Drive Unit

7/28/2019 Drive Unit

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Voltec Electric Drive System Overview

Exceeding customer expectations was top of mind for the Chevrolet Volt

engineers as they developed the Voltec electric drive system. Since the Volt

is the industrys first electric vehicle with extended-range capability, the

team focused on delivering the most efficient, yet fun-to-drive experience inboth electric and extended-range operation.

VOLTEC ELECTRIC DRIVEKinematic Architecture

Axle Differential

Traction Motor

Battery Pack

2.16 ratio

GeneratorPlanetary Sun Gear

C3C1

Planetary Ring Gear

Planetary Carrier

Final Drive Gearing

C2

Inverter

Unlike most battery electric vehicles, which use a single motor with a fixed reduction

gear that steps down the motor speed to synchronize with the wheel speed, the

Chevrolet Volt uses a unique electric drive unit to boost efficiency. The efficiency of any

electric motor always drops off as it approaches its maximum rotational speed. The Volt

drive unit consists of two motors, three clutches and a planetary gear set that improve

overall efficiency by reducing the combined rotational speed of the electric motors. This

configuration reduces battery drain at highway speeds, adding up to two miles of

additional EV range.

The Volts motors and gear-set are mounted in-line with the industrys first range-extending internal combustion engine. Two of the clutches are used to either lock the

ring gear of the planetary gear-set or connect it to the generator/motor depending on the

mode. The third clutch connects the internal combustion engine to the generator/motor

to provide range extension capability.

This innovative new drive unit has four distinct operating modes:


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ELECTRIC DRIVING

C3C1

C2

3.24 ratio

2.16 ratio

Low Speed(1-Motor)

Single Motor EV Driving

In this mode, the primary traction motor provides all propulsion at lower vehicle speeds

and hard accelerations, drawing all of its energy from the battery. The ring gear is

locked and the generator/motor is decoupled from both the engine and gear-set. The

traction motor can use up to 111 kilowatts of power and deliver 273 pound-feet of

smooth, direct torque to provide spirited off-the-line acceleration.


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ELECTRIC DRIVING

C3C1

C2

3.24 ratio

2.16 ratio

1.45 ratio

High Speed(2-Motor)

Two Motor EV Driving

As vehicle speed increases, the ring gear is unlocked and coupled to the

generator/motor. This allows the two motors to work in tandem to provide blended

output with higher electrical efficiency. Using the blended output of the slower running

motors allowed the team to extract up to two extra miles of pure electric operating rangein highway driving.


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C3C1

C2

3.24 ratio

2.16 ratio

EXTENDED RANGE DRIVINGLow Speed(1-Motor Series)

Single Motor Extended-Range Driving

Once the battery has reached its minimum state of charge, the 1.4-liter engine is

coupled to the motor/generator via the third clutch. At lower speeds and hard

accelerations the Volt is propelled by the traction motor alone with the ring gear locked.

The engine-driven generator and battery provides electricity to the traction motor via the

inverter. On an average basis, the engine-driven generator will maintain the battery at a

minimum state of charge for extended range operation.

Since the most efficient way to charge the Volts battery is to plug it in, the generator is

only used to maintain minimum battery state of charge. If the battery is drawn down

below the minimum level during acceleration or when mountain mode is engaged below

about 45 percent charge, the generator will charge the battery up to its minimum state

of charge and then maintain it there.


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EXTENDED RANGE DRIVING

C3C1

C2

3.24 ratio

2.16 ratio

1.45 ratio

High Speed(2-Motor Combined)

Two Motor Extended-Range Combined Driving

The blended two motor electric propulsion strategy used at higher speeds in EV driving

has also been adapted for extended-range driving. The clutches that connect the

generator/motor to both the engine and the ring gear are engaged, combining the

engine and both motors to drive the Volt via the planetary gear set. All of the propulsionenergy is seamlessly blended via the planetary gear and sent to the final drive.

Even in combined extended-range driving, the Volt uses electric power delivered by the

traction motor -- the engine cannot propel the Volt unless the traction motor is also

powered. That is because, in order for a planetary gear-set to transmit torque, two of

the three main elements (ring gear, sun gear, planet carrier) must be driven, or one

locked, with the third element providing the output. In the case of the Volt, the traction

motor is used in this mode to provide reaction torque for the sun gear, enabling

propulsion of the vehicle.

By seamlessly blending power from the engine and two electric motors, this

sophisticated technology allows the Volt to achieve 10-15 percent better efficiency at

highway speeds than would have been possible by using only the single traction motor.

At the same time, the Volt always delivers a solid electric driving experience, even in

extended range driving, by utilizing the large battery for full electric launches even

during brisk accelerations.


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Contacts:Kevin M. KellyManager, Electric Vehicle and Hybrid CommunicationsDesk: (313) 665-0898Mobile: (313) 316-9742

[email protected]

Randy FoxPhone 313-667-4128Mobile [email protected]
mailto:[email protected]:[email protected]?Subject=GM%20Media%20Onlinemailto:[email protected]:[email protected]?Subject=GM%20Media%20Online

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