A Mild Hybrid Engine-Solid Oxide Fuel Cell Vehicle Configuration Using a Continuously Variable Power-Split Transmission

Abstract

This paper focuses on a mild hybrid vehicle configuration design using a continuously variable power-split transmission (CVPST) with a solid oxide fuel cell (SOFC) as an auxiliary power unit (APU), which can provide electrical energy to an electric motor, recharge batteries and when necessary, supply energy to the vehicle’s electrical features. The advantage of this configuration design is that the IC (internal combustion) engine will use all its power capacity to only propel the vehicle and will not need to divert power for extra devices. When more power is needed, as in hills, extra load or highway acceleration pass, the electric motor can assist with an amount of power. Another advantage and interesting feature from the SOFC is that it is compatible with conventional petroleum fuels with a simple partial oxidation reforming process. It has less stringent requirements for reformate by using carbon monoxide (CO) directly as a fuel and has less sensitivity to contaminants. Mild hybrid vehicles are the probable primary candidates for near term mass market due to the low incremental costs, which is accomplished by minimizing the electrical machines and battery size. Yet, it is also considered that it improves fuel consumption and efficiency as a result of using a smaller IC engine. The mild hybrid may have the potential to provide the right cost and benefit balance in the short term, until the development of full hybrids and fuel cell vehicles can compete with standard IC engine vehicles in the market. Continuously variable transmissions (CVTs) have an infinitely variable input-output speed relationship, which allows the IC engine to operate more time in the optimum range. Continuously variable power-split transmissions were developed in order to reduce the fraction of power passing through the variator and consequently, expand its power capacity. In this paper a CVPST is used in a hybrid electric vehicle (HEV) application. This type of transmission has a planetary gear train (PGT), which can provide a branch for an electric motor that can be used in the mild hybrid electric fuel cell vehicle configuration proposed in this paper. This electric motor can either be powered by a SOFC and/or a battery.