General Motors has developed a prototype of its existing two-mode transmission (2MH4EV) specifically designed for front-wheel drive, plug-in hybrid vehicles. At the 2011 SAE World Congress, GM outlined the operation of this prototype transmission, claiming that the unit adds an input-brake clutch to the automaker's existing two-mode system that enables enhanced electric vehicle capability.

GM says that the trans features two additional electric-only modes – EV1 and EV2 – that allow a plug-in hybrid to tackle urban driving using only battery power. EV1 allows the vehicle to operate in electric-only mode in low-speed driving conditions, while EV2 makes it possible to drive at higher speeds using only battery power. GM explains the operation its two-mode prototype trans like this:
In addition to the existing engine-on operating modes EVT1, EVT2 and fixed gears FG1, FG2, FG3 and FG4 as well as the low-speed electric-only mode EV0, the two new electric-only modes EV1 and EV2 cover the entire low-torque, low-speed region assuming a sufficient amount of battery power.
GM says that it has fitted one of its vehicle with this prototype trans and has already tested and refined it, implying that this two-mode is almost ready for action.

[Source: Green Car Congress]

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