Compressors

1907 Michelin & Cie France
1907 Michelin & Cie France
1907 Michelin & Cie France

First patent filed for a free-piston air compressor

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1918 J.A. McIntyre
1918 J.A. McIntyre
1918 J.A. McIntyre

Free piston compressor, never realized

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1925 Conrad Kohler, Switzerland
1925 Conrad Kohler, Switzerland
1925 Conrad Kohler, Switzerland

Free piston compressor, never realized

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1924 Hugo Junkers, Germany
1924 Hugo Junkers, Germany
1924 Hugo Junkers, Germany

Free-piston compressor with opposed pistons and rack and pinion gear synchronization. Basis for the air compressors built from the mid thirties, especially in the use in German WW2 submarines.

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1925 Hugo Junkers, Synchronization
1925 Hugo Junkers, Synchronization
1925 Hugo Junkers, Synchronization

The trials of Hugo Junkers to simplify the piston synchronization. Ultimately, on this issue all manufacturers of free-piston engines failed - with the exception of Pescara - Sigma.

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rack and pinion gear synchronization
Typical rack and pinion gear synchronization
Typical rack and pinion gear synchronization, as all the other designers had to use it, because Pescara patented both rocker and later a mass-neutral synchronization gear. The system has serious disadvantages because of the high acceleration forces.

Typical piston assembly of the early Pescara engines
Typical piston assembly of the early Pescara engines
Typical piston set of the early Pescara engines. The original rocker was later replaced by an inherently balanced and space-saving system. Thanks to this, the Pescara engines had a breakthrough after WW2.

1930's Junkers
1930's Junkers
1930's Junkers
1930's Junkers
1930's Junkers

In the early thirties, the Junkers free-piston engine was calculated by Pescara engineer Robert Huber, in order to come up with money for commissioned work.

After annexation of the Junkers-plants by the German Nazis, and the use of these compressors at the German submarines, Robert Huber dissociated from Junkers and he never spoke a word again about this.

The Junkers free-piston engine was never developed significantly further by the Junkers company.


Start of a Junkers free-piston compressor
Start of a Junkers free-piston compressor. First, the pistons are moved to the outer dead point position using the synchronous linkage. Then, 30 bar pressured air is blown to throw the two pistons against the center. Diesel is injected and the engine runs at once.
1925 Raul Pateras Pescara
1925 Raul Pateras Pescara
1925 Raul Pateras Pescara

Single piston-cylinder compressor of Raul Pateras Pescara. Pescara had the idea to propel his helicopter with this engine. The engine, however, could not be realized in this version.

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The famous Pescara helicopters
The famous Pescara helicopters
Why Pescara invented the free piston compressor

The famous Pescara helicopters (first flight 1922) had a very heavy propulsion. The idea was to drive the rotor by means of compressed air through a system of a hollow shaft and nozzles at the blade tips. Pescara expected remarkable weight savings. This idea, however, was never realized.

The famous Pescara helicopter
1922 first flight of the famous Pescara helicopter
1922 first flight of the famous Pescara helicopter

That spring (1924), a French inventor (Pescara) came to Stodola (ETH Zurich) looking for a "bright young man" to engineer some of his revolutionary ideas on a light propelling plant for a helicopter.

It was fortunate that Pescara, the dreamer and glib-tongued persuader, chose Huber the engineer, who was young and capable and devoid of any inhibitions on the constructional details to be used in developing the new free piston machinery. Under his supervision, over twenty-five different sizes and types of free piston machinery were designed and seventeen were built and tested -

AMERICAN SOCIETY OF NAVAL ENGINEERS, 1950


AC-2 first running free piston engine
AC-2 first running free piston engine

​1927: This historic photograph shows the first experimental engine AC-2 from Pescara, on the test bench near Paris in Meudon-Val-Fleury, France.

The experiments performed by Robert Huber correspond to the work of Rudolf DieselNicolaus Otto and Felix Wankel.

This engine, however, bears the name of its inventor, Pescara, whereas it was designed and built by Swiss engineer Robert Huber.

Birth of the fourth motor system in addition to Otto (gasoline), Diesel, and Wankel

This engine was operated on gasoline. That time Bosch launched diesel injection pumps and injectors on the market, and soon Robert Huber designed the second prototype - similar to the AC-2, but with direct diesel injection.

Share of "Société des Auto-Compresseurs Pescara"

1931 Raul Pateras Pescara, France
1931 Raul Pateras Pescara, France
1931 Raul Pateras Pescara, France

Free-piston compressor with opposed pistons. Synchronization through connecting rods and a rocker. Built from the early thirties as air compressors for various applications. Compared with Junkers, the design was much more elegant and simplified.

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​1932 early Pescara prototype
​1932 early Pescara prototype
1932 early Pescara prototype

This early opposed piston compressor AC-6 already had a Bosch direct diesel injection. It was started by means of a spring system. Even today, the restored engine starts at once at minus 5 degrees Celsius, without any preheating.

1932 early Pescara prototype
AC-6 "Maison Breguet" air compressor
AC-6 "Maison Breguet" air compressor
​Serial version of the AC-6 prototype above. Approximately 80 pieces of this type were built and sold.

S26 with technical data
S26 with technical data
Subsequently, several different free-piston compressor types were desiged. More than 2000 units were sold in the thirties.

Example S26 with technical data

LC-1 Pneumatic operated steam locomotive
LC-1 Pneumatic operated steam locomotive
LC-1 Pneumatic operated steam locomotive
LC-1 Pneumatic operated steam locomotive
1934 LC-1

To reduce the risk of explosion, a mine locomotive was equipped with a free piston compressor. The locomotive ran with compressed air instead of steam and had therefore no longer an open fireplace.

During this work, Robert Huber came up with the idea for the free piston-turbine drive which is, so far, the most successful application of a free-piston engine.

1937 AC-24 "Alsthom Belfort" air compressor
1937 AC-24 "Alsthom Belfort" air compressor
1937 AC-24 "Alsthom Belfort" air compressor

​Among the built compressors there were several vertical types of an enormous size.


Drawing

Chantier du Trocadero, Paris, 1936
Chantier du Trocadero, Paris, 1936
1937 AC-13 compressor
1937 AC-13 compressor
1938 S-13 "Alsthom Belfort" air compressor
1938 S-13 "Alsthom Belfort" air compressor. Due to WW2, further development of free-piston compressor was abandoned.
Miniature free-piston engine compressor
Miniature free-piston engine compressor research at the University of Minnesota.
Since 2002 

Miniature free-piston engine compressor research at the University of Minnesota.