There are many different vibration sources in a car. Engine, gears, road roughness, impacts against the wheels cause vibration and sound that can decrease the parts and the car durability as well as affect drivability, safety and passengers and community comfort.
In 4×4 cars, some extra vibration sources are the parts responsible for transmitting the torque and power to the rear wheels. Each of them has their own vibration modes, excited mostly by its imbalance or by the second order engine vibration.
The engine vibration is a very well known phenomena and the rear driveshaft is designed not to have any vibration mode in the range of frequencies that the engine works or its second order.
The imbalance of a driveshaft is also a design requirement. That means, the acceptable imbalance of the driveshaft is limited to a maximum value. Of course this limitation should not be extremely conservative because it would raise the needs in terms of constructive technologies used to make it - and the cost, therefore.
Other class of vibrational effects related to the driveshaft and rotative couplings (like gears and U-joints) is “backlash”. It is caused by a vibration between the two rotative elements when they do not spin at the same exactly velocity because of a rotational gap between them.
The present work explains a resonation mode phenomenon on the driveshaft, caused by its own imbalance, when the vehicle is traveling in a defined velocity range and a backlash effect. It presents also one way to avoid these problems by changing the natural frequency of the driveline for one of its vibration modes and setting it out of the normal range of rotation velocities used and the way this solution contributes also to minimize backlash problems and other vibrations transmitted trough the driveshaft.