Abstract
Vehicle Noise Vibrations and Harshness (NVH) characteristics are closely related to how customer perceives it in terms of brand quality. Vehicle NVH characteristics are largely driven by powertrain (PT) sound quality. In the race to cut carbon dioxide emissions and boost fuel efficiency, there is broad consensus among vehicle manufacturers that downsizing the internal combustion engine should be a part of the process. This downsizing leads to a variety of NVH concerns across a broad frequency range. This paper presents the results for the NVH Refinement of Front Wheel Drive (FWD) compact sports utility vehicle with a 4cylinder 1.5-liter diesel engine mated with a 6 speed manual transmission. The vehicle strategy called for superior NVH performance compared to contemporary benchmark vehicles and one of the key areas identified to achieve this target is gear rattle. Gear rattle is an audible noise transmitted from the impact between the transmission gear teeth and results in poor sound quality. This can have a negative impact on the customer perception about overall quality of the vehicle. Engine torsional fluctuations passing through the gearbox cause gear rattle. Hence, tuning the torsional characteristics of components in PT becomes vital in vehicle development process. With Stringent cost and timeline targets for vehicle development program prohibit the use of known solutions such as Dual Mass Flywheel (DMF) and Centrifugal Pendulum Absorber (CPA) etc. Current work describes the steps taken to improve gear rattle by reducing Torsional fluctuations at the transmission input by optimizing torsional characteristics of PT elements such as flywheel inertia, engine torque delivery, clutch hysteresis, clutch pre-damper/main damper stiffness and drive-shaft stiffness. Gear micro geometry and macro geometry parameters were also optimized along with the above listed parameters to reduce the susceptibility to gear rattle. These measures led to significant reduction in the angular acceleration levels at transmission input, which lead to notable reduction in the perception of gear rattle during the jury evaluation of the subject vehicle.