Jiaozuo brake

General working principle of braking system

The general working principle of a braking system is to use the mutual friction between non rotating components connected to the vehicle body (or frame) and rotating components connected to the wheels (or transmission shaft) to prevent the rotation or tendency of the wheels.

A simple schematic diagram of the hydraulic braking system can be used to illustrate the working principle of the braking system. A metal brake drum with an inner circular surface as the working surface is fixed on the wheel hub and rotates with the wheel. On the fixed brake base plate, there are two support pins supporting the lower ends of the two curved brake shoes. The outer circular surface of the brake shoe is equipped with friction plates. The brake base plate is also equipped with a hydraulic brake wheel cylinder, which is connected to the hydraulic brake master cylinder installed on the frame using oil pipe 5. The piston 3 in the master cylinder can be operated by the driver through the brake pedal mechanism.

When the driver steps down on the brake pedal to compress the brake fluid, the wheel cylinder piston presses the brake shoes against the brake drum under hydraulic pressure, causing the brake drum to reduce its rotational speed or remain stationary.

The resistance torque that must be applied to stop or decelerate the mechanical operating components is called the braking torque. The braking torque is the basis for designing and selecting brakes, and its size is determined by the mechanical type and working requirements. The performance of the friction materials (brake components) used on the brake directly affects the braking process, and the main factors affecting its performance are the working temperature and temperature rise rate. Friction materials should have high and stable friction coefficients and good wear resistance. Friction materials are divided into two categories: metallic and non-metallic. The former commonly used include cast iron, steel, bronze, and powder metallurgy friction materials, while the latter includes leather, rubber, wood, and asbestos.

When understanding the braking system of a certain car model, you may often hear the words "front disc rear drum" or "front disc rear drum". So, what exactly does it mean? Recently, some readers asked questions about the automobile brake system via email, such as the difference between disc brake and drum brake, the difference between ventilated disc and solid disc, etc.

At present, many middle and low-end models with small engine displacement in the car market mostly use "front disc and rear drum" brake systems, that is, the front wheel uses disc brakes, and the rear wheel uses drum brakes, such as the common FAW Volkswagen Jetta Jetta, Changan Suzuki Oto and Antelope, BYD Fryer, Dongfeng Dongfeng Yueda Kia Qianlima, Shanghai GM Sail, etc. Let's first briefly understand the drum brakes commonly used in the rear wheels.

The actual application difference is very obvious, and the disc brake is better than the drum brake. The asbestos material in brake drums can cause cancer. Drum brake and disc brake have their own advantages and disadvantages. In terms of braking effect, the difference between drum brake and disc brake is not significant, because when braking, it is the friction between the tires and the ground that gradually stops the car. If the car body is small and lightweight, using drum brakes on the rear wheels is enough to generate sufficient friction between the tires and the ground. If the rear wheels use disc brakes, the ABS and EBD systems will automatically reduce their braking force to ensure that the rear wheels do not lose grip and slip or lock up.

In terms of heat dissipation, disc brakes dissipate heat faster than drum brakes, and ventilated disc brakes have better heat dissipation effects; In terms of sensitivity, the disc brake will be higher, but in rainy days when the road is muddy, the braking effect will be greatly reduced when the brake disc is stained with mud, which is also the disadvantage of the disc brake; In terms of cost, drum brakes are lower than disc brakes and have a longer service life. Therefore, some mid to low end vehicles often use drum brakes, while models above mid to high end use four wheel disc brakes.

From the point of view of economy and practicality, car designers generally adopt a hybrid form, with front wheel Disc brake and rear wheel drum brake. During the braking process of a four-wheel sedan, due to the effect of inertia, the load on the front wheels usually accounts for 70% -80% of the total load of the car, so the braking force on the front wheels is greater than that on the rear wheels. In order to save costs, car manufacturers use Disc brake at the front wheel and drum brake at the rear wheel. For medium and high class cars with four-wheel Disc brake, the front wheel ventilated Disc brake is used for better heat dissipation, and the rear wheel is also used for non ventilated disc brake, which is also the reason for cost. After all, the manufacturing process of the ventilation disc type is much more complex, and the price is relatively expensive. With the development of material science and the reduction of cost, Disc brake has the tendency to gradually replace drum brake in the field of cars.

Generally, brakes apply braking torque to rotating components through their fixed components, reducing the rotational angular velocity of the latter. At the same time, they rely on the adhesion between the wheels and the ground to generate braking force on the road surface to slow down the car. Any brake that generates braking torque through the friction between fixed components and the working surface of rotating components is called a friction brake. The friction brakes currently used in automobiles can be divided into two categories: drum and disc brakes.

The brake system is called a wheel brake, where the rotating components are fixed on the wheel or half axle, and the braking torque directly acts on both sides of the wheel. The rotating component is fixed on the transmission shaft of the transmission system, and its braking torque is distributed to the brakes on both sides of the wheels through the drive axle, which is called the central brake.