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Volt Introduces Revolutionary Voltec System

2011-12-09

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The heart of the Holden Volt is its advanced Voltec propulsion system, the world’s first plug-in, electrically driven, extended-range system in a production vehicle.

It delivers ultra-high efficiency unlike any other vehicle, with between 60 and 80 kilometres of pure electric driving (depending on terrain, driving techniques and temperature), plus an onboard petrol engine that works as a generator to recharge the battery while driving extending Volt’s range to a total of more than 500km.

Volt is not a hybrid.  It is the industry’s only electrically-driven vehicle with range-extending capability.  Volt can be driven across town or across the country in all climates, without compromise.

“The Voltec system in the Chevrolet and Holden Volt is part of GM’s ongoing commitment to put cleaner, more efficient vehicles on the road quickly and affordably,” said Mike Devereux, Holden Chairman and Managing Director.

Volt redefines electric driving in an innovative, intuitive and efficient – yet responsive – way.  Its all-electric range comes from its T-shaped, 198.1 kilogram lithium-ion battery pack.  

Combined with an advanced, 111-kW electric drive unit, it delivers 60 to 80 kilometres of pure electric operation, depending on driving conditions, on a fully charged battery.

In extended-range mode, which activates when the battery’s energy is depleted, power is seamlessly inverted from a technically advanced, 1.4L, 63-kW engine to the electric drive.

Volt’s lithium-ion battery pack is durable, efficient

Developed by GM in conjunction with battery cell supplier LG Chem, the Volt battery pack is one of the first lithium-ion battery packs offered on a high-volume production vehicle.  It is assembled at GM’s own battery assembly facility in Brownstown Township, near Detroit, the first such facility in the U.S. built by a major automaker.

The Volt battery is designed to provide value, safety, quality, reliability, performance and durability. Major features include:

• Thermal management for durability and reliability: Because batteries can be sensitive to temperature changes, the Volt pack is climate-controlled via an exclusive active liquid control system that continually monitors and maintains the battery pack temperature for optimum performance and durability.  Circulating liquid (consisting of coolant and distilled water) passes through a series of internal heat exchangers in the battery modules.  Volt features the only mass-produced battery that can be warmed or cooled.  It is designed to provide reliable operation, when plugged in, at temperatures as low as -25 Centigrade and as high as +50 Centigrade.  In cold weather, the battery is preheated during charging to provide full power capability.  In hot weather – the most challenging environment for a battery – Volt’s battery can be chilled during charging.  Volt’s thermal management system can also be powered during driving either by the battery or engine.

• Diagnostics for safety and performance: Volt’s battery management system continuously monitors the battery in real-time for optimum operations.  More than 500 diagnostics run at 10 times per second, keeping track of the Volt’s battery pack; 85 percent of the diagnostics ensure the battery pack is operating safely, while the remaining 15 percent keep track of battery performance and life.

• Cell design and chemistry for performance and efficiency: GM’s selection of a prismatic cell design and LG Chem’s manganese spinel lithium-ion chemistry is designed to provide long life and high power output, with a properly maintained temperature.  This enables better vehicle acceleration and increased regenerative braking capability for improved vehicle efficiency.

• Energy management for durability: Fully charging or fully depleting a battery shortens its life.  Volt’s energy management system never fully charges or depletes the battery.  The Volt battery is controlled, or buffered, so it operates within a safe state-of-charge window of 65 percent.  In demanding situations (such as driving in Mountain mode), the battery state of charge will raise the lower limit to ensure there is adequate power when needed.  The battery’s top and bottom ‘buffer zones’ help ensure long life.

The battery pack is positioned in the centre tunnel of the vehicle and is protected by ultra high-strength steel.  It comprises nine linked battery modules that contain 288 prismatic lithium-ion battery cells, each of which functions as a building block.  

Each cell is approximately 13 x 18 centimetres, half a centimetre thick, and weighs about less than 0.5 kilograms.  It contains a carbon anode (negative electrode), manganese cathode (positive electrode) and safety-reinforced separator, the medium that isolates the electrodes, while still allowing the transfer of electrically charged ions between the elements in each cell.

Lithium-ion was chosen over nickel metal hydride for the Volt battery because it packs two to three times the power of a nickel metal hydride battery in a much smaller package.  It is also more efficient, offers more configurability, suffers little loss of charge when not in use and is less prone to ‘lazy battery’ syndrome, when batteries gradually lose their maximum energy capacity from repeated recharging after being partially discharged.

The Volt battery cells are encased in polymer-coated aluminium housings.  They are thermally efficient, safe and designed to withstand extreme heat, cold or dramatic temperature shifts.

Electric drive supplies power to the wheels

A 111-kW electric drive unit powers the Volt’s wheels at all times.  Positioned under the bonnet next to the engine, it packages a pair of electric motors and a multi-mode transaxle with continuously variable capability.  Unlike a conventional powertrain, there are no step gears within the unit, and no direct mechanical linkage from the engine, through the drive unit to the wheels. 

Inside the drive unit, one or both of the motors drives the vehicle based on performance and speed to optimise efficiency. One of the motors serves a dual function, either to help drive the wheels, or to operate as a generator to keep the battery pack at its minimum buffer.

To ensure the long-term durability of the electric motors, transmission fluid is pumped around and through the units to lubricate and keep the temperature down.  In addition, the wire used in the copper windings of the drive motor is designed to minimise heat build-up.

At higher loads and speeds, the second motor will activate as needed for efficiency.  The Voltec propulsion system optimiser evaluates the best efficiency point hundreds of times per second, and seamlessly switches from one-motor to two-motor operation to use as little energy as possible while still meeting the driver’s needs.

1.4 litre engine extends Volt’s range

What sets Volt apart from other electric vehicles is its ability to operate after the battery’s energy is depleted – a handy feature that eliminates the range limitations associated with electric-only vehicles.  Volt’s 500-plus kilometres of extended range comes from the refined 1.4 litre, 63kW petrol-powered engine that provides charge to the battery. 

The engine features a four-valve-per-cylinder/16-valve aluminium cylinder head and is designed for ease of maintenance.  Features include:

• Chain-drive application for low friction performance and lifetime, maintenance-free operation

• Piston-cooling oil jets for enhanced lubrication, increased longevity and longer maintenance levels

• Coil-on-plug ignition system eliminates spark plug wires and results in greater operating reliability and lower maintenance requirements

• Platinum-tipped spark plugs

Volt requires premium petrol because it optimises engine performance and ensures maximum fuel economy when operating in extended-range mode.

Three drive modes: Normal, Sport and Mountain

Volt is a one-of-a-kind global electric car designed to perform in all climates, and offers performance modes for varying driving styles and conditions.  Via a “Drive Mode” button on the centre stack, drivers can choose Normal, Sport or Mountain mode:

Normal mode: The default setting on Volt and the mode expected to be used most of the time, this provides the most efficiency.  When the energy level of the battery drops below the state-of-charge window, Volt enters extended-range operation, during which the engine automatically runs to sustain the charge and enable extended-range travel.

Sport mode: This mode automatically reconfigures the accelerator pedal response to provide quicker torque application in sport driving situations.  While it doesn’t provide a higher full power output, it does provide more sensitive feedback to driver inputs.

Mountain mode: Mountain mode automatically adjusts the system to provide needed power in mountainous environments, when vehicle performance could otherwise be compromised.  Mountain mode changes default settings to sustain a sufficient state of charge so that in the event supplemental power is needed, it can be available from the battery.  Drivers should select this mode after a full charge or 10 to 15 minutes before entering mountainous terrain to enable full vehicle capability up sustained grades.  While expected to be a rarely used feature, Mountain mode will limit electric range and maximum drive unit output power.

Recharging Volt is easy

If you can recharge a mobile phone, you can recharge the Volt.  It comes equipped with a 6-metre 240V charging cord conveniently stowed in the boot.  Owners can schedule immediate charging, or coordinate the charging time to accommodate lower electric rates during off-peak hours or the scheduled departure time.

Recharging from full battery depletion takes approximately four hours with the 3.3 kW 240V charge station.