SEARCH, IDEA, DEVELOPMENT
BRAKES OF THE FUTURE
It would seem that in the current difficult economic conditions there is no time for promising developments - no one thinks about them. Fortunately, not quite so. Today, Professor Valery SELIFONOV and candidate of technical sciences Nikolai VLADIMIROV talk about their research.
It's about disc brakes that gradually replaced drum brakes - first from the front axles of cars, and on many foreign cars and from the rear. What are their advantages? The braking torque on the wheels is proportional to the force generated by the drive. The response time is short, the brake mechanisms are compact, their mass is small compared to the drum, and worn pads are easy to replace. It is very important that when heated, the characteristics of disc brakes are quite stable. The temperature resistance is higher, in particular, due to the fact that the disks are better cooled.
Ventilated discs allowed to capture new bridgeheads: such brakes cope with a greater load. They can now be seen on trucks with a gross weight of over 12 tons, and on buses over 5 tons. True, on these machines the disc brake still needs to be improved.
It is known that the greater the mass of a car with a load, the more difficult it is to design brakes for it. The main reason is the very high energy that needs to be converted into heat and dissipated, so the friction surface is so large that the disk does not fit in the wheel. If it is reduced, it will crack due to temperature stresses. It is not easy with friction material for pads - undergoing strong thermal effects, it must resist wear, withstand contact with a disk that rotates at high speed, etc. By the way, designers of sports cars faced the same problem - it’s not by chance that they the wheels are larger than other trucks.
Now a few words about the drive. Here, too, designers have to overcome difficulties. For example, its gear ratio is not easy to select, since it is necessary to create a large force on the block, although the gap between the friction surfaces is small. It should also provide automatic compensation for wear pads. For a hydraulic drive, these issues have already been resolved, but for heavy machines, experts recommend pneumatic, especially since many of its components have long been mastered.
For several years, the department “Automobiles” of the Moscow State Academy of Automobile and Tractor Engineering has been engaged in disc brakes for heavy vehicles and buses. Not so long ago, a fundamentally new, we can say, non-standard solution to the problem was found - disc brakes with a liquid cooling system. They obtained a patent of the Russian Federation. What is the essence of the invention?
Friction material is now located not on the block, but on the disk (in the prototypes it is riveted). In a block made of cast iron, channels for liquid are made, which are connected to the cooling system by fittings (Fig. 1).
In an ordinary disc brake, the maximum temperature of a friction pair is 600–800 ° C, and the contact area of the parts is small, therefore, heat-resistant and durable friction materials are required. In the new design, this area is larger, and the temperature does not exceed 200–250 ° С. Material requirements are reduced, with less wear. True, a cooling system is needed, which is not so simple in design (Fig. 2). However, it is easy to place it on a large truck.
The prototype was created in the laboratory of the Academy and tested at the stand at the NIIATI (Yaroslavl). Studies have confirmed that the new design thermally loaded parts, indeed, much less. During cyclic braking, the temperature remains stable, which is important for the failure-free operation of the brakes. In general, the first results are encouraging.
Fig. 1. Disc brakes: a - existing design; b - new; 1 - disk; 2 - pads;