Energy comparison between different parallel hybrid vehicles architectures

Abstract

A great boom of hybrid vehicles has taken place on the automotive market in recent years, in particular, all these vehicles are now equipped with a continuously variable transmission (CVT) thanks to the use of a planetary gear train and two electric motor-generators. The benefit provided by this system is the possibility to optimally control the engine velocity from an energy standpoint; in addition, drive comfort is increased thanks to the continuously variable transmission. However, this is obtained at the cost of some amount of electrical losses in the components necessary to realize the above-mentioned structure. This paper aims to evaluate the overall efficiency of this particular power train on different road missions; the same missions will be simulated at the same time for an identical hybrid vehicle equipped with a conventional transmission system. In order to perform an energy analysis of the two architectures, one has to accurately address the main components generating energy losses: it will be thus presented the set of equations from which the mathematical stationary model of the CVT was obtained and how the different electric components and the internal combustion engine were modeled. In addition, a brief description on the CVT optimization logic will be reported, the validity of this process will be then confirmed by comparing the ICE working points deriving from it and those declared by Toyota. Finally, the fuel economy values coming from various road simulations will be compared in order to determine if or which hybrid architecture proves to be the most efficient one.