Towards Life Cycle Sustainability Assessment For Electric Powertrains In Hybrid And Plug-in Hybrid Buses

The global automotive industry is currently optimiazing and upgrading powertrain system as a breakthrough for the electrification.In a few years,the strong industrial policies quickly push China becoming the world's largest electric vehicles' market.The urban electric bus first outbreaks,but overheated policies lead to a variety of unsustainable problems.The sustainable development of China's electric bus industry needs to scientifically re-evaluate the sustainability of hybrid,plug-in hybrid and pure electric drive technologies in China's buses.In this paper,we focus on electric powertrain systems of hybrid electric vehicle(HEV)and plug-in hybrid electric vehicle(PHEV).Based on the theory of life cycle sustainable assessment,we build up the model to assess the sustainability of electric powertrain system(including motor,controller and battery).Then we make a comparative empirical research on the two driving systems by a large number of high precision data from the driving assembly manufacturer and bus company in Tianjin,Through the study,we can help manufacturing companies and bus companies to conduct sustainable assessment of technology path,to conduct green manufacture and to improve product performance and enhance social value in a economic way.The results show that the PHEV system is more sustainable than the HEV system under the current technical and economic conditions in China.With the greening of the power structure and the decline of the lithium batteries' price,the sustainability of the PHEV system will be improved in the next 5 years.In terms of the environmental impacts,the PHEV powertrain system has a lower impact on all environmental impact categories.For the three most current impact categories(climate warming,PM,and human toxicity)the PHEV system has a lower impact than the HEV system about 22%,26% and 28% respectively.For the HEV system and PHEV system,the life cycle stage with the greatest impact on the environment is the operation and use stage of buses,and the energy storage components(super capacitors and power storage batteries)are the key environmental impact sources.Compared with HEV system,PHEV system uses power lithium battery pack instead of the super capacitor module to optimize the energy storage configuration.It does not significantly increase the environmental load,but reduces the overall system fuel consumption of more than 20%.On the economic front,the PHEV system has a cost advantage over the HEV to both the manufacturer and the bus company,and the PHEV system will still have a cost advantage even if the country completely withdraws the purchasing and operating subsidy.The social dimension of the study shows that PHEV system brings more job opportunities and less impacts on human health,but increases the risk of work-related injuries.In the end,it is suggested that the manufacturer should increase the use of composite materials such as aluminum alloy and thermoplastic fiber as much as possible.The performance-machine design should be optimized to reduce the parts' weight,and to consider the reuse and the recycle of components.