Commercial vehicle safety innovation: WABCO pneumatic disc brakes

In Europe in the mid-1990s, ADB (Air Disc Brake) was widely used in commercial vehicles. Compared with the drum brake, the disc brake has quick heat dissipation, light weight, simple structure and convenient adjustment. Especially under high load, it not only has good high temperature resistance, stable braking effect, but also high thermal stability.

In China, the application of disc brakes in cars, light-duty, cargo trucks, luxury passenger cars and heavy-duty trucks is becoming more and more widely used. With the improvement of highway traffic conditions in China, (high-speed) highways have developed rapidly, and vehicle performance and speed have also been continuously improved. People travel more in pursuit of fast and comfortable riding methods. The disc brake can improve the active safety of the car, and it better solves the problems that the drum brake cannot be solved during the braking process, such as dust pollution, brake noise pollution, and frequent maintenance. It will be more widely used in cars. .

● Working principle of disc brake

Disc brakes are mainly composed of brake discs, oil cylinders (brake air chambers), brake calipers, oil (gas) pipes and other components, and liquid (gas) pressure as a power source. The disc brake uses the end surface of the rotating working brake disk (metal disk) as friction (surface). The friction bracket (material) (working surface consists of 2-4 friction plates) and its metal are installed on its fixed bracket The brakes (plates) composed of the bottom plate, these brakes (plates) and their tensioning devices are installed in the clamp caliper brackets across the sides of the brake disc, called brake calipers.

The brake disc is made of cast iron and fixed on the wheel, and rotates with the wheel. The oil cylinder (brake air chamber) is fixed on the caliper body of the brake and does not move. The two friction plates on the brake caliper are installed on both sides of the brake disc. The piston (push rod) of the oil cylinder (brake air chamber) is affected by the pressure of the liquid (air) sent by the oil (air) tube, and the friction plate is pressed against the brake disc to cause frictional braking, just like the rotation of the pliers. The plate in force forces the moving mechanism to stop moving.

Its main technical parameters are: rated braking torque, braking radius, brake disc outer diameter, brake disc thickness, inner brake lining radius, brake clearance, working stroke of air cylinder ejector rod, axial displacement of piston rod , The maximum stroke of the air cylinder jack, the opening and closing force of the friction lining, the thickness of the brake lining, the total area of the two brake linings, the brake efficiency factor and the braking efficiency, etc.

● Structural features of WABCO pneumatic disc brakes

WABCO disc brakes use a single-piston mechanism. Compared with similar products on the market, they achieve the best braking performance with the fewest parts and the lightest weight.

1. Single-piston mechanism, simpler structure and lighter weight

In the past, due to the relatively large friction plates of the vehicle, in order to avoid wedge-shaped wear, two push rods must be used. When adjusting the gap, it is necessary to use a very complicated adjustment mechanism to adjust the two push rods simultaneously. The quality of the system is increased and the probability of parts damage is increased due to the large number of parts. WABCO improved this, and launched the PAN series single-push rod actuating adjustment mechanism.

Compared with the double push rod actuating adjustment mechanism, the single push rod actuating adjustment mechanism has a simpler structure, fewer parts, more reliable performance, and a more compact structure, which effectively reduces the weight and failure rate of the assembly.

2. The patented push plate technology can effectively prevent partial wear, and can play a role of heat insulation

3. The structure of the guide pin is strong, and the work is more stable

The guide pin of WABCO single-push disc brake has the largest diameter among the same level products in the industry, and the work is more stable when guiding. One end of the guide pin is sealed with a metal end cover, and the other end is sealed with a double dustproof sheath, making the guide pin system safer and more durable.

4. Optimized friction plate size, longer life

Weiboco researched on the friction plate and found that reducing the surface area of the friction plate within a certain range had little effect on the life of the friction plate. Based on the above results, the friction plate surface area is reduced, and the material saved is used to increase the thickness of the friction plate, making the design more compact, the friction plate service time is longer, and the maintenance cost is greatly reduced.

5. The wear sensor monitors the wear of the friction plate

When the friction lining has been excessively worn, if it cannot be replaced in time, the brake disc may be damaged during braking. What's more serious is that the vehicle will lose braking, which is very likely to cause an accident. In order to better improve the safety of the vehicle, the WABCO PAN series disc brakes can be equipped with wear indicators, which can alert the driver when there are 3mm and 2mm remaining on the friction plate.

The wear indicator is installed on the friction plate, and the sensor head is a coil. The coil is fixed in place. The pre-alarm can be reached by providing two signals:

? When the coil contacts the brake disc

? When the coil wears out

● WABCO disc brake specifications and main parameters

WABCO's new generation of disc brakes, NG series disc brakes, is the latest generation of WABCO disc brakes based on the PAN series disc brakes.

The main features of NG disc brakes are simple structure, light weight, large braking torque, and improved pressure distribution on the outer friction plates. NG inherits the successful single-push patent technology of the PAN series. This design has a compact structure, high reliability and light weight. These improvements make NG22MAX the lightest disc brake on the market, including friction plates, which weighs only 39KG. In addition, the connection between NG and the bridge is simple. The reduction in the weight of NG series products greatly reduces the unsprung mass, thereby reducing the impact on the chassis. At the same time, the improved pressure distribution enhances the crack resistance of the brake disc, minimizing radial and tangential taper wear.

● The application of domestic automobile disc brakes

The application of disc brakes in automobiles is limited by the size of the wheel hubs. Hydraulic disc brakes are widely used in small cars, while pneumatic disc brakes are used in heavy vehicles. With the development of China's auto industry technology, especially the development of the car industry, the phenomenon of the use of disc brakes on automobiles will gradually become a scale. In particular, it plays an important role in improving vehicle performance, ensuring safety, improving comfort, and meeting people's ever-increasing needs for living materials and improving the living environment.

1. Small cars such as mini cars, cars, light trucks, etc.

During the braking process of the car, due to the inertia, the front wheel load usually accounts for 70% -80% of the total load of the car, so the braking force of the front wheel is greater than that of the rear wheel. From the perspective of economy and practicality, in order to save costs, manufacturers mostly adopt a hybrid matching method of front wheel disc brakes and rear wheel drum brakes. The front disc rear drum hybrid brake is also used because the axle load moves forward during emergency braking, and the requirements for front wheel braking performance are relatively high. This type of front brake mainly uses hydraulic disc brakes as the mainstream, and uses hydraulic oil as the brake. The transmission medium uses the hydraulic master pump as the power source, and the rear brake is matched with the hydraulic cylinder double-acting cylinder brake shoes.

At present, most cars, mini-cars, light trucks, SUVs, pickups, etc. are using front disc rear drum hybrid brakes. However, with the improvement of highway grades and the rise of vehicle grades, especially the mandatory implementation of national safety regulations, the use of disc brakes on both the front and rear wheels will be an inevitable development trend.

2. Large passenger car

Disc brake products have obvious technological advancement, good overall reliability, and integration of innovation and technical standards. European and American countries have used disc brakes for large buses since the early 1990s. By 2000, disc brakes (both front and rear brakes were discs) had become the standard configuration for urban buses in European and American countries. Since 1997, China has promoted disc brakes and ABS anti-lock brake systems on buses and trucks. However, due to the high price of imported products, it is mainly used in high-end products.

In 2004, the Ministry of Communications enforced the "must" for passenger cars with a height of more than 9m in height, and disc brakes became popular. Beijing, Shanghai, Guangzhou, Shenzhen, Wuhan and other bus companies are all using air pressure disc brakes that are matched for buses. At present, domestic well-known large manufacturers have mass produced high-end passenger cars with disc brakes.

3. Heavy-duty vehicles

As an applied new technology in the heavy-duty automobile industry, disc brakes are already mature products. The large domestic automobile manufacturers have completed the pre-type test and technical reserve work of the disc brakes in heavy vehicles. In some respects, the disc brakes can be said to become a new trend for the future development of heavy truck brake systems.

● Development trend of domestic automobile disc brakes

Developed countries such as Europe, the United States and Japan have equipped disc brakes as standard parts on multi-level cars, passenger cars, medium and heavy vehicles. With the promotion of national regulations, such as GB 7258-2004 "Technical Conditions for the Safety of Motor Vehicle Operation" (an updated version based on the 2004 edition) and GB 24407-2012 "Technical Conditions for the Safety of Special School Buses", it is expected that in the next few years, the disc type The brake will be quickly promoted and applied in China.

The new version of GB 7258 stipulates that the front axle of the dangerous goods transport vehicle and the front axle of passenger cars longer than 9m should be equipped with disc brakes; the new version of GB 24407 requires that disc brakes should be installed on the front wheels of special school buses. The issues that should be paid attention to in the research and development of modern automobile disc brakes are mainly to improve the braking efficiency of the brakes, prevent dust and rust, reduce weight, simplify the structure and reduce costs, the development of electronic alarms and intelligent systems is more practical Yoshihisa