A new mechanical variable valve actuation system for motorcycle engines

This paper deals with the design and manufacturing of a mechanical variable valve actuation system, developed as part of the MUR financed research project concerning the realization of a high performance motorcycle engine, through a partnership of Moto Morini S.P.A. (BO), Dell’Orto S.P.A. (MI), Istituto Motori - CNR (NA), and DIME - Università di Napoli Federico II. After a synthetic description of the main variable valve actuation methods currently employed (timing, duration and lift variation, cyclic cylinder deactivation), the paper presents the results of our mechanical variable valve actuation system, consisting of three main elements: cam, main rocker arm with fixed fulcrum and secondary rocker arm with mobile fulcrum. It enables valve lift variation through a simple translation of the intermediate element (system 1). The study has been conducted implementing a numerical procedure specifically designed to determine cam profile and the kinematic and dynamic characteristics of the whole system, starting from the following input data: rocker arm geometry, relative positions and inertial data of elements, spring stiffness and preloading, camshaft speed and valve lift law. The model has been validated against the conventional timing system using kinematic simulations. Results of the numerical procedure verify the validity of the variable valve actuation system, capable of a valve lift variation from 30% to 100% of the maximum lift, with a limited acceleration (lower than maximum values). Based on the numerical results, we are developing a new mechanical variable valve actuation system. The new system consists of the same three elements used previously, but they are connected in a different way (system 2). The newer system enables more general lift profile distributions with a similar geometric complexity. A maximum closing limited to 30% does not enable cyclic deactivation of some cylinders (strategy feasible on multicylinder engines) or exclusion of one or more valves (strategy feasible on multivalve engines). The activity was extended to research for a new solution (always a mechanical system), capable to allow inlet valves complete closing and timing and duration variation (system 3). This paper reports results reachable with the simplest system 1. This new system gives better perspectives of use for a new two-wheel vehicle engine.