Abstract An all-new electric variable transmission (EVT) developed by General Motors for rear-wheel-drive products is at the center of the plug-in hybrid electric vehicle (PHEV) propulsion system for the Cadillac CT6. This transmission includes two integrated electric motors, planetary gearing, and hydraulic clutches. It is capable of power-split-hybrid operation in continuously variable transmission (CVT) ratio ranges, parallel-hybrid operation in fixed gear ratios, and all-electric propulsion in different ratio combinations. Transmission operation, mechanical design, controls design, motor design, and output capability are explained, and simulation results used as the benchmark for final development are included. All-electric launch and driving, selectable regeneration, and power blending with the turbocharged engine provide smooth and seamless propulsion through the entire driving range. Introduction An all-new electric variable transmission (EVT) for the Cadillac CT6 plug-in hybrid electric vehicle (PHEV)[ 1] is part of General Motors (GM) second generation of dedicated electric transmissions for hybrid vehicles, the rear-wheel-drive (RWD) counterpart to the transaxle for the second generation Chevrolet V olt and other global front-wheel-drive (FWD) vehicles[ 2]. Like the second-generation V olt, the new EVT was designed from a “blank tablet”, starting with a systematic comparison of all known hybrid technology, to select the best for customers in efficiency, performance, drive quality, durability and other factors. The EVT delivers continuously-variable transmission (CVT) function and parallel hybrid and electric propulsion in one integrated package that fits into approximately the same space as a conventional planetary automatic transmission. Its engineering benefits directly from customer experience with the 2ML70 EVT produced and sold by GM in 2Mode Hybrid [ 3] full-size trucks and sport-utility vehicles, including luxury SUVs, making the new EVT for the CT6 a true next-generation product.The new EVT is the nexus of the PHEV propulsion system the Cadillac CT6 that also includes a 2.0L turbocharged direct-injection gasoline engine, a liquid-cooled lithium-ion battery pack, a traction power inverter module (TPIM) system controller, an accessory power module (APM) for supplying 12V power, and an on-board charger module (OBCM) for supplying grid energy to the system to reduce the use of petroleum fuel by the vehicle, beyond reductions that can be achieved with hybrid technology alone. The new EVT contains two electric propulsion motor-generators, an input damper, three planetary gear modules, five multi-plate clutches, and an electrically-powered hydraulic system for lubrication, motor cooling, and clutch actuation. Transmission Power-Flow and Operation The new EVT provides both electric propulsion and CVT function. When the engine is off, both of its two electric propulsion motor- generators, referred to simply as “motors”, can drive the output through planetary gearing, using the gearing to achieve one or two stages of torque multiplication. When the engine is on, one motor can act as a generator and the other can produce shaft power to transmit torque at a variable ratio, and the planetary gearing arrangement can amplify this action to transmit all of the engine torque from the input to the output with a variable ratio, without the need to convert all of the engine power into electricity and back again. In this way, the new EVT uses its electric motors, planetary gearing, and other components to achieve CVT action from the engine to the output without the need for a friction device such as a belt. The clutches allow the system controller to select from four different ways to do this, each most suitable for different ranges of ratios and other operating conditions.General Motors Electric Variable Transmission for Cadillac CT6 Sedan2016-01-1150 Published 04/05/2016 Alan Holmes, Jinmin