Dynamics of an innovative kinetic torque converter: functional modelling, simulations and experimental comparison

In the power transmission field, research aims to find a compromise between achieving high engine performance and low fuel consumption. Devices that allow power to be transmitted in rotary motion by varying the relative angular speed between the prime mover and the transferor mostly use constant transmission ratios, such as gearboxes, or continuous transmission ratios based on friction principles, such as belts, or hydraulic fluids. These last include the hydraulic torque converter, which allows power to be transferred from a mover, which may be an internal combustion engine or an electric motor, to a transferor, increasing the torque acting on the latter. The kinetic torque converter analysed here is based on a different operating principle: it does not use hydraulic fluid and transmits torque and rotational speed, that is power, from the input shaft to the output one through the dynamic effect generated by rotating eccentric masses. In the present study, functional models of this device are developed and its dynamic behaviour is simulated comparing the results with experimental tests. Starting from the existing six-stages prototype, a tridimensional functional model is developed with Computer Aided Design (CAD) Dassault SolidWorks software and its kinematic behaviour is investigated through the reconstruction of the equivalent quadrilateral mechanism. Additional functional CAD models are realised in order to pursue the static and dynamic balance of the device. The symmetry between the stages can be obtained with a different realisation of the input shaft and/or with a relative angular disposition between the stages properly realised to obtain a static balancing of the device. Moreover, analysing the trends of the moments of inertia during the simulated movement of the system, it is asserted that the sequence of the six stages opportunely realised must be repeated by mirroring with respect to the repetition plane in order to obtain a theoretically dynamically balanced device, as well. The critical issues related to the assembly configurations of the device are investigated through experimental analysis performed on a test bench; several trials are performed with variable operating conditions: effects of different angular speeds on the input shaft and of variable load on the output shaft are analysed. Test cases data are acquired by the software environment NI LabView and the measurements of angular speed and torque at input and output of the system are post-processed in Matlab. The results show a marked torque ripple due to the mounting configuration of the prototype analysed. In addition to testing and evaluation aspects of the torque converter discussed in the present study, an analytical model based on parametric writing of the equations of motion is developed. It is a powerful design tool that can be used in response to an application request. Modelling and simulation are performed through Matlab scripts which receive input information about the geometry of the stages and the inertial terms of the device components, as well as the initial conditions with respect to which the solver performs the integration of the equations of motion. Finally, finite element analyses are carried out both on single components of the device and on the assembly with suitable attention to non-holonomic contacts and friction problem, comparing the results obtained from SolidWorks Simulation and Altair HyperWorks.