Understanding the friction performance of brake pads

The quality of car parts is directly related to the reliability of vehicle braking. In addition to 100% safety, car owners also expect the best braking comfort, responsiveness, noiselessness and smoothness at all times. For brake pads, the most important thing is the choice of friction material, which basically determines the braking performance of the brake pads. Friction materials can be divided into four types based on basic materials: asbestos, NAO type (that is, asbestos-free organic type), semi-metal and special fiber. In 1999, my country banned the use of asbestos in friction plates. Currently, semi-metallic friction materials are commonly used in China, mainly steel or copper materials.

The performance of friction plates should have four basic requirements:

1. Appropriate friction coefficient and stability.

Friction coefficient is one of the most important technical indicators of friction materials, which determines the basic braking torque of the brake pad. Usually it is not a constant and changes with temperature, pressure, speed or surface state and friction environment. When affected by these factors, the friction coefficient changes less, which is the ideal friction coefficient. The national standard strictly requires manufacturers to indicate the friction coefficient on the packaging. The friction coefficient must be appropriate. If it is too high, it will cause wheel locking, loss of direction and burning during braking. If it is too low, the braking distance will be too long.

2. Reliable security.

Brake pads will generate instantaneous high temperatures when braking, especially when driving at high speed or during emergency braking. At high temperatures, the friction coefficient of the friction plate will decrease, which is called thermal decay. Thermal decay resistance determines the safety during high temperature conditions and emergency braking. The friction disc maintains its stability and recovery performance under various working conditions, that is, it requires good heat resistance, stable performance at high temperatures, low sensitivity under different humidity and water immersion, and can recover as soon as possible after being exposed to water. performance. At the same time, it must have good physical and mechanical properties, which can not only meet the requirements during processing, but also maintain good performance.

3. Satisfactory comfort.

Comfort is a direct reflection of friction performance, including braking feel, noise, dust, smoke, odor, etc. With the increase in private cars and the improvement of people's living standards, comfort has increasingly become an important indicator of friction plates on the premise of meeting the basic premise of safety. Among the comfort indicators, car owners are often most concerned about the noise of the brake pads. In fact, noise is also the most difficult problem for all friction material manufacturers to solve. Noise is caused by abnormal friction between the friction plate and the friction disc. The causes are very complex. Braking force, brake disc temperature, vehicle speed and climate conditions may all be the causes of noise. In addition, the causes of noise in the three different stages of braking initiation, braking implementation and brake release are different. If the noise frequency is between 0-500Hz, it will not be felt in the car, but if it exceeds 1500Hz, the car owner will clearly feel the braking noise.

4. Good wear resistance, reliability and durability.

This is an important indicator to measure the service life of friction materials, and it is also a product indicator that users generally pay attention to. Maintaining sufficient mechanical strength at room temperature and high temperature is an important factor affecting the reliability of the friction pad, but it is also required not to scratch the brake disc or brake drum. Its wear resistance is the main factor affecting durability. The main factors affecting wear during use are pressure, speed and temperature, with temperature being the first. The front brake pads can usually guarantee a service life of 30,000 to 50,000 kilometers, and the rear brake pads can usually guarantee a service life of 60,000 to 80,000 kilometers. The large particles of graphite and brass used in the brake pad material also reduce wear on the brake disc. In particular, the noise during use is reduced to a minimum to ensure no pollution to the environment. It produces no noise when braking and does not emit odor at high temperatures.

Due to friction, the friction pad will gradually be worn. Generally speaking, the lower the cost of the brake pad, the faster it will wear. The brake pads must be replaced in time after the friction material is used up, otherwise the steel plate and the brake disc will be in direct contact, eventually losing the braking effect and damaging the brake disc.

Friction coefficient of brake pad:

EE grade: 0.25-0.35 is suitable for European and American cars. The brake pads are relatively large and the friction coefficient is relatively low.

FF grade: 0.35-0.45 international standard friction coefficient.

GG level: 0.45-0.55 is suitable for European models, especially German cars. Because there is no speed limit when driving in Germany, the friction coefficient must be higher.

HH grade: 0.55-0.65 racing brake pads allow the friction coefficient to change under high temperature conditions. Generally, at 100 degrees, the friction coefficient increases or decreases by 0.08, and at 350 degrees, the friction coefficient increases or decreases by 0.14.

Suitable for use in the Chinese market, grade FF. The above are high standard requirements for friction materials, and it is difficult to fully meet them. Therefore, different requirements are put forward for different models and different usage conditions. In order to meet the needs of different users, brake pad products are also gradually developing into diversification.