(Los Angeles, November, 21, 2008) Hyundai will introduce its first hybrid drive system to the US market when the next generation Sonata debuts in 2010. The mid-sized sedan is expected to be the first production hybrid with a lithium polymer battery.

Hyundai/LG Chem lithium polymer cell

Hyundai's new hybrid system was developed entirely in-house and differs in several respects from most of the existing systems on the market. John Krafcik, Hyundai Motor America acting president and CEO explained some of the details of the new drivetrain to Green Fuels Forecast.

The highlight of the system is the new lithium polymer battery pack developed by LG Chem. The lithium ion cells used in most applications use a liquid electrolyte as the transfer medium for the electrons passing between the anodes and cathodes. If the cells overheat, the electrolyte can leak out which can trigger some of the fires that have been experienced with laptop computer batteries.

Hyundai hybrid battery module

The new batteries use a polymer gel between the electrodes which is considered more stable and flame resistant than the liquids. The individual cells are in a flat, rectangular format. Krafcik showed a sample of a cell and module. The cell is only 100 mm x 200 mm and approximately 6 mm thick. Groups of eight cells are arranged into a metal module and nine modules are installed in each battery pack for a car.

Most other carmakers are using liquid cooling for the lithium ion battery packs being developed for hybrid and electric cars in order to ensure thermal stability. Hyundai is able to get by with air cooling which will dramatically reduce cost and installation complexity.

hybrid Blue Drive platform

Another downside of current lithium batteries is the significantly higher cost, compared to lead acid or even nickel metal hydride. Krafcik tells GFF, "we believe we are at cost parity right now with nickel metal hydride which is pretty good, and that's going to get better and better."

Lithium polymer is a sub-set of lithium ion and Krafcik explains, "We think this is where lithium ion is going to end up. We couldn't be the first with hybrid so we want to be the best with where we end up, and being Hyundai we're focused on value and keeping it affordable."

Part of the affordability equation for Hyundai is the transmission. Most strong hybrid designs consist of an electronically controlled planetary gear, variable ratio transmission (EVT). The EVT is used for blending the drive torque from the electric drive motor and internal combustion engine. EVTs are mechanically complex and expensive to manufacture. Hyundai has chosen to use a modified version of a fixed-ratio 6-speed automatic gearbox for its system.

Hybrid battery pack

Krafcik explains "that it's one of those trade-offs, it's easy to keep throwing technology at a problem, but you end up with a price that folks can't afford or you can't make money." "We have to make money, we can't afford to subsidize this thing and we want a great price point." The 30 kW electric motor takes the place of the torque converter in the hybrid transmission. Krafcik explained that so far the engineers are not experiencing any issues with the smoothness of the blending between electric and engine torque with the fixed ratio transmission.

Another area where the Hyundai hybrid system varies from most others is the automatic start-stop functionality. Most hybrids use the electric traction motor to provide the start-stop functionality. Hyundai has separated this and uses an integrated starter-generator similar to that used by the General Motors mild hybrid system and several European vehicles that have auto start-stop. This unit provides the charging of the 12V battery, power for vehicle accessories and engine starting functionality.

The primary electric motor will be used to provide electric drive and boost capability for the Sonata. Unlike mild hybrid systems that can only provide boost, the Hyundai system can drive the car on electricity only. Responding the question of maximum electric drive speed, Krafcik tells GFF, "We're still far enough away from start of production, we're turning a lot of the knobs to decide where we're going to end up. I think it will be in the 20-30 mph range."

Hyundai hybrid schematic

With only 30 kW from the motor, it will take a very light throttle foot to accelerate up to those speeds, but backing off the gas at around town speeds will allow electric only cruising. "We're still deciding on the right balance between fuel economy and performance feel. It's a remarkable range of fuel economy difference we can achieve depending on how much we want to back off on power," says Krafcik. "One of the things we're doing right now is watching competitive actions to see where we can be if we wanted to achieve a leadership position. One thing I can say for now is that we'll beat the current in-market (Toyota) Camry (33 mpg city)."

Another area that Hyundai is focusing on for future models is mass reduction. Krafcik told GFF that the Sonata hybrid should weigh in at about 180 lbs less than the current Camry hybrid. Approximately 35-40 lbs of that weight advantage is due to the lithium polymer battery. The rest is due to weight reductions in the base vehicle which has been designed with a hybrid installation in mind from the beginning.

The gasoline engine version of the 2010 Sonata will launch in production form in late 2009, with the hybrid version following as a 2011 model during calendar 2010. At this time Hyundai is not announcing a price premium for the Sonata hybrid although Krafcik wants it to be the most affordable hybrid in the segment.