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2025
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Just knowing how to drive isn't enough; the most important thing is to know how to brake!
When it comes to big trucks, most people's impression is associated with danger. Indeed, there are quite a few accidents caused by brake failure or the inability to stop in time. However, truck drivers don’t want such incidents to happen either; it's not that they don't want to brake, but that they simply cannot stop completely. A truck itself weighs over ten tons, and with a full load of cargo, it becomes a gigantic beast. Achieving quick and effective braking is not an easy task.
Here, we might as well briefly understand the basic braking principle of trucks. Unlike the hydraulic brakes used in small cars, most large trucks use air brakes, which respond quickly and provide good braking performance. The air brake system consists of several components: an air compressor, also called an air pump; at least two air reservoirs; a main brake pump; quick release valves on the front wheels; relay valves on the rear wheels; four brake slack adjusters; four camshafts; eight brake shoes; and four wheel hubs that control the brakes. Just looking at these components seems complicated, but it aligns with the braking requirements of large trucks.
The basic principle of an air brake is to store the compressed air produced by the air compressor in two air tanks. One of these tanks is connected to the master pump. When the driver presses the brake pedal, the master brake pump operates, activating the relay valve. The other air tank pushes the actuator rod of the brake wheel cylinder, rotating the cam through the adjusting arm, causing the irregular cam to push the brake shoes apart and create friction with the wheel hub, thereby achieving braking.
The braking effect achieved this way is much better than that of regular cars. However, once our large trucks are loaded with cargo, the effect is not as ideal. Many drivers keep their foot on the brake pedal to control speed. Because the brake drum is in a state of friction for a long time, its temperature keeps rising, gradually losing its deceleration function. It is unknown how many truck drivers have lost their lives due to this brake system failure.To cool down and improve braking performance, drivers have come up with many methods, such as installing a water spraying device to cool the brakes while pressing them, preventing the brake pads from overheating. However, there are also significant drawbacks; in winter, the water can freeze. Is there really no safer method besides this "makeshift" approach? Many experienced drivers would likely respond immediately: "Isn't there engine braking?"
Yes, the engine compression brake is touted as a "miracle for downhill deceleration," but most drivers only know it exists without understanding why it works. If they don't understand the function of the compression brake, how can they make the most of its effectiveness?To put it simply, the compression brake is just a form of auxiliary braking. However, compared to the exhaust brake that drivers are more familiar with, the compression brake is much more effective. It leverages the engine’s working principle, releasing some of the air pressure during the power stroke in advance, which significantly reduces the engine’s output power and achieves a deceleration effect.
Many truck drivers are hesitant to boldly use engine compression braking, fearing that it might damage the engine. In fact, such concerns are completely unnecessary. When using engine compression braking, the fuel injectors do not spray fuel. While saving fuel, the cylinder pressure during compression braking is much lower compared to normal combustion, so it does not affect the engine's lifespan at all.Moreover, compression braking technology is mature and relatively affordable. Nowadays, most automakers equip their engines with compression braking systems as standard. For example, SAIC Hongyan's H6 engine comes standard with a compression braking system. The H6 engine incorporates advanced European technology and world-class quality, even exported to Europe and the United States. Additionally, FIAT's patented high-efficiency engine braking system, controlled via the ECU, offers more precise control, with braking efficiency reaching up to 80%. It effectively reduces brake pad wear while also lowering fuel consumption.
In-cylinder braking is a good technology. I hope truck drivers not only understand its principles but also use it frequently. Like the Cummins engine, its advanced in-cylinder braking system provides drivers with more than just safety; it can also extend the life of brakes and tires, thereby reducing vehicle operating costs.
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