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GM 2-Mode Hybrid Transmission for Plug-ins Developed
In brief: General Motors has developed a prototype of its 2-mode, front-wheel-drive (FWD) hybrid transmission with enhanced electric vehicle capability.
The transmission is meant specifically for plug-in hybrid vehicles. The 2MH4EV, as its called, was presented as a detailed paper at the SAE 2011 World Congress in Detroit earlier this month.
The drive unit includes an extra input-brake-clutch on the FWD system to enable electric-only modes in the variable trans. This gives the transmission the capability of covering the average urban cycle (low speed driving) in fixed-gear mode, saving power by reducing gearing loads. Electric-only operation is possible in either low or high speed, however, with two different transmission modes to cover them.
The base FWD 2-mode system uses two motors, planetary gear sets, and a system of four hydraulically-applied clutches to give two continuously variable speed-ratio ranges and four forward fixed gear ratios.
The two ranges are high and low, referring to their relative road speeds. The lower speed gives higher torque output while the higher speeds give better efficiency. The electric motors' turning speeds synchronize shifting automatically, giving smooth transitions.
The paper detailing the transmission was authored by GM's Hong Yang, Anthony Smith, Shawn Swales, and Joel Maguire. It's titled Development of Two-Mode Hybrid Powertrain with Enhanced EV Capability and is available as SAE paper #2011-01-0883.
And so ...
Interesting setup that could possibly push the Voltec powertrain into a more mainstream use.
Photo credits: GM / Young et al
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