| abstract |
The four-stroke engine comprises a cylinder block with at least one cylinder, provided with valves, in which cylinder the piston, fitted with at least one piston ring, is arranged, capable of moving up and down and connected to the crankshaft drive. In order to take present attitudes towards fuel saving and environmental pollution into account in the engine itself, without having to abandon the existing design principle, the engine is designed in such a way that the piston (1) is formed from pressed graphite in the form of heat-hardened carbon or electrographite with a bending strength in the order of at least 75 N/mm<2> and its head (2) heat-treated to prevent burn-off, at least on the exposed working surface (2'). At the same time at least the sliding surface (3) of the cylinder (4) is formed from the same material, but with running surfaces heat-treated, or a similar material such as siliconised carbon, silicon carbide, silicon nitrite or the like with approximately the same thermal expansion behaviour as that of the piston (1). The same goes for the piston ring (5) which, moreover, with regard to its elasticity is endowed with the necessary elasticity either by design or by the choice of sufficiently elastic material. Finally the bores (12) on the piston (1) for the piston pin (13) are designed with a play in relation to the outside diameter of the piston pin (13) in such way that there is minimal play at operating temperature. <IMAGE> |