Bond Graph Modelling of Power Transmission by Torque Converting Mechanisms

Abstract

Kinematically constrained motion is generally accepted as a fundamental requirement for a mechanism to function as a power transmitting device. There exists, however, a class of mechanism which although kinematically unconstrained, can, by incorporation of energy storage elements, function as a power transmitter. An example of such a mechanism is the automatic, variable ratio power transmission invented in the early twenties by G. Constantinesco, which generated a lot of interest among the engineering fraternity at the time. A typical device consists of a crank-driven nine-bar mechanism which possesses two degrees of mobility. The single velocity (or torque) source supplies the input power, which is transmitted to the output shaft by means of unidirectional drives. The characteristics of the energy storage element in conjunction with a single velocity (or torque) input and the external load fully determine the dynamic behavior of the device. During operation, the input energy is distributed between the load and the energy storage depending on the requirements of the load. For a given input power and external load, the device will adjust the velocity of the output shaft to absorb that power; i.e., it will operate as an automatic, variable ratio power transmission. This paper concentrates on the formulation of a general bond graph model for the mechanism. The model possesses mixed causality and non-linear structure. Some results of digital simulation of the bond graph model of a particular mechanism are provided.