The braking principle of brake pads

The working principle of brakes mainly comes from friction. By utilizing the friction between brake pads and brake discs (drums), as well as the friction between tires and the ground, the kinetic energy of vehicle movement is converted into heat energy after friction, which stops the vehicle. A good and efficient braking system must be able to provide stable, sufficient, and controllable braking force, and have good hydraulic transmission and heat dissipation capabilities, to ensure that the force applied by the driver from the brake pedal can be fully and effectively transmitted to the master cylinder and various sub cylinders, and to avoid hydraulic failure and brake recession caused by high heat. The braking systems on cars can be divided into two categories: disc and drum brakes, but apart from cost advantages, drum brakes are far less efficient than disc brakes.

friction

Friction refers to the resistance of motion between the contact surfaces of two moving objects. The magnitude of friction force (F) is directly proportional to the product of the friction coefficient (μ) and the normal pressure (N) in the vertical direction on the friction force surface, expressed in physical formula as F=μ N. For the braking system, (μ) refers to the friction coefficient between the brake pads and the brake disc, and N is the force exerted by the brake caliper piston on the brake pads (Pedial Force). The greater the coefficient of friction, the greater the frictional force generated. However, the coefficient of friction between the brake pads and the disc will change due to the high heat generated after friction, which means that the coefficient of friction (μ) varies with temperature. Each type of brake pad has a different coefficient of friction variation curve due to different materials. Therefore, different brake pads will have different optimal working temperatures and applicable working temperature ranges. This is something that everyone must know when choosing brake pads.

Transmission of braking force

The force exerted by the brake caliper piston on the brake pads is called the Pedal Force. The force exerted by the driver on the brake pedal is amplified by the lever of the pedal mechanism, and then amplified by the power boost using the principle of vacuum pressure difference to push the brake master cylinder. The hydraulic pressure generated by the brake master cylinder utilizes the incompressible power transmission effect of the liquid, which is transmitted through the brake oil pipes to each slave cylinder. The pressure is amplified using the Pascal principle, pushing the piston of the slave cylinder to apply force to the brake pads. Pascal's Law refers to the principle that the pressure of a liquid at any position within a closed container is the same.

Pressure is obtained by dividing the applied force by the force area. When the pressure is equal, we can achieve the effect of dynamic amplification by changing the ratio of the applied and force areas (P1=F1/A1=F2/A2=P2). When used in braking systems, the ratio of master cylinder to slave cylinder pressure is the ratio of master cylinder piston area to slave cylinder piston area.

Equipped with ABS

ABS：Anti-lock Brake System， As the name suggests, it is an anti lock braking system. Everyone knows that the maximum braking effect occurs in the moment before the tire locks up. If the braking force can be kept in balance with the tire friction, then the maximum braking effect will be achieved. When the braking force is greater than the friction force of the tire, it will cause the tire to lock up. Once the tire locks up, the friction between the tire and the ground will change from "static friction" to "dynamic friction", not only greatly reducing the friction force, but also losing the ability to turn and track. Due to the fact that tire locking is the result of comparing the braking force and the friction between the tire and the ground, the limit of tire locking during vehicle movement will vary at any time depending on the characteristics of the tire itself, the condition of the road surface, the positioning angle, tire pressure, and the characteristics of the suspension system. ABS uses speed sensors installed on four wheels to determine whether the tires are locked or not, eliminating the uncertainty of human sensory factors and accurately controlling the timely release of hydraulic pressure from the brake cylinder, achieving the goal of preventing brake locking. At present, most ABS systems adopt a design that can be continuously stepped on and off 12-60 times per second (12-60Hz), which is already an ultra-high level of performance compared to top professional racing drivers who can step on and off 3-6 times. The higher the frequency of stepping on and off, the closer it can maintain the braking force at the edge of the limit. The accuracy and reliability that ABS can achieve have exceeded human limits, so we say that ABS is the most cost-effective equipment when buying a car. Especially the relative danger of Air Bag is even more so.

Doubts about ABS

Recently, many reports have pointed out that cars equipped with ABS have a higher probability of accidents than those without ABS, which has led to many people questioning the effectiveness of ABS. This is caused by the general lack of understanding among car owners about the braking system and ABS. Many people mistakenly believe that installing ABS can increase the limit of braking force or tire to ground friction. In fact, although ABS can maintain the maximum braking force as much as possible, it cannot increase the limit. Here it is reiterated that the limit of friction between the tire and the ground is determined by the characteristics of the tire itself, the condition of the road surface, the positioning angle, tire pressure, and the characteristics of the suspension system, but does not include ABS. ABS can fully and effectively utilize the braking system's capabilities, but it is ineffective in improving braking force or friction. In addition, when using ABS for high-speed evasion in emergency situations, please remember to first perform the main deceleration action in a straight line before turning the steering wheel. When turning the steering wheel, do not release the brake pedal, and do not panic due to the feedback action from the ABS pedal. There are also many people who believe that ABS requires a big foot on the brake to be effective, which is another misconception about ABS. The anti lock braking system is only effective when the wheels lock up. If you drive on icy roads, as long as you lightly press the brake, the ABS may not stop moving; If you change to a set of large-sized hot melt tires with super strong grip and drive on a flat and dry road surface, if your braking system has not been strengthened, even if you step on the brake pedal with all your strength, the ABS may still not move because your braking force is not enough to lock the tires. If car dealers can effectively inform consumers of the above two points while selling cars equipped with ABS, then ABS can truly become an "active safety" equipment. Otherwise, if consumers feel confident when stepping on the brakes, the probability of accidents may increase instead of decreasing.