|Hyundai-Kia developed the CVT applied in the Elantra and Forte LPI Hybrids. Source: Hyundai. Click to enlarge.|
Hyundai-Kia developed its first, independent Continuously Variable Transmission (CVT) for application in the Hyundai Elantra LPI Hybrid (earlier post) and the Kia Forte LPI Hybrid (earlier post). The work on the CVT, which took three years, as well as other components of the hybrids, was carried out at the Namyang Research and Development facility in South Korea.
The LPI Hybrid is a mild hybrid powered by a 1.6-liter Liquefied Petroleum Injection Gamma engine; a 15 kW /105 N·m pancake type Permanent Magnet Synchronous Motor; the CVT; and a 180V, 5.3 Ah lithium-ion polymer battery (LIPB) pack (with cells from LG Chem) with forced air cooling. The Elantra LPI HEV emits 99 g/km of CO2 and 90% fewer emissions than an equivalent standard gasoline-powered Elantra. It qualifies as a Super Ultra Low Emission Vehicle (SULEV).
The Elantra LPI Hybrid has a fuel economy rating of 17.7 km/l (5.7 L/100km or 42 mpg US); gasoline-equivalent fuel economy is 22.7 km/l (4.4 L/100km, 53 mpg US). This represents a 47% improvement over a conventional 1.6L Elantra.
As we developed the Kia Forte LPI Hybrid it was clear that to maximize fuel efficiency we needed to use a CVT because its infinite number of gear ratios allowed us to optimize fuel consumption according to driving conditions.
And because of packaging issues a traditional transmission would have increased the overall length of the powertrain. Using the CVT allowed us to delete the torque converter of a traditional automatic transmission because we were able to utilise a starter clutch with a direct control solenoid valve to allow precise pressure control. All of this contributes additional reduction in fuel consumption.—Soo-Jin Hong of Hyundai-Kia’s Research and Development Planning Team
In general, use of a CVT contributes approximately a 7% fuel efficiency gain compared to standard four-speed automatics, and the calibration of the CVT allows for a smoother shift feel.
Hyundai-Kia engineers used a single-mass flywheel and one clutch—rather than the more normal dual-mass flywheel and two clutches—in order to reduce cost, length and weight. The additional benefit was that by careful tuning of the set-up the engineers were able to deliver a better response and performance.
Although Hyundai and Kia may consider applying the new CVT in other vehicles, modifications to the system would be required.
In the hybrid vehicle we have an additional electric motor available and that means we can use the starter clutch without changes to the final drive ratio. To use the CVT in non-hybrid vehicles we would have to add a torque converter in order to deliver acceptable uphill and start-up performance. But this development means that as our range of hybrid vehicles continues to develop we already have our own independent technology that we can apply to those future models.—Soo-Jin Hong