Kia introduces new mild hybrid powertrain, 7-speed DCT
4 March 2014
|Kia’s 48V mild hybrid system uses a lead-carbon battery. Click to enlarge.|
Kia revealed a new mild hybrid powertrain as well as its new 7-speed DCT at the Geneva Motor Show. (Earlier post.) Developed by Kia’s European R&D centre, the new hybrid system employs a 48V lead-carbon battery, which powers a small electric motor to increase the engine’s power output and cut exhaust emissions. The mild hybrid powertrain will be available on new diesel and gasoline production cars from Kia in the near future.
The development team behind the mild hybrid powertrain selected lead-carbon batteries over lithium-ion equivalents as they require no active cooling, are more easily recyclable at the end of the vehicle’s life and can function much more efficiently in sub-zero temperatures.
Kia’s mild hybrid system will enable a car to be driven in an electric-only mode at low speeds and when cruising, while the battery is recharged under deceleration at all speeds. In heavy traffic and on urban roads, the powertrain will also feature a stop-start system. Using a belt-driven starter generator—replacing the conventional alternator—the engine is able to restart with almost no noise or vibration.
The battery also supplies energy to an electric supercharger, which increases torque and power at low engine speeds. Engineers behind the development of the powertrain see the electric supercharger supporting a larger conventional turbocharger, which would seamlessly take over to provide greater power and torque as engine speeds rise.
The new hybrid system could also be fitted without the electric supercharger for a simpler powertrain layout in smaller models.
In applying the technology to production cars, Kia engineers are targeting reductions in CO2 emissions of up to 15%, while the electric supercharger is designed to deliver power increases of 15 to 20% depending on its application.
The new powertrain would also allow vehicle development engineers to reduce the size of a vehicle’s existing battery and starter motor.
|7-speed DCT. Click to enlarge.|
7-speed DCT. The new seven-speed dual-clutch transmission (DCT)—the first of its type from Kia—was engineered to balance greater fuel efficiency with improved performance and to deliver a sportier driving experience.
Designed as a more fuel efficient replacement for Kia’s existing six-speed automatic transmission, currently available as an option on the majority of Kia models, the new DCT combines the advantages of both manual and automatic transmissions while allowing for faster gear changes than both.
Throughout the development process, engineers have been targeting a 7% improvement in fuel efficiency and a 5% improvement in acceleration (0-100 km/h / 62 mph) over the existing six-speed DCT transmission.
NVH has also been a key focus for the team behind the DCT’s development, with an external damper providing a high level of refinement for the new transmission.
The DCT is made up of two dry clutches, each fitted with an electric motor-driven clutch actuator to improve fuel economy, and a pair of gear input shafts, one each for the odd and even gear ratios. This set-up enables the DCT to operate sequentially or to jump immediately to any of its seven forward gears (and reverse) depending on the driver’s requirements.
The continuous power delivery offered by the DCT minimizes the loss of torque by the powertrain during gear shifting and ensures a smoother drive in all conditions. The wide ratio coverage afforded to the engine by the seven-speed gearbox results in improved fuel efficiency and performance over rival six-speed DCTs.
The new seven-speed dual-clutch transmission will start to appear on production Kia cars in 2015.
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