Objective: The objective of this research is to reduce passive side i.e., chassis side vibrations which arise due to engine operation. As the engine is primary source of vibrations at idle condition hence the study has been conducted at idle rpm considering the vehicle is stationary. This research focuses on the parameters that affect and reduce engine vibrations. Methodology/Results: To study the vibrations, an engine model is developed replicating the real engine in MSC Adams. To ensure reasonable vibrations are predicted by CAE, these engine vibrations are correlated with test data in time domain. The multibody dynamics approach is suited to correlate with actual test data at relatively lower frequencies (<100 Hz). The engine model used is 4 stroke 4 cylinder 1.4L diesel engine with 6 speed manual transmission. The MBS model consists of the engine block, pistons, connecting rods, crankshaft, engine mounts, fly wheel, piston pins, subframe and chassis. This study is conducted in two phases. The first phase consisting of rigid body modeling, in this phase the base model is generated in MSC Adams wherein all parts of model are modelled as rigid components (no component flexibility is included). The second phase includes flexible body modelling, while flexibility of various components is introduced in the MBS model. Flexible crank, engine block, suspension subframe and chassis are introduced in the MBS model using MNF’s (Modal Neutral File). Engine cylinder pressure versus crank angle is given as an input to the MBD model. The pressure creates forces which act on the piston and brake torque is generated about the crankshaft. The simulation engine RPM is replicated in such a way that it would match the test conditions. Further, mount acceleration results were correlated with test results in Adams Postprocessor. Further to the baseline simulation, an exhaustive sensitivity study is performed to find key parameters which influence passive-side engine vibrations. The MBS model was also used to predict forces on the chassis/engine mounts. Furthermore, these forces can be obtained in time and frequency domain as well which will be helpful for engine NVH studies. Limitations: This model can only be able to determine the forces at reliably low frequencies due to software limitations. It is difficult to predict the thermal losses of engine and how they are affecting the simulation results. New offering/Conclusions: This research focus on appropriate modelling technique to predict the mount loads and being able determine the sensitivity parameters to reduce the engine vibrations. The flexible body modeling is a good way in order to correlate the simulation result with actual test data. By using flexible body modelling way, the correlation percentage can be increases up to 90%. Hence, the predicted results can be helpful for the further CAE studies and can also be helpful for the further engine studies. This modeling technique can predict the mount loads up to second vibration order.
Mr. Mandar Shilimkar, Project Engineer, Applus IDIADA Automotive Technology India Pvt. Ltd.