Common braking device[汽车维修知识]

Brake systemIt is a key component related to the safety of people and vehicles,CarThe braking system is equipped with a variety of devices in accordance with the requirements of reliability and labor saving.The most common ones are dual-circuit braking system and vacuum brakingSuperchargerEtc.
Most light vehicles use hydraulic brakes. Since they are hydraulic, they need to use pipelines. The dual-circuit brake system means that there are two independent hydraulic brake pipeline systems in the system, which play the role of insurance. Generally, front-wheel-drive cars usually adopt cross-diagonal lines. The front cavity of the master cylinder is connected to the brake pipes of the right front wheel and the left rear wheel, and the rear cavity is connected to the brake pipes of the left front wheel and the right rear wheel. Connected to form a crossed "X"-shaped diagonal line. The advantage of this is that when one braking system fails, the other system can still perform minimal braking without deviation. For rear-wheel drive cars, because of their heavy load, the front and rear wheels are mostly braked independently, that is, there are two sets of master cylinders, one set to control the front wheel braking, and the other to control the rear wheel braking.
As the name implies, the vacuum brake booster uses vacuum to boost pressure.This device is a power-assisted device, usually installed on the side wall of the engine compartment in front of the dashboard of the cab, and connected in series withBrake pedalBetween it and the brake master cylinder, it acts to increase the pedal force, thereby saving the driver's effort, so that some weak ladies or elderly people can also drive the car at will.
The working principle of the vacuum brake supercharger is to use the pressure difference between the negative pressure generated by the engine and the atmospheric pressure to force the rubber diaphragm in the supercharger to move and push the brake master cylinderPiston, In order to reduce the force of people stepping on the brake pedal.The rubber diaphragm inside the vacuum brake booster is divided into two cavities on both sides (A and B in the figure). When the brake pedal is not pressed, the engineIntake manifoldThe negative pressure is introduced into the cavities on both sides of the diaphragm, and the pressure is balanced, so the supercharger does not work; when the brake pedal is stepped on, the joystick moves to make the vacuum hole of the (B) cavity on the side of the rubber diaphragm of the supercharger (Connected to the engine intake manifold) is closed and the air hole is opened to allow outside air to enter. Since the air pressure in the chamber (B) is greater than the air pressure in the other chamber, the rubber diaphragm is forced to move and drives the piston of the brake master cylinder to move, thereby acting Pressurization effect; when the brake pedal is not stepped, the joystick is reset under the action of the compression spring, the air hole is closed, the vacuum hole is opened, the air pressure in the two chambers of the supercharger is equal, and the rubber diaphragm returns to the original Location.The car is in a hurry at high speedBrake, If the front and rear wheels are not balanced or the braking force is unbalanced, the tail flick and other out-of-control phenomena will occur. Theoretically, the ideal braking force distribution curve should be parabolic when the vehicle is empty or fully loaded, and the braking force distribution curve is determined by the position of the center of mass of the vehicle and the specific braking movement process, that is, the ideal The braking force should be distributed in proportion to the weight load of the front and rear wheels.Under the guidance of this idea, engineers developed a component called "proportional valve", which is similar toABSHydromechanical devices acting. Therefore, some vehicles that are not equipped with ABS anti-lock braking system are equipped with this device to keep the braking force in an ideal state and avoid or reduce the occurrence of out of control. The force of the brake pedal and the force caused by the change of the car load will cause the proportional valve to work.
If the proportional valve can sense the change of external force caused by the change of vehicle load and realize the load-sensing adjustment, this kind of proportional valve is called the load-sensing proportional valve. The load-sensing proportional valve uses the change in the distance between the body and the axle (external force) to change the preload of the spring, and adjusts accordingly as the vehicle load increases, so that an approximation can be obtained under any load condition Ideal braking force distribution. It is installed on the pipeline between the brake master cylinder and the rear wheel brake cylinder, and is composed of a shell, a plunger, a valve, and a spring. The oil inlet hole of the casing is communicated with the oil outlet of the brake master cylinder, and the oil outlet is communicated with the wheel brake cylinder.
When the external force is small, the plunger of the load-sensing proportional valve is pushed to the far right under the action of the spring preload, the two holes are connected, and the pressure of the master cylinder and the sub-cylinder are equal. When the external force is greater than the spring pre-tightening force, the plunger is forced to move left, so that the plunger contacts the valve and closes the valve, cutting off the channel from the master cylinder to the sub-cylinder; if the external force pressure continues to increase, it will cause the column The plug moves to the right, the plunger is out of contact with the valve, the valve is opened again, and the master cylinder and the sub-cylinder communicate with each other again. In this way, the repeated action of the proportional valve makes the hydraulic pressure of the sub-cylinder continuously adjusted, that is, the rear wheel braking force is continuously adjusted.

Related:

·What is platinumSpark plug? What is a dual platinum spark plug? What are the advantages of platinum spark plugs?
·What is an iridium spark plug and what are the advantages?
·Overhaul example of main components of Accord VTEC system[汽车维修知识]
·Talking about electronic braking force distribution system (EBD)[汽车修理常识]
·Maintenance of ABS system should pay attention to ten major problems[汽车修理常识]
·Brake shoe "simulated brake boring" process[汽车修理常识]