Hyundai and Kia Hybrid Systems

Hyundai and Kia take yet another approach to hybrid powertrains. While Toyota uses a planetary gear set and Honda uses a series-dominant layout with a single clutch, Hyundai and Kia use a conventional multi-speed automatic transmission with an electric motor sandwiched between the engine and transmission. This is a parallel hybrid design — the engine and electric motor both drive the wheels through the same gearbox.

The electric motor (about 30 to 60 kW depending on the model) is integrated into the transmission housing between the engine and the torque converter location. An Engine Disconnect Clutch (EDC) sits between the engine and the motor. When the vehicle is in EV mode, the EDC disconnects the engine completely, and the electric motor drives the wheels through the 6-speed automatic transmission. When more power is needed or the battery is low, the clutch engages the engine and both power sources drive the wheels through the transmission. The transmission shifts through its 6 gears like a normal automatic.

Because there is a real multi-speed transmission, the system can keep both the engine and electric motor in their most efficient operating ranges across a wide speed range. The 6-speed gearbox also gives the vehicle a familiar driving feel — it shifts gears like a conventional car. Many drivers cannot tell they are driving a hybrid. The engine-disconnect clutch also allows pure EV driving at highway speeds, which Toyota's older THS system could not do as effectively.

Hyundai uses this system in the Sonata Hybrid, Tucson Hybrid, Santa Fe Hybrid, and previously the Ioniq Hybrid. Kia uses it in the Sorento Hybrid, Sportage Hybrid, and Niro Hybrid. These vehicles are increasingly common in shops — the Tucson Hybrid and Sportage Hybrid are top sellers. Hyundai and Kia also use a 1.6-liter turbocharged Smartstream engine dedicated to hybrid applications, which provides more power than the naturally aspirated hybrid engines from other manufacturers.

Because the system uses a conventional automatic transmission, it requires ATF (Automatic Transmission Fluid) service like any other automatic — this is different from Toyota and Honda hybrids, which do not have traditional transmissions. The hybrid battery is a lithium-ion polymer pack, typically 1.1 to 1.6 kWh, located under the rear seat. The battery cooling system uses a dedicated fan drawing cabin air. The Engine Disconnect Clutch (EDC) can develop judder or slip over time, similar to a torque converter clutch — symptoms include vibration during engine engagement at low speed. The HSG (Hybrid Starter Generator) is a separate belt-driven component that starts the engine and generates electricity. Software updates have addressed some judder issues on earlier models.