Impact of Battery Electric Conversion on Rollover Safety of Large Passenger Buses per UN ECE R66

The electric conversion of a large passenger vehicle was investigated, in which the internal combustion engine and associated components were replaced by electric powertrain components. As this will have an influence on the rollover safety performance of the vehicle, compliance to the requirements of UN ECE Regulation No.66 was assessed. The vehicle geometry was captured through physical inspection. The unladen kerb mass of the vehicle was experimentally determined as 10660 kg. This mass excludes the mass of occupants as the vehicle is not fitted with occupant restraints. The location of the center of gravity was estimated using a representative CAD model. The center of gravity is located at a distance of 3580 mm behind the front axle and at a height of 1195 mm above the ground. An implicit nonlinear finite element (FE) analysis was conducted to quantify the energy absorption capability of a rollover hoop. This value was calculated as 5.65 kJ for a single rollover hoop and 67.80 kJ for the complete superstructure. The FE model, validated by an experimental quasi-static loading test, predicted the energy absorption capability within an error of <1%. The rollover safety performance of the electric converted vehicle, with various battery pack configurations, was assessed. The proposed configurations considered geometrical constraints and a minimum energy storage capacity related to a required travel range. The results indicated that the various proposed configurations, with vehicle masses ranging from 10765 kg to 11670 kg and center of gravity vertical heights from 1148 mm to 1200 mm, all adhered to the regulatory requirements. However, these configurations exhibited marginal compliance with excess energy capacities between 2.21 kJ (3.3%) and 4.65 kJ (6.9%), suggesting that careful consideration of the battery pack mass and positioning within the vehicle is required. The methodology outlined in this study thereby provides public transport bus service operators with a cost-effective approach for evaluating rollover safety compliance in the early design phase of performing an electric bus conversion.