Brake Pads: The Critical Line of Defense for Automotive Braking
In the complex structure of an automobile, brake pads are a key component ensuring driving safety. As the core part of the braking system, knowledge about their working principle, types, performance indicators, and replacement cycle is closely related to our travel safety.
1. Working Principle of Brake Pads
When you press the brake pedal, the piston in the master brake cylinder moves under pressure, pushing brake fluid along the pipeline to the wheel cylinders of each wheel. The piston in the wheel cylinder extends under the pressure of the brake fluid, pressing the brake pads tightly against the rotating brake disc or brake drum. At this point, strong friction is generated between the brake pads and them, converting the kinetic energy of the moving vehicle into thermal energy, reducing the wheel speed, and thus achieving deceleration or braking of the vehicle.
2. Diverse Types of Brake Pads
Classified by Brake Type
• Disc Brake Pads: Commonly used in passenger cars, featuring good heat dissipation and fast response.
• Drum Brake Shoes: Mostly used in large vehicles, with low cost but inferior heat dissipation and braking efficiency compared to disc brakes.
• Truck Brake Linings: Specifically designed for trucks to meet their braking needs under heavy load and complex working conditions.
Classified by Material
• Semi-Metallic Brake Pads: Containing a certain proportion of metal components, they have a high friction coefficient (0.4-0.5) and can withstand temperatures up to around 400°C, but tend to produce noise at low temperatures and cause more wear to brake discs.
• Low-Metallic Brake Pads: With lower metal content, they improve some shortcomings of semi-metallic ones but have a shorter service life.
• Non-Metallic Brake Pads: Made of aramid, glass fiber, and other fibrous materials, their performance varies by formula and process.
• Carbon Fiber Brake Pads: Possessing excellent thermal conductivity and high-temperature resistance, they cause little wear to brake discs and have a long service life, but are expensive and mainly used in aircraft, high-end sports cars, etc.
• Ceramic Brake Pads: Made by mixing ceramic fibers and curing with organic binders, they have a stable friction coefficient (0.4-0.5), balanced high and low-temperature performance, can withstand temperatures above 600°C, wear slowly, have a long service life, produce little noise during braking, and rarely generate brake dust.
3. Key Performance Indicators
• Braking Performance: Related to daily braking effect, usually measured by friction coefficient. The state stipulates that the friction coefficient of brake pads at 100°C should be between 0.3-0.7, and that of ordinary vehicles is generally 0.28-0.40.
• Fade Performance & Recovery Performance: Test the performance of brake pads during high-temperature continuous braking; high-quality ones have low fade rate and fast recovery.
• Wear: Related to material, driving habits, and road conditions; good wear resistance reduces replacement costs.
• Noise: Influenced by multiple factors, with brake pad hardness being one-overly hard pads tend to generate noise.
• Others: Including shear strength, hardness, compressibility, etc., which collectively affect performance and service life.
4. Replacement Cycle & Judgment Methods
The replacement cycle of brake pads is not fixed, as it is affected by usage frequency, driving habits, road conditions, and material. Generally, front brake pads are replaced every 30,000-50,000 kilometers, and rear ones every 50,000-80,000 kilometers.
Judgment methods:
1. Thickness Observation: Replace when wear leaves only 2-3mm.
2. Noise Listening: A sharp squeaking sound may indicate the wear limit is reached.
3. Brake Feeling: A soft pedal, longer stroke, or increased braking distance suggests a need for inspection and replacement.
Though small in size, brake pads shoulder the important responsibility of vehicle braking. Understanding this knowledge helps us choose suitable brake pads and replace them timely to ensure travel safety.
