A Roller Chain Drive Model Including Contact with Guide-Bars

Abstract

A model of a roller chain drive is developed and applied to the simulation and analysis of roller chain drives of large marine diesel engines. The model includes the impact with guide-bars that are the motion delimiter components on the chain strands between the sprockets. The main components of the roller chain drive model include the sprockets with different sizes and the chain made of rollers and links, which are represented by rigid bodies, mass particles and springs-damper assemblies respectively. The guide-bars are modelled as rigid bodies with a roller-guide contact representation as continuous force. The model of the roller-chain drive now proposed departs from an earlier model where two contact/impact methods are proposed to describe the contact between the rollers of the chain and the teeth of the sprockets. These different formulations are based on unilateral constraints and continuous force methods, respectively. In the unilateral constraint methodology the kinematic constraints are introduced in the system anytime a contact between the rollers and the sprockets is detected. The condition for the constraint addition is based on the relative distance between the roller centre and the sprocket centre, i.e. a constraint is added when such distance is less than the pitch radius. The unilateral kinematic constraint is removed when its associated constraint reaction force, applied on the roller, is in the direction of the root of the sprocket teeth. In order to improve the numerical efficiency of the methodology only the first and last roller seated on each sprocket and the two free rollers nearest to the sprocket are checked for capture or release. It is assumed that all the rollers in the chain, between the first and last seated rollers are in contact with the sprocket. In the continuous force method the roller-sprocket contact, is represented by forces applied on each seated roller and in the respective sprocket teeth. These forces are functions of the pseudo penetrations between roller and sprocket, impacting velocities and a restitution coefficient. In the continuous force method, an arc of circle approximates the geometry of the tooth profile. In both models it is assumed that all the rollers of a chain strand are not in contact with any particular sprocket. The contact between the rollers of the chain strands and the guide-bars is modelled with the continuous force model. The methodology is implemented in a computational code to study the dynamics of the drive, including the chain flexibility, transversal and longitudinal vibrations and contact forces between the chain and sprockets. The models proposed effectively represent the polygonal effect, always present in this type of drives, and therefore, all vibration dynamics associated to it. The inclusion of the guide-bars allows the usage of the chain drive model in situations relevant for implementation of the real diesel engines in large maritime vessels.