Passenger vehicles are used as one of the frequently used and versatile mode of transport. Commercial buses cater to short to long distance travel for city as well as highway applications. Thus, passenger ride comfort becomes paramount for the salability of the vehicle. Generally, it is observed that the rear seat experiences the worst ride comfort characteristics due to rear overhang and pitching characteristics of buses. Therefore the objective of this project is to improve the rear seat vibrations of passenger bus by tuning damper characteristics. Shock absorbers, being a low cost and easily interchangeable component is tuned first before optimizing other suspension parameters. The methodology is as follows: first, a 4 degree of freedom mathematical model is created on MATLAB Simulink R2015a environment. Time domain data is obtained by road load data analysis and used as an input for the mathematical model. An experimentation was carried out on the bus at speeds of 20 km/h over a single hump to obtain actual acceleration time domain data. The model is then correlated with actual test over a single hump.
After setting up baseline results, tuning of damper is carried out. First low speed compression range is tuned to obtain better ride comfort characteristics over Class A road and results are observed. This is done by varying the damping force from 5kgf to 100kgf in speeds between 0.05 m/s to 0.25 m/s in compression. Thereafter, high speed rebound range is tuned over a single hump by varying the damping force between 1000 kgf to 4000 kgf in speeds between 1m/s to 3 m/s in rebound travel and results are obtained. Finally, fitment of data in Ride Comfort Index is carried out as per ISO 2631. Therefore a comprehensive and parametric damper tuning sheet is prepared considering the natural frequency, critical damping coefficient and damping ratio.
