Did really the Chinese invent the “Diff” some 4600 years ago ?

Well, it seams so….

The Legend

The legend tells us that by time of Huangdi, known as the founder of the Chinese nation, there lived another tribal leader, Chi You, who was skilled at making weapons and waging war. He seems having attacked the tribe of Yandi, and rode into the lands of Huangdi. Huangdi was angered by this and went to war with Yandi, initially suffering several defeats.

At some stage in the fighting, Chi You conjured up a thick fog to confound Huangdi’s men. They used the south-pointing chariot to find their way and they were ultimately victorious.

History

The first recordings date back to 2600 BCE. The south-pointing chariot was used as a navigational tool for the military or those traveling in the Gobi desert.

the south-pointing chariot

Another recording is to be found in the Sanguo Zhi (Records of the Three Kingdoms) that the 3rd century CE mechanical engineer Ma Jun from the Kingdom of Wei was the inventor of the south-pointing chariot (also called the south-pointing carriage).

After being mocked by Permanent Counsellor Gaotang Long and the Cavalry General Qin Lang that he could not reproduce what they deemed a non-historical and nonsensical pursuit, Ma Jun retorted “Empty arguments with words cannot (in any way) compare with a test which will show practical results”. After inventing the device and proving those who were doubtful wrong, he was praised by many, including his contemporary Fu Xuan, a noted poet of his age.

After Ma Jun the south-pointing chariot was re-invented by Zu Chongzhi (429–500 CE), after the details of its instructions had been lost temporarily in China. During the Tang Dynasty (618–907 CE) and Song Dynasty (960–1279 CE) the south-pointing chariot was combined with another mechanical wheeled vehicle, the distance-measuring odometer.

Some early historical records state that the south-pointing chariot was invented around the first millennium BCE, but such evidence is obscure.

The Mechanism

There is a widely believed hypothesis that most, if not all, south-pointing chariots worked by means of differential gears. A differential is an assembly of gears, nowadays used in almost all automobiles except some electric and hybrid-electric ones, which has three shafts linking it to the external world. They are conveniently labelled A, B, and C. The gears cause the rotation speed of Shaft A to be proportional to the sum of the rotation speeds of Shafts B and C. There are no other limitations on the rotation speeds of the shafts.

Here is a funny tutorial of how differential gears work..

The hypothesis that there were south-pointing chariots with differential gears originated in the 20th Century. People who were familiar with modern, e.g. automotive, uses of differentials interpreted some of the ancient Chinese descriptions in ways that agreed with their own ideas. Essentially, they re-invented the south-pointing chariot, as it had previously been re-invented several times in antiquity.

Working chariots that use differentials have been constructed in recent decades. Whether any such chariots existed previously is not known with certainty.

the south-pointing chariot mechanism

If the hypothesis is true, then the Chinese probably knew about differentials centuries before Europeans.

The Greeks used an even more complex Mechanism for astronomy

When Jacques-Yves Cousteau started to dive in the natural museum which is the Mediteranean Sea he found a Roman ship sunk around 100 BCE which containd the Antikythera Mechanism…

In our days exposed in the Archeological Museum in Athens, the Antikythera Mechanism allows calculating the position of the planets, moon and sun and was made about 100 B.C. An x-ray of the mechanism, revealed it to be complex, containing a sophisticated differential system of 30 to 70 gears.

the Antikythera Mechanism displayed in Athens

Use in modern times

The first true differential gear definitely known to have been used in the Western world was by Joseph Williamson in 1720. He used a differential for correcting the equation of time for a clock that displayed both mean and solar time. Even then, the differential was not fully appreciated in Europe until James White emphasized its importance and provided details for it in his Century of Inventions (1822).

At the dawn of automotive industry, cars of that time transmitted engine power to the wheels in a simple fashion that was easy for non-engineers to visualize. The engine drove a set of bevel reduction gears that drove a shaft and pulley. Leather belts extended between the pulley and geared wheels on an axle. One wheel, the small one, got the car going by meshing with a ring gear on one of the driving wheels. The big wheel then took over to get the car to hustle along at a top speed of 20 mph. If the car encountered a hill that it did not have the power to climb, the driver would come to a dead stop so he could engage the small wheel.

Thus did British auto pioneer F. W. Lanchester describe the transmissions in his cars: “One belt-driven HIGH gear that will go over everything and one bel-driven LOW gear in case the car had to climb a tree.”

In 1895 Panhard-Levassor launched a revolutionary automobile which has served as the prototype for most vehicles built in the 90 years since then. Unlike other cars of that day, it possessed a vertically mounted engine in the front of the vehicle that drove the rear wheels through a clutch, 3-speed sliding gear transmission and chain-driven axle. The only modern features missing from the setup were a differential rear axle and driveshaft. These came along three years later, in 1898, when millionaire-turned-auto-hobbyist Louis Renault connected a vertical engine with transmission to a “live” rear axle by means of a metal shaft.

Panhard & Levassor in their revolutionary 1895 automobile

The live rear axle — which Renault adapted from an idea developed in 1893 by an American, C. E. Duryea — was called the differential rear axle. It used a number of gears to overcome the problem of rapid tire wear, which resulted on turns with the “dead” axles used by all other carmakers. “Differential” referred to the ability of the unit to turn the outer driving wheel faster than the inner driving wheel, eliminating tire scuffing in turns.

By 1904, the Panhard-Levassor sliding gear manual transmission had been adopted by most carmakers. In one form or another, it has remained in use until recent times. Obviously, there have been improvements, the most significant being the invention of a synchronizing system that permits drive and driven gears to be brought into mesh with each other smoothly without gear clashing. This system allows both sets of gears to reach the same speed before they are engaged. The first of these synchromesh transmissions was introduced by Cadillac in 1928. An improvement to the design patented by Porsche is widely used today.

Well, just one more thing to mention…the torsen differentials. These are torque sensitive differentials which means that if you loose grip the diff would block itself making your wheels turn at the same speed just like the cars before the 1895 Panhard-Levassor.

This makes your audi quattro, subaru or humvee (and only these) progress in the snow even if you have grip on only one wheel.

sources : wikipedia, Extensive knowledge of the auto industry

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