Browse Publications Technical Papers 2011-26-0069
2011-01-19

Idle Vibrations Refinement of a Passenger Car 2011-26-0069

The idle NVH refinement gives the customer a feel of overall quality of the vehicle. The psycho-acoustic perception of the driver/passenger during idling is primarily influenced by the power train refinement and its isolation from the passenger compartment. Power train mounting system plays a vital role in attaining the required idle NVH refinement. The modern cars being designed for higher power to weight ratio, with more powerful engines and lighter frame work has made the task of NVH refinement more difficult. The response of the lighter structure to load variation at idle due to operation of ancillary systems like HVAC, and electrical systems such as head lamps, fog lamps, wipers etc. causes discomfort to the passenger.
This paper describes an approach towards identifying the key factors governing the idle vibration of the vehicle in steady state as well as in transient operation. Increased steady state vibrations at idle was observed with engine in fully loaded condition while transient idle shake was observed with variation in the loading. Root-cause analysis consists of study of power train rigid body dynamics and tuning by varying the speed, mount stiffness to address the effect of transmissibility and the use of LRC alternator to improve loading pattern of the engine. The analysis indicates the power train pitching mode close to the fundamental excitation frequency at full load with elevated vehicle idling speed. This results in higher vibration transmissibility, which deteriorates perception with speed fluctuations. The proposed solutions improved the objective and subjective perception of tactile vibrations during idling.

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