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I don't know if you have noticed that large vehicles, such as trucks and buses, often make short, high-frequency noises similar to "tui tui tui" when they slow down.

The loud "fart" sound of big trucks and buses starts with a thrilling accident and a great invention that relies on nepotism to avoid failure.

The fart sound of trucks and buses has something to do with the oil they burn. Many large vehicles burn diesel instead of car gasoline, while diesel trucks use diesel engines instead of car gasoline engines.

Photo Source: wikimedia this is because of all the engines, diesel engines have the highest thermal efficiency. According to the American Society of Mechanical Engineers (ASME), the compression ratio of diesel engines is twice that of gasoline engines, which means that the performance of diesel engines is better than that of gasoline engines, so diesel engines are commonly used in heavy trucks.

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 diesel engine in the United States is called Clessie Lyle Cummins, and now Cummins trucks use his last name. At the beginning of the 20th century, however, diesel trucks were not as popular as they are now.

In August 1931, in order to promote and prove the strength of the diesel engine they developed, Cummins and his buddies Ford Moyer and Dave Evans planned to drive the Cummins diesel truck in shifts from New York to Los Angeles, hoping to set a speed record. What Cummins didn't expect was that he almost set a record for a truck accident.

The Cummins trio took a photo in front of the diesel truck they were driving in front of the AAA. Source: the American Society of Mechanical Engineers (ASME) actually invented diesel engines with the same braking devices as gasoline engines, which were slowed down by friction similar to "brake pads". As soon as Cummins and his partner hit the road, they found that the "brake pads" could not stop the diesel truck, which put a lot of pressure on the braking system of the diesel car.

This epiphany was sublimated on a dangerous road in California.

This place is the Cajon Pass. It is a steep and tortuous rocky mountain road 56 kilometers long, interspersed with many intersections, which, in today's view, is a truck's underworld.

Located in California's Cajon pass (Cajon Pass). Photo source: wikipediaCummins recalls that when he arrived near the Cajon pass that day, Dave was about to change shifts with him, and he warned Cummins that everyone must be woken up. But when we got there, the brake pads were so hot that they couldn't stand it at all. In his words, he tried to slow down "hopelessly", but to no avail. The two brothers in the back also woke up because the speed was too high.

Then a dramatic scene appeared. In the distance, something glowing red is crossing the crossroads. They looked intently at the fact that it was a freight train. Cummins said that both Dave and Ford collapsed and were behind trying to slow down by sound waves (yelling). Fortunately, when their truck reached the crossroads, the train just grazed its ass and the three men did not die on the spot.

The thrilling journey did set a record: the journey across 5172 kilometers took only 97 hours and 20 minutes. But the scene of brake failure also cast a lifelong shadow on Cummins.

Twenty-four years later, Cummins, who has retired, began to design diesel engine brakes in his basement that would not be damaged by friction. In 1957, Cummins finally came up with a solution in a hotel in Philadelphia. His plan is to use the diesel engine to hit the brakes himself.

The elderly Cummins is still working on diesel engines. Image: the American Society of Mechanical Engineers (ASME) brake system is called Gyokobo engine Brake (Jacobs brake), often referred to as Jack Brake (Jake Brake), or compression release engine brake.

The principle of Jack's brake is not complicated, it actually depends on "discouraging" to slow down, which depends on the four-stroke cycle of the diesel engine.

The four-stroke cycle can be simply summed up as: inhaling (intake), holding breath (compression), ignition, farting (exhaust).

The four-stroke cycle of a diesel engine. Image source: the engine inhales air during the suction phase of the jacobsvehiclesystems.com.

In the breath-holding compression stage, the air is compressed. According to the equation of state of the ideal gas, the smaller the volume of the gas, the higher the temperature, so the diesel is ignited, and the third stage is reached.

In the final exhaust phase, the exploding gas expands, pushing the piston down and inputting mechanical energy into the vehicle. Then the piston retracts and the exhaust gas is discharged.

Cummins revamped the exhaust pipe so that the driver could manually open the exhaust valve to vent the hot gas before diesel power was injected into the truck, while absorbing the truck's power to repeat the process, eventually causing the truck to lose power and slow down.

The Jack brakes (right) designed by Cummins will vent the gas after compression, "leaking" the fuel power. Photo: jacobsvehiclesystems.com applied for a patent for this design that year. Although later practice has proved that Jack brakes can effectively extend the life of diesel engines (Jake brakes can extend the life of traditional brakes by 2-3 times), no mainstream automaker was optimistic about this new braking system at that time. And it finally came out on a layer of nepotism.

It turned out that Cummins's eldest nephew was arranged by his parents to go on a blind date with the daughter of Jacobs Manufacturing Company, then the vice president of the world's largest drill bit maker.

The two men made eye contact with each other as soon as they met, and their in-laws made eye contact with each other. The woman's parents showed a strong interest in Cummins's invention. Thus in 1961, the first truck with Jack braking system, the Cummins NH series, was shipped. Of course, the name of the woman's company Jacobs is also the origin of the name Zenkebo engine brake.

According to the American Society of Mechanical Engineers, Jack brakes have been standard for heavy diesel trucks in the United States and around the world for decades (such as CAT, Mack), and later used in American military vehicles. China's Dongfeng dCi, Yuchai 6K, Xi'an Cummins and other manufacturers also install Jack brake system.

Photo Source: wikimedia is listed as the 81st National Mechanical Engineering Historical Landmark (National Historic Mechanical Engineering Landmark) because of its contribution to diesel truck performance and safe driving.

Up to now, Jack brake is still the mainstream auxiliary braking system of heavy truck.

However, Jack brakes also have many shortcomings. the first is the loud noise caused by gas vibration during exhaust. As a result, Jack brakes are often banned near dense residential areas.

A sign that forbids Jack to brake. Photo Source: wikipedia in addition, Jack brakes will emit a lot of exhaust gas as soon as they are turned on, which is very polluting. Now many countries have put forward environmental requirements for diesel engines, so Jack brakes are also subject to competitive pressure from new braking systems such as turbochargers.

Photo Source: finally, wikipedia would like to point out that large vehicles often have many braking systems, and the long and mournful "cutting" sound of many buses and trucks when they stop does not come from Jack's brakes, but from another common braking system-pneumatic brakes.

The sound of pneumatic braking

To put it simply, a pneumatic brake is a braking system that uses high-pressure air to step on the brake. When the driver starts the pneumatic brake, the high-pressure gas is discharged and the wheel stops rolling at the same time. The discouraging sound of the high-pressure gas is the source of the "fart sound" of the big car parking.

All in all:

Overtaking depends on inhalation, parking on farting, and safety on "transportation".

This article comes from the official Wechat account: take Science Home (ID:steamforkids), author: Qijun

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