Get to Know the 2011 Chevrolet Volt
Inside the 4ET50 Transmission The 4ET50 transmission primarily
consists of: • A torque dampener (in place of a torque converter)
• An integrated main and auxiliary pump
• A planetary gear set • Three clutch assemblies • A hydraulic control system • Two internal electric generator/ drive-motor assemblies
• Torque Dampener — The torque
dampener is used in place of a torque converter. The torque dampener con- tains internal torsional springs, fluid, an input shaft, and a clutch. The torque dampener assembly acts as a spring- loaded coupling to smooth the torque from the engine to the transmission. The torque dampener provides a mechani- cal, direct-drive coupling between the engine and transmission. The internal clutch is only applied during engine starting and stopping. Integrated Main and Auxiliary
Pumps — The integrated main fluid pump and auxiliary pump are located in the pump cover. The main pump is mechanical; it maintains hydrau- lic system pressure while the internal combustion engine is operating. The electric auxiliary pump is controlled by the HPCM (hybrid power control mod- ule) and is primarily used to maintain hydraulic pressure while the internal combustion engine is off. Planetary Gear Set — The plane-
tary gear set in this transmission is used to provide gear reduction only. Clutch Assemblies — The 4ET50
transmission is equipped with three clutch sets: 1. Variable High and 2-3-4 clutch 2. Variable Low and 1-2 Reverse clutch
3. 1-3 Reverse clutch The multiple-disc clutches com-
bine with the planetary gear set and an electric drive motor to deliver the different ratios in forward and reverse. Hydraulic Control System —
The hydraulic control system includes the main fluid pump; auxiliary fluid pump; and the TCM, valve body, and solenoid pack assembly. The base pres-
10 Figure 7 GEARS January/February 2012
sure in the hydraulic system is con- trolled by the pressure regulator valve, located in pump housing. Each indi- vidual clutch has its own accumulator circuit to cushion shift feel. The TCM, valve body, and solenoid pack are a complete unit and can only be replaced as an assembly. Electric Generator/Drive-Motor
Assemblies — The 4ET50 transmis- sion incorporates two electric com- bination generator/ drive-motor assemblies. These assembles are referred to as generator/ drive-motor assembly A and generator drive- motor assembly B. Generator/drive-
motor A is rated at 55KW and generator/ drive-motor B is rated at 111KW. Generator/drive-
motor A is primarily used to start the engine, provide charging volt- age to the high volt- age battery system, and assist generator/ drive-motor B during high torque demands. Generator/drive-motor B is primarily used for vehicle propulsion. Both generator/drive- motors are used during
regenerative braking. Well there you have it: We’ve
taken a brief look at the 2011 Chevrolet Volt with the new 4ET50 transmission and its new electric drive system. In future issues of GEARS, look for
articles where we’ll introduce the diag- nostic and rebuild procedures needed to keep these trannys rolling.
Figure 6
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