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The Pecqueur differential, mechanical genius on your wrist

Image - The Pecqueur differential, mechanical genius on your wrist

Watchmaker Onésiphore Pecqueur, a child of the French Revolution and heir to the spirit of the Enlightenment, was a gifted inventor. While working as head of the workshop for the Conservatory of Arts and Crafts in Paris, he developed a gear system known as the differential, whose many applications in watchmaking, car mechanics and industry are still relevant today. We are celebrating his pioneering spirit and mechanical genius in the exclusive watches that grant access to the Club Pecqueur Motorists.

We know very little about Onésiphore Pecqueur, beyond the fact that he was a precocious student. Legend has it that he completed his watchmaking apprenticeship in just a few months, rather than the generally required four years. In 1819, at the age of 27, he submitted a clock to the Exhibition of Products of French Industry which had two mechanically linked dials, showing both sidereal and mean time. The jury, which included one Abraham-Louis Breguet, awarded him a silver medal for inventing a gear that “maintains both communicating movements at acceptable rates of speed.”

The engineer continued to develop what the scientific community was already calling “Pecqueur gears”. At the fifth French Industry exhibition in 1823, he won a gold medal after unveiling a number of concrete applications of his technology, combining his gears with steam power (the steam engine, which kicked off the Industrial Revolution, was invented by James Watt in 1769). The medal was granted in anticipation of the many industrial applications for his invention. Thanks to these “Pecqueur gears”, the jury explained, it would be possible to “solve a host of mechanical problems, the resolution of which is of direct interest to the industrial arts.”

On 25 April 1828, Pecqueur registered a patent for a brand new steam carriage that would earn him a place in the history of the motor car. According to the description, the drive of the carriage – a steam engine installed in the front – was transmitted to the two wheels on the rear axle by a central shaft. This was connected to the shafts of the two rear wheels via a “mechanism that directs the power to each wheel without affecting their independence.” In other words, when rounding a bend, the inside wheel slowed down while the outer one increased its speed to compensate.

This invention, which made it possible to harmonise the rotation of driving wheels attached to the same axle when rounding a bend, was later called the “mechanical differential”. Today it is still widely used in our cars and other four-wheeled vehicles. There are very few inventions that originated in the world of watchmaking that can claim to have had such a broad impact. And that is why Onésiphore Pecqueur is considered the world’s first automobile engineer.

When we needed to look for a way to signal membership of a club for enthusiasts of the Mechanical Arts, Patrick Bornhauser, President and founder of BPM Group, very quickly decided that a piece of Mechanical Art would be both extremely relevant and highly symbolic. So a watch was the perfect choice: it’s mechanically ambitious, compact and useful. He also decided that this watch should perpetuate both Pecqueur’s innovative spirit and his pioneering invention.

That required nothing less than the creation of a new and unique GMT mechanism incorporating a Pecqueur differential. In order to bring Pecqueur’s original concept into the 21st century, the mechanism would incorporate a second time zone without the need to set a reference city, or to know offhand the number of hours to add or subtract from home time.

Behind this apparent simplicity lies considerable complexity, which could only be entrusted to master watchmakers with experience in the most sophisticated horological techniques. Le Temps Manufacture (LTM), based in Fleurier, Switzerland, rose to the challenge. The engineers from this renowned watch manufacturer were responsible for the design and development of the PECQUEUR LTM 5021 movement that drives the Club Pecqueur Motorists watch.

“The main advantage of the Differential is that it does not disrupt the watch’s operation during a time zone change, thus enhancing precision,” explains Hamdi Chatti, who spearheaded the Pecqueur Motorists watch project. In other words, the heart of the PECQUEUR LTM 5021 calibre continues to beat at a frequency of 28,800 vibrations per hour, or four ticks per second, even while the second time zone is being adjusted. This maintains the balance-spring pair’s isochronism throughout the 60-hour power reserve of the movement. The overall harmony of the calibre belies its complexity: it contains 237 components within a thickness of just 7.75 mm and a housing diameter of 37.8 mm.

You will be wearing a technical feat worthy of Onésiphore Pecqueur himself, on your wrist!