In this thesis, we describe some tools based on computer algebra techniques and methods. They are designed to enhance the performances and capabilities of software systems for multibody system dynamics modelling. We are interested in automatically generating a set of differential equations modelling the dynamics of such systems from their physical descriptions. In the first chapter, we precisely define the mechanical and mathematical objects that are useful for the study of multibody system dynamics. We show that an important problem arising in the study of closed-loop systems is the nature of the set of admissible configurations. The second chapter is a detailled study, on one significant example, of various methods to generate the equations of motion. This is oriented toward implementation in a computer algebra systems. We show the interest of symbolic techniques and specify the tools that are needed. In the third chapter, we present the symbolic tools that we have developped to help the design and construction of a generator of the equations of multibody system dynamics. In the last chapter, we try to solve the problem of the determination of the dimension of the configuration manifold in the case of closed-loop systems. Several methods, based on algebraic, probabilistic and geometrical techniques are presented, implemented and experimented.
