CN108501910A - A kind of vehicle master cylinder constant frequency pressure regulating formula braking anti-lock method - Google Patents

Abstract

The invention relates to a brake anti-lock braking method of a vehicle master cylinder with constant frequency and pressure regulation, comprising the following steps: 1) controlling the piston of the master cylinder to move back and forth, so that the hydraulic pressure of the master cylinder can fluctuate; 2) judging whether the wheel cylinder needs to be increased 3) Monitor the current speed of the vehicle in real time, and when the speed is less than 5m/s, the ABS system will stop functioning to prevent locking. Compared with the prior art, the invention has the advantages of simplified structure, good anti-lock effect and the like.

Description

A vehicle master cylinder fixed-frequency voltage regulation brake anti-lock method

technical field

The invention relates to the technical field of automobiles, in particular to a vehicle master cylinder fixed-frequency voltage-regulating brake anti-lock method.

Background technique

The promotion and popularization of new energy vehicles, especially electric vehicles, has promoted the development of the brake system in the direction of brake-by-wire, which is not only consistent with the development trend of modern automobiles towards modularization, integration, and mechatronics, but also in line with the development of automobiles for braking. New requirements of the system.

Brake-by-wire systems can be divided into two categories, electro-hydraulic brakes (EHB) and electro-mechanical brakes (EMB). Among them, EHB replaces some mechanical parts in the traditional braking system with electronic components, and still retains the original mature and reliable hydraulic braking system to ensure the reliability of the braking system; at the same time, the EHB system can still use 12V vehicle-mounted For the power supply, the circuit system of the existing vehicle can meet the requirements. In addition, the EHB system has the advantages of safety, comfort, fast response, easy regenerative braking, and precise control of braking force. As for the EHB system, smooth, precise and fast hydraulic pressure control is the basic requirement for the braking system of the car.

The pressure regulator of a traditional ABS system generally consists of an accumulator, a hydraulic pump, and a solenoid valve (4 booster valves, 4 pressure relief valves). Due to the adoption of the integrated electronic hydraulic braking system, if the original ESC system is used, it will be redundant and wasteful in terms of structure, function and cost. Because, unlike traditional braking systems, EHB can be completely decoupled from the brake pedal, so that the master cylinder pressure can be controlled arbitrarily without affecting the pedal feel. The vehicle anti-lock braking safety priority method based on the integrated electro-hydraulic system proposed by the present invention uses only one electromagnetic valve for each wheel to realize the increase and decrease of pressure, and there is no difference between a pressure boost valve and a pressure relief valve, and hydraulic pressure is no longer used. Pump, low pressure accumulator. Although its structure has obvious advantages compared with the traditional ABS system, the control strategy needs to be redesigned to realize the ABS function.

Contents of the invention

The object of the present invention is to provide a brake anti-lock braking method of a vehicle master cylinder fixed-frequency voltage regulation in order to overcome the above-mentioned defects in the prior art.

The purpose of the present invention can be achieved through the following technical solutions:

A brake anti-lock braking method of a vehicle master cylinder fixed-frequency voltage regulation, comprising the following steps:

1) Control the piston of the main cylinder to move back and forth, so that the hydraulic pressure of the main cylinder can fluctuate;

2) Determine whether the wheel cylinder needs to be boosted or depressurized, and open or close the solenoid valve corresponding to the wheel cylinder;

3) Monitor the current speed of the vehicle in real time, and when the speed is less than 5m/s, the ABS system will stop functioning to prevent locking.

2. The anti-lock braking method according to claim 1, wherein said step 2) specifically comprises the following steps:

21) Set two thresholds A ₁ and A ₂ for the slip ratio of each wheel;

22) When the wheel slip rate exceeds the threshold value _A1 , the wheel cylinder needs to be depressurized; when the wheel slip rate is less than the threshold value _A2 , the wheel cylinder needs to be boosted;

23) When a wheel cylinder needs to be depressurized and the hydraulic pressure of the wheel cylinder is greater than the hydraulic pressure of the master cylinder, the solenoid valve corresponding to the wheel cylinder is opened, otherwise it is closed. When a certain wheel cylinder needs to be boosted, and At this time, when the hydraulic pressure of the wheel cylinder is lower than the hydraulic pressure of the master cylinder, the electromagnetic valve corresponding to the wheel cylinder is opened, otherwise it is closed.

The fluctuation range of the hydraulic pressure of the master cylinder varies with the adhesion coefficient of the road surface, and is obtained through test calibration.

The hydraulic pressure fluctuation of the master cylinder adopts a sinusoidal signal as the input signal of the motor torque command, superimposes two sinusoidal signals as the input of the motor torque command, and controls the motor by adjusting the period, amplitude and phase value of the two sinusoidal signals Output different torques to adjust the hydraulic pressure range of the master cylinder.

The formula for calculating the slip rate is:

Among them, λ is the slip ratio, V _x is the vehicle speed, w is the wheel angular velocity, and r is the wheel radius.

The method is realized by an integrated electro-hydraulic braking system, said integrated electro-hydraulic braking system comprising:

Brake pedal unit: including brake pedal assembly and pedal simulator, used to provide the driver with a reasonable brake pedal feeling and reflect the driver's driving intention;

Active pressure building unit: including motor, worm gear and rack, which is used to convert the rotational torque of the motor into translational thrust on the rack, thereby pushing the master cylinder to generate corresponding brake hydraulic pressure;

Brake execution unit: including brake master cylinder, brake wheel cylinder, solenoid valve, liquid storage tank and hydraulic pipeline, used to convert the thrust on the rack of the active pressure building unit into the hydraulic pressure of each wheel cylinder, and The corresponding braking torque is generated on the brake disc through the friction pad at the end of the brake wheel cylinder;

Control unit: including the vehicle controller, hydraulic pressure sensor, hydraulic pressure sensor, pedal displacement sensor, pedal force sensor and connecting lines, used to calculate the driver's driving intention after the vehicle controller obtains the pedal force and pedal stroke signals, And generate the target brake pressure, and realize the pressure closed-loop control through the feedback signal of the pressure sensor.

In the integrated electro-hydraulic braking system, each wheel only uses one solenoid valve to realize increasing and decreasing pressure.

The solenoid valve is a high-speed switching solenoid valve controlled by PWM or a linear solenoid valve controlled by position feedback.

Compared with the prior art, the present invention has the following advantages:

1. Simplified structure: The ABS of the integrated electronic hydraulic braking system has undergone great changes in the pressure regulator. Each wheel only uses a solenoid valve to realize the increase and decrease of pressure. The hydraulic pump and low-pressure accumulator are used again, which simplifies the structure of the braking system and saves costs.

2. Good anti-lock braking effect: In terms of control algorithm, the ABS master cylinder fixed frequency and pressure regulation strategy is designed. The anti-lock braking function of the road surface is attached to improve the driving safety of the vehicle.

Description of drawings

Fig. 1 is a logic block diagram of the constant-frequency voltage-regulating control of the anti-lock braking master cylinder of a vehicle based on the integrated electronic hydraulic braking system of the present invention.

Fig. 2 The method of obtaining the fluctuation range of the hydraulic pressure of the master cylinder.

Figure 3 shows the structure of the integrated electro-hydraulic system used.

In the figure, 1. Electronic control unit, 2. Permanent magnet synchronous motor, 3. Reduction transmission mechanism, 4. Liquid storage tank, 5. Normally open solenoid valve, 6. Hydraulic pressure sensor, 7. Brake wheel cylinder, 8. Brake master cylinder, 9, decoupling cylinder, 10, pedal simulator, 11, pedal displacement sensor, 12, brake pedal.

Figure 4 is a schematic diagram of the strategy of constant frequency and voltage regulation for the master cylinder.

Fig. 5 is a response diagram of a vehicle without applying the anti-lock braking strategy on a low-attachment road surface, wherein Fig. (5a) is a response diagram of vehicle speed, and Fig. (5b) is a response diagram of braking distance. .

Fig. 6 is the control effect diagram obtained by applying the above-mentioned fixed frequency and pressure regulation strategy of the anti-lock brake master cylinder of the vehicle on the low-attachment road surface. Among them, Fig. Figure (6c) is the diagram of the situation of the opening and closing of the solenoid valve, and Figure (6d) is the diagram of the braking distance response.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example

As shown in Figure 1, this embodiment provides a vehicle brake anti-lock braking master cylinder constant-frequency voltage regulation strategy based on an integrated electronic hydraulic braking system. The control strategy requires the master cylinder piston to move back and forth, so that the master cylinder The hydraulic pressure keeps rising and falling repeatedly. When a wheel cylinder needs to be depressurized and the hydraulic pressure of the wheel cylinder is greater than the hydraulic pressure of the master cylinder, the solenoid valve corresponding to the wheel cylinder is opened, otherwise it is closed. Similarly, when a wheel cylinder needs to be boosted and the hydraulic pressure of the wheel cylinder is lower than the hydraulic pressure of the master cylinder, the solenoid valve corresponding to the wheel cylinder is opened, otherwise it is closed.

When the vehicle brakes, if the speed of the vehicle is higher than the linear velocity of each wheel, there will be slip between the tire and the road surface, and the degree of slip is expressed by the slip rate.

In the formula: λ——slip ratio;

V _x —vehicle speed;

w——wheel angular velocity;

r - the radius of the wheel.

Set two threshold values A ₁ and A ₂ for the slip ratio of each wheel. When the slip ratio of the wheel exceeds the threshold value A ₁ , it indicates that the wheel cylinder needs to be depressurized; when the slip ratio of the wheel is less than the threshold value A ₂ indicates that the wheel cylinder needs to be boosted. At the same time, the vehicle speed is monitored. When the vehicle speed is less than 5m/s, the ABS system stops functioning regardless of the value of the slip rate.

As shown in Fig. 2, the hydraulic pressure fluctuation range of the master cylinder is different on road surfaces with different adhesion coefficients, and the fluctuation range is obtained through test calibration. The hydraulic pressure fluctuation of the master cylinder uses the sinusoidal signal as the input signal of the motor torque command, and uses the superposition of two sinusoidal signals as the input of the motor torque command, and controls the output of the motor at different rotation speeds by adjusting the period, amplitude and phase value of the two sinusoidal signals. Torque, so as to better adjust the hydraulic pressure range of the master cylinder.

As shown in Figure 3, the integrated electronic hydraulic braking system includes:

Brake pedal unit, including brake pedal assembly, pedal simulator, etc. Its function is to provide the driver with a reasonable brake pedal feeling and at the same time reflect the driver's driving intention.

Active pressure building unit, including motor, worm gear, rack and so on. Its function is to convert the rotational torque of the motor into the translational thrust on the rack, thereby pushing the master cylinder to generate corresponding brake fluid pressure.

Brake execution unit, including brake master cylinder, brake wheel cylinder, solenoid valve, liquid storage tank, hydraulic pipeline, etc. Its function is to be responsible for converting the thrust on the rack of the active pressure building unit into the hydraulic pressure of each wheel cylinder, and finally through the friction pads at the end of the brake wheel cylinder to act on the brake disc to generate corresponding braking torque.

Control unit, including vehicle controller, hydraulic pressure sensor, hydraulic pressure sensor, pedal displacement sensor, pedal force sensor and related circuits. Its function is that the vehicle controller obtains the pedal force and pedal stroke signals to calculate the driver's driving intention, coordinates with other systems of the vehicle to obtain the target braking pressure, and realizes pressure closed-loop control through the feedback signal of the pressure sensor.

Compared with the structure of the traditional ABS system, the integrated electro-hydraulic braking system has undergone great changes in the pressure regulator. Each wheel only uses a solenoid valve to realize the increase and decrease of pressure, and there is no pressure-increasing valve or pressure-reducing valve. points, hydraulic pumps and low-pressure accumulators are no longer used.

The solenoid valve is a high-speed switching solenoid valve controlled by PWM or a linear solenoid valve controlled by position feedback.

Combining with Figure 4, it is easier to understand the working principle of the master cylinder constant frequency voltage regulation. The sinusoidal signal of the thin solid line is the hydraulic pressure signal of the master cylinder, which is constantly vibrating at a certain frequency and amplitude, and the four thick solid lines represent the actual wheel cylinder hydraulic pressure of the four brake wheel cylinders respectively. Taking the left front wheel as an example, after judging that the wheel needs to be decompressed according to the current slip ratio of the wheel, when the hydraulic pressure value of the master cylinder (i.e. the thin solid line) is smaller than the actual hydraulic pressure value of the wheel cylinder (i.e. the thick dot-dash line), The corresponding solenoid valve is opened, and if the hydraulic pressure value of the master cylinder is not less than the actual hydraulic pressure value of the wheel cylinder, the corresponding solenoid valve is closed. The rest of the wheels follow the same logic.

In order to verify the effectiveness of the proposed vehicle anti-lock brake safety priority strategy, the hardware-in-the-loop test bench built based on the brake test was carried out on high and low adhesion roads respectively. The adhesion coefficient of the low-adhesion road surface is 0.2, and the initial vehicle speed is 60km/h. Figure 5 shows the vehicle speed, wheel speed and braking distance under the fixed-frequency voltage regulation strategy of the anti-lock brake master cylinder without applying the vehicle brake. Zero, the slip ratio becomes 1, that is, all four wheels are locked. Figure 6 shows when the ABS master cylinder fixed-frequency pressure regulation strategy works, the change of the hydraulic pressure of the wheel cylinder of the corresponding master cylinder, the change of the wheel speed, the opening and closing of the four solenoid valves, and the braking distance at this time. On low-adhesion roads, the ABS master cylinder fixed-frequency voltage regulation strategy realizes the anti-lock function. During the braking process, the slip ratios of the four wheels all vibrate near the optimal slip ratio. The braking distance is 66.47m, which is 66.47m compared Decreases without control. Effectively restrain the wheel slippage, reduce the braking distance, and ensure the safety and stability of the vehicle.

Claims (8)

1. A vehicle master cylinder constant frequency pressure regulating type anti-lock braking method is characterized by comprising the following steps:

1) controlling the main cylinder piston to move back and forth to enable the main cylinder hydraulic pressure to fluctuate;

2) judging whether the wheel cylinder needs to be pressurized or depressurized, and opening or closing an electromagnetic valve corresponding to the wheel cylinder;

3) and monitoring the current speed of the vehicle in real time, and stopping the ABS system to prevent locking when the speed of the vehicle is less than 5 m/s.

2. The method as claimed in claim 1, wherein the step 2) comprises the steps of:

21) two threshold values A are set for the slip ratio of each wheel₁And A₂；

22) When the wheel slip ratio exceeds the threshold value A₁When the pressure of the wheel cylinder is reduced, the pressure of the wheel cylinder is reduced; when the wheel slip ratio is less than the threshold value A₂When the pressure of the wheel cylinder is increased, the wheel cylinder needs to be increased;

23) when a certain wheel cylinder needs to be depressurized and the wheel cylinder hydraulic pressure is greater than the master cylinder hydraulic pressure, the electromagnetic valve corresponding to the wheel cylinder is opened, otherwise, the electromagnetic valve is closed, when a certain wheel cylinder needs to be pressurized and the wheel cylinder hydraulic pressure is less than the master cylinder hydraulic pressure, the electromagnetic valve corresponding to the wheel cylinder is opened, and otherwise, the electromagnetic valve is closed.

3. The method of claim 1, wherein the range of the master cylinder hydraulic pressure fluctuation varies with the road surface adhesion coefficient and is obtained by a test calibration.

4. The method as claimed in claim 1, wherein the master cylinder hydraulic pressure fluctuation uses a sinusoidal signal as an input signal of the motor torque command, two sinusoidal signals are superimposed as an input of the motor torque command, and the motor is controlled to output different torques by adjusting periods, amplitudes and phase values of the two sinusoidal signals, thereby adjusting the master cylinder hydraulic pressure range.

5. The method of claim 1, wherein the slip ratio is calculated by the following equation:

wherein,λ is slip ratio, V_xIs the vehicle speed, w is the wheel angular velocity, and r is the wheel radius.

6. A vehicle master cylinder constant frequency modulated anti-lock brake method according to any one of claims 1 to 5, wherein the method is implemented by an integrated electro-hydraulic brake system comprising:

a brake pedal unit: the brake pedal simulator comprises a brake pedal assembly and a pedal simulator, and is used for providing reasonable brake pedal feeling for a driver and reflecting the driving intention of the driver;

an active voltage building unit: the brake system comprises a motor, a worm wheel and a worm and a rack, and is used for converting the rotating torque of the motor into translational thrust on the rack so as to push a master cylinder to generate corresponding brake hydraulic pressure;

a brake execution unit: the brake system comprises a brake master cylinder, brake wheel cylinders, an electromagnetic valve, a liquid storage tank and a hydraulic pipeline, wherein the brake master cylinder is used for converting the thrust on a rack of an active pressure building unit into hydraulic pressure of each wheel cylinder, and a corresponding brake torque is generated by the action of a friction pad at the end of each brake wheel cylinder on a brake disc;

a control unit: the system comprises a vehicle controller, a hydraulic pressure sensor, a pedal displacement sensor, a pedal force sensor and a connecting circuit, and is used for calculating the driving intention of a driver after the vehicle controller acquires a pedal force and a pedal stroke signal, generating target brake pressure and realizing pressure closed-loop control through a feedback signal of the pressure sensor.

7. The method of claim 6, wherein only one solenoid valve is used for each wheel to increase or decrease pressure in the integrated electro-hydraulic brake system.

8. The method of claim 6, wherein the solenoid valve is a high speed switching solenoid valve controlled by PWM or a linear solenoid valve controlled by position feedback.