Analysis of Transmission Efficiency of a Plug-In Hybrid Vehicle Based on Operating Modes

Hybrid powertrain systems have become mature technologies because they are able to achieve high-fuel efficiencies and improve driving performances. In order to maximize the use of electric machines, new transmission systems are incorporated into the hybrid powertrains. The Cadillac CT6 plug-in, developed for a luxury sedan, implements a new multimode hybrid powertrain and activates the operating modes according to the driving conditions. This study investigates the operation of the transmission system of the Cadillac CT6 plug-into understand the design and the control concept of the vehicle. The transmission of the vehicle consists of 11 operating modes, including four electric driving modes and seven hybrid driving modes, whereas 32 operating modes can become available by controlling five clutches with the combination of three planetary gear sets. Methodologies used to analyze the operating modes and the transmission efficiencies are introduced in this study. It has thus become possible to understand that the vehicle selects only the 11 operating modes to realize straightforward shifting performances and switches the modes to achieve increased transmission efficiencies over the entire driving speed range. The study is envisaged to be helpful to engineers who want to develop hybrid powertrains and their controllers by providing systematic processes to analyze the operation and the transmission efficiency.