The rotary combustion engine is sometimes confused with "rotary" aircraft engines which are actually piston cylinders arranged in a circle - The whole engine rotates. They came into vogue in the first World War; I believe that these engines were initially created by Bavarian Motor Works (BMW), but haven't researched that yet.
There are three main types of true rotary engines:
1) Wankels: Engines withe eccentric shafts. These appear to be the most populous, and is the topic here.
2) Scissor action: These use vanes/pistons. Presently looking for some information on these.
3) Revolving block (a.k.a. 'Cat and Mouse' type): these are related to pumps and compressors where
the pump drives and the compressor is driven.
Designs for rotary engines were proposed as early as 1588 by Ramelli (See below). It took the automotive industry and the creation of the Otto cycle engine in 1876 for the Rotary combustion engine to get off the ground, and it also took Dr. Wankel's organization of 862 configuration pairs. Only 584 of these were proven practical.
There were over 2000 patents for rotary pistons filed prior to the early 1900s (I wonder if Einstein saw any while he was a patent clerk? That would be some interesting trivia...)
Below is a list of years and people associated with the rotary engine.
1588
Ramelli, an Italian engineer invented a water pump which continues to be used in oil pumps and compressors.
1636
Pappenheim, a German engineer invented the gear pump which is still used to lubricate engines. This gear pump made it possible to dispense with the reciprocating slide valves used by Ramelli.
Pappenheim drove his machine by an overshot water wheel set in motion by a stream and was used to feed water fountains. The emperor Ferdinand II granted him a “privilege” - the equivalent of a patent in respect of this invention.
Even in the 17th century, engineers were trying to solve the problem of “leak-proofing” between moving parts and this problem continues to be the Achilles heel of the rotary piston engine although Mazda would seem to have reduced this problem to manageable proportions.
1650
Otto von Guericke built a vacuum pump which employed leather washers to prevent leakage between cylinder and piston.
1782
James Watt who invented the steam engine’s connecting rod crank mechanism which made it possible to convert the piston’s reciprocating motion into rotary motion designed an oscillating piston machine in which a wing-shaped rotary blade performed an almost complete revolution uncovering inlet ports in a chamber separated off by a curved radial wall.
1799
One of Watt’s co-workers, Murdock, adapted Pappenheim’s gear pump to create a rotary piston steam engine.
1846
Elijah Galloway built the first rotary piston engine with inner epicycloid and enveloping outer line.
1859
Jones, modified Pappenheim’s gear pump and produced a double rotor with only two teeth per gear. Rootes compressors and pumps employ this principle.
1900
Alotham and Franchot designed a vane compressor comprising a bust rotating inside a cycloidal housing.
1901
The American, Cooley, lodged a patent for a rotary piston engine with an internal epicycloid and enveloping outer chamber.
1908
The Englishman, Umpleby, transformed Cooley’s steam engine into an internal combustion engine but experienced problems with gas tightness.
1923
A Swedish patent was granted to Wallinder and Skoog in respect of a true rotary piston thermal engine with toothed meshing, enveloping interior hypocycloid and internal five pointed rotor with a 5:6 rotation ratio which could be used as either a two or four stroke internal combustion engine.
1938
Sensaud and Lavaud, (the French engineers responsible for the Traction Avant automatic gearbox which was a failure) applied for a patent for a rotary piston engine with internally meshing gears in a hypocycloid housing and a 5:6 reduction ratio. Both Renault and Citroën, at the instigation of the French Air Ministry provided backing for this project and a number of engines were built at Batignolles. Unfortunately the engine failed to live up to expectations and the project was abandoned.
1943
The Swiss manufacturer Bernard Maillard built an air compressor based on a British patent for a rotary piston machine with a 2:3 ratio and internal hypocycloid surfaced chambers. Leakage under pressure made it impossible to use this design as a thermal engine.
1933
Dr. Ing Felix Heinrich Wankel (1902-1988) applies for patent on the DKM engine, and receives the patent in 1936. After working with NSU, the KKM engine is also produced.
Present Day
Mazda has worked out problems with gas tightness, and produced quite a few Wankel powered vehicles, most notably the RX-7 series.
