Arriving in U.S Kia dealer showrooms early next year, the Optima Hybrid is the brand’s first-ever hybrid for North America and uses a ‘full parallel hybrid system’ to deliver a unique blend of performance – acceleration to 62mph in 9.2 seconds, top speed 121mph – and economy, achieving a 40.7% mpg improvement compared with a regular Optima.
“Although these new technologies presented our engineers with a series of complex challenges to overcome, the resulting Optima Hybrid delivers a fully automatic, seamless and enjoyable drive, together with real-world benefits for our customers,” adds Mr. Lee.
When setting off the Optima Hybrid operates in Electric Mode. As vehicle speed rises, the Hybrid Starter motor/Generator (HSG) starts the petrol engine and the clutch is closed, allowing the engine to take over the task of propelling the car. The electric motor switches into hybrid operation and serves as both a secondary engine (during full acceleration and hill-climbing) and a generator to recharge the battery pack as necessary. Whenever the car comes to a stop for more than a few seconds, the petrol engine automatically shuts off to completely eliminate tailpipe emissions.
When braking, the electric motor converts kinetic energy into electricity for storage in the battery pack. The 8.5 kW HSG also functions as a generator to re-charge the battery pack if the state of charge is low and when the car is stationary. Throughout the entire driving experience, under all conditions, the entire hybrid operation is automatic and seamless.
Described by Kia engineers as a Transmission-Mounted-Electric-Drive (TMED), the 30kW IPM electric motor sits within the car’s extended transmission casing (between the petrol engine and the automatic gearbox) and is the world’s first oil-cooled system.
Compared with nickel-metal hydride batteries, lithium polymer batteries weigh 20-to-30% less, occupy 40% less volume and are 10% more efficient. They also hold their charge for 25% longer than nickel metal hydride batteries and are so reliable that the Optima’s battery pack will not require replacing during the vehicle’s lifespan – at least 10 years and 150,000 miles.
The complete hybrid system is controlled by the Optima’s Hybrid Control Unit (HCU) which acts as the car’s mastermind and integrates the smooth operation of the engine’s ECU, transmission’s TCU, battery management system (BMS), low voltage converter (LDC). This brain also gives the Optima a ‘Fail-Safe’ back-up capability and a ‘Limp-home’ mode.
Taking advantage of the instant and continuously available torque from the electric motor, Kia modified its popular 2.4 litre Theta II engine to operate on an Atkinson cycle, raising the compression ratio by 20% to maximize its efficiency and achieving a 10% fuel saving over a regular Theta engine. This cycle generates a little less torque, but the electric motor compensates for any loss and consequently, the Optima Hybrid’s overall power and torque outputs are greater than the regular model.
For the Optima Hybrid, Kia has modified the 6 speed automatic transmission found on the conventional Optima for hybrid application. The traditional torque converter is replaced with an electric motor and a high-efficiency oil pump. This new gearbox allows EV mode operation, maximizes regeneration of kinetic energy during braking and also provides a more responsive drive than a CVT system.
Energy and fuel-saving technologies features in the Optima Hybrid include a regenerative braking system, electric – rather than hydraulic – assisted power steering, and an electric air compressor capable of delivering high air-conditioning performance.
Two independent liquid cooling systems are fitted to the Optima Hybrid powertrain. The standard high-temperature circuit manages engine cooling and passenger compartment heating. The second low-temperature circuit cools the hybrid starter-generator and the power electronics. The boot-mounted battery pack does not require liquid cooling and its temperature is controlled by a simple ventilation fan beneath the rear parcel shelf.
Aside from its unique hybrid powertrain the new Optima Hybrid incorporates all the technical features and the multiple choice of premium comfort and convenience equipment offered by its regular stablemates.
All Optima models share common major dimensions and a unitary construction. Featuring front-wheel-drive, Optima utilises independent suspension systems, with MacPherson struts in the front and a multi-link layout at the rear.
Inside, the instrument panel has an ECO Guide to promote economical driving habits and is contoured toward the driver to suggest a cockpit feel with precise gauges and controls for an overall sport performance experience without sacrificing comfort or roominess.
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