Vibrations
The entire drive train of a conventional motor vehicle consisting of engine, clutch, transmission, cardan shaft, axle and tires, is a system which is susceptible to torsional vibrations and can be excited to critical vibrations. Fig. 3-120 shows the torsional vibration model of a drive train consisting of rotational masses and spring-damper elements.
Vibrations are undesirable for different reasons:
All vehicle structures and aggregates would be loaded to a higher level mechanically and would thus have to be dimensioned more stable otherwise their life-span would be reduced,
Vibrations in the drive train can impair driving comfort as well as driving safety (e.g. Bonanza effect),
Vibration produces noise which imposes a strain on vehicle passengers and the environment.
The wind noise in passenger cars today has been sharply decreased by aerodynamic optimization such that noise from the engine and drivetrain in the maximum speed range is no longer masked. Meanwhile, the sensitivity to vibrations and noises in less comfort-orientated vehicles, e.g. trucks, is also growing.
The task of effectively compensating vibrations is complicated by:
Fuel consumption and emission optimized engines which partly generate unfavorable vibrations, e.g. direct-injection diesel engines,
New, drive train components optimized for minimum losses (e.g. light-running transmissions) which do not effectively insulate vibrations,
Engines and drive train components are flexibly assembled based on the modular principle for economic reasons. As a consequence, specialised damping cannot be realized.
For the design and evaluation of the effects of vibration-damping, the following measures are used:
Vibration calculations,
Objective measurements, and
Subjective measurements