ABSTRACT The two-mode hybrid system has several advantages over a one-mode EVT system: greater ability to transmit power mechanically and minimize electrical recirculation power, maximize fuel economy improvement and best meet demanding vehicle requirements. Extending the two-mode hybrid electric vehicle (HEV) to two-mode plug-in hybrid electric vehicle (PHEV) is significant not only to make the internal combustion engine (ICE)-based vehicle cleaner and more efficient in the near term, but also to provide a potential path to battery electric vehicles in the future. For PHEV, the enhanced electric drive capability is of vital importance to achieve best efficiency and best electric only performance. This paper describes the development of a prototype two- mode hybrid powertrain with enhanced EV capability (2MH4EV). The prototype drive unit includes an additional input brake to the existing General Motors FWD 2-mode HEV system. This enables two new electric-only modes in addition to the existing EVT modes and fixed gears. These two electric-only modes have the capability to cover the entire FTP urban cycle with a properly sized high voltage battery. Hardware design, systems and controls development are described in detail in this paper. Vehicle implementation, testing, and real world assessment of the enhanced electric- only propulsion, mode transition and drivability will also be presented. INTRODUCTION General Motors has developed a two-mode hybrid transmission for transverse front wheel drive vehicles [ 1]. Its electrically-variable transmission architecture incorporates a pair of electric motors, two planetary gear sets and a system of clutches to deliver two continuously-variable speed-ratioranges or “modes”, and is similar to the GM 2Mode Hybrid™ for full-size rear wheel drive trucks [2]. In addition to the two variable modes, four clutches in the two-mode hybrid transmission provide four forward fixed gear ratios. The two- mode hybrid powertrain and corresponding hybrid vehicle system deliver up to 50% improvement in EPA unadjusted composite fuel economy. A vehicle equipped with an EVT transmission can be driven by the electric motor with the engine at zero speed (electric drive). In an input-split (also known as series-parallel) architecture, one motor may propel the vehicle while the other has to be used to maintain the engine at zero speed in order to avoid engine factional and pumping losses. However, this single-motor electric propulsion has limited electric launch and acceleration capability and is not optimal for efficiency and heat rejection to cover the entire FTP cycle electrically. By grounding the engine with an input-brake clutch at the transmission input node, both motors can be used to propel the vehicle electrically. This way, vehicle propulsion load can be shared with two motors in either of the two EVT modes. However, in order to take full advantage of the two-mode hybrid system to achieve best system efficiency, mode transition and engine start-stop control need to be developed for the new electric-only modes involved with the input-brake clutch. Due to the complexity of controlling the input brake during mode transition and engine start/stop events, a proof- of-concept development of the 2MH4EV powertrain was undertaken to demonstrate charge-depletion operation and achieve quick and seamless transitions between two new electrical modes, as well as engine start-stop control between the electric modes and the hybrid modes. Development of Two-Mode Hybrid Powertrain with Enhanced EV Capability2011-01-0883 Published 04/12/2011 Hong Yang, Anthony Smith, Shawn Swales and Joel Maguire General Motors Company Copyright © 2011 SAE International doi:10.4271/2011-01-0883 SAE Int. J. Engines | Volume 4 | Issue 1 1058Downloaded from SAE International by Univ of Nottingham - Kings Meadow Campus, Sunday, August 12, 2018This paper starts with an overview of the two-mode hybrid operating principles, an