PH Origins: Supercharging

The concept of pressurising the intake of an engine, in order to increase the charge density and boost performance, is almost as old as internal combustion itself - and originates from the minds of the earliest innovators in the field.

Engineer Gottlieb Daimler, one of the leading pioneers of the internal combustion engine and later founder of a company which ultimately become Daimler AG, is seemingly among the first to have conceived the idea of forced induction.

In May 1885, he applied for a patent on an upright single-cylinder engine nicknamed the 'grandfather clock' due to its appearance. This engine, which had been co-developed with Wilhelm Maybach, featured a valve in the head of the piston and a pumping chamber below it - which had a larger volume than the cylinder above it.

As the piston travelled down the bore, a combustible mixture would be forced through the valve in the piston. This action would supposedly deliver more mixture into the cylinder than it could otherwise naturally aspirate. More air in the combustion chamber meant there was more oxygen available, meaning more fuel could be burnt to produce more power.

This method of induction allowed Daimler to work around the issue of overly small valves in the cylinder head, which would have otherwise restricted the engine's performance. The result was 0.5bhp at a then-impressive 700rpm; this engine then went into Daimler's first vehicle, a wooden motorcycle. Daimler then created his first car by fitting a modified 1.1bhp version of his creation into a carriage frame, in 1886, the year the patent for the engine was approved.

Others were investigating similar methods: compression-ignition trailblazer Rudolf Diesel discussed ways to raise the pressure of the incoming charge in a patent, covering various engine improvements, dated June 1895.

In December 1902, however, French industrialist and automotive pioneer Louis Renault first described what we would recognise today as a supercharger. His patent, 'Improvements to four-stroke engines', describes a set-up consisting of an engine-driven compressor feeding the engine's intake.

Renault outlined how the device would increase 'the gas inlet pressure in the cylinders of four-stroke combustion engines' - and how that the 'effect of the explosion [in the engine] will be greater, which will consequently increase the power of the engine.'

He also proposed the concept of a clutched supercharger, for when maximum power output wasn't required. Scottish engineer Sir Dugald Clerk also experimented with supercharging, explaining its benefits in a lecture given in 1904. He described experiments where air at above atmospheric pressure was introduced to the combustion chamber of a test engine - which, reportedly, increased the thermal efficiency of the engine by almost seven per cent.

By this point, the idea of forced induction was catching on in earnest. Over in the United States, in 1904, the Searchmont Motor Company was liquidated. The remains were purchased by former Searchmont engineer Lee Chadwick, who established Fairmount Engineering Works - later renamed Chadwick Engineering Works - and began producing cars.

Chadwick revelled in the pursuit of power and in motorsports victories, so was always looking for methods with which to gain an edge over rival offerings. At the time, 'blowers' for industrial applications were not uncommon. The classic 'Roots' design, featuring meshing lobes, had been patented in 1860 and was often used to force air into blast furnaces; similarly, newly developed and improved centrifugal blowers and pumps were being pressed into action in the early 1900s in industrial applications.

These, Chadwick concluded, could be used to feed a carburettor with pressurised air - and ramp up the output of his engines. In 1907, experimentation began when a centrifugal compressor was bolted onto the factory 'Black Bess' race car. Its performance was remarkable, with the car achieving a claimed 109mph during testing and winning the 'Giant's Despair' hill climb in 1908. The option of a supercharger was reputedly then made available for factory cars in 1909.

Supercharging was making waves in the aviation industry, too, as manufacturers sought ways to both improve performance and maintain it at higher altitudes, where the air was thinner. In 1911, the American Murray-Willat company introduced a rotary engine - where the crankcase and cylinders rotate around a stationary crank, not the later Wankel-type engine we nowadays associate with that term - with an integrated vane-type supercharger.

The outbreak of World War I led to further supercharger development as aircraft got heavier and needed to fly faster and higher. Many automotive companies, lending their manufacturing and design facilities to the war efforts, were involved in these research and development projects.

One company that gained experience with forced induction during World War I was Daimler Motoren Gesellschaft - DMG - which had been established by Gottlieb Daimler and had produced cars since 1892. Its Mercedes-branded D.IVa six-cylinder aircraft engine, in July 1918, had been equipped with an AEG centrifugal supercharger. An AEG G.V biplane bomber, outfitted with a pair of these force-fed engines, promptly climbed to an impressive 20,000 feet during trials.

When the war drew to a close in 1918, countless German industrial operations found themselves with a surplus of both staff and facilities. The Treaty of Versailles prohibited the manufacture and export of German military products, though - so many of these companies switched to car production to remain in business.

DMG had an ageing line up of vehicles, though, and wasn't in a competitive position. It didn't want to waste its supercharger experience, either, but the Treaty of Versailles limited aviation engine design and production as well. To counter both points, DMG took steps to develop a new, modern automobile with this hopefully attention-grabbing hardware.

Initial trials took place using a Roots-type blower on one of the company's Mercedes-Knight sleeve valve engines but several problems were encountered, so supercharging was applied to more conventional powerplants. A sound solution was found when an existing four-cylinder, 2.6-litre engine was fitted with a Roots supercharger, mounted vertically and driven off the nose of the crank via a clutch.

Technical director Paul Daimler, the eldest child of company founder Gottlieb Daimler, also designed a new 1.6-litre four-cylinder engine that was designed to use a supercharger from the outset. It produced 38bhp, while the larger 2.6-litre engine produced a substantial 64bhp; each reportedly put out around twice the output of their naturally aspirated equivalents.

These engines subsequently went into models initially called the 6/20 and 10/35 Mercedes, which were unveiled at the Berlin Motor Show in September 1921 - but series production, and the supercharged era, didn't start in earnest until the end of 1922. Driver Max Sailer also won the production car category in the Targa Florio in April 1922 and, from that point on, interest was high and development rapid.

By 1926, following a merger that resulted in the new brand Mercedes-Benz, the 6.3-litre six-cylinder supercharged 24/100/140 variant was producing 138bhp. Then, in 1934, the 500K was introduced. The 'K' stood for 'Kompressor' and this badging would be used by Mercedes-Benz for decades to come. Mercedes wasn't the only one employing supercharging, though, with other companies such as Alfa, Bugatti and Delage putting forced induction to use in their racing cars.

Auto Union, Audi's predecessor, also made notable achievements with supercharging. Its Type C streamliner, which was unveiled at a race held in 1937 at the AVUS circuit, packed a Roots-blown 6.0-litre V16. Thanks to 28 psi of boost, it thundered out a staggering 512bhp at 5000rpm - which, on the Frankfurt to Darmstadt autobahn, allowed it to exceed 248mph.

Alas, it was World War II that further drove the advancement of supercharging, as the performance requirements of combat aircraft increased. Multi-stage, multi-speed superchargers were produced, as well as myriad compound-charged set-ups.

The understanding of supercharging techniques - as well as engine materials, ignition and fuelling systems - improved considerably during this period and, in the decades following the war, manufacturers and hot rodders alike began to flock to the power-adding technology. The core principle remained unchanged, however: more air and fuel in, more power out.

Read more:

Dual-clutch transmissions - PH Origins

How does a supercharger work? - PH Explains

Cruise control - PH Origins

P.H. O'meter

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