When the big car slows down, why is there a series of violent farts?

I do n’t know if you have noticed it. When large vehicles, such as trucks and bus deceleration, often emit a high -frequency short noise similar to “TUI TUI TUI”.

The huge "fart" sound of large trucks and buss should start with a great invention that has no failure from a thrilling accident and a dressed belt relationship.

Trucks and bus "fart" is related to the oil they burned. Many large vehicles are burned with diesel instead of gasoline of cars, and the engine used in diesel trucks is a diesel engine, not the gasoline engine of a car.

Image source: wikimedia

This is because among all engines, the thermal efficiency of the diesel engine is the highest. According to the American Society of Mechanical Engineers (ASME), the compression ratio of the diesel engine is twice the gasoline engine, which means that the performance of the diesel engine is better than the gasoline engine, so heavy cards generally use diesel engines.

The diesel engine was first invented by the German Rudolf Diesel at the end of the 19th century. The United States also has its own diesel engine. The father of the US diesel engine is called Clessie Lyle Cummins. Now the Cononis engine is used by his surname. However, at the beginning of the 20th century, diesel engine trucks have not been so popular.

In August 1931, in order to promote and prove the strength of the diesel engine he developed, Cummins and friends Ford Moyer and Dave Evans intend to drive the diesel truck of the three -person shift to drive the Cummins. Record. What Cummins did not expect was that he almost set a record of a truck accident.

The Cummins trio was witnessed under the witness of the American Automobile Association, in front of the diesel trucks they drove at the time. Picture source: American Mechanical Engineer Society (ASME)

In fact, the brake (brake) device equipped at the beginning of the diesel engine is the same as the gasoline engine. It relies on the friction and deceleration of devices similar to "brake pads". As soon as Cummins and friends were on the road, they found that the "brake pads" could not stop the diesel engine truck, which put a lot of pressure on the brake system of the diesel vehicle.

This enlightenment has been sublimated on a dangerous channel in California.

This place is Cajon Pass. It is a steep and twisted stone mountain road of 56 kilometers long. There are a lot of crossroads on the mountain road. From the current eyes, it is a truck.

Cajon Pass in California. Image source: wikipedia

Cummins recalled that when he opened to Kahong Road that day, Dave happened to change his class with him. He warned Cummins that everyone must wake everyone up. But when it is really there, the brake pads have been rubbed hot and unable to stand at all. In his original words, he tried to slow down, but he didn't use it at all. The two brothers behind were also awakened because of the high speed.

Then, a dramatic scene appeared. There is a red light in the distance that is crossing the crossroads. They looked at the train that turned out to be a cargo. Cummins said that Dave and Ford both collapsed, and tried to slow down by sound waves (yelling) later. Fortunately, when their trucks were driving at the crossroads, the buttocks of the train just rubbed, and the three of them finally did not die on the spot.

The thrilling journey did set a record: the distance spanning 5172 kilometers only took 97 hours and 20 minutes. But the scene of the brakes failed also left Cummins for a lifelong shadow.

After 24 years, Cummins, which has been retired, began to design in its basement. The diesel engine brake system that will not be rubbed. In 1957, Cummins finally thought of a solution in a hotel in Philadelphia. His solution is to step on the brakes with the diesel engine.

Elderly Cummins is also undergoing diesel engines. Picture source: American Mechanical Engineer Society (ASME)

This brake system is called Jacobs Brake, which is often called Jake Brake, or compressed the release of the mobilization mechanism.

The principle of Jack's brake is not complicated. It actually depends on the "discouraged" to slow down, and this depends on the four -stroke cycle of the diesel engine.

The four -stroke cycle can be simply attributed to: inhalation (intake), holding breath (compression), ignition, fart (exhaust).

The four -stroke cycle of diesel engine. Image source: jacobsvehiclesystems.com

In the inhaling stage, the engine inhaled the air.

During the stamping stage, the air was compressed. According to the ideal gas state equation, the smaller the gas volume, the higher the temperature, so that the diesel is ignited and the third stage is achieved.

In the final exhaust stage, the explosive gas swelling, pushing the piston down, and entering mechanical energy for the vehicle. Then, the piston shrinks back and discharge the exhaust gas.

Cummins has been transformed to the exhaust pipe, allowing drivers to manually open the exhaust valve. Before diesel, the hot gas is discharged from the driver. At the same time, the driving force is reused to repeat the process. Finally, the truck will lose power and decelerate.

The Jack brake (right) designed by Cummins will discharge the gas after compression and "leak" the fuel power. Image source: jacobsvehiclesystems.com

He applied for a patent for this design that year. Although later practice has proved that Jack's brake can effectively extend the life of the diesel engine (all can also say that Jack's brake can extend the life of the traditional brake by 2-3 times), but there was no mainstream car manufacturer at the time. And its ultimate emergence is still relying on a layer of skirt relationship.

It turned out that Cummins's big nephew was arranged for a blind date by his father and mother. The blind date was the daughter of vice chairman of Jacobs Manufacturing Company, the world's largest drilling barrier.

The two people were right when they met, and their pro -family looked at each other. The woman's parents showed a strong interest in the invention of Cummins. In this way, in 1961, the first truck Cummins NH series with Jack brake system was lealed. Of course, the female company's name Jacobs is also the origin of the name of the mechanism.

The American Mechanical Engineer Society said that in the following decades, Jack's brake has been the standard for the United States and the world's heavy diesel trucks (such as CAT and MACK). Later, the US military vehicles also used this braking device. my country's Dongfeng DCI, Yuchai 6K, Xi'an Conominus and other manufacturers also use the Jack brake system.

Image source: wikimedia

Because of the contribution to the performance and safe driving of diesel trucks, Jack's brakes were included in the 81st National Historic Mechanical Engineering Landmark.

Until now, Jack's brake is still the mainstream auxiliary braking system of heavy cards.

However, there are many disadvantages of Jack's brake. The first is the huge noise caused by gas vibration during exhaust. Therefore, Jack's brakes are often prohibited in the densely residential area.

Signing for Jack to brake. Image source: wikipedia

In addition, as soon as Jack brakes, many exhaust gas will be expelled, and pollution is very large. Now many countries have put forward environmental protection requirements for diesel engines, so Jack's brake has also been competitive pressure from the new brake system (such as turbocharged).

Image source: wikipedia

In the end, there are often many brake systems for large vehicles. Many buses and trucks do not come from Jack brakes when the long and sorrowful "cut" sound is from another common brake system when it is parking. Pneumatic motivation.

Sound braking sound

Simply put, pneumatic motivation is a braking system that uses high -voltage air to step on the brakes. When the driver starts the pneumatic braking, the high -pressure gas is discharged and the wheels stop rolling. The discouraged sound of this high -pressure gas is the source of the "fart" of the large car.

all in all:

Cover source: wikimedia

Reference materials:

https://docs.qq.com/doc/dvhh0bxjjckfwcm1c

Reprinted content only represents the author's point of view

Does not represent the position of the Institute of Physics of the Chinese Academy of Sciences

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Source: Take the science home

Edit: Tibetan idiot

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