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The GM “Voltec” 4ET50 Multi-Mode Electric Transaxle
Abstract:
The Chevrolet Volt is an electric vehicle (EV) that operates
exclusively on battery power as long as useful energy is available
in the battery pack under normal conditions. After the battery is
depleted of available energy, extended-range (ER) driving uses fuel
energy in an internal combustion engine (ICE), an on-board
generator, and a large electric driving motor. This extended-range
electric vehicle (EREV) utilizes electric energy in an automobile
more effectively than a plug-in hybrid electric vehicle (PHEV),
which characteristically blends electric and engine power together
during driving. A specialized EREV powertrain, called the
"Voltec," drives the Volt through its entire range of
speed and acceleration with battery power alone, within the limit
of battery energy, thereby displacing more fuel with electricity,
emitting less CO₂, and producing less cold-start emissions than a
PHEV operating in real-world conditions.
The Voltec powertrain architecture provides four modes of
operation, including two that are unique and maximize the
Volt's efficiency and performance. The specialized electric
transaxle, known as the 4ET50, enables patented operating modes
both to improve electric driving range when operating as a Battery
Electric Vehicle (BEV) and to reduce fuel consumption when
extending range by operating with the ICE.
Historically, most EVs have used a single-speed electric
transaxle with one motor and a fixed gear reduction. The
single-speed gear reduction is a simple arrangement that takes
advantage of the wide speed range of electric motors. While this
arrangement can work well, the wide speed range of most electric
motors comes at the price of a well-known loss of efficiency at
higher motor speeds for most types of motors. Consequently,
two-speed transmissions have been proposed for BEVs that can
improve both tractive effort and efficiency although with the
attendant additional extra gear shift hardware and controls.
The Voltec 4ET50 multi-mode electric transaxle introduces a
unique two-motor EV driving mode that allows both the driving motor
and the generator to simultaneously provide tractive effort while
reducing electric motor speeds and the total associated electric
motor losses. This new operating mode, however, does not introduce
the torque discontinuities associated with a two-speed EV drive.
For ER operation, the Voltec transaxle uses the same hardware and
controls that enable one-motor and two-motor EV operation to
provide both the completely decoupled action of a pure series
hybrid, as well as a more efficient powerflow with decoupled action
for driving at light loads and high vehicle speed.
Construction of the General Motors Company Voltec 4ET50
transaxle employs significant re-use of the General Motors Company
front-wheel-drive Two-Mode Hybrid 2MT70 transaxle with
modifications to enable all-speed and full-power EV operation. A
new high power driving motor, optimized generator, and modified
control elements allow the two EV driving modes and the two ER
driving modes to be realized in the Chevrolet Volt.
Recommended Content
| Journal Article | The Voltec 4ET50 Electric Drive System |
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| Journal Article | The Next Generation “Voltec” Extended Range EV Propulsion System |