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Multi-Piece Oil Control Rings
Three-Piece Oil Control Rings

Three-piece oil control rings consist of two thin steel rings, known as rails (segments), and an expander-spacer which holds the rails at the required relative axial distance while simultaneously pressing them against the cylinder wall. With regard to the expander-spacer design, three fundamental styles have become established on the world market and lend their name to the 3-piece systems described below. If the expander-spacer is made from a nitridable steel, then nitriding can provide effective protection against secondary wear.
Whereas in the past the running faces of steel rails were always chromed, today they are increasingly nitrided all over and used in combination with a nitrided expander-spacer in order to satisfy tougher demands on engine durability and stricter emissions legislation. Such a design offers excellent wear protection of the running face and optimal protection against secondary wear between the expander-spacer and rails.
Conformability of 3-piece rings can be optimized by the use of rails with a smaller radial wall thickness.

VF System::
An expander-spacer made from a slotted steel strip bent into a U-shape, the open side facing towards the inside diameter. The expander-spacer is usually made from simple carbon steel and is therefore not nitrided. A similar type in a nitridable Cr-Ni steel also exists.

MF System::
The expander-spacer consists of a Cr-Ni steel strip in which axial humps are formed. Systems with an untreated expander-spacer and chromed rails as well as all-nitrided systems are in use.

SS50 System::
The SS50 expander-spacer, like the MF type, is made from Cr-Ni steel but by contrast the steel strip is humped in the radial direction. Such systems also are in service with an untreated expander-spacer and chromed rails or in an all-nitrided version for tougher demands.


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