtained based on the front caliper braking force-rear caliper braking force-pipe pressure curve obtained by pre-calibration. 3 . . 3. The hydraulic control method according to claim 2, wherein the calculation of the target braking pressure P _target comprises: Request value based on deceleration command

Calculate the total caliper braking force F _xbtotal ; Based on the front caliper braking force-rear caliper braking force-pipe pressure curve, when the total caliper braking force F _xbtotal is satisfied, the pipeline hydraulic pressure P _max corresponding to the front caliper braking force and the rear caliper braking force is obtained; The line hydraulic pressure P _max is taken as the target brake pressure P _target . 4 . The hydraulic control method according to claim 3 , further comprising: correcting the pipeline hydraulic pressure P _max , and using the corrected pipeline hydraulic pressure as the target braking pressure P _target , the target braking pressure P target . 5 . Brake pressure P _target =P _max +a, where a is a setting parameter. 5 . The hydraulic control method according to claim 1 , wherein the longitudinal posture of the vehicle is determined by the pitch angle θ and the vertical bouncing displacement z of the front of the vehicle. 6 . 6. The hydraulic control method when following the vehicle brake according to claim 5, it is characterized in that: when the pitch angle θ is greater than the set pitch angle threshold value, and the head vertical bouncing displacement z is greater than the set head vertical bouncing When the displacement threshold is exceeded, it is determined that the longitudinal pose of the vehicle exceeds the calibrated pose threshold. 7 . The hydraulic control method according to claim 1 , wherein the pressure relief control comprises: Close the inlet valve and open the outlet valve intermittently. 8 . The hydraulic control method according to claim 1 , wherein the second pressure maintaining control comprises: The liquid outlet valve LRAV is closed, the liquid inlet valve LREV is opened, and the DC motor M drives the hydraulic pump to work until the pressure rises to the set pressure, and the liquid inlet valve LREV is closed. 9 . The hydraulic control method according to claim 1 , wherein the liquid outlet valve is a linear switch valve, and the liquid outlet valve is controlled by pulses. 10 . 10. A computer-readable storage medium storing a computer program, characterized in that: when the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 9 are implemented .

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