This invention relates to a piston ring assembly, particularly an oil scraper piston ring assembly which is of small axial height and which is formed of an expander spring ring made particularly of a resilient strip material and at least one annular lamina which lies at least partially on a plurality of radially extending and circumferentially serially arranged tongues of the expander spring. Further, the lamina abuts generally axially bent legs which form part of the tongues and which have radially inwardly oriented extensions.
U.S. Pat. No. 3,627,333 discloses a three-part piston ring assembly which has two annular laminae and an annular expander spring disposed therebetween. This piston ring system is of low axial heigh and is installed in piston grooves for wiping oil along the cylinder wall in an internal combustion engine. The metal strip expander spring is, as viewed circumferentially, provided with slots which extend in an alternating circumferential series, from the radially inner and the radially outer circular edge of the annular strip. In this manner a circumferential series of radially oriented resilient tongues are obtained. In the radially inner zone of the expander spring approximately axially bent legs are provided which are alternatingly oriented in opposite directions and which serve for the radial support of each lamina. The resilient, radially extending tongues form a support surface for the two laminae. In addition to a low axial height, such a piston ring assembly also has a relatively small radial wall thickness. Such an expander spring design results in very short leverage arms, and thus a hard spring characteristic is obtained. Disadvantageously, hard spring characteristics, in turn, lead during operation to a rapid drop of the tangential force of the piston ring as wear occurs.
In the piston ring construction disclosed in German Pat. No. 3,208,396, by virtue of the use of a radially wide strip material, a softer spring characteristic of the expander spring is obtained. The axially bent legs radially engage behind the laminae and have radially inwardly extending continuations. While the advantages sought for are achieved, the radial wall thickness of the piston ring assembly is necessarily increased. Such dimensional change requires deeper piston grooves which, however, may cause strength problems in the piston design.
U.S. Pat. No. 2,855,254 discloses a two-part piston ring assembly which is formed of an axially relatively large piston ring and an expander spring which is made of a strip material with a rectangular or round cross section and which extends, with alternating portions, axially adjacent and radially behind the piston ring. The expander spring legs which extend radially behind the piston ring may be oriented at an acute angle to the inner circumferential face (side) of the piston ring. In this manner, a contacting of the expander spring by the piston ring occurs only along the inner circumferential piston ring edge which is oriented towards the expander spring.
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