Holden has re-engineered the vehicle safety structure that protects the battery pack following fires which broke out in collision damaged vehicles while being stored. The pack is reinforced with additional metal structure integrated into the underbody to help prevent intrusions into the pack in a severe side collision. These modifications will be made on Volts in the field in the US and all Holden Volts will arrive in the country with these modifications
Additional changes to the coolant system
A Holden spokesperson said: “These enhancements will provide our customers with added peace of mind. The system will provide advanced notification of any breach to the coolant system and advise the customer to bring the vehicle in for service. A sensor will be installed to the battery cooling reservoir bottle to monitor coolant levels. If the coolant falls below the recommended level, the customer will be alerted to have the battery system serviced.
“A tamper-resistant bracket will also be installed to the top of the battery coolant reservoir to help prevent coolant overfills”.
Technical specs of the Voltec propulsion system
The heart of the Holden Volt is its advanced Voltec propulsion system, the which GM says is world’s first plug-in, electrically driven, extended-range system in a production vehicle.
It has a range of between 60 and 80 kilometres of pure electric driving, 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.
Its all-electric range comes from its T-shaped, 198.1 kilogram lithium-ion battery pack.
Volt’s lithium-ion battery pack
GM says the Volt battery pack is one of the first lithium-ion battery packs offered on a high-volume production vehicle.
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. Circulating liquid (consisting of coolant and distilled water) passes through a series of internal heat exchangers in the battery modules. 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 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.
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.
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.
Recharging from full battery depletion takes approximately four hours with the 3.3 kW 240V charge station.
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