1 overview
Automobile braking system is a series of special devices that can reduce the speed of automobile forcibly. The main function of the braking system is to slow down or even stop the moving car, keep the speed of the downhill car stable, and keep the stopped car motionless.
2 classification
1. Automobile braking system can be divided into:
Service braking system: a set of special devices to slow down or even stop a moving car, which is often used during driving.
Second braking system: a set of devices to ensure that the car can still slow down or stop when the service braking system fails.
Parking brake system: It is operated by the driver's hand, so it is also called handbrake system. Its function is to keep cars that have been parked on various roads in place.
Auxiliary braking system: a set of devices used to stabilize the speed of a car when it goes down a long slope.
The service braking system and parking braking system are the minimum equipment of each automobile braking system, and only some automobiles are equipped with an auxiliary braking system and a second braking system.
2. According to the braking energy can be divided into:
Hand braking system: The driver's physical strength is the only braking energy.
Dynamic braking system: converts the power generated into hydraulic pressure and air pressure as braking energy.
Servo braking system: the hydraulic pressure (or air pressure) converted from manpower and engine power is used as braking energy.
3. According to the transmission mode of braking energy, the braking system can be divided into:
Mechanical: transmit braking energy by mechanical means.
Hydraulic type: braking energy is transmitted by hydraulic pressure.
Pneumatic type: braking energy is transmitted by air pressure.
3 composition
The braking system is mainly composed of four parts: energy supply device, control device, transmission device and brake.
1. Energy supply device: including various components for supplying and adjusting the energy required for braking and improving the state of energy transmission medium. For example, the human body can be used as braking energy.
2. Control device: including various components that generate braking effect and control braking effect. Such as a brake pedal.
3. Transmission device: including various components and pipelines that transfer braking energy to the brakes. Such as brake master cylinder, wheel cylinder and connecting pipeline.
4. Brake: a component that generates a force that hinders the movement or movement trend of the vehicle.
4 Brake
Friction brakes used in various automobiles can be divided into drum type and disc type.
The rotating element in the drum friction pair is a brake drum, the working surface is a cylindrical surface, the disc-shaped rotating element is a disc-shaped brake disc, and the working surface is the disc end surface.
Drum brake
Drum brake mainly includes brake wheel cylinder, brake shoe, brake drum, friction plate and return spring. Mainly through the hydraulic device, the friction plate rubs against the inner side of the brake drum rotating with the old wheel, so as to achieve the braking effect.
When the brake pedal is depressed, the piston of the brake master cylinder is pushed to move, and then pressure is generated in the oil circuit; Brake fluid transfers pressure to the brake cylinder of the wheel to push the piston, and the piston pushes the brake shoe to move outward, so that the friction plate and the brake drum rub, thus generating braking force. It can be seen from the structure that the drum brake works in a relatively closed environment, and the heat generated in the braking process is not easy to dissipate, and frequent braking affects the braking effect. However, drum brakes can provide high braking force and are widely used in heavy vehicles.
Disc brake
Disc brake, also called disc brake, is mainly composed of brake disc, caliper, friction plate, cylinder and oil pipe. The disc brake applies pressure to the caliper through the hydraulic system, so that the brake friction plate rubs against the brake disc rotating with the wheel, thus achieving the purpose of braking.
Unlike closed drum brakes, disc brakes are open. The heat generated in the braking process can be quickly dissipated, which has good braking efficiency. Now it has been widely used in cars. 5ABSABS is the abbreviation of English anti-lock braking system. According to statistics, when a car suddenly brakes, more than 90% drivers often slam on the brake pedal with one foot. At this time, the car is very easy to slip and sideslip, which is also commonly known as "tail flick". There are many reasons for automobile sideslip, such as driving speed, ground condition, tire structure, etc. But the most fundamental reason is that the rolling friction between the tire and the ground will suddenly become sliding friction when the automobile brakes suddenly, and the grip of the tire will almost be lost. At this time, it will be useless for the driver to twist the steering wheel. Aiming at the root cause of this side slip phenomenon, automobile experts have developed a set of anti-skid braking devices such as ABS. ABS is mainly composed of ECU control unit, wheel speed sensor, brake pressure regulating device and brake control circuit. During the braking process, the ABS control unit continuously obtains the wheel speed signal from the wheel speed sensor and processes it to judge whether the wheel is about to lock up. The characteristic of ABS braking is that when the wheel tends to the locking critical point, the pressure of the brake cylinder does not increase with the increase of the pressure of the main brake pump, but changes near the locking critical point.
If it is judged that the wheel is not locked, the brake pressure regulating device will not work and the braking force will continue to increase; If it is judged that a wheel is about to lock up, ECU sends an instruction to the brake pressure regulating device to close the passage between the brake cylinder and the brake wheel cylinder, so that the brake wheel pressure will not increase; If it is judged that the wheel is locked and dragged, an instruction is sent to the brake pressure adjusting device to reduce the oil pressure of the brake wheel cylinder and the braking force. In the past, consumers used to regard ABS as an important indicator when buying a car. With the development of technology, at present, most domestic cars adopt ABS as the standard configuration. Strictly speaking, the function of ABS is mainly to ensure the maneuverability and stability of the vehicle itself when braking within the physical limit performance. At the same time, it can also prevent the pure slip of the tire during acceleration, and improve the acceleration performance and handling stability. 6ESP
Electronic Stability Program (ESP) is a patent of Bosch Company. Other companies have developed similar systems, such as BMW's DSC, Toyota's VSC and so on. ESP system is actually an extension of ABS (Anti-lock Braking System) and ASR (Anti-skid Driving Wheel System), which can be said to be the highest form of anti-skid device for automobiles at present. It is mainly composed of control assembly, steering sensor (monitoring the steering angle of the steering wheel), wheel sensor (monitoring the rotating speed of each wheel), sideslip sensor (monitoring the rotation state of the car body around the longitudinal axis), lateral acceleration sensor (monitoring the centrifugal force when the car turns) and so on. The control unit judges the driving state of the vehicle through the signals of these sensors, and then sends out control instructions.
When the car is driving fast or turning, the lateral force will make the car unstable and prone to accidents. ESP system can prevent problems before they happen. When an obstacle suddenly appears in front of the vehicle, the driver must turn left quickly. At this time, the steering sensor transmits this signal to the ESP control assembly, and the sideslip sensor and the lateral acceleration sensor signal that the vehicle is understeer, which means that the vehicle will directly rush to the obstacle. Then the ESP system will brake the rear wheel in an instant, generating the reaction force needed for steering, so that the car can drive according to the steering intention. The hand brake of the manipulator is connected to the rear brake shoe with a steel wire rope to brake the car. Long-term use of hand brake will lead to plastic deformation of steel wire. Because this deformation is irreversible, long-term use will reduce the utility and increase the stroke of the handbrake.
There is also a return spring used in conjunction with the handbrake. When the handbrake is pulled, the spring is elongated; When the handbrake is released, the spring returns to its original length. When the handbrake is used for a long time, the spring will deform accordingly. When any part is used frequently for a long time, its utility will be reduced. Hand braking principle
After the handbrake is pulled, it uses a hydraulic slave cylinder to push the hydraulic master cylinder under the car to move, and then drives the air valve (this is designed so that the cab can't hear the sound of air), and then brakes the transmission shaft after the air valve moves. 8 electronic handbrake
Full name of electronic handbrake EPB: Electric parking brake (EPB) refers to a technology that integrates the functions of temporary braking during driving and long-term braking after parking, and realizes parking braking through electronic control. In fact, EPB is an upgraded version of the traditional handbrake, which turns the hand of the traditional handbrake into electric. Electronic handbrake uses computer to control motor to clamp or loosen handbrake, and uses button P instead of handbrake handle. The whole control logic is not complicated. The traditional hand brake needs to be released manually by the driver or skillfully matched with the throttle and clutch when starting on the ramp to start comfortably. The automatic parking function is provided with accurate parking force by the controller through the slope sensor. When starting, the parking control unit automatically releases the parking brake when the driving force is greater than the driving resistance by calculating the information provided by the clutch distance sensor, the clutch kneading speed sensor and the accelerator pedal sensor, so that the car can start smoothly. 9 abstract
With the continuous improvement of automobile power, the development of braking technology must also follow closely. As the premise of automobile active safety, we need not only the improvement of braking performance, but also how to make the automobile braking system more intelligent and minimize man-made accidents, which is the direction of future automobile and parts manufacturers.
(This article is partly from the Internet)