Design, Construction and Testing of Hypocycloid Machines

The hypocycloid mechanism, in its basic or modified version, can be used in reciprocating machines as an alternative solution to the conventional crankshaft-connecting rod system. This kinematic device is quite old in concept, but still gives rise to some research since it has some positive mechanical features, and it allows several functions to be easily combined. In the hypocycloid mechanism in fact the connecting rod has a perfectly sinusoidal straight-line motion, a characteristic that theoretically reduces the piston side thrust to zero and permits a perfect balance of inertia forces without auxiliary rotating shafts. Moreover, by means of a second head with suitable seals that prevent leakage to the crankcase, the lower portion of the cylinder can be used as a second working chamber without using the crosshead thus reducing the dimensions of the double acting machine. The authors have undertaken theoretical and experimental research in order to evaluate the positive features, in particular those concerning the possibility of the combination of functions, and to compare these characteristics with the evident shortcomings. This has led to the design and construction of a double acting compressor, whose performances have been compared with those of a traditional compressor. A perfectly balanced two-stroke engine, with the scavenging pump separated from the crankcase, has also been constructed and tested.