As early as 1924 Felix Wankel realized that sealing would be one of the biggest problems in developing a rotary combustion engine. In the late 20's and early 30's he made many experiments. His research in this field allowed him to make several advances. These led to contracts with BMW and other companies.
There are two kinds of areas on the rotor that need
sealing: the apices (plural of apex) and the sides. The
peripheral housings are actually slightly larger than a true
epitrochoid gloss. This is
done to improve sealing by preventing unnecessary seal movement.
Mazda Seal Design
Before 1986, Mazda apex seals had two pieces, one of which is a small triangle. Since 1986, the long piece was split along its length horizontally so now the apex seal is composed of three pieces. The thickness was reduced from 3 mm to 2 mm. These seals are backed with a single spring bar before 1986 and two spring bars from 1986 on.
The material is cast iron alloy. The top rubbing surface is chill hardened by an electron beam.
The side seals are 1.0 mm before 1986 and 0.7 mm there-after. They are made of sintered iron. This provides some self-lubrication as it rubs against the nitrided iron surface of the side housing.
Water seals are used between the peripheral and side housings gloss]. In 1986 the grooves in which they fit were moved from the peripheral to the side housing (ends and center plates).
Eco-Max is using ceramic seals for its single-rotor engine.
Matsura, Kenji and Terasaki, Kazuo, "Measurement of the relative behavior of a rotary engine apex seal to the side of a slot using magnetic induction" [title is only approximate], Transactions of the Japan Society of Mechanical Engineers Part B, V 56, n. 526, June 1990 p. 1812-1817. ISSN: 0387-5016. Abstract: Behavior measurements have been made of a carbon-impregnated aluminum apex seal of 6-mm thickness and a chilled cast iron apex seal of 3 mm thickness. A new magnetic induction system consisting of transmitting, resonance and receiving printed-board coils was devised. An induction-type sensor was connected with the resonance coil, being intermediate between the others. Quantitative measurements with high frequency response became possible with this system. It was found that at speeds higher than about 3000 rpm and loads higher than 2/4, the cast iron apex seal had a tendency to vibrate after the shift from the trailing to the leading side of the slot after the minor axis of the engine on the ignition side. 12 Refs. In Japanese.