Why do most trucks use air brakes, not hydraulic fluid brakes?

Pneumatic pressure is stored in the gas tank through the engine air pump, and then the gas is delivered to the various lines through the gas line control valve, and the gas is naturally pressurized through the concentration, and this pressure output again does not require any energy to do. Gas pressure is not only fast, but does not produce any heat.

Hydraulic brakes are different, first of all, there is a hydraulic pump, the hydraulic fluid can not be compressed to produce natural energy, only when the hydraulic pump works to apply pressure will produce force. When the truck needs to brake, several wheel brakes will be activated at the same time, because the hydraulic fluid can not store energy, so the only way to achieve this is to increase the engine horsepower to increase the hydraulic pump pressure. This logic obviously doesn't work, and when you brake and boost at the same time when you're not out of gear it creates exactly the opposite force.

The air pressure can be set to a certain value, such as the capacity of the tank, and the applied pressure will not exceed that setting, which can better protect the hardware. The braking system of a truck works through a lot of mechanical linkages, and if the pressure exceeds this value, the parts will be deformed and twisted.

Hydraulic brakes work by applying pressure to move a piston rod, although they can also be set to a certain value through a dispensing valve, which doesn't allow for better control when you're tapping the brakes or need to stop. You can't stop if you don't reach a certain value, and reaching a certain value can cause damage to the hardware because the pressure generated by a hydraulic cylinder is usually very high even though you can set a pressure value.

Pneumatic brakes vent gas when a certain air pressure is reached, and this venting is done at zero cost. Hydraulic brakes must also recover hydraulic fluid, which requires an additional set of recovery lines compared to pneumatic brakes, as well as a hydraulic fluid cooling system, making the system more complex, costly, and slow.

The parts controlled by the truck air pressure are more and more, such as: brake system, exhaust brake system, airbag shock system, clutch system, etc. The gas can be stored in advance, and the flow speed is faster, does not produce any heat, does not need any recycling system, and the cost is low, these characteristics are hydraulic brake system can not be done.

Why do trucks use gas brakes instead of hydraulic fluid brakes?

1. The working principle of the oil brake is to use the brake master pump, the hydraulic oil is pressurized, the pressure can be in the brake sub-pump to make the brake shoes work to achieve the purpose of braking.

Oil brake has a simple structure, small installation space, just need brake master pump, sub-pump, oil cup and connecting pipeline, no other ancillary equipment.

The oil brake is characterized by a slightly slower reaction speed, soft braking and less force.

Oil brake is mostly in small and medium-sized cars, small size, simple structure, oil brake in the engine off, the pressure will soon be released, step on the brakes a few times on the pressure, braking duration is short.

Therefore, the oil brake is mostly used in small and medium-sized cars, which are lightweight, small, simple, and small, and do not require a lot of strength.

2. Air Brake: The compressed air generated by the air pump is used to push the brake shoes, thus achieving the purpose of braking.

The structure of the air brake is complex, in addition to the brake master cylinder, pump, brake lines, there are pumps, storage cylinders, high-pressure controllers, relay valves and other components, need to install a large space, and in order to ensure the safety of the rear brake pump are now disconnected from the air brake.

Air brake brakes are characterized by: rapid response, braking rough, strong. When the engine is turned off, the gas stored in the high-pressure tank can make the brake continue to work for a long time until the gas pressure is insufficient, and the brake lasts for a long time.

So the air brake is mostly used on large trucks and buses, which have a large weight, large space, and a large load, and require a large braking force, a long distance, and a very fast response time, so that the emergency braking can be responded to in a timely manner.

These are the reasons why trucks use air brakes, not hydraulic oil brakes.

Big cars with pneumatic brakes, small cars with hydraulic brakes almost become the standard today, in fact, in the past there is a brake called air top hydraulic brakes , this braking method in the conventional pneumatic braking system in series with a set of hydraulic braking system (almost with the car's braking system, the design improves pneumatic braking is too abrupt force, so that the brakes become linear, and then the brakes become more linear. This design improves the overly abrupt force of the pneumatic brake, allowing the brake to become a little more linear, and secondly improves the braking response speed, air brakes and hydraulic brakes compared to the victory in the strength of the greater (at least eight atmospheres), but not as responsive as hydraulic brakes, because after all, there is compression of the gas, while the liquid is almost equivalent to the incompressible, in the past in the Mitsubishi, Isuzu, some of the trucks on the gas top of the oil brakes is very common.

But with Japan's geography, landscape, and ultimately heavy trucks are not overly reliant on, so the air-over-oil brakes are mostly used on light trucks; to put it simply, Japan's geographic area is small and surrounded by the sea on all sides; so large-scale transportation in Japan can be accomplished directly by sea, the cargo ship's capacity is sufficient; and we have this, North America, and the European continent is different because of the geographic area of the depth of the too large, so the Land transportation is extremely dependent on, so road transportation becomes extremely important, so the European trucks, American trucks are air brakes, and our heavy trucks are more the introduction of European truck technology, so our heavy trucks are also air brakes, so the last century in the 1990s the popular air top oil brakes gradually can not be seen, which is enough to prove that air brakes are difficult to give up for heavy trucks (as shown in the above picture of the East Germany's enamel W50 trucks are). The air-topped oil brakes are the same for the East German W50 trucks shown above.)

Heavy trucks with pneumatic brakes instead of hydraulic brakes, not to reduce costs; in fact, the braking system of heavy trucks, far more complex than our passenger cars, more high-end, more expensive, because heavy trucks run up to carry the kinetic energy is far too much than the passenger cars; our passenger cars are often more than 200nm enough to use, and heavy trucks are not the power of a class compared to the passenger cars, heavy trucks are not a level of power. At least 2000N-M or more, passenger cars to complete the 01 speed and then slow but 15 seconds, and fully loaded heavy trucks to complete the 01 speed, at least also have to spend 50 seconds; so run up a fully loaded heavy trucks, contains too much kinetic energy, want to stop a fully loaded, high-speed heavy trucks is very difficult; the requirements of the braking system not only enough braking power, but also need to be sufficiently stable!

So why don't heavy trucks use hydraulic brakes? In fact, there is still the possibility of boiling brake fluid, as shown in the figure above, even if it is dot 5, the dry boiling point is only up to 260, of course, such a high boiling point for passenger cars is enough, but heavy trucks braking heat generated is too large, often see heavy trucks braking wheels are burned examples, right? So a fully loaded heavy truck in a long downhill section if the heat generated by frequent braking is too easy to cause the brake fluid to boil, a large number of bubbles in the brake line, the brakes will be soft or even lose braking ability, because once a large number of bubbles in the brake line, it is equivalent to adding a useless trip, the gas is compressed, so the braking ability will be seriously reduced!

In addition to the hidden danger of boiling brake fluid, the heat generated when braking heavy trucks is also easy to lead to the hydraulic wheel cylinder closed bowl is directly melted, or fall off, which directly leads to brake fluid leakage, so that the car completely lost the braking ability, so compared with the more solid, direct pneumatic brakes, the hydraulic brakes are fragile, at least for heavy trucks are fragile; so whether it is heavy trucks or trains with a greater weight. The weight of the train, the braking system are pneumatic braking, not hydraulic, because these large-scale mechanical braking heat, hydraulic braking system is difficult to withstand, the sealing system is mostly rubber products, rubber products how to withstand high heat is a major problem, so to ensure the continued stability of the harsh operating environment, air brakes are the first choice for heavy trucks!

So domestic and foreign heavy trucks will choose air brakes, it is not just a question of braking power; gas top oil braking power can also meet the requirements of pure hydraulic braking if equipped with hydraulic pumps, braking power can also be up to standard; so with the braking force factor is no way to distinguish between the air brakes, hydraulic, the key still lies in the stability of the air brakes in this regard is more desirable; unlike a small car, a small car is more prone to drive fast, So the response speed of the brake is very critical, so the hydraulic brake is the most suitable; heavy trucks run slow, but their own kinetic energy is too large, so strong enough braking power is the most critical, fully loaded heavy trucks even if the speed of 20 kilometers per hour (slow enough, right?), the braking distance will also be very long, so the response speed of the brake is not the first (and will not be slowed down too much), braking is the focus of the power!

Large trucks with air brakes mainly for these reasons: air brake cost than oil brake cost is low and environmentally friendly, air brake operation is easier than the oil brake, air brake than the oil brake power, air brakes than oil brakes easier layout, compressed air transfer speed than oil easy maintenance. Not only in China, most of the large trucks in foreign countries are also air brakes.

Why big trucks are using air brakes

High sensitivity, low maintenance costs, good safety

The four-circuit protection valve distributes the gas to the individual cylinders, with four chambers at six pressures not working, and six or more chambers fully working, preventing one chamber from malfunctioning and the other chambers from functioning normally, and allowing enough time for repair at the service station. or valve malfunction will not cause a brake failure.