The core function of the electric braking system is to make the driving car decelerate or even stop forcibly according to the driver's intention, so that the stopped car can be stabilized under various road conditions (including on the slope), so that it can drive downhill. The speed of the car is stably controlled. At present, electric braking systems mainly include pneumatic braking systems and hydraulic braking systems. Pneumatic braking uses high-pressure gas as the braking medium, which is then sent to each brake cylinder through the pipeline to achieve the braking effect; hydraulic braking is the brake master cylinder using the brake fluid as the braking medium, through the brake The pipeline is delivered to each brake cylinder to achieve the braking effect.
1. Air brake system
The pneumatic braking system is based on the traditional pneumatic braking system, which replaces some mechanical components with electric components, and the electric control components and electric motors drive the compressor to generate compressed gas to provide pneumatic braking force.
(1) Composition of pneumatic braking system
The main key parts include:
1) Quick release valve
2) Condenser
3) Dryer
4) Four-circuit protection valve
If one circuit of the service brake system fails, the air of the other three circuits will leak from the failed circuit until the dynamic closing pressure.
5) Brake master cylinder.
6) Hand brake valve. The hand brake valve is used to manipulate the emergency brake and parking brake of a vehicle with a spring brake. It is realized by inflating and deflating the spring air chamber of the spring brake.
7) Relay valve.
Principle of Braking System
The electric air compressor first enters the compressed air into the dryer through the condenser (condenser). After the compressed air is cooled in the dryer and separated from oil and water, it enters the four-circuit valve and is divided into four circuits: one circuit passes through the front brake air reservoir , The rear chamber of the dual-chamber brake valve and the quick release valve lead to the forward brake chamber: the other circuit leads to the rear brake chamber through the rear brake reservoir, the front chamber of the dual-chamber brake valve and the relay valve ; The other two circuits are respectively used for parking brake and provide air source for other assemblies. When one of the circuits fails, the other circuit can still continue to work to maintain the car with a certain braking ability, thereby improving the safety of the car.
The simple principle of the pneumatic braking system is shown in Figure 3-128. In the picture, the compressed air in the air reservoir is supplied to the inlet of the brake pedal, and the other is supplied to the inlet of the pressure control module. When the driver steps on the brake pedal, the electronic control unit senses the driver's braking intention according to the signal from the brake pedal displacement sensor, and calculates the brake gas according to the wheel speed sensor signal and the brake pad wear sensor signal sent by the pressure control module. The electronic control unit sends a control signal to the pressure control module through the CAN bus to open the air pressure required in the chamber, and the compressed air enters the brake air chamber through the pressure control module to realize the control of the pressure in the brake air chamber.
When the electronic control part of the brake system fails, as the humidifier steps on the brake pedal, the compressed air in the air supply pipe at the inlet of the brake pedal enters the control pipeline, thereby controlling the outlet of the pressure control module to open, and the compressed air can also pass through the pressure The control module enters the brake chamber and activates the brake to apply frictional braking torque.
The characteristics of the pneumatic braking system are as follows: Unlike the traditional pneumatic braking system, which controls the solenoid valve action of the brake field through the pressure control pipeline, the control signal issued by the electronic control unit in the pneumatic braking system transmits the air in a very short time. At the solenoid valve upstream of the chamber, and control it to perform corresponding actions, shorten the "pressure building time" for the air pressure to reach the control chamber after the brake pedal is stepped on, shorten the braking distance, and improve the braking safety.
2. Hydraulic brake system
The hydraulic braking system is based on the traditional hydraulic braking system, which replaces some mechanical components with electronic components, and the hydraulic braking force is generated by the electronic control components.
(1) Composition of hydraulic brake system
The hydraulic brake system is generally composed of brake pedal, pedal stroke sensor, pedal feel simulator, pressure supply unit partial pressure adjustment unit, electronic control unit, pressure sensor, brake master cylinder, brake wheel cylinder, liquid storage tank, brake Moving piping
The pressure supply unit establishes the brake pressure for the brake pipeline. According to the different ways of establishing the brake pressure, the external pressure supply unit can be divided into two categories: the pressure supply unit based on the high-pressure accumulator and the electric brake master cylinder. Pressure supply single line
① Pressure supply unit based on high pressure accumulator. The pressure supply unit based on the high-pressure accumulator is composed of an electric motor and a high-pressure accumulator. The brake fluid in the liquid storage tank enters the high-pressure accumulator through the electric motor and the pump to establish the brake pressure.
② Pressure supply unit based on electric brake master cylinder. The new pressure supply unit based on the electric brake master is composed of a motor transmission mechanism (ball screw or worm gear) and a brake master cylinder. The torque of the motor is converted into linear thrust through a roller screw or a worm gear. At the same time, the ball screw and worm gear are used as a reducer. The motor speed is reduced to increase the torque and push the master cylinder piston to build up the brake pressure.
(2) Principle of hydraulic brake system
The schematic diagram of the hydraulic brake system based on the high-pressure accumulator is shown in the picture. The high-pressure accumulator in the pressure supply unit always stores high-pressure brake fluid. When the pressure is insufficient, the pump is driven by the motor to pump the brake fluid in the reservoir into the high-pressure accumulator to establish a high-pressure brake source. . When the driver steps on the brake pedal, the brake fluid in the storage tank enters the pedal feel simulator through the brake master cylinder. The pedal feel simulator provides the driver with a pedal feel similar to the traditional brake system. At the same time, the electronic control unit senses the driver’s brake pattern according to the pedal stroke sensor signal, and controls the solenoid valve group in the hydraulic adjustment unit to control the brake fluid from the high-pressure accumulator into the wheel brake cylinder, and finally achieve wheel alignment. Control of cylinder brake pressure.
When the pressure supply unit fails, the backup valve opens, and the brake fluid in the brake master cylinder can enter the brake wheel cylinder to ensure
The vehicle still has a certain amount of braking power.
The schematic diagram of the hydraulic brake system based on the electric brake master cylinder is shown . The driver's braking demand is detected by the step sensor and input into the electronic control unit. The electronic control unit controls the electric motor to directly drive the transmission mechanism. The pedal and push rod together move through the coupling mechanism to push the brake master cylinder piston to establish braking pressure. The brake fluid from the brake master cylinder enters the brake wheel cylinder through the hydraulic adjustment unit. The pedal force compensator located in the coupling mechanism can eliminate the change of pedal force, thereby ensuring a certain brake pedal feel of the driver.
When the pressure supply unit fails, the brake pedal can still directly push the brake master cylinder to generate enough braking force to meet the braking requirements.
For the above two hydraulic braking systems, when the braking force of a certain wheel needs to be adjusted independently, the solenoid valve group corresponding to the wheel cylinder in the hydraulic adjustment unit will be increased according to the wheel cylinder pressure sensor signal and the target wheel cylinder pressure. The control of pressure, decompression or pressure holding realizes the control of the braking force of the wheel.
(3) Features of hydraulic brake system
The hydraulic brake system has changed the pressure establishment method, and the decoupling brake pedal force no longer affects the braking force of the whole vehicle. A variety of vehicle control functions such as automatic emergency brake control and electronic parking brake are integrated.
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