Mild hybrid prototype car cuts fuel consumption by 17 per cent

Jos© Avila, Member of the Executive Board of Continental and President of the Powertrain Division, says: "To achieve this level of hybridisation, we have integrated and systematically networked key technologies from the Continental and Schaeffler portfolios into the GTC. The results we've achieved with the vehicle demonstrate the potential of this strategy in a car whose engine was nominated "International Engine of the Year in 2012 and 2013' for its efficiency and performance."

Prof. Peter Gutzmer, responsible for the Schaeffler Executive Board for Research and Development, explains what sets the engine apart: "Thanks to the interaction between components and technologies in the GTC, we can leverage these effects to offer the motorist tangible on-road advantages in terms of fuel consumption and driveability."

The project partners optimised every aspect of the GTC's powertrain engineering - appropriately adapted Continental injection and engine control units replace the equivalent systems in the Ford Focus reference vehicle. Numerous innovative components and technologies were also added. Playing key roles are Continental's 48 Volt Eco Drive System as mild hybridisation and Schaeffler's electronic clutch (e-clutch) for power transmission, as well as its thermal management module. These are complemented by measures to reduce friction loss in the engine and an electrically heated catalytic converter (Emitec). With these components and an intelligent operating strategy, the GTC prototype not only improves overall fuel efficiency by 17 per cent, but also meets the limits set by the forthcoming Euro 6c emissions standard (2017/2018).

Recuperating energy

To ensure driveability of the 3-cylinder, 1.0-litre engine - despite the modified, ignition-timing-optimised operating strategy and to allow for the use of additional hybrid driving strategies - the GTC features an independent second drive unit, the 48 V Eco Drive System. This also includes an electric motor with integrated decoupling tensioner. The electric traction motor/generator is connected via a modified belt drive to the combustion engine. A DC/DC converter facilitates electrical energy flow between 12V and 48V levels by using a lithium-ion battery (dual-battery design). This hybridisation supports the combustion engine electrically in the lower RPM range (e-boost function) to ensure a good response without turbo lag. The highly efficient 48V recuperation provides the basis for this. In the NEDC (New European Driving Cycle - designed to assess the emissions levels of engines and fuel economy in passenger cars), the GTC can recuperate almost twice as much energy as the vehicle requires for the vehicle electrics.

In line with a strict design-to-cost approach, the GTC prototype is equipped with a conventional 6-gear manual transmission. Energy-saving functions such as "coasting' are also part of its drive strategy. The Schaeffler electronic clutch makes this possible, where the clutch decouples the engine from the drive train when the vehicle is coasting. As no air needs to be compressed in the combustion chambers when the engine is idle, more energy is available for recuperation. This energy, in turn, facilitates other efficiency-enhancing measures, one example being the electrically heated catalytic converter. This uses the recuperation energy from the previous drive cycle to attain a faster working temperature for cold starts.

In addition, a Schaeffler split cooling architecture with rotary slide valve facilitates graduated thermal management in the GTC. Its purpose is to combat the challenges posed by innovative hybrid drive strategies. The engine can be temporarily decoupled from the coolant cycle in order to more quickly attain the required temperature or to retain its temperature for longer periods. This rapid heat-up reduces engine friction losses, which in turn, increases efficiency, a goal also pursued by using friction-optimised components. As part of a forward-looking operating strategy, cooling can also be switched off in time for an anticipated recuperation phase (downhill stretch).

Hybridisation and electrification

The standard Continental engine control unit (ECU) used in the GTC is also designed to relieve the combustion engine of the complex task of controlling the mild hybrid components, including the operating strategy. The ECU gets a head start on the forthcoming EMS 3 (Engine Management System 3) platform strategy. Its open AUTOSAR-based system architecture flexibly supports a variety of partitioning schemes and electronic topologies in conjunction with hybridisation and electrification.

With manual transmissions, vehicle efficiency is maximised when the driver, the optimised individual components and the vehicle functions are synchronised. For this reason, the ECU makes recommendations on optimised gearshift ratios. The additional electric driving torque allows the driver to use these optimised gearshift ratios without any negative impact on driveability, helping to improve fuel economy on the road.

For more information about teh Mild Hybrid car, please email [email protected], or go to www.schaeffler.co.uk.