Effect of variable payload on Vehicle dynamics of Passenger buses in Indian usage conditions
To be published on November 21, 2019 by SAE International in United States
Event: NuGen Summit
A high impetus from Government on road infrastructure development, is giving a fillip to passenger CV space. This has resulted in making the passenger CV segment lucrative enough, thereby pulling in many operators in the business. The quality of road has immensely improved over a decade, as a result of which the average speed and hence the quantum of distance covered by passenger buses has increased significantly. People are preferring to travel in buses over trains, owing to at par ticket cost, high availability, reduced travel time and also improved level of comfort. Aligned to the market need and the trend, OEM's are offering buses with capable powertrains to cater the need of speed, reduced trip time as well as a lot of attention is also being paid to tune in the comfort level for long hauls. A big chunk of passenger travel is catered by the bus operators especially during major festivals in India. However, the passenger demand is not so consistent in this industry due to seasonality and hence is the operator earnings, as there are a number of operators in this business leading to high competition amongst themselves. As a result, the ticket pricing is highly variable in lean and peak seasons. To rationalize their operating income, operators resort to alternate methods of earnings by transporting cargo along with passenger in lean seasons. In lean season maximum focus is there in ferrying cargo. Accordingly, the bus operators customize the bus body during building, by raising floor height, keeping saloon height the bare minimum. Raised floor height offers large cargo space. However, different operators make a customized body as per their choice, and so is the loading pattern. There not a very effective control (rather Governance) on the bus body building as well as the kind of payload it ferries. This poses an extreme challenge in front of OEM's - to design for passenger or for cargo? A more rational question for an OEM would be, how to keep vehicle dynamics attuned to the needs. The answer cannot be left to the helm of operator as he would rather choose pure business. This paper analyses the impact of this paradoxical situation and discusses measured to overcome this. The discussion is in parlance to comfort as well as safety of passenger considering variable load pattern in city and intercity applications. The approach involves, distilling the contributing parameters, like impact on center of gravity, braking & steering performance, fuel economy, tyre life, vehicle agility. Thereafter, subjective evaluation thereof followed by objective testing. Finally, a correlation is established between subjective and objective evaluation results to determine the target specification of the bus. Finally the paper discussed method to meet the target.