1. Field of the Invention
The present invention relates to a rotary piston engine and a method for designing the same.
2. Description of the Prior Art
The rotary piston engine is an engine wherein a generally-triangular rotor is accommodated in a rotor chamber which is formed by a rotor housing having a trochoid inner surface and side housings provided on both sides of the rotor housing. In the rotary piston engine, three working chambers defined by the rotor and the housings move in the circumferential direction as the rotor spins to sequentially passes the intake interval, the compression interval, the expansion interval, and the exhaust interval (see, for example, Japanese Laid-Open Patent Publication No. H5-202761). A rotary piston engine disclosed in this publication has an intake port formed in the side housing and an exhaust port formed in the rotor housing. Namely, this rotary piston engine employs a so-called peripheral exhaust system.
However, the peripheral-exhaust rotary piston engine has such a disadvantage that the intake open timing and the exhaust open timing partially overlap so that a large quantity of residual exhaust gas is carried over into the next interval. Namely, the peripheral-exhaust rotary piston engine has an increased internal EGR (Exhaust Gas Recirculation) quantity. Therefore, to secure stable combustion, the air fuel mixture needs to be richer than the theoretical air fuel ratio (stoichiometric air fuel ratio).
Japanese Laid-Open Patent Publication No. H7-11969 discloses a rotary piston engine employing a so-called side exhaust system wherein the exhaust port is formed in the side housing. This system can eliminate the overlap of the intake open timing and the exhaust open timing. As a result, the residual exhaust gas carried over into the next interval is reduced, and stable combustion is realized even at the theoretical air fuel ratio. As a result, the side-exhaust rotary piston engine achieves smaller fuel consumption than the peripheral-exhaust rotary piston engine.