Two-Scale Command Shaping for Reducing NVH during Engine Shutdown

Two-scale command shaping is a recently proposed feedforward control method aimed at mitigating undesirable vibrations in nonlinear systems. The TSCS strategy uses a scale separation to cancel oscillations arising from nonlinear behavior of the system, and command shaping of the remaining linear problem. One promising application of TSCS is in reducing engine restart and shutdown vibrations found in conventional and in hybrid electric vehicle powertrains equipped with start-stop features. The efficacy of the TSCS during internal combustion engine restart has been demonstrated theoretically and experimentally in the authors’ prior works. The present article presents simulation results and describes the verified experimental apparatus used to study TSCS as applied to the ICE shutdown case. The apparatus represents a typical HEV powertrain and consists of a 1.03 L three-cylinder diesel ICE coupled to a permanent magnet alternating current electric machine through a spur gear coupling. The EM is mounted on a plate and welded frame and is used to implement a given TSCS-designed torque profile to the ICE through Controlled Area Network messaging during its shutdown. Data is taken by on-board encoders and a Laser Doppler vibrometer. Application of the TSCS requires the estimation of the vibration modes of the system. To overcome possible inaccuracies, different approaches can be used, such as zero vibration, zero vibration and derivative and extra-insensitive input shapers. Robustness of these methods is then assessed by variation of the natural frequencies. Simulation results show the effectiveness of the TSCS strategy in significantly reducing undesirable powertrain and frame vibrations during ICE shutdown.