This paper was accepted for publication in the journal Journal of sound and vibration and the definitive version is available at http://dx.doi.org/10.1016/j.jsv.2007.01.034The rattle phenomenon in vehicular transmissions and its impact on the automotive industry have been widely reported in the literature. A variety of palliative measures have been suggested for attenuation of rattle such as use of backlash eliminators, clutch dampers or dual-mass flywheels. These palliative measures incur further costs and can have untoward implications in powertrain noise and vibration problems. A fundamental investigation of the dynamics of impacting gears is undoubtedly the way forward for a root cause solution. This paper introduces a new approach for understanding the interactions between the transmission gears during engine idle conditions by taking into account the effect of lubrication. Gear impacting surfaces are treated as lubricated conjunctions rather than the usually reported dry impacting solids. Depending on load and speed of entraining motion of the lubricant into the contact domains, the regime of lubrication alters. In this paper, the influence of lubricant in torsional vibration of lightly loaded idling gears is examined which promotes iso-viscous hydrodynamic conditions. It is shown that the lubricant film under these conditions behaves as a time-varying non-linear spring-damper element. Spectral analysis of the system response is compared to the findings of the linearised system

Real cylinder bores are out-of-round and axially asymmetrical. The top compression ring, nominally an incomplete circle, is subjected to ring tension and cyclic combustion force in order to conform to the bore surface. The bounding surfaces are rough and their conjunction is subject to a transient tribological state. Therefore, the ring–bore conjunction is only partially conforming for most of the engine cycle. The conjunction may be viewed as a problem of scale, depending on the analysis carried out at a certain bore order (out-of-roundness). Therefore, the contact may be viewed as a multi-lobed rough conjunction, where the regime of lubrication may vary from hydrodynamics to mix with dominant asperity friction at piston reversals. Measured bores and ring profiles are used to predict conjunctional power loss and percentage fuel energy consumed. Furthermore, lubricant’s flow through the ring is predicted throughout the engine cycle. These measures are key industrial design drivers for fuel efficiency and reduction of emissions. The results show that the effect of bore out-of-roundness can be even more significant than the surface topography.

The new generations of compact high output power-to-weight ratio internal combustion engines generate broadband torsional oscillations, transmitted to lightly damped drivetrain systems. A novel approach to mitigate these untoward vibrations can be the use of nonlinear absorbers. These act as Nonlinear Energy Sinks (NESs). The NES is coupled to the primary (drivetrain) structure, inducing passive irreversible targeted energy transfer (TET) from the drivetrain system to the NES. During this process, the vibration energy is directed from the lower-frequency modes of the structure to the higher ones. Thereafter, vibrations can be either dissipated through structural damping or consumed by the NES. This paper uses a lumped parameter model of an automotive driveline to simulate the effect of TET and the assumed modal energy redistribution. Significant redistribution of vibratory energy is observed through TET. Furthermore, the integrated optimization process highlights the most effective configuration and parametric evaluation for use of NES.