Some of the most significant comfort disturbances in heavy vehicles can often be related to the wheels. In those cases, the vibration of the vehicle is excited by for example force variations within the tire, ovality of the tire or imbalance in the wheel. The disturbances are dependent on vehicle speed and are often perceived as most unpleasant at cruising speed on a motorway, at around 90 km/h.
Truck manufacturers want to increase the robustness against this type of disturbance, since this results in an improved operator comfort. But it also makes it possible to lower the requirements on the suppliers of tires and rims, and thereby there is a financial gain for both customer and manufacturer.
The aim with this project is to increase the understanding of wheel induced vibrations. In order to achieve this a literature survey has been performed on the subject. Furthermore, the phenomenon has been studied analytically by using a quarter car model which includes a brush tire model. The model is scripted in MATLAB.
Simulations have been performed to analyse the effect on the chassis when forces excited by mass imbalance and radial run out are introduced.
When looking at the second harmonic radial run out imperfection the unsprung mass, i.e the wheel, starts to bounce during the settling time.
Also when comparing two different weights of a mass imbalance the power increase of the vibration in the sprung mass is much larger than the power increase of the unsprung mass at the specific frequency. This implies that the excitation frequency, the wheel rotation frequency in this case, is a harmonic repetition of the sprung mass undamped natural frequency.
To avoid this phenomenon the undamped natural frequency of the sprung mass must change either by adding a damper or by changing the weight or the spring stiffness. The simulation is run with a damper although without it the power increase would be much larger.
2013. , 48 p.