In-Plane and Out-of-Plane Elastodynamics of Thin Rings and Seals

R Turnbull,R Rahmani,H Rahnejat

doi:10.1115/1.4043526

Abstract

Thin curved rings used mostly as seals, including in internal combustion engines undergo complex elastodynamic behavior when subjected to a combination of normal radial loading and tangential shear with friction. In turn, their complex modal behavior often results in loss of sealing, increased friction, and power loss. This paper presents a new finite difference approach to determine the response of thin incomplete circular rings. Two interchangeable approaches are presented; one embedding mass and stiffness components in a unified frequency-dependent matrix, and the other making use of equivalent mass and stiffness matrices for the ring structure. The versatility of the developed finite difference formulation can also allow for efficient modification to account for multiple dynamically changing ring support locations around its structure. Very good agreement is observed between the numerical predictions and experimental measurements, particularly with new precision noncontact measurements using laser Doppler vibrometry. The influence of geometric parameters on the frequency response of a high performance motorsport engine's piston compression ring demonstrates the degree of importance of various geometrical parameters on ring dynamic response.

Highlights

Elastodynamics of thin rings plays an important role in the functional performance of many machines, where they are mostly used for the primary purpose of sealing
Accurate determination of complex elastodynamics of rings and seals is a prerequisite for the prediction of sealing performance, comprising leakage, pressure loss, and frictional assessment
The power losses associated with such seals is best demonstrated by the piston compression ring of internal combustion engines

Summary

Introduction

Elastodynamics of thin rings plays an important role in the functional performance of many machines, where they are mostly used for the primary purpose of sealing. Thin incomplete circular rings are used as compression rings for sealing the combustion chamber in internal combustion engines. The intention is to guard against the escape of combustion gasses to the bottom-end of the engine. The compression rings are subjected to a plethora of forces such as contact forces with the cylinder bore surface and with their retaining piston groove lands. There are applied forces due to radial ring tension, the varying gas force pushing the ring onto the cylinder surface, and friction with the cylinder bore surface. In practice the elastodynamic behavior of the compression ring is quite complex and affects its ideal function

Methods

Results

Conclusion