Experimental Determination of Rigid Body Properties of a Powertrain Unit for NVH Refinement 2014-01-0039
This paper establishes quick and accurate methods to experimentally determine the rigid body properties of a powertrain unit namely, the centre of gravity, the moment of inertia and the torque roll axis and also the rigid body dynamics of mounting system such as the rigid body modes, kinetic energy distribution, and elastic roll axis.
The centre of gravity is determined using single point suspension and laser pointer to locate the axis passing through the centre of gravity. A special unifilar pendulum test rig is developed for determining the moment of inertia where an accelerometer measures the rotational oscillations for a given time period and the moment of inertia is determined by solving a set of inertial ellipsoid equations. An easy method of reorienting the powertrain is demonstrated in this paper. The torque roll axis is determined by generating a torsional excitation about the crankshaft axis of a freely suspended powertrain and by locating the centre of rotation of the powertrain in two different planes.
The rigid body modes are determined by modal analysis on a standalone mounting arrangement required for proper excitation of the six degrees of freedom. After determining the translational and rotational modal frequencies, the kinetic energy is calculated for each mode frequency and the contribution of different modes at a particular frequency are determined.
The elastic roll axis is determined in a similar manner as that of the torque roll axis; the difference in elastic roll axis estimation is that the powertrain is mounted on elastomeric mounts on a standalone test rig. The technique reduces the development time for power train mounting systems and also enhances vehicle design.